the star formation newsletterreipurth/newsletter/newsletter248.pdfstart, ﬁlled with much anxiety,...

THE STAR FORMATION NEWSLETTERAn electronic publication dedicated to early stellar/planetary evolution and molecular clouds

No. 248 — 11 August 2013 Editor: Bo Reipurth ([email protected])

The Star Formation Newsletter

Editor: Bo [email protected]

Technical Editor: Eli [email protected]

Technical Assistant: Hsi-Wei [email protected]

Editorial Board

Joao AlvesAlan Boss

Jerome BouvierLee Hartmann

Thomas HenningPaul Ho

Jes JorgensenCharles J. Lada

Thijs KouwenhovenMichael R. MeyerRalph Pudritz

Luis Felipe RodrıguezEwine van Dishoeck

Hans Zinnecker

The Star Formation Newsletter is a vehicle forfast distribution of information of interest for as-tronomers working on star and planet formationand molecular clouds. You can submit materialfor the following sections: Abstracts of recently

accepted papers (only for papers sent to refereedjournals), Abstracts of recently accepted major re-

views (not standard conference contributions), Dis-

sertation Abstracts (presenting abstracts of newPh.D dissertations), Meetings (announcing meet-ings broadly of interest to the star and planet for-mation and early solar system community), New

Jobs (advertising jobs specifically aimed towardspersons within the areas of the Newsletter), andShort Announcements (where you can inform or re-quest information from the community). Addition-ally, the Newsletter brings short overview articleson objects of special interest, physical processes ortheoretical results, the early solar system, as wellas occasional interviews.

Newsletter Archivewww.ifa.hawaii.edu/users/reipurth/newsletter.htm

List of Contents

Interview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

My Favorite Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Abstracts of Newly Accepted Papers . . . . . . . . . . 10

Dissertation Abstracts . . . . . . . . . . . . . . . . . . . . . . . . 44

Meetings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Meetings of Possible Interest . . . . . . . . . . . . . . . . . . 47

Cover Picture

The image, obtained with the Hubble Space Tele-scope, shows photoevaporating globules embeddedin the Carina Nebula.

Image courtesy NASA, ESA, N. Smith (Universityof California, Berkeley), and The Hubble HeritageTeam (STScI/AURA)

Submitting your abstracts

Latex macros for submitting abstractsand dissertation abstracts (by e-mail [email protected]) are appended to eachCall for Abstracts. You can also submit via theNewsletter web interface at http://www2.ifa.

hawaii.edu/star-formation/index.cfm

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David Hollenbachin conversation with Bo Reipurth

Q: You had a slow start to your research career? Was that

circumstances or choice?

A: It was a combination of the two. The circumstanceswere these. I was from a small, conservative town in west-ern Michigan, and left that area to do my PhD at Cornellin 1964. I then left Cornell to do a postdoc at Harvardin 1968. For those too young to experience those years,let me say they were intense and, for me, life changingand mind changing. There was ”the War”, civil rights andblack power, women’s liberation, and major changes in theway you thought about relationships, religion, politics, theenvironment, music, drugs, dress and work. By the timeI got to Harvard, I was very alienated from the statusquo. It seemed that academia was a competitive gamecompared to the issues of the military industrial complex,the devastation of the environment, the oppression of mi-norities and women, the complicity of the media, and theisolation of the individual consumer in ”established” soci-ety. So I wasted two years at Harvard, and worked mainlywith a group of folks starting one of the first organic foodstores and restaurants in Cambridge. My wife and I thenleft to join the commune which provided much of the or-ganic food on a farm in Vermont.

The choices were these. I had an epiphany in Vermont.My wife and I were starved for intellectual stimulation.The thought came to me that one should make the mostof one’s abilities in the world. So I chose to return toacademia, and was lucky (jobs were very scarce then, asthey are now) to get physics and astronomy teaching jobsin Colorado from 1971 to 1975. I had gone to graduateschool thinking I would be a college teacher, like my fa-ther, so I returned to that vision. However, I discoveredthat I had too much ”stage fright” to be in front of classafter class. So my second choice, which was even more dif-

ficult, was to give up my tenure track position and go tothe University of California at Berkeley on a second post-doc, essentially, to pursue research. I loved the people inthe astronomy department there, and they were incredi-bly supportive to me, especially Chris McKee, with whomI have had a lifelong collaboration and friendship. Even-tually, in 1980, I got my permanent position at NASAAmes, but maintained ties to UC Berkeley. My teachingexperience actually gave me a much better foundation onwhich to do research, and I found that I loved research andworking one on one with graduate students and postdocs,rather than teaching large classes.

I might say, also, that a 1977 workshop in Erice, Italy oninfrared astronomy had a profound influence on my career.I left really feeling that infrared astronomy was going to bevery exciting in the coming decades, and decided to focusmy research on areas relevant to infrared astronomy. Thatultimately led to my being hired at NASA Ames, since IRastronomy was one of its key areas with the Kuiper Air-borne Observatory, and its involvement in IRAS, SIRTF(Spitzer), and LDR (this idea eventually ended up as Her-schel). I also met a graduate student, Xander Tielens, inErice, and he became my first postdoc at NASA Ames af-ter he graduated from Leiden. It was, as you say, a slowstart, filled with much anxiety, but very interesting andrewarding. Luck and relationships had a lot to do with it.

Q: Your two first papers, from 1971, dealt with the role of

grains in the formation of molecular hydrogen, and they

have had a major influence on the subject. How have your

results held up 40+ years hence?

A: Of course, I am prejudiced, but I think they have heldup quite well. One of the key issues then and now is that,on a pure surface with weak van der Waal forces dominat-ing and no enhanced binding sites, the hydrogen atomswould evaporate (sublimate) before finding each other toform a molecule if the grain temperature was more thanabout 10-20 K. Such results were found in the laboratoryin the 80’s and 90’s by Vidali, Pirronello and their cowork-ers. However, there could be sites where at least partialchemical bonds held the atomic hydrogen, so that it wouldnot evaporate from the surface. In our 1971 paper, we al-lowed for this by having what we called ”impurity sites”,although the number of them was a free parameter.

On the theoretical front, there has been much elaborationlately of this idea, by Cazaux and Tielens, and by Cuppenet al. These studies indicate that even at grain tempera-tures as high as 100 K, the formation rates of molecularhydrogen may only be down roughly an order of magni-tude from their low temperature rates.

On the observational front, it is clear that in PDRs withnearby massive stars the grains are heated to at least 50 Kand still the molecular hydrogen is forming quite efficiently

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on their surfaces (Habart et al had a nice paper on thisin 2004). Interstellar grain surfaces are likely so complexthat, at this point, I favor this approach of observing PDRsand inferring the rates of molecular hydrogen formation asa function of grain temperature by matching observationswith PDR models.

Q: Your most cited work is the series of papers on molecule

formation and infrared emission in fast interstellar shocks

together with Chris McKee. When you worked on this, did

you realize that this would have such a profound impact in

the community?

A: I got interested in shock waves through my friend DickMcCray, who had worked on the expansion of wind-drivenbubbles in the ISM. He called the ISM ”violent”, and thatimpressed me. When I got to Berkeley, there had beensome observations of vibrational emission of molecular hy-drogen in Orion by Treffers, Gautier and Larson, and SteveBeckwith and coworkers also observed it around this time.Mike Shull was visiting Berkeley and he and I worked onshock models of this emission. That was the start. Then, Istarted working with Chris and we went much more deeplyinto shocks, expanding the velocity range of the shocksand the postshock chemistry and infrared emission. FromDick’s comments on the violent interstellar medium, I didthink that theoretical models of shocks would have a bigimpact. We could see observationally that the ISM wasshaped by expanding HII regions, winds, and supernovae-driven shocks. I will confess one thing, however. Withthe exception of my work on masers, shocks were a littledisappointing to me. The reason is that I love it whentheory matches well with observation, that is so satisfy-ing! However, the problem with shocks then was that thetelescopes had too poor angular resolution, so that theshock regions were a mix of shocks of various speeds andpreshock densities, so that to match, say, 4 infrared lines,you needed 4 shocks of various speeds! I am exaggerating,but I do remember frustration.

Q: Your Annual Reviews article with Xander Tielens on

Dense Photodissoctaion Regions summarized our under-

standing of these regions at the time. Since then, have we

gained any observational or theoretical understanding that

has changed the way we see PDRs?

A: I think the big change since those reviews has been inunderstanding that grain surface chemistry has a big im-pact on the chemical structure of PDRs and of molecularclouds. As a footnote, I would say it is getting increas-ingly difficult to say where a PDR ends, and an opaquemolecular core begins. Even at depths of AV ∼ 10 into acloud, the effects of FUV radiation can be important notonly dissociating molecules, but in photodesorbing themoff the grain surfaces. By grain surface chemistry I do notmean the formation of molecular hydrogen here, but thefreezing out of species like oxygen and carbon on grain sur-

faces, and potential chemical reactions of these elementson the grain surfaces. My own group has been workinghard on this problem, and so have a number of PDR mod-elers in Europe and the US. Observationally, one of thekey stimulants to this work has been the observed lowabundance of gas phase water and molecular oxygen (seenby SWAS, Odin and Herschel, for example), as well as re-cent observations of molecular ions like OH+, H2O

+, andH3O

+.

Another thing that comes to mind is the possible role ofturbulence in PDRs, stressed especially by Falgarone andher collaborators, in heating the gas and modifying thechemistry. PDR models sometimes seem to lack sufficientheating to explain the observations of, for example, mid JCO transitions or pure rotational H2 transitions. In a way,this is like a model which combines shocks and PDRs.

Q: Your latest paper is on interstellar H2O masers. How

have your thoughts on such masers evolved since you first

began work on this 20 years ago?

A: There have been considerably more observations in thepast 20 years that give evidence that water masers areoften connected with shocks, especially shocks driven byjets and outflows around young stars into the very densemedium that surrounds these objects. So even though Iwas convinced by our maser shock models of 1989-1992, Iam even more convinced now.

One thing I have struggled with, and we address in our re-cent paper, is the question of whether C shocks or J shocksare the dominant maser excitation mechanism. Kaufmanand Neufeld theoretically examined C shock masers, andMelnick and collaborators observed water masers from dif-ferent levels, and they showed that there are water masersthat are likely to be excited in C shocks, which can pro-duce a hotter masing region than the J shock that we mod-eled. In these sources, the higher lying maser lines wererelatively strong compared to the lower lying 22 GHz linewhich is typically observed. However, our analysis sug-gests that J shocks are likely a very significant source ofwater maser emission in general, especially in the largenumber of water masers where the 22 GHz line is observed,but the higher lines are not.

The interesting thing that connects this question witha previous one, is that the J shock masers rely on thereformation of molecular hydrogen (the J shocks destroypre-existing H2 and other molecules) on relatively warmgrain surfaces. The shocks that produce masers have highpreshock hydrogen densities of greater than 106 cm−3 and,as a result, heat the postshock grains to temperatures of50-100 K. So we must rely on molecular hydrogen forma-tion at these fairly high grain temperatures. Once the H2

reforms, rapid chemical reactions convert all the oxygennot in CO into H2O and the warm H2O is collisionally

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excited to produce the maser transitions.

Q: You did early work on the dispersal of disks around

young stars, summarized in your Protostars and Planets

IV review. Is this subject at the moment driven by obser-

vations or by theory?

A: My sense is that the theoretical models have becomevery detailed, with considerable chemistry, heating andcooling, radiative transfer, hydrodynamics, and consider-ation of the effects of both viscous evolution and photo-evaporation. The observations of gas lines are difficultas the lines are weak and the grain continuum strong.Many of the observations have been of grain continuumspectra (SEDs). In addition, to make better progress weneed spectrally resolved data, or resolving powers of a fewkm/s in the IR and sub-km/s at the submillimeter and mil-limeter wavelengths that probe the outer disk. Resolvingthe disks spatially would also help, but that requires sub-arcsecond resolution. So I think observations (especiallyof the gas) lag theory a bit, even though we theorists havebeen greatly stimulated by those available. ALMA shouldreally help the situation. I look forward to seeing ALMAdata as it comes in, and to heterodyne receivers on SOFIAthat can observe the [OI] 63 um line.

Q: Who would you say have had the most important in-

fluence on your scientific career?

A: The first important influence was Ed Salpeter, my PhDadvisor at Cornell. He was an inspiration to me as a per-son and as a great scientist. Then, Dick McCray, whobecame my friend in Cambridge (actually housed me andmy wife as we retreated from Vermont), and then laterinspired me to get back into research. My first researchpaper after Harvard was with Dick, a collaboration whereI commuted to Boulder to work with him during my lasttwo years teaching in Colorado Springs. Chris McKee gaveme a second chance, perhaps risky on his part given mysketchy history, by awarding me a 3-year postdoc in 1977.Since then, he has been a constant influence and inspira-tion. When I got to NASA Ames in 1979, Ed Ericksonbecame a strong influence and introduced me to the in-tricacies of IR spectroscopic observations and instrumen-tation. Xander Tielens came to Ames in about 1982 asmy first postdoc, and remained a long-time collaborator,friend, and influence. Finally, Frank Shu, who was such astrong influence on the Center for Star Formation Studies,which I ran from 1985 to about 2005. This Center was acollaboration of theorists at NASA Ames, UC Berkeley,and UC Santa Cruz, and had a strong influence, I think,on all who attended our monthly meetings and summerworkshops. The discussions were lively, and Frank was of-ten at the center of them. An example I can give of thestimulating effect of such a group interaction was that myown interest in disk dispersal and photoevaporation grewfrom discussions at the Center, and my first papers on the

subject had Frank as a co-author. This work remains tothis day as my favorite research topic.

Q: You moved into the Sierra Mountains when you retired.

How has that change in your life been?

A: That is a very long story, but I will be brief. In away, this move was a return to “unfinished business” fromthe days of Vermont. My wife and I just had not gottenenough of the country life, and had grown tired of theurban life. We love nature, backpacking, hiking, crosscountry skiing, growing our own vegetables and fruit, evenraising cows now (although they are ”pets” and mobilelawnmowers on our 50 acres, and not for slaughter). LikeVermont, we have a sort of communal situation. However,there is no lack of intellectual stimulation here, as therewas in Vermont. For example, there are 4 other couplesup here who have retired or semi-retired from astronomyresearch, and there are a number of artists, journalists,K-12 teachers, etc. Some are starting wineries, which wehighly encourage! Oddly enough, there is more social lifethan my wife and I experienced in Berkeley, where welived for 30 years. In the city, our friends were alwaysso busy and hassled! And traffic and parking! Both mywife and I continue to work, thanks to the marvel of highspeed internet, and visits to talk with colleagues in theBay area. One difference for me is that I get to work onjust the things I am most interested in.

Q: What are the scientific issues that currently most in-

terest you?

A: My big interest right now is trying to understand theevolution of protoplanetary disks. I have the good for-tune to have a great collaborator, Uma Gorti, and she andI are making models of the evolution of disks, includingphotoevaporation, winds, viscous evolution, planet forma-tion and its effect on disks, grain evolution, etc. We arehoping to get funding to construct comprehensive modelsthat follow evolution for millions of years, and perhapseven understand why Kepler has seen so many Neptunes,compared with Jupiters.

The second big interest is in mapping [CII] 158um emis-sion in the Galaxy with km/s resolution and combiningthese observations with those of atomic H 21 cm, [CI] finestructure, and CO rotational emission to try to understandhow giant molecular clouds form and dissipate. This is abig effort with a large group including Chris Walker, PaulGoldsmith, Juergen Stutzki, and a host of others and weare hopeful of getting a second flight of our STO (Strato-spheric Terahertz Observatory) balloon mission for thispurpose.

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My Favorite Object

Westerlund 1by Morten Andersen

Most stars form in clusters and in clustered environments.Any complete theory of star formation thus have to beable to reproduce the observations of young clusters andclustered star formation. Although many low mass starforming regions have been observed in details, our knowl-edge of very massive ones (more massive than 104 M⊙) islimited. The massive clusters provide us with a unique linkto extragalactic astronomy since only massive star clusterscan be detected as individual objects at cosmological dis-tances. However, they are either marginally resolved orunresolved outside the Local Group and their propertieshave to be obtained through their integrated properties.

The embedded cluster mass function is, at least as foundwithin 2 kpc, well represented by a power law with a slopeof −2 in linear units (Lada & Lada 2003). Therefore,for statistical reasons, massive clusters are relatively rareand they are therefore also expected to be far away onaverage. This has proved to be the case in that clustersmore massive than some 104 M⊙ are located at 6 kpcor more (NGC 3603, the Arches and R 136 in the LargeMagellanic Cloud). Fortunately, however, Westerlund 1was realized to be the most massive young star clusterknown in the Galaxy and only at a distance of 3-5 kpc.The closer distance combined with a larger core radiusthan e.g. NGC 3603 makes it a much easier target toobserve.

The importance of Westerlund 1

Westerlund 1 is a unique object in the Galaxy. It has beenknown since the early 60s when Bengt Westerlund noticeda heavily reddened cluster (Westerlund 1961). Early in-frared photometry revealed a dozen stars brighter than 5

mag in the K band (Borgman et al. 1970). During thenext decades a picture emerged that this was indeed ayoung cluster with a large population of O/B supergiantsand possibly M supergiants (Westerlund 1987). The youthled to the suggestion that the high reddening was directlyassociated with the cluster.

The early studies were severely limited by spatial resolu-tion and the low sensitivity at near-infrared wavelengths.The next breakthrough was the advent of the near-infraredimaging arrays. It then became directly clear that West-erlund 1 indeed is a massive cluster. Fig. 1 shows a JHKcolor composite of the central 4′×4′ of Westerlund 1. Thelarge contrast between the bright supergiants in the clusterand the fainter, much more numerous, low-mass stars isan observational challenge. Whereas the supergiants havemagnitudes as bright as H=6, an 0.1 M⊙ 4 Myr pre-mainsequence star will have an apparent magnitude of H=19due to extinction and distance.

Figure 1: JHK image of Westerlund 1 as seen with theNTT/SOfI (from Brandner et al. 2005). The field-of-viewis 4′ × 4′, corresponding to 4.8pc×4.8pc for a distance of4kpc. The faintest stars visible are around 3 M⊙.

To determine the massive evolved stellar content of West-erlund 1, Clark et al. (2005) obtained additional spectra ofsome 50 objects in the cluster, found them all to be post-main sequence objects and suggested that the initial clus-ter mass, extrapolating the IMF to the full stellar regime,could be as high as 105 M⊙. This would be a comparable

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mass to R136 in the 30 Dor region in the Large Magel-lanic Cloud. Later studies based on deeper photometricdata have revised this mass estimate to some 50·103 M⊙

(Brandner et al. 2008, Gennaro et al. 2011, Andersen etal. in prep). Nevertheless, Westerlund 1 is the most mas-sive young cluster known in the Galaxy and it thus offersa unique opportunity to study a supermassive star clusterin a detail impossible for the extragalactic analogues.

Evolved stars

The large population of evolved stars suggests that thecluster is at least 3-4 Myr old. Additional evidence of aslightly evolved cluster is the presence of a neutron star lo-cated only 1.6’ from the cluster center (Muno et al. 2006)which would be a remnant from a previous supernova.Westerlund 1 is an excellent laboratory to study the prop-erties of evolved stars. The rich population of evolvedstars allows detailed studies of evolved stars that are allof similar ages. Clark et al. (2005) determined the ageof the cluster from the massive star forming content to be4-5 Myr. Through a thorough campaign identifying targetobjects through narrow band imaging and follow-up spec-troscopy they found that there is well over 100 stars in thecluster with an initial mass over 30 M⊙, a mass that wasalso estimated to be the cluster’s turn-off mass. The highmass content spans a large range of spectral classes fromover a dozen WR stars to 25 OB supergiants and 6 yel-low hypergiants. The presence of the hypergiants togetherwith the red supergiants made Clark et al. (2010) suggestthat the transition between the most massive stars and theless massive stars in the “Conti scheme” (where the highmass stars do not evolve through a cool red super-giantphase, see Clark et al. 2010) is above 40 M⊙.

The large number of massive stars within a small areaof the sky further allows for more effective studies of thebinary properties of massive stars. Photometric variabil-ity studies have identified several eclipsing binaries in thecluster (Bonanos 2007) in addition to many variable stars,including WR stars and red supergiants. Mass ratios havefurther been determined for the eclipsing binary systems.Further studies of the multiplicity among the massive starsare carried out with the VLT/FLAMES Westerlund 1 sur-vey. Many spectroscopic binaries are discovered in the sur-vey which provide strong constraints on the binary prop-erties of massive stars. For example, as shown in Fig. 2,the combination of a radial velocity curve and eclipse mea-surements for the star Wd13 have provided an initial massof 40 M⊙ which then sets a lower limit on the origin starof the pulsar in the cluster (Koumpia & Bonanos 2012,Richie et al 2010).

Figure 2: An example of the combination of radial veloc-ity curves light curves, in this case for the near-contact,double-lined system Wd13 (from Koumpia & Bananos2012). The current-day masses for the primary and sec-ondary are 32.9± 1.9 and 21.1± 1.1 M⊙, respectively.

Main sequence stars

Main sequence stars are much better understood than thebright evolved stars in the cluster, they are still relativelyeasy to observe, and they are rather numerous in Wester-lund 1. They are therefore well suited to determine thecluster parameters. Brandner et al. (2008) obtained near-infrared imaging and derived photometry of stars from themain sequence turn-off down to below 3.4 M⊙ which wasthe completeness limit of the data. Lower mass objectswere detected but due to crowding only a small fractionof the cluster members expected to be there were resolvedand detected. The effect of crowding and the loss of starswere confirmed with artificial star experiments. The studydetermined the intermediate mass Initial Mass Function ofthe cluster which was found to be well represented by apower-law with a slope close to the Salpeter value. Theyfurther found that the cluster is elongated with an eccen-tricity of around 0.2

Gennaro et al. (2011) extended on the work of Brandner

7

et al. and provided more detailed completeness correctionsto compensate for crowding while taking the non-sphericalshape of Westerlund 1 into account and employing a moreelaborate field star subtraction. They found the clusterto be more elongated with an axis ratio of 3 : 2, with thelower-mass objects showing a higher ellipticity than thehigh mass stars.

The origin of the elongation is not clear. The cluster iselongated almost along the Galactic plane, but this maybe a coincidence. One possibility could be a merger oftwo clusters. However, as discussed below, there is noevidence for a large age spread within the cluster, whichplaces rather strict limits on the formation scenarios forsuch two clusters in that their age difference must havebeen a Myr or less.

The size of Westerlund 1 has been estimated by Lim et al.(2013). Using a larger field of view than the observationsin Brandner et al. they estimated a radius of the clusterof 2.5’, corresponding to 2.8kpc.

Pre-main sequence stars

Based on the age of the cluster it is expected that starsbelow about 2-3 M⊙ are still in their pre-main sequencephase. Reaching these objects is difficult since they are rel-atively faint once both extinction and distance are takeninto account. Further, a combination of the high stel-lar density within the cluster and the presence of the ex-tremely bright supergiants in the cluster precludes identi-fication of individual objects with standard ground basedobservations. Although it was clear from previous ground-based work that there is a main sequence population, thesensitivity and resolution were not sufficient to probe be-low around a solar mass, and the completeness of the datawas around 3 M⊙. High spatial resolution is necessary,either with adaptive optics from the ground or with theHST from space. Several current programs are targetingthe low-mass content in the cluster. Andersen et al. (inprep) have imaged the cluster with HST/WFC3 over a4’×4’ (4.8 × 4.8 pc) in order to characterize the InitialMass function of the cluster down to 0.1 M⊙ outside themost crowded central region. For the first time this al-lows the peak of the IMF to be identified in a massive starcluster. The data shows a rich population of pre-mainsequence stars as shown in Fig. 3.

By adopting pre-main sequence evolutionary tracks theyhave shown that the IMF in the cluster is close to the fieldstar IMF and the IMF in other star forming regions. Thisplaces strong constraints on any cluster formation modelthat predicts IMF variations as a function of cluster mass.

Kudryavtseva et al. (2012) utilized VLT NAOS/CONICAadaptive optics imaging over a 20” field of view. Togetherwith the later epoch HST data they obtained a proper mo-

Figure 3: J-H color-magnitude diagram of Westerlundbased on deep J and H band HST data (Andersen et al. inprep). The color coding indicate membership probabilityof each star. Overplotted is a Baraffe et al. (1998) 4 Myrisochrone shifted to the distance of Westerlund 1 and red-dened by Av = 10.3. The highest mass available for theBaraffe et al. isochrone is 1.4 M⊙. The cluster sequencecontinues to higher masses. The red, formally high prob-ability, objects at J −H ∼ 2 and H 15 are unrelated fieldred giants along the line og sight.

tion selected sample of the cluster where the field star con-tamination is reduced compared to single epoch imaging.They examined whether there is an age spread within thecluster for the low-mass content. Based on objects closeto the main sequence/pre-main sequence transition theydeduced that the data were consistent with a rather smallage spread of some 0.4 Myr or less.

Mass segregation within Westerlund 1

It was already suspected from the work on the most mas-sive stars that the cluster is mass segregated, i.e. the mas-sive stars are more centrally concentrated than the aver-age stars. The imaging survey by Brandner et al. (2008)showed that this is true for the stellar population between3.4 and 27 M⊙, the lower mass limit being the complete-ness limit of their observations. Within the central 0.75pc the slope of the derived mass function was found to be−0.6 compared to a Salpeter slope of −1.35. Conversely,a steeper slope of −1.7 was found between 2.1 and 3.3pc. This was confirmed by Lim et al. (2013) using largescale optical imaging together with near-infrared imaging.There does not appear to be any discernable mass segre-gation in the lower mass (down to 1 M⊙) stellar content atleast outside a radius of 0.75 pc. Detecting and obtainingphotometry of low-mass objects within this radius is dif-

8

ficult due to crowding and bright stars. This is a similarpicture of mass segregation as the younger Orion NebulaCluster where the massive stars are mass segregated butnot the low-mass stars.

Gennaro et al. (2011) argue that based on the age anddensity of the cluster, the mass segregation of the massivestars can have a dynamical origin and it is not necessaryfor the mass segregation to be primordial.

The fate of Westerlund 1

Is Westerlund 1 a bound or unbound entity? Due to itsmass it could potentially evolve into a low-mass globu-lar cluster if it is not destroyed due to interactions in theGalactic disk. Although the three dimensional structureis not currently available, it is possible to determine theradial velocity dispersion of the cluster. A single epochnear-infrared long slit spectroscopy scan of the clusterwas used for the first attempts to determine the radialvelocity dispersion (Mengel et al. 2007). The velocitydispersion based on 4 stars with clear CO band head ab-sorption in the K-band was found to be relatively low,5.8±2.1kms−1. Later multi-epoch optical spectroscopy ofa sample of bright stars were obtained to place firmer lim-its on the velocity dispersion. One important limitationof single epoch observations of massive stars in particularis the high frequency of multiple systems. The relativemotion around a binary center of gravity can severely in-crease the observed radial velocity dispersion. Cottaar etal. (2012) showed with a sub-set of stars that indeed thevelocity dispersion was lower, 2.1+3.3

−2.1kms−1. For the mostrecent photometric cluster mass estimates they deducedthat the cluster is sub-virial at the 90% level and theycould rule out that the cluster is super-virial at the 97%level. The cluster is therefore expected to be able to sur-vive for a long time and could in principle evolve into alow-mass globular cluster over time. However, due to itslocation in the Galactic plane, it is likely to be dispersed.Encounters with other star clusters and giant molecularclouds can heat the cluster and it can then easier disperseand become a part of the field star population.

Future studies of Westerlund 1

Although much has already been learned about Wester-lund 1 in the last decade it still holds many secrets thatwill be revealed in the future. In the coming years it will bepossible to obtain proper motions of the individual starsin the cluster in a similar manner to what has been donefor NGC 3603 (Rochau et al. 2010) and the Arches clus-ter (Clarkson et al. 2011). Unlike the previous studyby Kudryavtseva et al., this can now be done for the fullcluster with the HST. A proper motion selected samplewill help resolve the confusion between cluster and field

stars, particularly at larger radii where the contaminationis substantial. This is especially true for the low-mass starand brown dwarf content where field stars are confusingin the color-magnitude diagrams. In addition to providemuch cleaner samples of cluster members, the proper mo-tion samples can be used to derive the velocity dispersionof the cluster members. So far, the optical radial veloc-ity surveys have been restricted to the high mass contentwhereas with the proper motion data the low-mass con-tent can be obtained as well. The velocity dispersion fordifferent mass ranges will be a powerful diagnostic of masssegregation in the cluster.

Studies of spectroscopic binaries and variable stars canbe pushed even further. Near-infrared monitoring providethe possibility to identify low-mass eclipsing binaries. Thelarge number of pre-main sequence stars in the clustermakes it almost guaranteed that many will be present.This will in turn allow dynamical mass ratio estimates ofbinaries within a single cluster over more than an order ofmagnitude in mass within a single cluster, and assuminga single age for the cluster will allow tests of post- andpre-main sequence objects at the same time.

Finally, the brown-dwarf initial mass function is essentiallyunexplored. Although the present deep HST observationshave discovered brown dwarfs in Westerlund 1, the crowd-ing and contrast precluded any good estimates of theirnumber density. This will change in the coming years andfor example JWST will easily be able to both image thebrown dwarf content and to obtain spectra of individualobjects to ensure they are members and not reddened fieldstars.

References:

Andersen, M. et al. in prep.

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Borgman, J., Koornneef, J., & Slingerland, J. 1970, A&A, 4, 248

Bonanos, A. Z. 2007, AJ, 133, 2696

Brandner, W., Clark, J. S., Stolte, A., Waters, R., Negueruela, I., &

Goodwin, S. P. 2008, A&A, 478, 137

Brandner, W., Clark, J. S., Stolte, A., et al. 2008, A&A, 478, 137

Clark, J. S. et al. 2005, A&A, 434, 949

Clark, J. S., Negueruela, I., Ritchie, B., Crowther, P., & Dougherty,

S. 2010, The Messenger, 142, 31

Clarkson, W. I. et al. 2012, ApJ, 751, 132

Cottaar, M., Meyer, M. R., Andersen, M., & Espinoza, P. 2012,

A&A, 539, A5

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RAS, 412, 2469

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Lim, B., Chun, M.-Y., Sung, H., et al. 2013, AJ, 145, 46

Mengel, S., & Tacconi-Garman, L. E. 2007, A&A, 466, 151

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Ritchie, B. W. et al. 2010, A&A, 520, A48

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Westerlund, B. E. 1987, A&AS, 70, 311

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Abstracts of recently accepted papers

Viscous Evolution and Photoevaporation of Circumstellar Disks due to External FUVRadiation Fields

Kassandra R. Anderson1,2, Fred C. Adams1,2 and Nuria Calvet2

1 Physics Department, University of Michigan, Ann Arbor, MI 48109, USA2 Astronomy Department, University of Michigan, Ann Arbor, MI 48109, USA

E-mail contact: kassand at umich.edu

This paper explores the effects of FUV radiation fields from external stars on circumstellar disk evolution. Disksresiding in young clusters can be exposed to extreme levels of FUV flux from nearby OB stars, and observationsshow that disks in such environments are being actively photoevaporated. Typical FUV flux levels can be factorsof ∼ 102 − 104 higher than the interstellar value. These fields are effective in driving mass loss from circumstellardisks because they act at large radial distance from the host star, i.e., where most of the disk mass is located, andwhere the gravitational potential well is shallow. We combine viscous evolution (an α-disk model) with an existingFUV photoevaporation model to derive constraints on disk lifetimes, and to determine disk properties as functions oftime, including mass loss rates, disk masses, and radii. We also consider the effects of X-ray photoevaporation fromthe host star using an existing model, and show that for disks around solar-mass stars, externally-generated FUVfields are often the dominant mechanism in depleting disk material. For sufficiently large viscosities, FUV fields canefficiently photoevaporate disks over the entire range of parameter space. Disks with viscosity parameter α = 10−3

are effectively dispersed within 1-3 Myr; for higher viscosities (α = 10−2) disks are dispersed within ∼ 0.25− 0.5 Myr.Furthermore, disk radii are truncated to less than ∼ 100 AU, which can possibly affect the formation of planets. Ourmodel predictions are consistent with the range of observed masses and radii of proplyds in the Orion Nebula Cluster.

Accepted by The Astrophysical Journal

http://arxiv.org/pdf/1307.4368v1.pdf

Long-term Evolution of Photoevaporating Protoplanetary Disks

Jaehan Bae1, Lee Hartmann1, Zhaohuan Zhu2 and Charles Gammie3,4

1 Department of Astronomy, University of Michigan, 500 Church St., Ann Arbor, MI 48105, USA2 Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Peyton Hall, Princeton, NJ 08544, USA3 Department of Astronomy, University of Illinois Urbana-Champaign, 1002 W. Green St., Urbana, IL 61801, USA4 Department of Physics, University of Illinois Urbana-Champaign, 1110 W. Green St., Urbana, IL 61801, USA

E-mail contact: jaehbae at umich.edu

We perform calculations of our one-dimensional, two-zone disk model to study the long-term evolution of the circumstel-lar disk. In particular, we adopt published photoevaporation prescriptions and examine whether the photoevaporativeloss alone, coupled with a range of initial angular momenta of the protostellar cloud, can explain the observed declineof the frequency of optically-thick dusty disks with increasing age. In the parameter space we explore, disks haveaccreting and/or non-accreting transitional phases lasting of <∼20 % of their lifetime, which is in reasonable agreementwith observed statistics. Assuming that photoevaporation controls disk clearing, we find that initial angular momen-tum distribution of clouds needs to be weighted in favor of slowly rotating protostellar cloud cores. Again, assuminginner disk dispersal by photoevaporation, we conjecture that this skewed angular momentum distribution is a resultof fragmentation into binary or multiple stellar systems in rapidly-rotating cores. Accreting and non-accreting transi-tional disks show different evolutionary paths on the M −Rwall plane, which possibly explains the different observedproperties between the two populations. However, we further find that scaling the photoevaporation rates downwardby a factor of 10 makes it difficult to clear the disks on the observed timescales, showing that the precise value of thephotoevaporative loss is crucial to setting the clearing times. While our results apply only to pure photoevaporative

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loss (plus disk accretion), there may be implications for models in which planets clear disks preferentially at radii oforder 10 AU.


http://arxiv.org/pdf/1307.2585

A non-LTE radiative transfer model to study ionized outflows and disks. The case ofMWC349A

A. Baez-Rubio1, J. Martın-Pintado1, C. Thum2, and P. Planesas3

1 Centro de Astrobiologıa (CSIC-INTA), Ctra de Torrejon a Ajalvir, km 4, 28850 Torrejon de Ardoz, Madrid, Spain2 Instituto de Radio Astronomıa Milimetrica (IRAM), Avenida Divina Pastora, 7, Nıucleo Central, E 18012 Granada,Spain3 Observatorio Astronomico Nacional (IGN), Alfonso XII 3, E-28014 Madrid, Spain

E-mail contact: baezra at cab.inta-csic.es

Context. The best example of a massive star with an ionized outflow launched from its photoevaporating disk isMWC349A. The large amount of reported radio-continuum and radio-recombination line observations toward thisgalactic UC-HII region offers a unique possibility to build a model of the ionized envelope of this source.Aims. To understand the physical conditions and kinematics of the ionized region of the circumstellar disk and alsoof the outflow of MWC349A.Methods. We compared the bulk of radio-continuum maps, radio-recombination line profiles, and the H30α centroidmap published to date with the predictions of our non-LTE 3D radiative transfer model, MORELI (MOdel for RE-combination LInes), which we describe here in detail.Results. Our non-LTE 3D radiative transfer model provides new evidence that the UC-HII region of MWC349A iscomposed of an ionized circumstellar disk rotating in Keplerian fashion around a star of 38 M⊙, and an ionized outflowexpanding with a terminal velocity of 60 km s−1 and rotating in the same sense as the disk. The model shows thatwhile maser amplification is the dominant process involved for Hnα radio-recombination line (RRL) emission withquantum numbers n < 41, stimulated emission is relevant for the emission of RRLs with n > 41 up at least the H76αline.Conclusions. For the first time, we present a model of MWC349A which satisfactorily explains the vast amount ofreported observational data for a very wide range of frequencies and angular resolutions.

Accepted by A&A


Young stellar clusters in the Rosette molecular cloud. Arguments against triggered starformation

L. Cambresy1, G. Marton2, O. Feher3, L.V. Toth3, and N. Schneider4

1 Observatoire astronomique de Strasbourg, Universite de Strasbourg, CNRS, UMR 7550, 11 rue de l’Universite, 67000Strasbourg, France2 Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, KonkolyThege 15-17, H-1121 Budapest, Hungary3 Eotvos Lorand University, Department of Astronomy, Pazmany Peter setany 1/A, 1117 Budapest, Hungary4 Laboratoire d’Astrophysique de Bordeaux, CNRS/INSU, Universite de Bordeaux, BP 89, 33271 Floirac cedex, France

E-mail contact: cambresy at astro.unistra.fr

The Rosette complex is a well studied region of the galactic plane which presents the apparent characteristics of atriggered star forming region. This is however still debated as no strong evidence corroborates this statement. Wefocus on characterizing the young stellar population in the Rosette complex to improve our understanding of theprocesses that regulate the star formation in this region. We propose an original method that relies on the jointanalysis of the star color and density in the near-infrared. It leads to mapping the molecular cloud spatial distributionand detecting the embedded clusters with their characterization in terms of member number and age estimation. Wehave identified 13 clusters, 2 of which are new discoveries, and we estimate that the total number of young stellar

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objects in the Rosette ranges between 4000 and 8000 members. We find that the age distribution of the young clustersis not consistent with a general triggered scenario for the star formation in this molecular cloud. This study provesthat the Rosette complex evolution is not governed by the influence of its OB star population. It suggests that thesimple morphological appearance of an active region is not sufficient to conclude much about the triggering role in thestar formation process. Our method of constraining the cluster properties using UKIDSS and WISE data has provenefficient, and studies of other regions of the galactic plane would definitely benefit from this approach.

Accepted by A&A


CEN34 – High-Mass YSO in M17 or Background Post-AGB Star?

Zhiwei Chen1,2,3, Dieter Nurnberger2, Rolf Chini2,4, Yao Liu1, Min Fang1, and Zhibo Jiang1

1 Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijing Road, 210008 Nanjing, China2 Astronomisches Institut, RuhrUniversitat Bochum, Universitatsstrasse 150, 44801 Bochum, Germany3 University of Chinese Academy of Sciences, 100039 Beijing, China4 Instituto de Astronomıa, Universidad Catolica del Norte, Avenida Angamos 0610, Casilla 1280 Antofagasta, Chile

E-mail contact: zwchen at pmo.ac.cn

We investigate the proposed high-mass young stellar object (YSO) candidate CEN34, thought to be associated with thestar forming region M17. Its optical to near-infrared (550–2500 nm) spectrum reveals several photospheric absorptionfeatures, such as Hα, Ca triplet and CO bandheads but lacks any emission lines. The spectral features in the range8375–8770 A are used to constrain an effective temperature of 5250±250 (early-/mid-G) and a surface gravity of2.0±0.3 (supergiant). The spectral energy distribution of CEN34 resembles the SED of a high-mass YSO or anevolved star. Moreover, the observed temperature and surface gravity are identical for high-mass YSOs and evolvedstars. The radial velocity relative to LSR (VLSR) of CEN34 as obtained from various photospheric lines is of theorder of −60 km s−1 and thus distinct from the +25 km s−1 found for several OB stars in the cluster and for theassociated molecular cloud. The SED modeling yields ∼ 10−4 M⊙ of circumstellar material which contributes only atiny fraction to the total visual extinction (11 mag). In the case of a YSO, a dynamical ejection process is proposedto explain the VLSR difference between CEN34 and M17. Additionally, to match the temperature and luminosity, wespeculate that CEN34 had accumulated the bulk of its mass with accretion rate > 4 × 10−3 M⊙ yr−1 in a very shorttime span (∼103 yrs), and currently undergoes a phase of gravitational contraction without any further mass gain.However, all the aforementioned characteristics of CEN34 are compatible with an evolved star of 5–7 M⊙ and an ageof 50–100 Myrs, most likely a background post-AGB star with a distance between 2.0 kpc and 4.5 kpc. We considerthe latter classification as the more likely interpretation. Further discrimination between the two possible scenariosshould come from the more strict confinement of CEN34’s distance.

Accepted by A&A


Stellar and circumstellar properties of visual binaries in the Orion Nebula Cluster

S. Correia1,2, G. Duchene3,4, B. Reipurth5,6, H. Zinnecker1,7,8, S. Daemgen9,10, M. G. Petr-Gotzens9,

R. Kohler11,12, Th. Ratzka13, C. Aspin5, Q. M. Konopacky14 and A. M. Ghez15,16

1 Leibniz-Institut fur Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany2 Institute for Astronomy, University of Hawaii, 34 Ohia Ku Street, Pukalani, HI 96768, USA3 Astronomy Department, University of California, Berkeley, CA 94720-3411, USA4 UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d’Astrophysique de GrenobleUMR 5274, 38041 Grenoble,France5 Institute for Astronomy, University of Hawaii, 640 N. Aohoku Place, Hilo, HI 96720, USA6 NASA Astrobiology Institute7 Deutsches SOFIA Institut, Universitat Stuttgart, Pfaffenwaldring 29, 70569 Stuttgart, Germany8 SOFIA Science Center, NASA-Ames Research Center, MS 232-12, Moffett Field, CA 94035, USA9 European Southern Observatory, Karl Schwartzschild Str. 2, 85748 Garching bei Munchen, Germany

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10 Department of Astronomy & Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4,Canada11 Max-Planck-Institut fur Astronomie, Konigstuhl 17, 69117 Heidelberg, Germany12 Landessternwarte, Zentrum fur Astronomie der Universitat Heidelberg, Konigstuhl, 69117 Heidelberg, Germany13 Universitats-Sternwarte Munchen, Ludwig-Maximilians-Universitat, Scheinerstr. 1, 81679 Munchen, Germany14 Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto M5S 3H4,Ontario, Canada15 Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547, USA16 Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, CA 90095-1565, USA

E-mail contact: sergeco at gmail.com

Our general understanding of multiple star and planet formation is primarily based on observations of young multiplesystems in low density regions like Tau-Aur and Oph. Since many, if not most, of the stars are born in clusters,observational constraints from young binaries in those environments are fundamental for understanding both theformation of multiple systems and planets in multiple systems throughout the Galaxy. We build upon the largestsurvey for young binaries in the Orion Nebula Cluster (ONC) which is based on Hubble Space Telescope observationsto derive both stellar and circumstellar properties of newborn binary systems in this cluster environment. We presentAdaptive Optics spatially-resolved JHKL’-band photometry and K-band R∼ 5000 spectra for a sample of 8 ONCbinary systems from this database. We characterize the stellar properties of binary components and obtain a censusof protoplanetary disks through K-L’ color excess. For a combined sample of ONC binaries including 7 additionalsystems with NIR spectroscopy from the literature, we derive mass ratio and relative age distributions. We comparethe stellar and circumstellar properties of binaries in ONC with those in Tau-Aur and Oph from samples of binarieswith stellar properties derived for each component from spectra and/or visual photometry and with a disk censusobtained through K-L color excess. The mass ratio distribution of ONC binaries is found to be indistinguishable fromthat of Tau-Aur and, to some extent, to that of Oph in the separation range 85-560AU and for primary mass in therange 0.15 to 0.8M⊙. A trend toward a lower mass ratio with larger separation is suggested in ONC binaries whichis not seen in Tau-Aur binaries. The components of ONC binaries are found to be significantly more coeval than theoverall ONC population and as coeval as components of binaries in Tau-Aur and Oph. There is a hint of a largerfraction of mixed pairs, i.e. systems with a disk around only one component, in wide ONC binaries in comparison towide binaries in Tau-Aur and Oph within the same primary mass range that could be caused by hierarchical triples.The mass ratio distributions of mixed and unmixed pairs in the overall population of T Tauri binaries are shown tobe different. Some of these trends require confirmation with observations of a larger sample of binary systems.

Accepted by A&A


Berkeley 94 and Berkeley 96: Two Young Clusters with Different Dynamical Evolution

A.J. Delgado1, A.A Djupvik2, M.T. Costado1 and E.J. Alfaro1

1 Instituto de Astrofısica de Andalucıa (IAA-CSIC), Glorieta de la Astronomıa, 18008-Granada, Spain2 Nordic Optical Telescope (NOT), Apdo. 474, 38700 Santa Cruz de La Palma, Spain.

E-mail contact: delgado at iaa.es

We have performed multiband UBVRcIcJHKs photometry of two young clusters located at large Galactocentricdistances in the direction of the Perseus spiral arm. The obtained distances and colour excesses amount to 3.9±0.11kpc, E(B − V )=0.62±0.05 for Berkeley 94, and 4.3±0.15 kpc, E(B − V )=0.58±0.06 for Berkeley 96. The respectiveages, as measured from the comparison of the upper colour-magnitude diagrams to model isochrones, amount tolog10Age(yr)=7.5±0.07, and 7.0±0.07, respectively. A sequence of optical PMS members is proposed in both clusters.In addition, samples of objects showing (H − Ks) excess are found. Part of these are suggested to be PMS clustermembers of lower mass than the optical candidates. The spatial distribution of these sources, the comparison to galacticmodels and to the expected number of contaminating distant red galaxies, and the spectral energy distribution inparticular cases support this suggestion. According to the results from numerical simulations, the spatial distributionsof members in different mass ranges are interpreted as suggesting different initial conditions and evolutionary dynamicalpaths for the clusters. Berkeley 94 would have formed under supervirial conditions, and followed the so-called warmcollapse model in its evolution, whereas Berkeley 96 would have formed with a subvirial structure, and would have

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evolved following a cold collapse path. Both processes would be able to reproduce the suggested degree of masssegregation and their spatial distribution by mass range. Finally, the mass distributions of the clusters, from the mostmassive stars down to PMS stars around 1.3 M⊙, are calculated. An acceptable general agreement with the SalpeterIMF slope is found.

Accepted by MNRAS


Photometric determination of the mass accretion rates of pre-main sequence stars. IV.Recent star formation in NGC602

Guido De Marchi1, Giacomo Beccari2 and Nino Panagia3,4,5

1 European Space Agency, Keplerlaan 1, 2200 AG Noordwijk, Netherlands2 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany3 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA4 INAF–NA, Osservatorio Astronomico di Capodimonte, Salita Moiariello, 16 80131 Naples, Italy5 Supernova Limited, OYV #131, Northsound Rd., Virgin Gorda, British Virgin Islands, VG 1155

E-mail contact: gdemarchi at rssd.esa.int

We have studied the young stellar populations in NGC602, in the Small Magellanic Cloud, using a novel method thatwe have developed to combine Hubble Space Telescope photometry in the V , I, and Hα bands. We have identifiedabout 300 pre-main sequence (PMS) stars, all of which are still undergoing active mass accretion, and have determinedtheir physical parameters (effective temperature, luminosity, age, mass and mass accretion rate). Our analysis showsthat star formation has been present in this field over the last 60Myr. In addition, we can recognise at least twoclear, distinct, and prominent episodes in the recent past: one about 2Myr ago, but still ongoing in regions of highernebulosity, and one (or more) older than 30Myr, encompassing both stars dispersed in the field and two smallerclusters located about 100 arcsec north of the centre of NGC602. The relative locations of younger and older PMSstars do not imply a causal effect or triggering of one generation on the other. The strength of the two episodesappears to be comparable, but the episode occurring more than 30Myr ago might have been even stronger than thecurrent one. We have investigated the evolution of the mass accretion rate Macc as a function of the stellar parametersfinding that log Macc ≃ −0.6 log t+ logm+ c, where t is the age of the star, m its mass and c is a decreasing functionof the metallicity.

Accepted by Astrophys. J.


Pre-main sequence stars older than 8Myr in the Eagle Nebula

Guido De Marchi1, Nino Panagia2,3,4, M. G. Guarcello5 and Rosaria Bonito6

1 European Space Agency, Keplerlaan 1, 2200 AG Noordwijk, Netherlands2 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA3 INAF–NA, Osservatorio Astronomico di Capodimonte, Salita Moiariello, 16 80131 Naples, Italy4 Supernova Limited, OYV #131, Northsound Rd., Virgin Gorda, British Virgin Islands, VG 11555 Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138, USA6 Dipartimento di Fisica e Chimica, Universita di Palermo and INAF–PA, Osservatorio Astronomico di Palermo,Piazza del Parlamento 1, 90134 Palermo, Italy

E-mail contact: gdemarchi at rssd.esa.int

Attention is given to a population of 110 stars in the NGC 6611 cluster of the Eagle Nebula that have prominentnear-infrared (NIR) excess and optical colours typical of pre-main sequence (PMS) stars older than 8Myr. At leasthalf of those for which spectroscopy exists have a Hα emission line profile revealing active accretion. In principle,the V − I colours of all these stars would be consistent with those of young PMS objects (< 1Myr) whose radiationis heavily obscured by a circumstellar disc seen at high inclination and in small part scattered towards the observerby the back side of the disc. However, using theoretical models it is shown here that objects of this type can onlyaccount for a few percent of this population. In fact, the spatial distribution of these objects, their X-ray luminosities,

14

their optical brightness, their positions in the colour–magnitude diagram and the weak Li absorption lines of the starsstudied spectroscopically suggest that most of them are at least 8 times older than the ∼ 1Myr-old PMS stars alreadyknown in this cluster and could be as old as ∼ 30Myr. This is the largest homogeneous sample to date of GalacticPMS stars considerably older than 8Myr that are still actively accreting from a circumstellar disc and it allows us toset a lower limit of 7% to the disc frequency at ∼ 16Myr in NGC6611. These values imply a characteristic exponentiallifetime of ∼ 6Myr for disc dissipation.

Accepted by MNRAS


DIGIT: Herschel and Spitzer spectro-imaging of SMM3 and SMM4 in Serpens

O. Dionatos1,2,3, J. K. Jørgensen 2,1, J. D. Green4, G. J. Herczeg5, N. J. Evans II 4, L. E. Kristensen6,

J. E. Lindberg1,2 and E. F. van Dishoeck 6,7

1 Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, ØsterVoldgade 5 – 7, DK-1350 Copenhagen K. Denmark2 Niels Bohr Institute, University of Copenhagen. Juliane Maries Vej 30, DK-2100 Copenhagen Ø. Denmark3 University of Vienna, Department of Astronomy, Turkenschanzstrasse 17, A-1180, Vienna, Austria4 University of Texas at Austin, Department of Astronomy, 2515 Speedway, Stop C1400, Austin, TX 78712-1205, USA5 Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing, 100871, PR China6 Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands7 Max Planck Institut fur Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching, Germany

E-mail contact: odysseas at nbi.ku.dk

We report on spectro-imaging observations employing Spitzer/IRS and Herschel/PACS, aiming to constrain the phys-ical conditions around SMM3 and SMM4 in Serpens. The combined power of both instruments provides an almostcomplete wavelength coverage between 5 and 200 µm at an angular resolution of 10”. We detect line emission from allmajor molecular (H2, CO, H2O and OH) and many atomic ([OI], [CII], [FeII], [SiII] and [SI]) coolants. Line emissiontends to peak at distances of 10” - 20” from the protostellar sources, at positions of known outflow shocks. The onlyexception is [CII] which likely traces a PDR excited from the neighboring source SMM6. Excitation analysis indicatesthat H2 and CO originate from gas at two distinct rotational temperatures of 300 K and 1000 K, while H2O and OHemission corresponds to rotational temperatures of 100 - 200 K. The morphological and physical association betweenCO and H2 suggests a common excitation mechanism which allows direct comparisons between the two molecules.The CO/H2 abundance ratio varies from 10−5 in the warm gas up to 10−4 in the hotter regions. While both C- andJ-shocks can account for the observed molecular emission, J-shocks are strongly advocated by the atomic emission andline ratio diagnostics that provide simpler and more homogeneous solutions for the excitation of CO and H2. C-shocksdescribe better the emission from H2O and OH. The variations in the CO/H2 abundance ratio for gas at differenttemperatures can be interpreted by their reformation rates in dissociative J-type shocks, or the simultaneous influenceof both C and J shocks.

Accepted by Astronomy & Astrophysics


Planetesimal formation via sweep-up growth at the inner edge of dead zones

Joanna Drazkowska1,2, Fredrik Windmark1,2 and Cornelis P. Dullemond1

1 Heidelberg University, Center for Astronomy, Institute for Theoretical Astrophysics, Albert-Ueberle-Str. 2, 69120Heidelberg, Germany2 Member of the International Max Planck Research School for Astronomy and Astrophysics at the Heidelberg Uni-versity

E-mail contact: drazkowska at uni-heidelberg.de

The early stages of planet formation are still not well understood. Coagulation models have revealed numerousobstacles to the dust growth, such as the bouncing, fragmentation and radial drift barriers. We study the interplaybetween dust coagulation and drift in order to determine the conditions in protoplanetary disk that support the

15

formation of planetesimals. We focus on planetesimal formation via sweep-up and investigate whether it can takeplace in a realistic protoplanetary disk. We have developed a new numerical model that resolves spatial distributionof dust in the radial and vertical dimension. The model uses representative particles approach to follow the dustevolution in protoplanetary disk. The coagulation and fragmentation of solids is taken into account using MonteCarlo method. A collision model adopting the mass transfer effect, that can occur for different-sized dust aggregatecollisions, is implemented. We focus on a protoplanetary disk including a pressure bump caused by a steep declineof turbulent viscosity around the snow line. Our results show that sufficient resolution of the vertical disk structurein dust coagulation codes is necessary to obtain adequately short growth timescales, especially in the case of a lowturbulence region. We find that a sharp radial variation of the turbulence strength at the inner edge of dead zonepromotes planetesimal formation in several ways. It provides a pressure bump that efficiently prevents the dust fromdrifting inwards. It also causes a radial variation in the size of aggregates at which growth barriers occur, favoring thegrowth of large aggregates via sweeping up of small particles. In our model, by employing an ad hoc alpha viscositychange near the snow line, it is possible to grow planetesimals by incremental growth on timescales of approximately105 years.



The Gould’s Belt Very Large Array Survey I: The Ophiuchus complex

Sergio Dzib1, Laurent Loinard1,2, Amy J. Mioduszewski3, Luis F. Rodrıguez1,4, Gisela N. Ortiz-Leon1,

Gerardo Pech1, Juana L. Rivera1, Rosa M. Torres5, Andrew F. Boden6, Lee Hartmann7, Neal J. Evans

II8, Cesar Briceno9 and John Tobin10

1 Centro de Radioastronomıa y Astrofısica, Universidad Nacional Autonoma de Mexico Apartado Postal 3-72, 58090,Morelia, Michoacan, Mexico2 Max Planck Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany3 National Radio Astronomy Observatory, Domenici Science Operations Center, 1003 Lopezville Road, Socorro, NM87801, USA4 King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia5 Paul Harris 9065, Las Condes, Santiago, Chile6 Division of Physics, Math, and Astronomy, California Institute of Technology, 1200 E California Blvd., Pasadena,CA 91125, USA7 Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48105, USA8 Department of Astronomy, The University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712, USA9 Centro de Investigaciones de Astronomıa, Merida 5101-A, Venezuela10 National Radio Astronomy Observatory, Charlottesville, VA 22903

E-mail contact: s.dzib at crya.unam.mx

We present large-scale (∼ 2000 square arcminutes), deep (∼ 20 µJy), high-resolution (∼ 1′′) radio observations of theOphiuchus star-forming complex obtained with the Karl G. Jansky Very Large Array at λ = 4 and 6 cm. In total,189 sources were detected, 56 of them associated with known young stellar sources, and 4 with known extragalacticobjects; the other 129 remain unclassified, but most of them are most probably background quasars. The vast majorityof the young stars detected at radio wavelengths have spectral types K or M, although we also detect 4 objects ofA/F/B types and 2 brown dwarf candidates. At least half of these young stars are non-thermal (gyrosynchrotron)sources, with active coronas characterized by high levels of variability, negative spectral indices, and (in some cases)significant circular polarization. As expected, there is a clear tendency for the fraction of non-thermal sources toincrease from the younger (Class 0/I or flat spectrum) to the more evolved (Class III or weak line T Tauri) stars.The young stars detected both in X-rays and at radio wavelengths broadly follow a Gudel-Benz relation, but with adifferent normalization than the most radio-active types of stars. Finally, we detect a ∼ 70 mJy compact extragalacticsource near the center of the Ophiuchus core, which should be used as gain calibrator for any future radio observationsof this region.

Accepted by ApJ


16

Herschel observations of the Sgr B2 cores: Hydrides, warm CO, and cold dust

M. Etxaluze1, J.R. Goicoechea1, J. Cernicharo1, E.T. Polehampton2,3, A. Noriega-Crespo4, S. Molinari5,

B.M. Swinyard2,6, R. Wu7 , and J. Bally8

1 Departamento de Astrofısica. Centro de Astrobiologıa. CSIC-INTA. Torrejon de Ardoz, 28850 Madrid, Spain2 RAL Space, Rutherford Appleton Laboratory, Oxfordshire, OX11 0QX, UK3 Institute for Space Imaging Science, Department of Physics & Astronomy, University of Lethbridge, Lethbridge, ABT1K3M4, Canada4 Spitzer Science Center, 91125 Pasadena, USA5 INAF-IFSI, I-00133 Roma, Italy6 Dept. of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK7 Commissariat A l’Energie Atomique, Service d’Astrophysique, Saclay, 91191 ‘ Gif-sur-Yvette, France8 CASA, University of Colorado, Boulder, USA 80309

E-mail contact: etxaluzeam at cab.inta-csic.es

Sagittarius B2 (Sgr B2) is one of the most massive and luminous star-forming regions in the Galaxy and shows chemicaland physical conditions similar to those in distant extragalactic starbursts. We present large-scale far-IR/submmphotometric images and spectroscopic maps taken with the PACS and SPIRE instruments onboard Herschel. Thespectra towards the Sgr B2 star-forming cores, B2(M) and B2(N), are characterized by strong CO line emission,emission lines from high-density tracers (HCN, HCO+, and H2S), [N II] 205 µm emission from ionized gas, andabsorption lines from hydride molecules (OH+, H2O

+, H2O, CH+, CH, SH+, HF, NH, NH2, and NH3). The rotationalpopulation diagrams of CO suggest the presence of two gas temperature components: an extended warm component,which is associated with the extended envelope, and a hotter component, which is seen towards the B2(M) andB2(N) cores. As observed in other Galactic Center clouds, the gas temperatures are significantly higher than the dusttemperatures inferred from photometric images. We determined far-IR and total dust masses in the cores. Non-localthermodynamic equilibrium models of the CO excitation were used to constrain the averaged gas density in the cores.A uniform luminosity ratio is measured along the extended envelope, suggesting that the same mechanism dominatesthe heating of the molecular gas at large scales. The detection of high-density molecular tracers and of strong [NII] 205 µm line emission towards the cores suggests that their morphology must be clumpy to allow UV radiation toescape from the inner HII regions. Together with shocks, the strong UV radiation field is likely responsible for theheating of the hot CO component. At larger scales, photodissociation regions models can explain both the observedCO line ratios and the uniform L(CO)/LFIR luminosity ratios.

Accepted by A&A


Bipolar jets launched from accretion disks.II. Formation of asymmetric jets and counter jets

Christian Fendt1 and Somayeh Sheikhnezami1

1 Max Planck Institute for Astronomy, Heidelberg, Germany

E-mail contact: fendt at mpia.de

We investigate the jet launching from accretion disks, in particular the formation of intrinsically asymmetric jet /counter-jet systems. We perform axisymmetric MHD simulations of the disk-jet structure on a bipolar computationaldomain covering both hemispheres. We apply various models such as: asymmetric disks with (initially) differentscale height in each hemisphere; symmetric disks into which a local disturbance is injected; and jets launched intoan asymmetric disk corona. We consider both a standard global magnetic diffusivity distribution and a novel localdiffusivity model. Typical disk evolution first shows substantial disk warping and then results in asymmetric outflowswith 10- 30% mass flux difference. We find that the magnetic diffusivity profile is essential for establishing a long-term outflow asymmetry. We conclude that bipolar asymmetry in protostellar and extra-galactic jets can indeed begenerated intrinsically and maintained over long time by disk asymmetries and the standard jet launching mechanism.

Accepted by ApJ

17

Diffuse Molecular Cloud Densities from UV Measurements of CO Absorption

Paul Goldsmith1

1Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena CA 91109, USA

E-mail contact: paul.f.goldsmith at jpl.nasa.gov

We use UV measurements of interstellar CO towards nearby stars to calculate the density in the diffuse molecularclouds containing the molecules responsible for the observed absorption. Chemical models and recent calculationsof the excitation rate coefficients indicate that the regions in which CO is found have hydrogen predominantly inmolecular form. We carry out statistical equilibrium calculations using CO–H2 collision rates to solve for the H2

density in the observed sources without including effects of radiative trapping. We have assumed kinetic temperaturesof 50 K and 100 K, finding this choice to make relatively little difference to the lowest transition. For the sources havingT ex10 only, for which we could determine upper and lower density limits, we find < n(H2) > = 49 cm−3. While we can

find a consistent density range for a good fraction of the sources having either two or three values of the excitationtemperature, there is a suggestion that the higher–J transitions are sampling clouds or regions within diffuse molecularcloud material that have higher densities than the material sampled by the J = 1–0 transition. The assumed kinetictemperature and derived H2 density are anticorrelated when the J = 2–1 transition data, the J = 3–2 transition data,or both are included. For sources with either two or three values of the excitation temperature, we find average valuesof the midpoint of the density range that is consistent with all of the observations equal to 68 cm−3 for T k = 100 Kand 92 cm−3 for T k = 50 K. The data for this set of sources imply that diffuse molecular clouds are characterized byan average thermal pressure between 4600 and 6800 Kcm−3.


Do Giant Planets Survive Type II Migration?

Yasuhiro Hasegawa1 and Shigeru Ida2

1 Institute of Astronomy and Astrophysics, Academia Sinica (ASIAA), Taipei 10641, Taiwan2 Earth-Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152-8551, Japan

E-mail contact: yasu at asiaa.sinica.edu.tw

Planetary migration is one of the most serious problems to systematically understand the observations of exoplanets.We clarify that the theoretically predicted type II migration is too fast, as well as type I migration, by developingdetailed analytical arguments in which the timescale of type II migration is compared with the disk lifetime. In thedisk-dominated regime, the type II migration timescale is characterized by a local viscous diffusion timescale, while thedisk lifetime characterized by a global diffusion timescale that is much longer than the local one. Even in the planet-dominated regime where the inertia of the planet mass reduces the migration speed, the timescale is still shorter thanthe disk lifetime except in the final disk evolution stage where the total disk mass decays below the planet mass. Thissuggests that most giant planets plunge into the central stars within the disk lifetime, and it contradicts the exoplanetobservations that gas giants are piled up at r>∼1AU. We examine additional processes that may arise in protoplanetarydisks: dead zones, photoevaporation of gas, and gas flow across a gap formed by a type II migrator. Although theymake the type II migration timescale closer to the disk lifetime, we show that none of them can act as an effectivebarrier for rapid type II migration with the current knowledge of these processes. We point out that gas flow acrossa gap and the fraction of the flow accreted onto the planets are uncertain and they may have a potential to solve theproblem. Much more detailed investigation for each process may be needed to explain the observed distribution of gasgiants in extrasolar planetary systems.

Accepted by ApJ


Survival of interstellar molecules to prestellar dense core collapse and early phases ofdisk formation

Ugo Hincelin1, Valentine Wakelam2,3, Benoit Commercon4, Franck Hersant2,3 and Stephane Guilloteau2,3

1 Department of Chemistry, University of Virginia, Charlottesville, VA 22904, USA2 Univ. Bordeaux, LAB, UMR 5804, F-33270, Floirac, France

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3 CNRS, LAB, UMR 5804, F-33270, Floirac, France4 Laboratoire de radioastronomie, LERMA, Observatoire de Paris, Ecole Normale Superieure (UMR 8112 CNRS), 24rue Lhomond, 75231 Paris Cedex 05, France

E-mail contact: ugo.hincelin at virginia.edu

An outstanding question of astrobiology is the link between the chemical composition of planets, comets and otherSolar System bodies and the molecules formed in the interstellar medium. Understanding the chemical and physicalevolution of the matter leading to the formation of protoplanetary disks is an important step for this. We bringsome new stones to this longstanding problem using three-dimensional chemical simulations of the early phases of diskformation: we interfaced the full gas-grain chemical model Nautilus with the radiation-magneto-hydrodynamic modelRAMSES, for different configurations and intensities of magnetic field. Our results show that the chemical content(gas and ices) is globally conserved during the collapsing process, from the parent molecular cloud to the young disksurrounding the first Larson core. A qualitative comparison with cometary composition suggests that comets areconstituted of different phases, some molecules being direct tracers of interstellar chemistry, while others, includingcomplex molecules, seem to have been formed in disks, where higher densities and temperatures allow for an activegrain surface chemistry. The latter phase, and its connection with the formation of the first Larson core, remains tobe modelled.



The G305 star-forming complex: radio continuum and molecular line observations

L. Hindson1,2,3, M.A. Thompson2, J.S. Urquhart3,7, A. Faimali2, M. Johnston-Hollitt1, J.S. Clark4, B.

Davies5,6

1 School of Chemical and Physical Science, Victoria University of Wellington, PO Box 600, Wellington 6140, NewZealand2 Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, CollegeLane, Hateld, AL10 9AB, UK3 ATNF, CSIRO Astronomy and Space Science, P.O. Box 76, Epping, NSW 1710, Australia4 Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK5 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK6 School of Physics & Astronomy, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK7 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany

E-mail contact: l.hindson at herts.ac.uk

We present 109-115 GHz (3 mm) wide-field spectral line observations of 12CO, 13CO and C18O J = 1–0 molecularemission and 5.5 and 8.8 GHz (6 and 3 cm) radio continuum emission towards the high-mass star forming complexknown as G305. The morphology of G305 is dominated by a large evacuated cavity at the centre of the complex drivenby clusters of O stars surrounded by molecular gas. Our goals are to determine the physical properties of the molecularenvironment and reveal the relationship between the molecular and ionised gas and star formation in G305. This isin an effort to characterise the star-forming environment and constrain the star formation history in an attempt toevaluate the impact of high-mass stars on the evolution of the G305 complex.Analysis of CO emission in G305 reveals 156 molecular clumps with the following physical characteristics. The 5.5 and8.8GHz radio continuum emission reveals an extended low surface brightness ionised environment within which weidentify 15 large-scale features with a further eight smaller sources projected within these features. By comparing tomid infrared emission and archival data, we identify nine HII regions, seven compact HII regions, one UC HII region,four extended regions. The total integrated flux of the radio continuum emission at 5.5 GHz is ∼180 Jy correspondingto a Lyman continuum output of 2.4 × 1050 photons s−1. We compare the ionised and molecular environment withoptically identified high-mass stars and ongoing star formation, identified from the literature. Analysis of this datasetreveals a star formation rate of 0.008–0.016 and efficiency of 7–12%, allows us to probe the star formation history ofthe region and discuss the impact of high-mass stars on the evolution of G305.

Accepted by MNRAS


19

ALMA Resolves 30 Doradus: Sub-parsec Molecular Cloud Structure Near the ClosestSuper-Star Cluster

Remy Indebetouw1,2, Crystal Brogan1, C.-H. Rosie Chen3, Adam Leroy1, Kelsey Johnson2, Erik

Muller4, Suzanne Madden5, Diane Cormier6, Frederic Galliano5, Annie Hughes7, Todd Hunter1, Akiko

Kawamura4, Amanda Kepley1, Vianney Lebouteiller5, Margaret Meixner8, Joana M. Oliveira9, Toshikazu

Onishi10, Tatiana Vasyunina11

1 National Radio Astronomy Observatory, 520 Edgemont Road Charlottesville, VA 22903, USA2 Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903-0818, USA3 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, D-53121, Bonn, Germany4 ALMA-J Project Office, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan5 Service dAstrophysique, Commissariat a LEnergie Atomique de Saclay, 91191 Gif-sur-Yvette, France6 Institut fur theoretische Astrophysik, Zentrum fur Astronomie der Universitat Heidelberg, Albert-Ueberle Str. 2,D-69120 Heidelberg, Germany7 Max-Planck-Institut fur Astronomie, Konigstuhl 17, D-69117, Heidelberg, Germany8 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA9 School of Physical and Geographical Sciences, Lennard-Jones Laboratories, Keele University, Staordshire ST5 5BG,UK10 Department of Physical Science, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku,Sakai, Osaka 599-8531, Japan11 Department of Chemistry, University of Virginia, Charlottesville, VA 22903, USA

E-mail contact: rindebet at nrao.edu

We present ALMA observations of 30 Doradus – the highest resolution view of molecular gas in an extragalacticstar formation region to date (∼0.4pc × 0.6pc). The 30Dor-10 cloud north of R136 was mapped in 12CO 2–1,13CO 2–1, C18O 2–1, 1.3mm continuum, the H30α recombination line, and two H2CO 3–2 transitions. Most 12COemission is associated with small filaments and clumps (<1pc, ∼1000 M⊙ at the current resolution). Some clumpsare associated with protostars, including ”pillars of creation” photoablated by intense radiation from R136. Emissionfrom molecular clouds is often analyzed by decomposition into approximately beam-sized clumps. Such clumps in 30Doradus follow similar trends in size, linewidth, and surface density to Milky Way clumps. The 30 Doradus clumpshave somewhat larger linewidths for a given size than predicted by Larson’s scaling relation, consistent with pressureconfinement. They extend to higher surface density at a given size and linewidth compared to clouds studied at 10pcresolution. These trends are also true of clumps in Galactic infrared-dark clouds; higher resolution observations ofboth environments are required. Consistency of clump masses calculated from dust continuum, CO, and the virialtheorem reveals that the CO abundance in 30 Doradus clumps is not significantly different from the LMC mean, butthe dust abundance may be reduced by ∼2. There are no strong trends in clump properties with distance from R136;dense clumps are not strongly affected by the external radiation field, but there is a modest trend towards lower denseclump filling fraction deeper in the cloud.

Accepted by ApJ


An azimuthal asymmetry in the LkHα 330 disk

Andrea Isella1, Laura M. Perez2, John M. Carpenter3, Luca Ricci3, Sean Andrews4, and Katherine

Rosenfeld4

1 Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125, USA2 Jansky fellow, NRAO, Socorro, NM, USA3 Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125, USA4 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

E-mail contact: isella at astro.caltech.edu

Theory predicts that giant planets and low mass stellar companions shape circumstellar disks by opening annular gapsin the gas and dust spatial distribution. For more than a decade it has been debated whether this is the dominantprocess that leads to the formation of transitional disks. In this paper, we present millimeter-wave interferometric

20

observations of the transitional disk around the young intermediate mass star LkHα 330. These observations reveala lopsided ring in the 1.3 mm dust thermal emission characterized by a radius of about 100 AU and an azimuthalintensity variation of a factor of 2. By comparing the observations with a Gaussian parametric model, we find thatthe observed asymmetry is consistent with a circular arc, that extends azimuthally by about 90◦ and emits about 1/3of the total continuum flux at 1.3 mm. Hydrodynamic simulations show that this structure is similar to the azimuthalasymmetries in the disk surface density that might be produced by the dynamical interaction with unseen low masscompanions orbiting within 70 AU from the central star. We argue that such asymmetries might lead to azimuthalvariations in the millimeter-wave dust opacity and in the dust temperature, which will also affect the millimeter-wave continuum emission. Alternative explanations for the observed asymmetry that do not require the presence ofcompanions cannot be ruled out with the existing data. Further observations of both the dust and molecular gasemission are required to derive firm conclusions on the origin of the asymmetry observed in the LkHα 330 disk.

Accepted by ApJ


A Multiplicity Census of Intermediate-Mass Stars in Scorpius-Centaurus

Markus Janson1,8, David Lafreniere2, Ray Jayawardhana3 , Mariangela Bonavita3,4, Julien H. Girard5,

Alexis Brandeker6, John E. Gizis7

1 Department of Astrophysical Sciences, Princeton University, Princeton, NJ, USA2 Department of Physics, University of Montreal, Montreal, QC, Canada3 Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON, Canada4 Osservatorio Astronomico di Padova - INAF, Padova, Italy5 European Southern Observatory, Santiago, Chile6 Department of Astronomy, Stockholm University, Stockholm, Sweden7 Department of Physics and Astronomy, University of Delaware, Newark, DE, USA8 Hubble fellow

E-mail contact: janson at astro.princeton.edu

Stellar multiplicity properties have been studied for much of the range from the lowest to the highest stellar masses,but intermediate-mass stars from F-type to late A-type have received relatively little attention. Here we report on aGemini/NICI snapshot imaging survey of 138 such stars in the young Scorpius-Centaurus (Sco-Cen) region, for thepurpose of studying multiplicity with sensitivity down to planetary masses at wide separations. In addition to twobrown dwarfs and a companion straddling the hydrogen burning limit we reported previously, here we present 26new stellar companions and determine a multiplicity fraction within 0.′′1–5.′′0 of 21±4%. Depending on the adoptedsemi-major axis distribution, our results imply a total multiplicity in the range of ∼60–80%, which further supportsthe known trend of a smoothly continuous increase in the multiplicity fraction as a function of primary stellar mass. Asurprising feature in the sample is a distinct lack of nearly equal-mass binaries, for which we discuss possible reasons.The survey yielded no additional companions below or near the deuterium-burning limit, implying that their frequencyat >200 AU separations is not quite as high as might be inferred from previous detections of such objects within theSco-Cen region.

Accepted by ApJ


Modelling Carbon Radio Recombination Line observation towards the Ultra-CompactH ii region W48A

S. Jeyakumar1,3 and D. Anish Roshi2

1 Departamento de Astronomıa, Universidad de Guanajuato, AP 144, Guanajuato CP 36000, Mexico2 National Radio Astronomy Observatory, Charlottesville, VA 22903-4608, USA3 Raman Research Institute, C. V. Raman Avenue, Sadashivanagar, Bangalore - 560 080, India

E-mail contact: sjk at astro.ugto.mx

We model Carbon Recombination Line (CRL) emission from the Photo Dissociation Region (PDR) surrounding the

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Ultra-Compact (UC) H ii region W48A. Our modelling shows that the inner regions (AV ∼ 1) of the C ii layer in thePDR contribute significantly to the CRL emission. The dependence of line ratios of CRL emission with the densityof the PDR and the far ultra-violet (FUV) radiation incident on the region is explored over a large range of theseparameters that are typical for the environments of UCH ii regions. We find that by observing a suitable set of CRLs itis possible to constrain the density of the PDR. If the neutral density in the PDR is high (≥ 107 cm−3 ) CRL emissionis bright at high frequencies (≥ 20 GHz), and absorption lines from such regions can be detected at low frequencies(≤ 10 GHz). Modelling CRL observations towards W48A shows that the UCH ii region is embedded in a molecularcloud of density of about 4 × 107 cm−3 .

Accepted by MNRAS

Large-scale mapping of the massive star-forming region RCW38 in the [CII] and PAHemission

H. Kaneda1, T. Nakagawa2, S.K. Ghosh3, D.K. Ojha3, D. Ishihara1, T. Kondo1, J.P. Ninan3, M.

Tanabe1, Y. Fukui1, Y. Hattori1, T. Onaka4, K. Torii1, and M. Yamagishi1

1 Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan2 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 252-5210, Japan3 Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India4 Department of Astronomy, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan

E-mail contact: kaneda at u.phys.nagoya-u.ac.jp

We investigate the large-scale structure of the interstellar medium (ISM) around the massive star cluster RCW 38in the [CII] 158 µm line and polycyclic aromatic hydrocarbon (PAH) emission. We carried out [CII] line mappingof an area of ∼30′ × 15′ for RCW 38 by a Fabry-Perot spectrometer on a 100 cm balloon-borne telescope with anangular resolution of ∼1.′5. We compared the [CII] intensity map with the PAH and dust emission maps obtained bythe AKARI satellite. The [CII] emission shows a highly nonuniform distribution around the cluster, exhibiting thestructure widely extended to the north and the east from the center. The [CII] intensity rapidly drops toward thesouthwest direction, where a CO cloud appears to dominate. We decompose the 3–160 µm spectral energy distributionsof the surrounding ISM structure into PAH as well as warm and cool dust components with the help of 2.5–5 µmspectra. We find that the [CII] emission spatially corresponds to the PAH emission better than to the dust emission,confirming the relative importance of PAHs for photo-electric heating of gas in photo-dissociation regions. A naiveinterpretation based on our observational results indicates that molecular clouds associated with RCW38 are locatedboth on the side of and behind the cluster.

Accepted by A&A


Fluffy dust forms icy planetesimals by static compression

Akimasa Kataoka1,2, Hidekazu Tanaka3, Satoshi Okuzumi4, and Koji Wada5

1 Department of Astronomical Science, School of Physical Sciences, Graduate University for Advanced Studies (SO-KENDAI), Mitaka, Tokyo 181-8588, Japan2 National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan3 Institute of Low Temperature Science, Hokkaido University, Kita, Sapporo 060-0819, Japan4 Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo, 152-8551, Japan5 Planetary Exploration Research Center, Chiba Institute of Technology, Narashino, Chiba, 275-0016, Japan

E-mail contact: akimasa.kataoka at nao.ac.jp

Context: In planetesimal formation theory, several barriers have been proposed, which are bouncing, fragmentation,and radial drift problems. To understand the structure evolution of dust aggregates is a key in the planetesimalformation. Dust grains become fluffy by coagulation in protoplanetary disks. However, once they become fluffy, theyare not sufficiently compressed by collisional compression to form compact planetesimals.Aims: We aim to reveal the pathway of the dust structure evolution from dust grains to compact planetesimals.

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Methods: Using the compressive strength formula, we analytically investigate how fluffy dust aggregates are compressedby static compression due to ram pressure of the disk gas and self gravity of the aggregates in protoplanetary disks.Results: We reveal the pathway of the porosity evolution from dust grains via fluffy aggregates to form planetesimals,circumventing the barriers in planetesimal formation. The aggregates are compressed by the disk gas to the densityof 10−3 g cm−3 in coagulation, which is more compact than the case with collisional compression. Then, they arecompressed more by self gravity to 10−1 g cm−3 when the radius is 10 km. Although the gas compression deceleratethe growth, they grow enough rapidly to avoid the radial drift barrier when the orbital radius is < 6 AU in a typicaldisk. Conclusions: We propose fluffy dust growth scenario from grains to planetesimals. It enables the icy planetesimalformation in a wide range beyond the snowline in protoplanetary disks. This result proposes a concrete initial conditionof planetesimals for the later stages of the planet formation.

Accepted by A&A letters


Observational evidence for dissociative shocks in the inner 100 AU of low-mass proto-stars using Herschel-HIFI

L.E. Kristensen1,2, E.F. van Dishoeck1,3, A.O. Benz4, S. Bruderer3, R. Visser5, and S.F. Wamper6,7

1 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, the Netherlands2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA3 Max Planck Institut fur Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany4 Institute for Astronomy, ETH Zurich, 8093 Zurich, Switzerland5 Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA6 Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, ØsterVoldgade 5-7, DK-1350 Copenhagen K, Denmark7 Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen Ø, Denmark

E-mail contact: lkristensen at cfa.harvard.edu

Herschel-HIFI spectra of H2O towards low-mass protostars show a distinct velocity component not seen in observationsfrom the ground of CO or other species. The aim is to characterise this component in terms of excitation conditionsand physical origin. A velocity component with an offset of ∼10 km s−1 detected in spectra of the H2O 110–101557 GHz transition towards six low-mass protostars in the ’Water in star-forming regions with Herschel’ (WISH)programme is also seen in higher-excited H2O lines. The emission from this component is quantified and excitationconditions are inferred using 1D slab models. Data are compared to observations of hydrides (high-J CO, OH+, CH+,C+, OH) where the same component is uniquely detected. The velocity component is detected in all 6 targeted H2Otransitions (Eup ∼ 50–250 K), and in CO 16–15 towards one source, Ser SMM1. Inferred excitation conditions implythat the emission arises in dense (n ∼ 5 × 106–108 cm−3) and hot (T ∼ 750 K) gas. The H2O and CO columndensities are ∼1016 and 1018 cm−2, respectively, implying a low H2O abundance of 10−2 with respect to CO. Thehigh column densities of ions such as OH+ and CH+ (both ∼1013 cm−2) indicate an origin close to the protostarwhere the UV field is strong enough that these species are abundant. The estimated radius of the emitting region is100AU. This component likely arises in dissociative shocks close to the protostar, an interpretation corroborated by acomparison with models of such shocks. Furthermore, one of the sources, IRAS4A, shows temporal variability in theoffset component over a period of two years which is expected from shocks in dense media. High-J CO gas detectedwith Herschel-PACS with Trot ∼ 700 K is identified as arising in the same component and traces the part of the shockwhere H2 reforms. Thus, H2O reveals new dynamical components, even on small spatial scales in low-mass protostars.

Accepted by A&A


Configurations of Bounded and Free-floating Planets in Very Young Open Clusters

Hui-Gen Liu, Hui Zhang, and Ji-Lin Zhou

School of Astronomy and Space Science & Key Laboratory of Modern Astronomy and Astrophysics in Ministry ofEducation, Nanjing University, Nanjing 2100093, China

E-mail contact: huigen at nju.edu.cn

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Open clusters (OCs) are usually young and suitable for studying the formation and evolution of planetary systems.Hitherto, only four planets have been found with radial velocity measurements in OCs. Meanwhile, a lot of free-floatingplanets (FFPs) have been detected. We utilize N-body simulations to investigate the evolution and final configurationsof multi-planetary systems in very young open clusters with an age <10 Myr. After an evolution of 10 Myr, 61%–72% of the planets remain bounded and more than 55% of the planetary systems will maintain their initial orbitalconfigurations. For systems with one planet ejected, more than 25% of them have the surviving planets in misalignedorbits. In the clusters, the fraction of planetary systems with misalignment is > 6%, and only 1% have planets inretrograde orbits. We also obtain a positive correlation between the survival planet number and the distance fromthe cluster center r: planetary systems with a larger r tend to be more stable. Moreover, stars with a mass >2.5 M⊙

are likely unstable and lose their planets. These results are roughly consistent with current observations. Planetarysystems in binaries are less stable and we achieve a rough criterion: most of the binary systems with ab(1− e2b) >100AU can keep all the initial planets survived. Finally, 80% of the FFPs are ejected out of the clusters, while the rest(∼20%) still stay in host clusters and most of them are concentrated in the center (<2 pc).

Accepted by ApJ


Proper motions of young stars in Chamaeleon. II. New kinematical candidate membersof Chamaeleon I and II

Belen Lopez Martı1, Francisco Jimenez-Esteban1,2,3, Amelia Bayo4,5, David Barrado1,6, Enrique Solano1,2,

Herve Bouy1 and Carlos Rodrigo1,2

1 Centro de Astrobiologıa (INTA-CSIC), Villanueva de la Canada, Spain2 Spanish Virtual Observatory, Spain3 Suffolk University, Madrid Campus, Madrid, Spain4 European Southern Observatory, Santiago, Chile5 Max-Planck-Institut fur Astronomie, Heidelberg, Germany6 Calar Alto Observatory -Centro Astronomico Hispano-Aleman, Almerıa, Spain

E-mail contact: belen at cab.inta-csic.es

Context: The Chamaeleon star-forming region has been extensively studied in the last decades. However, most studieshave been confined to the densest parts of the clouds. In a previous paper, we analysed the kinematical properties ofthe spectroscopically confirmed population of the Chamaeleon I and II clouds.Aims: We want to search for new kinematical candidate members to the Chamaeleon I and II moving groups, extendingthe studied area beyond the clouds, and to characterize these new populations using available information from publicdatabases and catalogues. We also want to check if the populations of the moving groups are confined to the presentdark clouds.Methods: Kinematic candidate members were initially selected on the basis of proper motions and colours using theFourth US Naval Observatory CCD Astrograph Catalog (UCAC4). The SEDs of the objects were constructed usingphotometry retrieved from the Virtual Observatory and other resources, and fitted to models of stellar photospheresto derive effective temperatures, gravity values, and luminosities. Masses and ages were estimated by comparisonwith theoretical evolutionary tracks in a Hertzprung-Russell diagram. Objects with ages <∼20 Myr were selected asprobable members of the moving groups.Results: We have identified 51 and 14 candidate members to the Chamaeleon I and II moving groups, respectively,of which 17 and 1, respectively, are classified as probable young stars according to the SED analysis. Another objectin Chamaeleon I located slightly above the 1 Myr isochrone is classified as a possible young star. All these objectsare diskless stars with masses in the range 0.3-1.4M⊙ and ages consistent with those reported for the correspondingconfirmed members. They tend to be located at the boundaries of or outside the dark clouds, preferably to thenorth-east and south-east in the case of Chamaeleon I, and to the north-east in the case of Chamaeleon II.Conclusions: The kinematical population of Chamaeleon I and II could be larger and spread over a larger area of thesky than suggested by previous studies. However, the results of this study should be confirmed with spectroscopicdata and more precise kinematic information.

Accepted by Astronomy and Astrophysics


24

Accurate determination of accretion and photospheric parameters in Young Stellar Ob-jects: the case of two candidate old disks in the Orion Nebula Cluster

C.F. Manara1, G. Beccari1, N. Da Rio2, G. De Marchi2, A. Natta3,4, L. Ricci5, M. Robberto6 and L.

Testi1,3,7

1 European Southern Observatory, Karl Schwarzschild Str. 2, 85748 Garching, Germany2 European Space Agency, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands3 INAF - Osservatorio Astrofisico di Arcetri, Largo E.Fermi 5, I-50125 Firenze, Italy4 School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland5 California Institute of Technology, 1200 East California Boulervard, 91125 Pasadena, CA, USA6 Space Telescope Science Institute, 3700 San Martin Dr., Baltimore MD, 21218, USA7 Excellence Cluster Universe, Boltzmannstr. 2, 85748 Garching, Germany

E-mail contact: cmanara at eso.org

Context. Current planet formation models are largely based on the observational constraint that protoplanetary diskshave lifetime ∼3 Myr. Recent studies, however, report the existence of pre-Main-Sequence stars with signatures ofaccretion (strictly connected with the presence of circumstellar disks) and photometrically determined ages of 30 Myr,or more.Aims. Here we present a spectroscopic study of two major age outliers in the Orion Nebula Cluster. We use broadband, intermediate resolution VLT/X-Shooter spectra combined with an accurate method to determine the stellarparameters and the related age of the targets to confirm their peculiar age estimates and the presence of ongoingaccretion.Methods. The analysis is based on a multi-component fitting technique, which derives simultaneously spectral type,extinction, and accretion properties of the objects. With this method we confirm and quantify the ongoing accretion.From the photospheric parameters of the stars we derive their position on the H-R Diagram, and the age given byevolutionary models. Together with other age indicators like the lithium equivalent width we estimate with highaccuracy the age of the objects.Results. Our study shows that the two objects analyzed are not older than the typical population of the Orion NebulaCluster. Our results show that, while photometric determination of the photospheric parameters are an accuratemethod to estimate the parameters of the bulk of young stellar populations, those of individual objects with high ac-cretion rates and extinction may be affected by large uncertainties. Broad band spectroscopic determinations shouldthus be used to confirm the nature of individual objects.Conclusions. The analysis carried out in this paper shows that this method allows us to obtain an accurate determina-tion of the photospheric parameters of accreting young stellar objects in any nearby star-forming region. We suggestthat our detailed, broadband spectroscopy method should be used to derive accurate properties of candidate oldand accreting young stellar objects in star forming regions. We also discuss how a similarly accurate determination ofstellar properties can be obtained through a combination of photometric and spectroscopic data.



Interferometric observations of nitrogen-bearing molecular species in the star-formingcore ahead of HH 80N

Josep M. Masque1,2, Josep M. Girart3, Guillem Anglada2, Mayra Osorio2, Robert Estalella1 and Maria

T. Beltran4

1 Departament d’Astronomia i Meteorologia, Universitat de Barcelona, Martı i Franques 1, 08028 Barcelona, Catalunya,Spain2 Instituto de Astrofısica de Andalucıa, CSIC, Camino Bajo de Huetor 50, E-18008 Granada, Spain3 Institut de Ciencies de l’Espai, (CSIC-IEEC), Campus UAB, Facultat de Ciencies, Torre C5 - parell 2, 08193 Bel-laterra, Catalunya, Spain4 INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

E-mail contact: j.masque at crya.unam.mx

We present VLA NH3 and PdBI NH2D and HN13C observations of the star forming core ahead of HH 80N, the optically

25

obscured northern counterpart of the Herbig-Haro objects HH 80/81. The main goal is to determine the kinematicalinformation of the high density regions of the core (n >

∼ 105 cm−3), missed in previous works due to the depletion of thespecies observed (e.g. CS). The obtained maps show different kinematical signatures between the eastern and westernparts of the core, suggesting a possible dynamical interaction of the core with the HH 80/81/80N outflow. The analysisof the Position-Velocity (PV) plots of these species rules out a previous interpretation of having a molecular ring-likestructure of 6×104 AU of radius traced by CS infalling onto a central protostar found in the core (IRS1). High degreeof NH3 deuteration, with respect to the central part of the core harboring IRS1, is derived in the eastern part, wherea dust condensation (SE) is located. This deuteration trend of NH3 suggests that SE is in a prestellar evolutionarystage, earlier than that of the IRS1. Since SE is the closest condensation to the HH 80N/81/80N outflow, in case ofhaving outflow-core dynamical interaction, it should be perturbed first and be the most evolved condensation in thecore. Therefore, the derived evolutionary sequence for SE and IRS1 makes the outflow triggered star formation onIRS1 unlikely.

Accepted by ApJ


ALMA imaging of the CO snowline of the HD 163296 disk with DCO+

G.S. Mathews1, P.D. Klaassen1, A. Juhasz1, D. Harsono1,2, E. Chapillon3, E.F. van Dishoeck1,4, D.

Espada5,6, I. de Gregorio-Monsalvo5,7, A. Hales8, M.R. Hogerheijde1, J.C. Mottram1, M.G. Rawlings9,

S. Takahashi3, and L. Testi7,10

1 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands2 SRON Netherlands Institute for Space Research, PO Box 9700 AV, Groningen, The Netherlands3 Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), P.O. Box 23-141, Taipei 10617, Taiwan4 Max-Planck-Institut fur Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany5 National Astronomical Observatory of Japan (NAOJ), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan6 NAOJ Chile Observatory7 European Southern Observatory, Karl Schwarzschild Str 2, D-85748 Garching bei Munchen, Germany8 Joint ALMA Observatory (JAO), Alonso de Cordova 3107, Vitacura, Santiago, Chile9 National Radio Astronomical Observatory (NRAO), 520 Edgemont Road, Charlottesville, VA 22903, USA10 INAF - Osservatorio Astrosico di Arcetri, Largo E. Fermi 5, 50125,Firenze, Italy

E-mail contact: gmathews at strw.leidenuniv.nl

The high spatial and line sensitivity of ALMA opens the possibility of resolving emission from molecules in circumstellardisks. With an understanding of physical conditions under which molecules have high abundance, they can be used asdirect tracers of distinct physical regions. In particular, DCO+ is expected to have an enhanced abundance within afew Kelvin of the CO freezeout temperature of 19 K, making it a useful probe of the cold disk midplane. We compareALMA line observations of HD 163296 to a grid of models. We vary the upper- and lower-limit temperatures ofthe region in which DCO+ is present as well as the abundance of DCO+ in order to fit channel maps of the DCO+

J=5–4 line. To determine the abundance enhancement compared to the general interstellar medium, we carry outsimilar fitting to HCO+ J=4–3 and H13CO+ J=4–3 observations. ALMA images show centrally peaked extendedemission from HCO+ and H13CO+. DCO+ emission lies in a resolved ring from ∼110 to 160 AU. The outer radiusapproximately corresponds to the size of the CO snowline as measured by previous lower resolution observations ofCO lines in this disk. The ALMA DCO+ data now resolve and image the CO snowline directly. In the best fittingmodels, HCO+ exists in a region extending from the 19 K isotherm to the photodissociation layer with an abundanceof 3 × 10−10 relative to H2. DCO+ exists within the 19–21 K region of the disk with an abundance ratio [DCO+] /[HCO+] = 0.3. This represents a factor of 104 enhancement of the DCO+ abundance within this narrow region of theHD 163296 disk. Such a high enhancement has only previously been seen in prestellar cores. The inferred abundancesprovide a lower limit to the ionization fraction in the midplane of the cold outer disk (approximately greater than4× 10−10), and suggest the utility of DCO+ as a tracer of its parent molecule H2D

+. Abridged

Accepted by A&A


26

YSO accretion shocks: magnetic, chromospheric or stochastic flow effects can suppressfluctuations of X-ray emission

T. Matsakos1,2,3, J.-P. Chieze2, C. Stehle3, M. Gonzalez4, L. Ibgui3, L. de Sa2,3, T. Lanz5, S. Orlando6,

R. Bonito7,6, C. Argiroff7,6, F. Reale7,6and G. Peres7,6

1 CEA, IRAMIS, Service Photons, Atomes et Molecules, 91191 Gif-sur-Yvette, France2 Laboratoire AIM, CEA/DSM - CNRS - Universite Paris Diderot, IRFU/Service dAstrophysique, CEA Saclay, Ormedes Merisiers, 91191 Gif-sur-Yvette, France3 LERMA, Observatoire de Paris, Universite Pierre et Marie Curie and CNRS, 5 Place J. Janssen, 92195 Meudon,France4 Universite Paris Diderot, Sorbonne Paris Cite, AIM, UMR 7158, CEA, CNRS, 91191 Gif-sur-Yvette, France5 Laboratoire Lagrange, Universite de Nice-Sophia Antipolis, CNRS, Observatoire de la Cote d’Azur, 06304 Nice cedex4, France6 INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy7 Dipartimento di Fisica e Chimica, Universita degli Studi di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy

E-mail contact: titos.matsakos at gmail.com

Context. Theoretical arguments and numerical simulations of radiative shocks produced by the impact of the accretinggas onto young stars predict quasi-periodic oscillations in the emitted radiation. However, observational data do notshow evidence of such periodicity.Aims. We investigate whether physically plausible perturbations in the accretion column or in the chromosphere coulddisrupt the shock structure influencing the observability of the oscillatory behavior.Methods. We performed local 2D magneto-hydrodynamical simulations of an accretion shock impacting a chromo-sphere, taking optically thin radiation losses and thermal conduction into account. We investigated the effects ofseveral perturbation types, such as clumps in the accretion stream or chromospheric fluctuations, and also explored awide range of plasma-β values.Results. In the case of a weak magnetic field, the post-shock region shows chaotic motion and mixing, smoothingout the perturbations and retaining a global periodic signature. On the other hand, a strong magnetic field confinesthe plasma in flux tubes, which leads to the formation of fibrils that oscillate independently. Realistic values for theamplitude, length, and time scales of the perturbation are capable of bringing the fibril oscillations out of phase,suppressing the periodicity of the emission.Conclusions. The strength of a locally uniform magnetic field in YSO accretion shocks determines the structure ofthe post-shock region, namely, whether it will be somewhat homogeneous or if it will split up to form a collection offibrils. In the second case, the size and shape of the fibrils is found to depend strongly on the plasma-β value but noton the perturbation type. Therefore, the actual value of the protostellar magnetic field is expected to play a criticalrole in the time dependence of the observable emission.

Accepted by A&A


ALMA observations of the massive molecular outflow G331.512-0.103

Manuel Merello1,2, Leonardo Bronfman1, Guido Garay1, Nadia Lo1, Neal J. Evans II2, Lars-Ake

Nyman3, Juan R. Corts3 and Maria R. Cunningham4

1 Departamento de Astronomıa, Universidad de Chile, Casilla 36-D, Santiago, Chile2 The University of Texas at Austin, Department of Astronomy, 2515 Speedway, Stop C1400, Austin, Texas 78712-12053 Joint ALMA Observatory (JAO), Alonso de Cordova 3107, Vitacura, Santiago, Chile4 School of Physics, University of New South Wales, Sydney, NSW 2052, Australia

E-mail contact: manuel at astro.as.utexas.edu

The object of this study is one of the most energetic and luminous molecular outflows known in the Galaxy, G331.512-0.103. Observations with ALMA Band 7 (350 GHz; 0.86 mm) reveal a very compact, extremely young bipolar outflowand a more symmetric outflowing shocked shell surrounding a very small region of ionized gas. The velocities of thebipolar outflow are about 70 km s−1 on either side of the systemic velocity. The expansion velocity of the shockedshell is ∼24 km s−1, implying a crossing time of about 2000 yrs. Along the symmetry axis of the outflow, there is a

27

velocity feature, which could be a molecular ”bullet” of high-velocity dense material. The source is one of the youngestexamples of massive molecular outflow found associated with a high-mass star.

Accepted by ApJ Letters


Growth of grains in Brown Dwarf disks

Farzana Meru1, Marina Galvagni2 and Christoph Olczak3,4,5

1 Institut fur Astronomie, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland2 Institute of Theoretical Physics, Universitat Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland3 Astronomisches Rechen-Institut (ARI), Zentrum fur Astronomie Universitat Heidelberg, Monchhofstrasse 12-14,69120 Heidelberg, Germany4 Max-Planck-Institut fur Astronomie (MPIA), Konigstuhl 17, 69117 Heidelberg, Germany5 National Astronomical Observatories of China, Chinese Academy of Sciences (NAOC/CAS), 20A Datun Lu, ChaoyangDistrict, Beijing 100012, China

E-mail contact: farzana.meru at phys.ethz.ch

We perform coagulation and fragmentation simulations using the new physically-motivated model by Garaud et al.2013 to determine growth locally in brown dwarf disks. We show that large grains can grow and that if brown dwarfdisks are scaled down versions of T Tauri disks (in terms of stellar mass, disk mass and disk radius) growth at anequivalent location with respect to the disk truncation radius can occur to the same size in both disks. We show thatsimilar growth occurs because the collisional timescales in the two disks are comparable. Our model may thereforepotentially explain the recent observations of grain growth to millimetre sizes in brown dwarf disks, as seen in T Tauridisks.

Accepted by ApJ Letters


New and updated stellar parameters for 71 evolved planet hosts. On the metallicity -giant planet connection

A. Mortier1,2, N.C. Santos1,2, S.G. Sousa1,3, V.Zh. Adibekyan1, E. Delgado Mena1, M.Tsantaki1,2, G.

Israelian3,4 and M. Mayor5

1 Centro de Astrofısica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal2 Departamento de Fısica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Portugal3 Instituto de Astrofısica de Canarias, 38200 La Laguna, Tenerife, Spain4 Departemento de Astrofısica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain5 Observatoire de Geneve, Universite de Geneve, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland

E-mail contact: amortier at astro.up.pt

Context. It is still being debated whether the well-known metallicity - giant planet correlation for dwarf stars is alsovalid for giant stars. For this reason, having precise metallicities is very important. Precise stellar parameters arealso crucial to planetary research for several other reasons. Different methods can provide different results that leadto discrepancies in the analysis of planet hosts.

Aims. To study the impact of different analyses on the metallicity scale for evolved stars, we compare different ironline lists to use in the atmospheric parameter derivation of evolved stars. Therefore, we use a sample of 71 evolvedstars with planets. With these new homogeneous parameters, we revisit the metallicity - giant planet connection forevolved stars.

Methods. A spectroscopic analysis based on Kurucz models in local thermodynamic equilibrium (LTE) was performedthrough the MOOG code to derive the atmospheric parameters. Two different iron line list sets were used, one builtfor cool FGK stars in general, and the other for giant FGK stars. Masses were calculated through isochrone fitting,using the Padova models. Kolmogorov-Smirnov tests (K-S tests) were then performed on the metallicity distributionsof various different samples of evolved stars and red giants.

28

Results. All parameters compare well using a line list set, designed specifically for cool and solar-like stars to providemore accurate temperatures. All parameters derived with this line list set are preferred and are thus adopted for futureanalysis. We find that evolved planet hosts are more metal-poor than dwarf stars with giant planets. However, a biasin giant stellar samples that are searched for planets is present. Because of a colour cut-off, metal-rich low-gravitystars are left out of the samples, making it hard to compare dwarf stars with giant stars. Furthermore, no metallicityenhancement is found for red giants with planets (log g < 3.0 dex) with respect to red giants without planets.



Stars on the run: escaping from stellar clusters

Guido R.I. Moyano Loyola1 and Jarrod R. Hurley1

1 Centre for Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218, Australia

E-mail contact: gmoyano at astro.swin.edu.au

A significant proportion of Milky Way stars are born in stellar clusters, which dissolve over time so that the membersbecome part of the disc and halo populations of the Galaxy. In the present work we will assume that these youngstellar clusters live mainly within the disc of the Galaxy and that they can have primordial binary percentages rangingfrom 0% to as high as 70%. We have evolved models of such clusters to an age of 4 Gyr through N-body simulations,paying attention to the stars and binaries that escape in the process. We have quantified the contribution of theseescaping stars to the Galaxy population by analysing their escape velocity and evolutionary stage at the moment ofescape. In this way we could analyse the mechanisms that produced these escapers, whether evaporation throughweak two- body encounters, energetic close encounters or stellar evolution events, e.g. supernovae. In our modelswe found that the percentage of primordial binaries in a star cluster does not produce significant variations in thevelocities of the stars that escape in the velocity range of 0–20 km s−1. However, in the high-velocity 20–100 km s−1

range the number of escapers increased markedly as the primordial binary percentage increased. We could also inferthat dissolving stellar clusters such as those that we have modelled can populate the Galactic halo with giant starsfor which the progenitors were stars of up to 2.4 M⊙. Furthermore, choices made for the velocity kicks of remnantsdo influence the production of hyper-velocity stars - and to a lesser extent stars in the high-velocity range - but onceagain the difference for the 99% of stars in the 0–20 km s−1 range is not significant.

Accepted by MNRAS


A survey of H2O, CO2 and CO ice features towards background stars and low massYSOs using AKARI.

Jennifer A. Noble1, Helen J. Fraser2, Yuri Aikawa3, Klaus M. Pontoppidan4 and Itsuki Sakon5

1 Aix-Marseille Universite, PIIM UMR 7345, 13397, Marseille, France.2 Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom.3 Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501, Japan.4 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, U.S.A.5 Department of Astronomy, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0003, Japan.

E-mail contact: helen.fraser at open.ac.uk

We present near infrared spectroscopic observations of 19 molecular clouds made using the AKARI satellite, and thedata reduction pipeline written to analyse those observations. The 2.5 – 5 µm spectra of 30 objects – 22 field starsbehind quiescent molecular clouds and eight low mass YSOs in cores – were successfully extracted using the pipeline.Those spectra are further analysed to calculate the column densities of key solid phase molecular species, includingH2O, CO2, CO, and OCN−. The profile of the H2O ice band is seen to vary across the objects observed and we suggestthat the extended red wing may be an evolutionary indicator of both dust and ice mantle properties. The observationof 22 spectra with fluxes as low as < 5 mJy towards background stars, including 15 where the column densities ofH2O, CO and CO2 were calculated, provides valuable data that could help to benchmark the initial conditions in

29

star-forming regions prior to the onset of star formation.

Accepted by ApJ


Testing protoplanetary disc dispersal with radio emission

James E. Owen1, Anna M.M. Scaife2and Barbara Ercolano3,4

1 Canadian Institute for Theoretical Astrophysics, 60 St. George Street, Toronto, M5S 3H8, Canada2 School of Physics & Astronomy, University of Southampton, Higheld, Southampton SO17 1BJ, England3 Excellence Cluster Universe, Boltzmannstr. 2, D-85748 Garching, Germany4 Universitats-Sternwarte Munchen, Scheinerstrasse 1, D-81679 Munchen, Germany

E-mail contact: jowen at cita.utoronto.ca

We consider continuum free-free radio emission from the upper atmosphere of protoplanetary discs as a probe ofthe ionized luminosity impinging upon the disc. Making use of previously computed hydrodynamic models of discphotoevaporation within the framework of EUV and X-ray irradiation, we use radiative transfer post-processingtechniques to predict the expected free-free emission from protoplanetary discs. In general, the free-free luminosityscales roughly linearly with ionizing luminosity in both EUV and X-ray driven scenarios, where the emission dominatesover the dust tail of the disc and is partial optically thin at cm wavelengths. We perform a test observation of GMAur at 14-18 GHz and detect an excess of radio emission above the dust tail to a very high level of confidence. Theobserved flux density and spectral index are consistent with free-free emission from the ionized disc in either the EUVor X-ray driven scenario. Finally, we suggest a possible route to testing the EUV and X-ray driven dispersal model ofprotoplanetary discs, by combining observed free-free flux densities with measurements of mass-accretion rates. On

the point of disc dispersal one would expect to find a M∗

2scaling with free-free flux in the case of EUV driven disc

dispersal or a M∗ scaling in the case of X-ray driven disc dispersal.

Accepted by MNRAS


The formation of systems with closely spaced low-mass planets and the application toKepler-36

S. Paardekooper1, H. Rein2,3 and W. Kley4

1 DAMTP, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, United Kingdom2 Institute for Advanced Study, 1 Einstein Drive, Princeton, NJ 08540, USA3 University of Toronto, Scarborough, 1265 Military Trail, Toronto, ON M1C 1A4, Canada4 Institut fuer Astronomie und Astrophysik, Universitaet Tuebingen, Auf der Morgenstelle 10, 72076 Tuebingen,Germany

E-mail contact: S.Paardekooper at damtp.cam.ac.uk

The Kepler-36 system consists of two planets that are spaced unusually close together, near the 7:6 mean motionresonance. While it is known that mean motion resonances can easily form by convergent migration, Kepler-36 is anextreme case due to the close spacing and the relatively high planet masses of 4 and 8 times that of the Earth. Inthis paper, we investigate whether such a system can be obtained by interactions with the protoplanetary disc. Thesediscs are thought to be turbulent and exhibit density fluctuations which might originate from the magneto-rotationalinstability. We adopt a realistic description for stochastic forces due to these density fluctuations and perform bothlong term hydrodynamical and N-body simulations. Our results show that planets in the Kepler-36 mass range canbe naturally assembled into a closely spaced planetary system for a wide range of migration parameters in a turbulentdisc similar to the minimum mass solar nebula. The final orbits of our formation scenarios tend to be Lagrange stable,even though large parts of the parameter space are chaotic and unstable.

Accepted by MNRAS


30

Infrared Emission and the Destruction of Dust in HII regions

Ya.N. Pavlyuchenkov1, M.S. Kirsanova1 and D.S. Wiebe1

1 Institute of Astronomy, Russian Academy of Sciences, Moscow, Russia

E-mail contact: pavyar at inasan.ru

The generation of infrared (IR) radiation and the observed IR intensity distribution at wavelengths of 8, 24, and100 micron in the ionized hydrogen region around a young, massive star is investigated. The evolution of the HIIregion is treated using a self-consistent chemical-dynamical model in which three dust populations are included –large silicate grains, small graphite grains, and polycyclic, aromatic hydrocarbons (PAHs). A radiative transfer modeltaking into account stochastic heating of small grains and macromolecules is used to model the IR spectral energydistribution. The computational results are compared with Spitzer and Herschel observations of the RCW 120 nebula.The contributions of collisions with gas particles and the radiation field of the star to stochastic heating of smallgrains are investigated. It is shown that a model with a homogeneous PAH content cannot reproduce the ring-likeIR-intensity distribution at 8 micron. A model in which PAHs are destroyed in the ionized region provides a means toexplain this intensity distribution. This model is in agreement with observations for realistic characteristic destructiontimes for the PAHs.

Accepted by Astronomy Reports


Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-Main Sequence Stars

Mark J. Pecaut1 and Eric E. Mamajek1

1 University of Rochester, Department of Physics and Astronomy, Rochester, NY 14627-0171, USA

E-mail contact: mpecaut at pas.rochester.edu

We present an analysis of the intrinsic colors and temperatures of 5–30 Myr old pre-main sequence (pre-MS) stars usingthe F0 through M9 type members of nearby, negligibly reddened groups: Eta Cha cluster, TW Hydra Association,Beta Pic Moving Group, and Tucana-Horologium Association. To check the consistency of spectral types from theliterature, we estimate new spectral types for 52 nearby pre-MS stars with spectral types F3 through M4 using opticalspectra taken with the SMARTS 1.5-m telescope. Combining these new types with published spectral types, andphotometry from the literature (Johnson-Cousins BVIc, 2MASS JHKs and WISE W1, W2, W3, and W4), we derive anew empirical spectral type-color sequence for 5–30 Myr old pre-MS stars. Colors for pre-MS stars match dwarf colorsfor some spectral types and colors, but for other spectral types and colors, deviations can exceed 0.3 mag. We estimateeffective temperatures (Teff) and bolometric corrections (BCs) for our pre-MS star sample through comparing theirphotometry to synthetic photometry generated using the BT-Settl grid of model atmosphere spectra. We derive a newTeff and BC scale for pre-MS stars, which should be a more appropriate match for T Tauri stars than often-adopteddwarf star scales. While our new Teff scale for pre-MS stars is within ∼100 K of dwarfs at a given spectral type forstars <G5, for G5 through K6, the pre-MS stars are ∼250 K cooler than their main sequence counterparts. Lastly, wepresent (1) a modern Teff , optical/IR color, and bolometric correction sequence for O9V-M9V MS stars based on anextensive literature survey, (2) a revised Q-method relation for dereddening UBV photometry of OB-type stars, and(3) introduce two candidate spectral standard stars as representatives of spectral types K8V and K9V.

Accepted by ApJ


Global collapse of molecular clouds as a formation mechanism for the most massivestars

N. Peretto1,2, G.A. Fuller3,4, A. Duarte-Cabral5,6 , A. Avison3,4, P. Hennebelle1, J.E. Pineda3,4,7, Ph.

Andre1, S. Bontemps5,6 , F. Motte1, N. Schneider5,6, S. Molinari8

1 Laboratoire AIM, CEA/DSM-CNRS-Universte Paris Diderot, IRFU/Service d’Astrophysique, C.E. Saclay, France2 School of Physics and Astronomy, Cardi University, Queens Buildings, The Parade, Cardi CF24 3AA, UK3 Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester, M13

31

9PL, UK4 UK ALMA Regional Centre node5 Universitet de Bordeaux, LAB, UMR5804, F-33270, Floirac, France6 CNRS, LAB, UMR5804, F-33270, Floirac, France7 European Southern Observatory (ESO), Garching, Germany8 IFSI, INAF, Area di Recerca di Tor Vergata, Via Fosso Cavaliere 100, I-00133, Roma, Italy

E-mail contact: nicolas.peretto at astro.cf.ac.uk

The relative importance of primordial molecular cloud fragmentation versus large-scale accretion still remains to beassessed in the context of massive core/star formation. Studying the kinematics of the dense gas surrounding massive-star progenitors can tell us the extent to which large-scale flow of material impacts the growth in mass of star-formingcores. Here we present a comprehensive dataset of the 5500(±800)M⊙ infrared dark cloud SDC335.579-0.272 (hereafterSDC335) which exhibits a network of cold, dense, parsec-long filaments. Atacama Large Millimeter Array (ALMA)Cycle 0 observations reveal two massive star-forming cores, MM1 and MM2, sitting at the centre of SDC335 where thefilaments intersect. With a gas mass of 545(+770

−385) M⊙ contained within a source diameter of 0.05 pc, MM1 is one ofthe most massive, compact protostellar cores ever observed in the Galaxy. As a whole, SDC335 could potentially forman OB cluster similar to the Trapezium cluster in Orion. ALMA and Mopra single-dish observations of the SDC335dense gas furthermore reveal that the kinematics of this hub-filament system are consistent with a global collapseof the cloud. These molecular-line data point towards an infall velocity Vinf = 0.7(±0.2) km s−1, and a total mass

infall rate Minf = 2.5(±1.0) × 10−3 M⊙ yr−1 towards the central pc-size region of SDC335. This infall rate brings750(±300) M⊙ of gas to the centre of the cloud per free-fall time (tff = 3 × 105 yr). This is enough to double themass already present in the central pc-size region in 3.5(+2.2

−1.0) × tff . These values suggest that the global collapse ofSDC335 over the past million year resulted in the formation of an early O-type star progenitor at the centre of thecloud’s gravitational potential well.

Accepted by A&A


CARMA observations of protostellar outflows in NGC 1333

Adele L. Plunkett1, Hector G. Arce1, Stuartt A. Corder2, Diego Mardones3, Anneila I. Sargent4 and

Scott L. Schnee5

1 Department of Astronomy, Yale University, P.O. Box 208101, New Haven CT 06520, USA2 Joint ALMA Observatory, Av. Alonso de Cordova 3107, Vitacura, Santiago, Chile3 Departameto de Astronomia, Universidad de Chile, Casilla 36-D, Santiago, Chile4 Astronomy Department, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125,USA5 National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA

E-mail contact: adele.plunkett at yale.edu

We present observations of outflows in the star-forming region NGC 1333 using the Combined Array for Researchin Millimeter-Wave Astronomy (CARMA). We combined the 12CO and 13CO (1 − 0) CARMA mosaics with datafrom the 14m Five College Radio Astronomy Observatory to probe the central, most dense and active region of thisprotostellar cluster at scales from 5′′ to 7′ (or 1000 AU to 0.5 pc at a distance of 235 pc). We map and identify12CO outflows, and along with 13CO data we estimate their mass, momentum, and energy. Within the 7′ × 7′ map,the 5′′ resolution allows for a detailed study of morphology and kinematics of outflows and outflow candidates, someof which were previously confused with other outflow emission in the region. In total, we identify 22 outflow lobes,as well as 9 dense circumstellar envelopes marked by continuum emission, of which 6 drive outflows. We calculatea total outflow mass, momentum, and energy within the mapped region of 6 M⊙, 19 M⊙ km s−1, and 7 ×1044 erg,respectively. Within this same region, we compare outflow kinematics with turbulence and gravitational energy, andwe suggest that outflows are likely important agents for the maintenance of turbulence in this region. In the earlieststages of star formation, outflows do not yet contribute enough energy to totally disrupt the clustered region wheremost star formation is happening, but have the potential to do so as the protostellar sources evolve. Our results can beused to constrain outflow properties, such as outflow strength, in numerical simulations of outflow-driven turbulencein clusters.

32

Accepted by Astrophysical Journal


An O2If* star found in isolation in the backyard of NGC 3603

A. Roman-Lopes1

1 Department of Physics - Universidad de La Serena - Cisternas, 1200 - La Serena - Chile

E-mail contact: roman at dfuls.cl

In this letter we communicate the identification of a new Galactic O2If* star (MTT 68) isolated at a projected lineardistance of 3 pc from the centre of the star-burst cluster NGC 3603. From its optical photometry I computed abolometric luminosity MBol = −10.7, which corresponds to a total stellar luminosity of 1.5 × 106 L⊙. It was found aninteresting similarity between MTT 68 and the well known multiple system HD 93129. From Hubble Space TelescopeF656N images of the NGC 3603 field, it was found that MTT 68 is actually a visual binary system with an angularseparation of 0.′′38, which corresponds to a projected (minimum) linear distance of rA−B = 1.4 × 10−2 pc. This valueis similar to that for the HD 93129A (O2If*) and HD 93129B (O3.5) pair, rA−B = 3.0 × 10−2 pc. On the other hand,HD93129A has a third closer companion named HD 93129Ab (O3.5) at only 0.′′053, and taking into account that theX-ray to total stellar luminosity ratio for the MTT 68 system (LX/LBol ∼ 10−5) is about two orders of magnitudeabove the canonical value expected for single stars, I suspect that the MTT 68 system probably hosts another massivecompanion not resolved by the HST archive images.

Accepted by MNRAS letters


Imaging of the CO Snow Line in a Solar Nebula Analog

Chunhua Qi1, Karin I. Oberg1,2, David J. Wilner1, Paola D’Alessio3, Edwin Bergin4, Sean M. Andrews1,

Geoffrey A. Blake5, Michiel R. Hogerheijde6 and Ewine F. van Dishoeck6,7

1 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA2 Departments of Chemistry and Astronomy, University of Virginia, Charlottesville, VA 22904, USA3 Centro de Radioastronomoa y Astrofisica, Universidad Nacional Autonoma de Mexico (UNAM), 58089 Mexico City,Mexico4 Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA5 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA6 Leiden Observatory, Leiden University, 2300 RA, Leiden, Netherlands7 Max Planck Institute for Extraterrestrial Physics, 85748, Garching, Germany

E-mail contact: cqi at cfa.harvard.edu

Planets form in the disks around young stars. Their formation efficiency and composition are intimately linked tothe protoplanetary disk locations of “snow lines” of abundant volatiles. We present chemical imaging of the COsnow line in the disk around TW Hya, an analog of the solar nebula, using high spatial and spectral resolution Ata-cama Large Millimeter/Submillimeter Array (ALMA) observations of N2H

+, a reactive ion present in large abundanceonly where CO is frozen out. The N2H

+ emission is distributed in a large ring, with an inner radius that matches COsnow line model predictions. The extracted CO snow line radius of ∼ 30 AU helps to assess models of the formationdynamics of the Solar System, when combined with measurements of the bulk composition of planets and comets.

Accepted by Science


HH 222: A Giant Herbig-Haro Flow from the Quadruple System V380 Ori

Bo Reipurth1, John Bally2, Colin Aspin1, M.S. Connelley1, T.R. Geballe3, Stefan Kraus4, Immo

Appenzeller5, and Adam Burgasser6

1 Institute for Astronomy, University of Hawaii at Manoa, 640 North Aohoku Place, Hilo, HI 96720, USA2 Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309, USA3 Gemini Observatory, 670 North Aohoku Place, Hilo, HI 96720, USA

33

4 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138, USA5 Landessternwarte Heidelberg, Konigstuhl 12, D-69117 Heidelberg, Germany6 Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093, USA

E-mail contact: reipurth at ifa.hawaii.edu

HH 222 is a giant shocked region in the L1641 cloud, and is popularly known as the Orion Streamers or ”the waterfall”on account of its unusual structure. At the center of these streamers are two infrared sources coincident with anonthermal radio jet aligned along the principal streamer. The unique morphology of HH 222 has long been associatedwith this radio jet. However, new infrared images show that the two sources are distant elliptical galaxies, indicatingthat the radio jet is merely an improbable line-of-sight coincidence. Accurate proper motion measurements of HH 222reveal that the shock structure is a giant bow shock moving directly away from the well-known, very young, HerbigBe star V380 Ori. The already known Herbig-Haro object HH 35 forms part of this flow. A new Herbig-Haro object,HH 1041, is found precisely in the opposite direction of HH 222 and is likely to form part of a counterflow. The totalprojected extent of this HH complex is 5.3 pc, making it among the largest HH flows known. A second outflow episodefrom V380 Ori is identified as a pair of HH objects, HH 1031 to the northwest and the already known HH 130 tothe southeast, along an axis that deviates from that of HH 222/HH 1041 by only 3.7◦. V380 Ori is a hierarchicalquadruple system, including a faint companion of spectral type M5 or M6, which at an age of ∼1 Myr corresponds toan object straddling the stellar-to-brown dwarf boundary. We suggest that the HH 222 giant bow shock is a directresult of the dynamical interactions that led to the conversion from an initial non-hierarchical multiple system intoa hierarchical configuration. This event occurred no more than 28,000 yr ago, as derived from the proper motions ofthe HH 222 giant bow shock.

Accepted by Astron. J.

http://www.ifa.hawaii.edu/users/reipurth/PREPRINTS/hh222.pdf

Resolving The Moth at Millimeter Wavelengths

Angelo Ricarte1, Noel Moldvai1, A. Meredith Hughes2, Gaspard Duchene1,3, Jonathan P. Williams4,

Sean M. Andrews5 and David J. Wilner5

1 University of California Berkeley, Department of Astronomy, 601 Campbell Hall, Berkeley, CA 94720, USA2 Wesleyan University Department of Astronomy, Van Vleck Observatory, 96 Foss Hill Drive, Middletown, CT 06459,USA3 UJF-Grenoble 1/ CNRS-INSU, Institut de Planetologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, BP 53,38041 Grenoble Cedex 9, France4 Institute for Astronomy, University of Hawaii, USA5 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

E-mail contact: angelo.ricarte at yale.edu

HD 61005, also known as “The Moth,” is one of only a handful of debris disks that exhibit swept-back “wings”thought to be caused by interaction with the ambient interstellar medium (ISM). We present 1.3mm SubmillimeterArray (SMA) observations of the debris disk around HD 61005 at a spatial resolution of 1.9 arcsec that resolve theemission from large grains for the first time. The disk exhibits a double-peaked morphology at millimeter wavelengths,consistent with an optically thin ring viewed close to edge-on. To investigate the disk structure and the properties ofthe dust grains we simultaneously model the spatially resolved 1.3mm visibilities and the unresolved spectral energydistribution. The temperatures indicated by the SED are consistent with expected temperatures for grains closeto the blowout size located at radii commensurate with the millimeter and scattered light data. We also performa visibility-domain analysis of the spatial distribution of millimeter-wavelength flux, incorporating constraints onthe disk geometry from scattered light imaging, and find suggestive evidence of wavelength-dependent structure. Themillimeter-wavelength emission apparently originates predominantly from the thin ring component rather than tracingthe “wings” observed in scattered light. The implied segregation of large dust grains in the ring is consistent with anISM-driven origin for the scattered light wings.



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The GALEX Nearby Young-Star Survey

David R. Rodriguez1, B. Zuckerman2, Joel H. Kastner3, M.S. Bessell4, Jacqueline K. Faherty1,5, Simon

J. Murphy4,6

1 Departamento de Astronoma, Universidad de Chile, Casilla 36-D, Santiago, Chile2 Dept. of Physics & Astronomy, University of California, Los Angeles 90095, USA3 Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester NY 146234 The Australian National University, Cotter Road, Weston Creek ACT 2611, Australia5 Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York,NY 100346 Gliese Fellow, Astronomisches Rechen-Institut, Zentrum fur Astronomie der Universitat Heidelberg, Germany 69120

E-mail contact: drodrigu at das.uchile.cl

We describe a method that exploits data from the GALEX ultraviolet and WISE and 2MASS infrared source catalogs,combined with proper motions and empirical pre-main sequence isochrones, to identify candidate nearby, young, low-mass stars. Applying our method across the full GALEX- covered sky, we identify 2031 mostly M-type stars that, foran assumed age of 10 (100) Myr, all lie within ∼150 (∼90) pc of Earth. The distribution of M spectral subclassesamong these ∼2000 candidate young stars peaks sharply in the range M3–M4; these subtypes constitute 50% ofthe sample, consistent with studies of the M star population in the immediate solar neighborhood. We focus on asubset of 58 of these candidate young M stars in the vicinity of the Tucana-Horologium Association. Only 20 of these58 candidates were detected in the ROSAT All-Sky X-ray Survey – reflecting the greater sensitivity of GALEX forpurposes of identifying active nearby, young stars, particularly for stars of type M4 and later. Based on statisticalanalysis of the kinematics and/or spectroscopic followup of these 58 M stars, we find that 50% (29 stars) indeed haveproperties consistent with Tuc-Hor membership, while 12 are potential new members of the Columba Association, andtwo may be AB Dor moving group members. Hence, ∼75% of our initial subsample of 58 candidates are likely membersof young (age ∼10–40 Myr) stellar moving groups within 100 pc, verifying that the stellar color- and kinematics-basedselection algorithms described here can be used to efficiently isolate nearby, young, low-mass objects from among thefield star population. Future studies will focus on characterizing additional subsamples selected from among this listof candidate nearby, young M stars.

Accepted by ApJ


Distinct Chemical Regions in the ”Prestellar” Infrared Dark Cloud (IRDC) G028.23-00.19

Patricio Sanhueza1, James M. Jackson1, Jonathan B. Foster2, Izaskun Jimenez-Serra3, William J.

Dirienzo4 and Thushara Pillai5

1 Institute for Astrophysical Research, Boston University, Boston, MA 02215, USA2 Yale Center for Astronomy and Astrophysics, Yale University, New Haven, CT 06520, USA3 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany4 Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903, USA5 Caltech, MC 249-17, 1200 East California Blvd, Pasadena, CA 91125, USA

E-mail contact: patricio at bu.edu

We have observed the IRDC G028.23-00.19 at 3.3 mm using CARMA. In its center, the IRDC hosts one of the mostmassive (∼1520 M⊙) quiescent, cold (12 K) clumps known (MM1). The low temperature, high NH2D abundance,narrow molecular line widths, and absence of embedded IR sources (from 3.6 to 70 µm) indicate that the clump is likelyprestellar. Strong SiO emission with broad line widths (6-9 km s−1) and high abundances (0.8-4 × 10−9) is detectedin the northern and southern regions of the IRDC, unassociated with MM1. We suggest that SiO is released to the gasphase from the dust grains through shocks produced by outflows from undetected intermediate-mass stars or clustersof low-mass stars deeply embedded in the IRDC. A weaker SiO component with narrow line widths (∼2 km s−1)and low abundances (4.3 × 10−11) is detected in the center-west region, consistent with either a “subcloud-subcloud”collision or an unresolved population of a few low-mass stars. We report widespread CH3OH emission throughout thewhole IRDC and the first detection of extended narrow methanol emission (∼2 km s−1) in a cold, massive prestellar

35

clump (MM1). We suggest that the most likely mechanism releasing methanol into the gas phase in such a cold regionis the exothermicity of grain-surface reactions. HN13C reveals that the IRDC is actually composed of two distinctsubstructures (“subclouds”) separated in velocity space by ∼1.4 km s−1. The narrow SiO component arises where thesubclouds overlap. The spatial distribution of C2H resembles that of NH2D, which suggests that C2H also traces coldgas in this IRDC.

Accepted by ApJ


Herschel PACS observations of shocked gas associated with the jets of L1448 and L1157

G. Santangelo1, B. Nisini1, S. Antoniucci1, C. Codella2, S. Cabrit3, T. Giannini1, G. Herczeg4, R.

Liseau5, M. Tafalla6 and E.F. van Dishoeck7,8

1 Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monteporzio Catone, Italy2 Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125 Florence, Italy3 LERMA, Observatoire de Paris, UMR 8112 of the CNRS, 61 Av. de L’Observatoire, 75014 Paris, France4 Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian Qu, 100871 Beijing,P.R. China5 Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439 92Onsala, Sweden6 Observatorio Astronomico Nacional (IGN), Alfonso XII 3, E-28014 Madrid, Spain7 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands8 Max Planck Institut fur Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany

E-mail contact: gina.santangelo at oa-roma.inaf.it

In the framework of the Water In Star-forming regions with Herschel (WISH) key program, several H2O (Eu >

190 K), high-J CO, [Oi], and OH transitions are mapped with Herschel -PACS in two shock positions along twoprototypical outflows around the low-luminosity sources L1448 and L1157. Previous Herschel -HIFI H2O observations(Eu = 53− 249 K) are also used. The aim is to derive a complete picture of the excitation conditions at the selectedshock positions. We adopted a large velocity gradient analysis (LVG) to derive the physical parameters of the H2Oand CO emitting gas. Complementary Spitzer mid-IR H2 data were used to derive the H2O abundance.

Consistent with other studies, at all selected shock spots a close spatial association between H2O, mid-IR H2, andhigh-J CO emission is found, whereas the low-J CO emission traces either entrained ambient gas or a remnant of anolder shock. The excitation analysis, conducted in detail at the L1448-B2 position, suggests that a two-componentmodel is needed to reproduce the H2O, CO, and mid-IR H2 lines: an extended warm component (T ∼ 450 K) is tracedby the H2O emission with Eu = 53 − 137 K and by the CO lines up to J = 22 − 21, and a compact hot component(T = 1100 K) is traced by the H2O emission with Eu > 190 K and by the higher-J CO transitions. At L1448-B2 weobtain an H2O abundance (3− 4)× 10−6 for the warm component and (0.3− 1.3)× 10−5 for the hot component anda CO abundance of a few 10−5 in both components. In L1448-B2 we also detect OH and blue-shifted [Oi] emission,spatially coincident with the other molecular lines and with [Feii] emission. This suggests a dissociative shock forthese species, related to the embedded atomic jet. On the other hand, a non-dissociative shock at the point of impactof the jet on the cloud is responsible for the H2O and CO emission. The other examined shock positions show an H2Oexcitation similar to L1448-B2, but a slightly higher H2O abundance (a factor of ∼ 4).

The two gas components may represent a gas stratification in the post-shock region. The extended and low-abundancewarm component traces the post-shocked gas that has already cooled down to a few hundred Kelvin, whereas thecompact and possibly higher-abundance hot component is associated with the gas that is currently undergoing ashock episode. This hot gas component is more affected by evolutionary effects on the timescales of the outflowpropagation, which explains the observed H2O abundance variations.

Accepted by Accepted for publication in Astronomy and Astrophysics


36

The long wavelength view of GG Tau A: Rocks in the Ring World

Anna M.M. Scaife

Department of Physics & Astronomy, University of Southampton, Higheld, Southampton, SO17 1BJ

E-mail contact: a.scaife at soton.ac.uk

We present the first detection of GG Tau A at centimeter-wavelengths, made with the Arcminute Microkelvin ImagerLarge Array (AMI-LA) at a frequency of 16 GHz (λ = 1.8 cm). The source is detected at > 6 σrms with an integratedflux density of S = 249±45 µJy. We use these new centimetre-wave data, in conjunction with additional measurementscompiled from the literature, to investigate the long wavelength tail of the dust emission from this unusual proto-planetary system. We use an MCMC based method to determine maximum likelihood parameters for a simpleparametric spectral model and consider the opacity and mass of the dust contributing to the microwave emission. Wederive a dust mass of approximately 0.1 M⊙, constrain the dimensions of the emitting region and find that the opacityindex at λ > 7mm is less than unity, implying a contribution to the dust population from grains exceeding 4 cm insize. We suggest that this indicates coagulation within the GG Tau A system has proceeded to the point where dustgrains have grown to the size of small rocks with dimensions of a few centimetres. Considering the relatively young ageof the GG Tau association, in combination with the low derived disk mass, we suggest that this system may providea useful test case for rapid core accretion planet formation models.

Accepted by MNRAS


New companions in the stellar systems of DI Cha, Sz 22, CHXR 32, and Cha Hα 5 inthe Cha I star-forming region

T.O.B. Schmidt1, N. Vogt2, R. Neuhauser1, A. Bedalov1,3, and T. Roell1

1 Astrophysikalisches Institut und Universitats-Sternwarte, Universitat Jena, Schillergaßchen 2-3, 07745 Jena, Ger-many2 Departamento de Fısica y Astronomıa, Universidad de Valparaıso, Avenida Gran Bretana 1111, Valparaıso, Chile3 Faculty of Natural Sciences, University of Split, Teslina 12. 21000 Split, Croatia

E-mail contact: tobi at astro.uni-jena.de

The star-forming regions in Chamaeleon (Cha) are among the nearest (distance ∼165 pc) and youngest (age ∼2Myrs) conglomerates of recently formed stars and among the ideal targets for studies of star formation. We searchfor new, hitherto unknown binary or multiple-star components and investigate their membership in Cha and theirgravitationally bound nature. We used the NACO instrument at the VLT UT 4/YEPUN of the Paranal Observatory,at 2 or 3 different epochs, in order to obtain relative and absolute astrometric measurements, as well as differentialphotometry in the J, H, and Ks band. On the basis of known proper motions and these observations, we analysedthe astrometric results in proper motion diagrams to eliminate possible (non-moving) background stars and establishco-moving binaries and multiples. DI Cha turns out to be a quadruple system with a hierachical structure, consistingof two binaries: a G2/M6 pair and a co-moving pair of two M5.5 dwarfs. For both pairs we detected orbital motion(P∼130 and ∼65 years), although in opposite directions. Sz 22 is a binary whose main component is embedded in acircumstellar disc or reflection nebula, accompanied by a co-moving M4.5 dwarf. CHXR 32 is a triple system, consistingof a single G5 star, weakened by an edge-on disc and a co-moving pair of M1/M3.5 dwarfs whose components showsignificant variations in their angular separation. Finally, Cha Hα 5 is a binary consisting of two unresolved M6.5dwarfs whose strong variations in position angle at its projected separation of only 8 AU imply an orbital period of∼46 years. DI Cha D and Cha Hα 5 A&B are right at the stellar mass limit and could possibly be brown dwarfs.In spite of various previously published studies of the star-forming regions in Cha we found four hitherto unknowncomponents in young low-mass binaries and multiple systems. (abridged)

Accepted by A&A


37

HST FUV imaging of DG Tau: Fluorescent molecular hydrogen emission from the wideangle outflow

P.C. Schneider1, J. Eisloffel2, M. Gudel3, H.M. Gunther4, G. Herczeg5, J. Robrade1, and J.H.M.M.

Schmitt1

1 Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg2 Thuringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany3 Universitat Wien, Dr.-Karl-Lueger-Ring 1, 1010 Wien, Austria4 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA5 The Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian Qu, Beijing100871, China

E-mail contact: cschneider at hs.uni-hamburg.de

One of the best-studied jets from all young stellar objects is the jet of DG Tau, which we imaged in the FUV withHST for the first time. These high spatial resolution images were obtained with long-pass filters and allow us toconstruct images tracing mainly molecular hydrogen and C IV emission. We find that the H2 emission appears as alimb-brightened cone with additional emission close to the jet axis. The length of the rims is about 0.′′3 or 42 AU(proj.) before their brightness strongly drops, and the opening angle is about 90◦. Comparing our FUV data withnear-IR data we find that the fluorescent H2 emission likely traces the outer, cooler part of the disk wind while anorigin of the H2 emission in the surface layers (atmosphere) of the (flared) disk is unlikely. Furthermore, the spatialshape of the H2 emission shows little variation over six years which suggests that the outer part of the disk wind israther stable and probably not associated with the formation of individual knots. The C IV image shows that theemission is concentrated towards the jet axis. We find no indications for additional C IV emission at larger distances,which strengthens the association with the X-ray emission observed to originate within the DG Tau jet.

Accepted by A&A


The low-mass stellar population in the young cluster Tr37: Disk evolution, accretion,and environment

A. Sicilia-Aguilar1, J. S. Kim2, A. Sobolev3, K. Getman4, Th. Henning5 and M. Fang1

1 Departamento de Fısica Teorica, Facultad de Ciencias, Universidad Autonoma de Madrid, 28049 Cantoblanco,Madrid, Spain2 Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-00653 Astronomical Observatory, Ural Federal University, Lenin Avenue 51, 620000 Ekaterinburg, Russia4 Department of Astronomy & Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University ParkPA 168025 Max-Planck-Institut fur Astronomie, Konigstuhl 17, 69117 Heidelberg, Germany

E-mail contact: aurora.sicilia at uam.es

We present a study of accretion and protoplanetary disks around M-type stars in the 4 Myr-old cluster Tr37. Witha well-studied solar-type population, Tr37 is a benchmark for disk evolution. We used low-resolution spectroscopy toidentify and classify 141 members (78 new ones) and 64 probable members, mostly M-type stars. Hα emission providesinformation about accretion. Optical, 2MASS, Spitzer, and WISE data are used to trace the SEDs and search fordisks. We construct radiative transfer models to explore the structures of full-disks, pre-transition, transition, anddust-depleted disks. Including the new members and the known solar-type stars, we confirm that a substantialfraction (∼2/5) of disks show signs of evolution, either as radial dust evolution (transition/pre-transition disks) or asa more global evolution (with low small-dust masses, dust settling, and weak/absent accretion signatures). Accretionis strongly dependent on the SED type. About half of the transition objects are consistent with no accretion, anddust-depleted disks have weak (or undetectable) accretion signatures, especially among M-type stars. The analysis ofaccretion and disk structure suggests a parallel evolution of dust and gas. We find several distinct classes of evolveddisks, based on SED type and accretion status, pointing to different disk dispersal mechanisms and probably differentevolutionary paths. Dust depletion and opening of inner holes appear to be independent processes: most transitiondisks are not dust-depleted, and most dust-depleted disks do not require inner holes. The differences in disk structure

38

between M-type and solar-type stars in Tr37 (4 Myr old) are not as remarkable as in the young, sparse, Coronet cluster(1-2 Myr old), suggesting that other factors, like the environment/interactions in each cluster, are likely to play animportant role in the disk evolution and dispersal. Finally, we also find some evidence of clumpy star formation ormini-clusters within Tr37.

Accepted by A&A


http://astro.ft.uam.es/aurora/aurora_publications.html

ATLASGAL — properties of compact H ii regions and their natal clumps

J. S. Urquhart1, M. A. Thompson2, T. J. T. Moore3, C. R. Purcell4, M. G. Hoare4, F. Schuller5, F.

Wyrowski1, T. Csengeri1, K. M. Menten1, S. L. Lumsden4, S. Kurtz6, C.M.Walmsley7,8, L. Bronfman9,

L. K.Morgan3, D. J. Eden3 and D.Russeil10

1 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, Bonn, Germany2 Science and Technology Research Institute, University of Hertfordshire, College Lane, Hatfield, AL10 9AB, UK3 Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birken-head, CH41 1LD, UK4 School of Physics and Astrophysics, University of Leeds, Leeds, LS2 9JT, UK5 European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile6 Centro de Radioastronomia y Astrofisica, Universidad Nacional Autonoma de Mexico, Antigua Carretera a Ptzcuaro# 8701 Morelia, 58089 Michoacan, Mexico7 Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy8 Dublin Institute for Advanced Studies, Burlington Road 10, Dublin 4, Ireland9 Departamento de Astronomıa, Universidad de Chile, Casilla 36-D, Santiago, Chile10 Aix Marseille Universite, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388, Marseille,France

E-mail contact: jurquhart at mpifr-bonn.mpg.de

We present a complete sample of molecular clumps containing compact and ultra-compact (UC) H ii regions betweenℓ = 10◦ and 60◦ and |b| < 1◦, identified by combining the the ATLASGAL sub-mm and CORNISH radio continuumsurveys with visual examination of archival infrared data. Our sample is complete to optically thin, compact andUCH ii regions driven by a zero age main sequence star of spectral type B0 or earlier embedded within a 1,000M⊙

clump. In total we identify 213 compact and UCH ii regions, associated with 170 clumps. Unambiguous kinematicdistances are derived for these clumps and used to estimate their masses and physical sizes, as well as the Lymancontinuum fluxes and sizes of their embedded H ii regions. We find a clear lower envelope for the surface density ofmolecular clumps hosting massive star formation of 0.05 g cm−2, which is consistent with a similar sample of clumpsassociated with 6.7GHz masers. The mass of the most massive embedded stars is closely correlated with the mass oftheir natal clump. Young B stars appear to be significantly more luminous in the ultraviolet than predicted by currentstellar atmosphere models. The properties of clumps associated with compact and UCH ii regions are very similar tothose associated with 6.7GHz methanol masers and we speculate that there is little evolution in the structure of themolecular clumps between these two phases. Finally, we identify a significant peak in the surface density of compactand UCH ii regions associated with the W49A star-forming complex, noting that this complex is truly one of themost massive and intense regions of star formation in the Galaxy.

Accepted by MNRAS


ATLASGAL — Environments of 6.7GHz methanol masers

J. S. Urquhart1, T. J. T. Moore2, F. Schuller3, F. Wyrowski1, K. M. Menten1, M. A. Thompson4, T.

Csengeri1, C. M. Walmsley5,6, L. Bronfman7 and C. Konig1

1 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, Bonn, Germany2 Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birken-

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head, CH41 1LD, UK3 European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile4 Science and Technology Research Institute, University of Hertfordshire, College Lane, Hatfield, AL10 9AB, UK5 Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy6 Dublin Institute for Advanced Studies, Burlington Road 10, Dublin 4, Ireland7 Departamento de Astronomıa, Universidad de Chile, Casilla 36-D, Santiago, Chile

E-mail contact: jurquhart at mpifr-bonn.mpg.de

Using the 870-µm APEX Telescope Large Area Survey of the Galaxy (ATLASGAL), we have identified 577 submil-limetre continuum sources with masers from the methanol multibeam (MMB) survey in the region 280◦ < ℓ < 20◦;| b | < 1.5◦. 94 per cent of methanol masers in the region are associated with sub-millimetre dust emission. We estimatemasses for ∼450 maser-associated sources and find that methanol masers are preferentially associated with massiveclumps. These clumps are centrally condensed, with envelope structures that appear to be scale-free, the mean maserposition being offset from the peak column density by 0 ± 4′′. Assuming a Kroupa initial mass function and a star-formation efficiency of ∼30per cent, we find that over two thirds of the clumps are likely to form clusters with masses>20M⊙. Furthermore, almost all clumps satisfy the empirical mass-size criterion for massive star formation. Bolo-metric luminosities taken from the literature for ∼100 clumps range between ∼100 and 106 L⊙. This confirms thelink between methanol masers and massive young stars for 90 per cent of our sample. The Galactic distribution ofsources suggests that the star-formation efficiency is significantly reduced in the Galactic-centre region, compared tothe rest of the survey area, where it is broadly constant, and shows a significant drop in the massive star-formationrate density in the outer Galaxy. We find no enhancement in source counts towards the southern Scutum-Centaurusarm tangent at ℓ ∼ 315◦, which suggests that this arm is not actively forming stars.

Accepted by MNRAS


http://adsabs.harvard.edu/abs/2013MNRAS.431.1752U

Simulations of protostellar collapse using multigroup radiation hydrodynamics. II. Thesecond collapse

Neil Vaytet1, Gilles Chabrier1,2, Edouard Audit3,4, Benoit Commercon5, Jacques Masson1, Jason

Ferguson6 and Franck Delahaye7

1 Ecole Normale Superieure de Lyon, CRAL, UMR CNRS 5574, Universite Lyon I, 46 Allee d’Italie, 69364 Lyon Cedex07, France2 School of Physics, University of Exeter, Exeter, EX4 4QL, UK3 Maison de la Simulation, USR 3441, CEA - CNRS - INRIA - Universite Paris-Sud - Universite de Versailles, 91191Gif-sur-Yvette, France4 CEA/DSM/IRFU, Service d’Astrophysique, Laboratoire AIM, CNRS, Universite Paris Diderot, 91191 Gif-sur-Yvette, France5 Laboratoire de radioastronomie, (UMR CNRS 8112), Ecole normale superieure et Observatoire de Paris, 24 rueLhomond, 75231 Paris Cedex 05, France6 Department of Physics, Wichita State University, Wichita, KS 67260-0032, USA7 LERMA, Observatoire de Paris, ENS, UPMC, UCP, CNRS, 5 Place Jules Janssen, 92190 Meudon, France

E-mail contact: neil.vaytet at ens-lyon.fr

Star formation begins with the gravitational collapse of a dense core inside a molecular cloud. As the collapseprogresses, the centre of the core begins to heat up as it becomes optically thick. The temperature and density inthe centre eventually reach high enough values where fusion reactions can ignite; the protostar is born. This sequenceof events entail many physical processes, of which radiative transfer is of paramount importance. Many simulationsof protostellar collapse make use of a grey treatment of radiative transfer coupled to the hydrodynamics. However,interstellar gas and dust opacities present large variations as a function of frequency. In this paper, we follow-upon a previous paper on the collapse and formation of Larson’s first core using multigroup radiation hydrodynamics(Paper I) by extending the calculations to the second phase of the collapse and the formation of Larson’s secondcore. We have made the use of a non-ideal gas equation of state as well as an extensive set of spectral opacities ina spherically symmetric fully implicit Godunov code to model all the phases of the collapse of a 0.1, 1 and 10 M⊙

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cloud cores. We find that, for a same central density, there are only small differences between the grey and multigroupsimulations. The first core accretion shock remains supercritical while the shock at the second core border is found tobe strongly subcritical with all the accreted energy being transfered to the core. The size of the first core was foundto vary somewhat in the different simulations (more unstable clouds form smaller first cores) while the size, mass andtemperature of the second cores are independent of initial cloud mass, size and temperature. Our simulations supportthe idea of a standard (universal) initial second core size of 0.003 AU and mass 0.0014 M⊙.

Accepted by A&A


The effect of episodic accretion on the phase transition of CO and CO2 in low-mass starformation

Eduard I. Vorobyov1, I. Baraffe2, T. Harries2 and G. Chabrier3

1 Institute of Astrophysics, University of Vienna, Vienna 1170, Austria2 University of Exeter, Physics and Astronomy, Stocker Road, EX4 4QL Exeter, UK3 Ecole Normale Superieure, Lyon, CRAL (UMR CNRS 5574), Universite de Lyon, France

E-mail contact: eduard.vorobiev at univie.ac.at

We study the evaporation and condensation of CO and CO2 during the embedded stages of low-mass star formationby using numerical simulations. We focus on the effect of luminosity bursts, similar in magnitude to FUors and EXors,on the gas-phase abundance of CO and CO2 in the protostellar disk and infalling envelope. The evolution of a youngprotostar and its environment is followed based on hydrodynamical models using the thin-disk approximation, coupledwith a stellar evolution code and phase transformations of CO and CO2. The accretion and associated luminositybursts in our model are caused by disk gravitational fragmentation followed by quick migration of the fragments ontothe forming protostar. We found that bursts with luminosity on the order of 100–200 L⊙ can evaporate CO ices inpart of the envelope. The typical freeze-out time of the gas-phase CO onto dust grains in the envelope (a few kyr)is much longer than the burst duration (100–200 yr). This results in an increased abundance of the gas-phase CO inthe envelope long after the system has returned into a quiescent stage. In contrast, luminosity bursts can evaporateCO2 ices only in the disk, where the freeze-out time of the gas-phase CO2 is comparable to the burst duration. Wethus confirm that luminosity bursts can leave long-lasting traces in the abundance of gas-phase CO in the infallingenvelope, enabling the detection of recent bursts as suggested by previous semi-analytical studies.



Three-Dimensional Radiation Transfer in Young Stellar Objects

B.A. Whitney1,2, T.P. Robitaille3, J.E. Bjorkman4, R. Dong5, M.J. Wol2, K. Wood6, and J. Honor1

1 University of Wisconsin, 475 N. Charter St., Madison, WI 537062 Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 803013 Max-Planck-Institute for Astronomy, Konigstuhl 17, 69117 Heidelberg, Germany4 Ritter Observatory, MS 113, Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606-33905 Department of Astrophysical Sciences, Princeton University, Princeton, NJ 085446 School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9AD

E-mail contact: bwhitney at astro.wisc.edu

We have updated our publicly available dust radiative transfer code (HOCHUNK3D) to include new emission processesand various 3-D geometries appropriate for forming stars. The 3-D geometries include warps and spirals in disks,accretion hotspots on the central star, fractal clumping density enhancements, and misaligned inner disks. Additionalaxisymmetric (2-D) features include gaps in disks and envelopes, ”puffed-up inner rims” in disks, multiple bipolarcavity walls, and iteration of disk vertical structure assuming hydrostatic equilibrium. We include the option forsimple power-law envelope geometry, which combined with fractal clumping, and bipolar cavities, can be used to

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model evolved stars as well as protostars. We include non-thermal emission from PAHs and very small grains, andexternal illumination from the interstellar radiation field. The grid structure was modified to allow multiple dustspecies in each cell; based on this, a simple prescription is implemented to model dust stratification.We describe these features in detail, and show example calculations of each. Some of the more interesting resultsinclude the following: 1) Outflow cavities may be more clumpy than infalling envelopes. 2) PAH emission in high-mass stars may be a better indicator of evolutionary stage than the broadband SED slope; and related to this,3) externally illuminated clumps and high-mass stars in optically thin clouds can masquerade as YSOs. 4) Ourhydrostatic equilibrium models suggest that dust settling is likely ubiquitous in T Tauri disks, in agreement withprevious observations.

Accepted by ApJS


A SCUBA-2 850µm survey of protoplanetary discs in the σ Orionis cluster

Jonathan P. Williams1, Lucas A. Cieza,1, Sean M. Andrews2, Iain M. Coulson3, Amy J. Barger4,5,

Caitlin M. Casey1, Chian-Chou Chen1, Lennox L. Cowie1, Michael Koss1, Nicholas Lee1 and David B.

Sanders1

1 Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96816 USA2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA3 Joint Astronomy Centre, 660 N. Aohoku Place, University Park, Hilo, HI 96 720, USA4 Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706, USA5 Department of Physics and Astronomy, University of Hawaii, 2505 Correa Road, Honolulu, HI 96822, USA

E-mail contact: jpw at ifa.hawaii.edu

We present the results from a large 850µm survey of the σOrionis cluster using the SCUBA-2 camera on the JamesClerk Maxwell Telescope. The 0.5◦ diameter circular region we surveyed contains 297 young stellar objects with an ageestimated at about 3Myr. We detect 9 of these objects, 8 of which have infrared excesses from an inner disc. We alsoserendipitously detect 3 non-stellar sources at > 5σ that are likely background submillimetre galaxies. The 9 detectedstars have inferred disc masses ranging from 5 to about 17MJup, assuming similar dust properties as Taurus discs andan ISM gas-to-dust ratio of 100. There is a net positive signal toward the positions of the individually undetectedinfrared excess sources indicating a mean disc mass of 0.5MJup. Stacking the emission toward those stars withoutinfrared excesses constrains their mean disc mass to less than 0.3MJup, or an equivalent Earth mass in dust. Thesubmillimetre luminosity distribution is significantly different from that in the younger Taurus region, indicating discmass evolution as star forming regions age and the infrared excess fraction decreases. Submillimeter Array observationsreveal CO emission toward 4 sources demonstrating that some, but probably not much, molecular gas remains in theserelatively evolved discs. These observations provide new constraints on the dust and gas mass of protoplanetary discsduring the giant planet building phase and provide a reference level for future studies of disc evolution.

Accepted by MNRAS


Deep observations of O2 toward a low-mass protostar with Herschel

Umut A. Yıldız1, Kinsuk Acharyya2, Paul F. Goldsmith3, Ewine F. van Dishoeck1,4, Gary Melnick5,

Ronald Snell6, Rene Liseau7, Jo-Hsin Chen3, Laurent Pagani8, Edwin Bergin9, Paola Caselli10,11, Eric

Herbst12, Lars E. Kristensen5, Ruud Visser9, Dariusz C. Lis13 and Maryvonne Gerin14

1 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands2 S.N. Bose National Centre for Basic Sciences, Salt Lake, Kolkata, 700098, India3 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena CA, 91109, USA4 Max Planck Institut fur Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany5 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA6 Department of Astronomy, LGRT 619, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003,USA

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7 Dept. of Earth & Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala,Sweden8 LERMA & UMR8112 du CNRS, Observatoire de Paris, 61 Av. de l’Observatoire, 75014, Paris, France9 Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA10 School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK11 INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy12 Departments of Chemistry, Astronomy, and Physics, The University of Virginia, Charlottesville, Virginia, USA13 California Institute of Technology, Cahill Center for Astronomy and Astrophysics 301-17, Pasadena, CA 91125,USA14 LRA/LERMA, CNRS, UMR8112, Observatoire de Paris & Ecole Normale Superieure, 24 rue Lhomond, 75231 ParisCedex 05, France

E-mail contact: yildiz at strw.leidenuniv.nl

Context: According to traditional gas-phase chemical models, O2 should be abundant in molecular clouds, but untilrecently, attempts to detect interstellar O2 line emission with ground- and space-based observatories have failed.Aims: Following the multi-line detections of O2 with low abundances in the Orion and ρ Oph A molecular clouds withHerschel, it is important to investigate other environments, and we here quantify the O2 abundance near a solar-massprotostar.Methods: Observations of molecular oxygen, O2, at 487 GHz toward a deeply embedded low-mass Class 0 protostar,NGC 1333-IRAS 4A, are presented, using the Heterodyne Instrument for the Far Infrared (HIFI) on the Herschel

Space Observatory. Complementary data of the chemically related NO and CO molecules are obtained as well. Thehigh spectral resolution data are analyzed using radiative transfer models to infer column densities and abundances,and are tested directly against full gas-grain chemical models.Results: The deep HIFI spectrum fails to show O2 at the velocity of the dense protostellar envelope, implying oneof the lowest abundance upper limits of O2/H2 at ≤6×10−9 (3σ). The O2/CO abundance ratio is less than 0.005.However, a tentative (4.5σ) detection of O2 is seen at the velocity of the surrounding NGC 1333 molecular cloud,shifted by 1 km s−1 relative to the protostar. For the protostellar envelope, pure gas-phase models and gas-grainchemical models require a long pre-collapse phase (∼0.7–1×106 years), during which atomic and molecular oxygen arefrozen out onto dust grains and fully converted to H2O, to avoid overproduction of O2 in the dense envelope. Thesame model also reproduces the limits on the chemically related NO molecule if hydrogenation of NO on the grains tomore complex molecules such as NH2OH, found in recent laboratory experiments, is included. The tentative detectionof O2 in the surrounding cloud is consistent with a low-density PDR model with small changes in reaction rates.Conclusions: The low O2 abundance in the collapsing envelope around a low-mass protostar suggests that the gas andice entering protoplanetary disks is very poor in O2.


http://adsabs.harvard.edu/abs/2013arXiv1307.8031Y

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Dissertation Abstracts

Surveying Star Formation in the Galaxy

Adam Ginsburg

Thesis work conducted at: Center for Astrophysics and Space Astronomy, University of Colorado, Boulder,Colorado, USA

Current address: 391 UCB Boulder, CO, USA 80309

Address as of October 2013: Karl-Schwarzschild-Strasse 2, 85748 Garching bei Munchen, Germany

Electronic mail: adam.g.ginsburg at gmail.com

Ph.D dissertation directed by: John Bally

Ph.D degree awarded: April 2013

I studied the formation of massive stars and clusters via millimeter, radio, and infrared observations. The BolocamGalactic Plane Survey (BGPS) was the first millimeter-wave blind survey of the plane of our Galaxy. I wrote the datareduction pipeline for this survey and produced the final publicly released data products. I ran extensive tests of thepipeline, using simulations to probe its performance.

The BGPS detected over 8000 1.1 mm sources, the largest sample at this wavelength ever detected. As a single-wavelength continuum survey, the BGPS serves as a finder chart for millimeter and radio observations. I thereforeperformed follow-up surveys of BGPS sources in CO 3-2 and formaldehyde, and others did similar follow-ups tomeasure velocities and distances towards these sources.

Formaldehyde observations of ultracompact HII regions and other millimeter-bright sources were used to measure thelocal molecular gas density. These measurements hint that density within molecular clouds does not follow a simplelognormal distribution. They also show that star-forming clouds all contain gas at density >

∼104 cm−3.

I used the BGPS source catalog to identify the most massive compact clumps within the galaxy, identifying 18 withmasses M > 104 M⊙ in the first quadrant of the Galactic plane. As these objects are all actively star-forming, thestarless timescale of massive proto-cluster clumps must be relatively short, with lifetimes <∼0.6 Myr.

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Meetings

The Orion Nebula Cluster as a Paradigm for Star Formationa Space Telescope Science Institute mini-workshop

Baltimore, MD, October 14-16, 2013

Objective:

As the nearest young cluster dominated by massive OB stars, the Orion Nebula Cluster plays a paradigmatic role inour understanding of star and planet formation. The wealth of ground-based and HST data collected in recent years isallowing to study with unprecedented detail the products of the star formation process: stellar mass distribution, agespread, mutiplicity, activity, cluster’s spatial and kinematic structure, etc. These data provide a fundamental referencefor comparison with other regions, as well as a critical benchmark for theoretical models and numerical simulations.

This workshop is an opportunity to discuss what we have learned from Orion so far, focusing on open problems andnew directions of observational and theoretical research. Emphasis will be given to the role played by the OrionNebula Cluster as a paradigm for the early solar environment, as well as for present-day star formation in differentenvironments, including the Galactic center and the Magellanic Clouds.

Organizing Committee:

Massimo Robberto, STScI (Chair)Nicola Da Rio, U. FloridaSelma de Mink, Carnegie/Caltech & PrincetonMario Gennaro, STScILee Hartmann, University of MichiganLynne A. Hillenbrand, CaltechDave Soderblom, STScIJonathan Tan, U. FloridaSherita Hanna (administrative support, [email protected])

http://www.stsci.edu/institute/conference/orion/

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Characterizing Planetary Systems Across the HR Diagram

28 July - 1 August 2014 – Cambridge, United Kingdom

The University of Cambridge Institute of Astronomy will host a 5 day scientific meeting to further our understandingof the formation and evolution of planetary systems. The meeting will focus on the full lifetime of planetary systems,from pre- to post-main sequence host star stages, and the connections that can be made by viewing these evolutionarystages as parts of a whole. In this way, the program aims to provide an integrative approach rather than focusing oneach stellar stage separately.

We will bring together participants from the growing diversity of planetary science disciplines: star-planet formation,solar system studies, exoplanets, debris disks, host star abundances and atmospheric pollution, stellar evolution, andplanetary dynamics. The conference can accommodate up to 150 people.

The overall goal of the meeting is to generate discussion and increase scientific interactions among the diverse com-munities interested in the formation, architecture, and evolution of planetary systems. Two themes that represent thespirit of the meeting are:

1) The physical and chemical connections between evolved planetary systems, their main-sequence counterparts, andthose forming in proto-planetary disks.

2) The scientific potential for extracting planetary system frequency, structure, chemistry, and dynamics at differentevolutionary phases and stellar populations.

Session Topics will include:

- Proto-planetary disk and planetary atmosphere chemistry- Planetesimal and solid planet compositions- Planet and debris populations- Host star elemental abundances and pollution- Planetary system and host star evolution

We hope to see you in Cambridge next summer!

SOC and LOC

Contact: [email protected]

http://www.ast.cam.ac.uk/meetings/2013/AcrossHR

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Meetings of Possible Interest

IAUS 302 - Magnetic Fields Throughout Stellar Evolution

26 - 30 August 2013 Biarritz, Francehttp://iaus302.sciencesconf.org

Meteoroids 2013. An International Conference on Minor Bodies in the Solar System

26 - 30 August 2013 Dep. of Physics, A.M. University, Poznan, Polandhttp://www.astro.amu.edu.pl/Meteoroids2013/index.php

Exoplanets and Brown Dwarfs

2 - 5 September 2013 de Havilland, University of Hertfordshire, Hatfield, Nr. London, UKno web site yet

Evolution of Star Clusters: From Star Formation to Cosmic Ages

24 - 27 September 2013Splinter Meeting E at the Annual Meeting of the Astronomische Gesellschaft, Tubingen, Germanyhttp://www-astro.physik.tu-berlin.de/~harfst/AG2013_SplinterE/

Dust Radiative Transfer - Codes and Benchmarks 9 - 11 October 2013http://ipag.osug.fr/RT13/index.php

The Orion Nebula Cluster as a Paradigm for Star Formation

14 - 16 October 2013 STScI, Baltimore, USAno web site yet

400 Years of Stellar Rotation

17 - 22 November 2013, Natal, Brazilhttp://www.dfte.ufrn.br/400rotation/

The Life Cycle of Dust in the Universe: Observations, Theory, and Laboratory Experiments

18 - 22 November 2013 Taipei, Taiwanhttp://events.asiaa.sinica.edu.tw/meeting/20131118/

An Olympian Symposium for Star Formation

26 - 30 May 2014 Paralia Katerinis, Mount Olympus, Greecehttp://zuserver2.star.ucl.ac.uk/$\sim$tb/

EPoS2014 The Early Phase of Star Formation

1 - 6 June 2014 Ringberg Castle, Tegernsee, Germanyhttp://www.mpia-hd.mpg.de/homes/stein/EPoS/epos.php

The Dance of Stars: Dense Stellar Systems from Infant to Old

2 - 6 June 2014 Bad Honnef, Germanyhttp://www.astro.uni-bonn.de/$\sim$sambaran/DS2014/index.html

The 18th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun

9 - 13 June 2014 Flagstaff, Arizona, USAhttp://www2.lowell.edu/workshops/coolstars18/

Summer School on Protoplanetary Disks: Theory and Modeling meet Observations

16 - 20 June 2014 Groningen, The Netherlandshttp://www.diana-project.com/summer-school

Characterizing Planetary Systems Across the HR Diagram

28 July - 1 August 2014 Inst. for Astronomy, Cambridge, USAhttp://www.ast.cam.ac.uk/meetings/2013/AcrossHR

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Living Together: Planets, Stellar Binaries and Stars with Planets

8 - 12 September 2014 Litomysl Castle, Litomysl, Czech Republichttp://astro.physics.muni.cz/kopal2014/

Planet Formation and Evolution 2014

10 - 12 September 2014 Kiel, Germanyhttp://www1.astrophysik.uni-kiel.de/$\sim$2014/main/

Towards Other Earths II. The Star-Planet Connection

15 - 19 September 2014 Portugalhttp://www.astro.up.pt/toe2014

Other meetings: http://www1.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/meetings/

Moving ... ??

If you move or your e-mail address changes, pleasesend the editor your new address. If the Newsletterbounces back from an address for three consecutivemonths, the address is deleted from the mailing list.

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the star formation newsletterreipurth/newsletter/newsletter248.pdfstart, ﬁlled with much anxiety,...

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