the star formation newsletter · hans zinnecker the star formation newsletter is a vehicle for ......

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

No. 244 — 7 April 2013 Editor: Bo Reipurth ([email protected])

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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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Abstracts of Newly Accepted Papers . . . . . . . . . . 13

Abstracts of Newly Accepted Major Reviews . 40

Dissertation Abstracts . . . . . . . . . . . . . . . . . . . . . . . . 41

New Jobs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

New and Upcoming Meetings . . . . . . . . . . . . . . . . . 44

Cover Picture

A view of the central part of the Carina complex,from a near-infrared JHK mosaic of HAWK-I im-ages obtained at ESO’s VLT. The bright clusterto the upper left is Trumpler 14; this is the second-richest cluster in the region after Trumpler 16 whichis associated with Eta Carinae. The large clusterto the right in the image is pointing towards Trum-pler 14, while the other cloud structure face Trum-pler 16 outside the image and towards the lowerleft. Courtesy ESO/T.Preibisch.

High resolution jpg files of the entire Carina clusterregion can be downloaded fromhttp://www.eso.org/public/images/eso1208a/

Submitting your abstracts

Latex macros for submitting abstractsand dissertation abstracts (by e-mail [email protected]) are appended toeach Call for Abstracts. You can alsosubmit via the Newsletter web inter-face at http://www2.ifa.hawaii.edu/star-formation/index.cfm

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Michal Simonin conversation with Lisa Prato

Q: How did you come to the US from Czechoslovakia?

A: My family arrived in Boston on February 1, 1948, toenable my father to start a postdoc at MIT. By the end ofthat month, Communists took over the Czech governmentand my parents decided to stay in the US. As membersof the bourgeoisie my family’s lives would have been verydifferent had we not emigrated and my sister and I wouldnot have received the education we did.

Q: Who was your PhD advisor, and which were the people

who had a formative influence on you as a young scientist?

A: Tommy Gold and Ian Axford co-advised me. Ed Salpeterwas also on my committee. They were enthusiastic andsupportive mentors. As an undergraduate at Harvard Iworked in Howard Emmons’ plasma physics lab. I learnedfrom him that I enjoyed research, that it was fun, and, inhindsight, that it was okay to give serious responsibilityto an undergraduate. My interests evolved from physicsto astronomy at that time.

Q: When did you become interested in young stars?

A: At Stony Brook in the early 1970’s, Dan Gezari, DickJoyce, Giovanna Righini and I carried out some of theearliest sub-mm observations from the ground. Molecularclouds identified by balloon-borne sub-mm observationswere natural targets. Interest in the molecular clouds nat-urally led to an interest in the young stars that heatedthem. This led to IR spectroscopy with Jackie Fischerand Fred Hamann, and, in the last decade, to much higherspectral and spatial resolution spectroscopy with Lisa Prato.

Antoine Labeyrie was a post-doc at Stony Brook in theearly 1970’s and with Dan Gezari and Bob Stachnik madethe first astronomical speckle interferometry observations.It was a blunder that I did not apply the technique toyoung stars when new instrumentation made that possible.

Dan, Dick, Giovanna and I also observed a very old star,

ours. My interest in the Sun goes way back: my first pub-lished paper concerned 3 mm solar observations. MiriamForman, my first PhD student, did a theoretical thesis onconvection in the solar wind.

Q: You have done pioneering work on PMS binaries using

lunar occultations, reaching remarkable resolution. Is thistechnique still competitive?

A: Wen-Ping Chen and I measured binary separationsas small as 10 mas with precisions of a few mas in theK-band. The technique remains competitive on 2−3 mclass telescopes with a single channel photometer. At verylarge telescopes you have the difficulties that the Fresnelpattern becomes smeared over the aperture and typicallyonly large format array detectors are available; you needspecialized software to read out subarrays fast. If the oc-cultation is a reappearance, you had better have excellentpointing and nerves of steel.

Q: I remember one of your papers back in 1997 that fasci-

nated me, dealing with the clustering of young stars. Whatwere your key findings, and how have these results held up?

A: I had long ago learned about Vera Rubin’s use ofthe 2-point correlation function to study the distributionof galaxies, so I was on the look-out for an application.Richard Larson’s 1995 paper did just that to the youngstars in Taurus. With Andrea Ghez, Christoph Leinert,and others I had just published our lunar occultation sur-vey of Taurus and Ophiuchus, and Prosser et al. (1994)had published a high resolution survey with the HST of thehigh star density region in the Orion Trapezium. Thus Icould apply and test Larson’s analysis on a larger databaseand include three star-forming regions.

Each of the three SFRs displayed two distinct domains inits 2-point correlation function, one produced by the distri-bution of binary separations and a second I attributed tothe large scale structure of the region. The break betweenthe two regimes moved to smaller angular separations withincreasing star density of the region. Later Tracy Beck car-ried out pioneering AO observations of the dense clusterin NGC 2024. Her 2-point correlation function analysisalso identified the two domains.

Very quickly following my paper, Matthew Bate and col-leagues (1998) showed by extensive modeling that my con-clusions about large scale structure were premature be-cause the analysis was very sensitive to boundary effects.The surveys of Ophiuchus and Orion were insufficientlyextensive in angular area. More recently, Kraus & Hillen-brand (2008) surveyed much larger areas in Taurus andOphiuchus and identified 3 regimes in their 2-point cor-relation functions: at the smaller angular scales, the tworegimes described above, and, at the largest scale, up to10 degrees or more, a regime they associated with the orig-inal, unrelaxed structure of the SFR.

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Q: You have used mm interferometric data to measure dy-

namical masses of T Tauri stars, getting results with 10%errors, mostly dominated by distance uncertainties. As

distances are becoming increasingly well known, and with

ALMA entering the scene, how accurately do you thinkwe can determine T Tauri masses? How accurately do

you think we need to determine T Tauri masses?

A: Stephane Guilloteau, Anne Dutrey, their collaborators,and I are now writing a paper in which we measure the ro-tations of several disks in Taurus using the CN(2-1) lineswith the IRAM Plateau de Bure interferometer and deter-mine the central stellar masses to an internal accuracy of∼2%. In our earlier work we had used CO lines. However,molecular clouds along the line of sight to young stars areoften opaque even in the higher frequency CO lines of theseveral isotopic forms, effectively blocking several veloc-ity channels from the rotation analysis. In a paper pub-lished earlier this year (Guilloteau et al. 2013) we showedthat the intervening molecular clouds are transparent inthe CN(2-1) lines, paving the way to mass determinationsusing ALMA on stars in heavily obscured regions in thesouthern hemisphere.

Masses measured by disk rotation scale with distance.Unfortunately, precise distances are not known for moststars in Taurus. However, young stars are often found inclumps. Parallax measurements of a few radio emittingstars by the Loinard/Torres group, and dynamical mea-surements to multiples as in Gail Schaefer’s work on V807Tau and our forthcoming paper on NTTS 045251+3016,are revealing the 3D structure of SFRs, allowing estimatesof distances to other clump members. To reach our goalof identifying evolutionary tracks that satisfy the empiri-cal data we will need precisions of at least ±5%. I thinkthe disk rotation technique will achieve this in Taurus andOphiuchus.

Q: The concept of stellar twins, originally put forward by

Leon Lucy, is intriguing. You have studied such twins.

What do you think are their origin?

A: The big hint is that the twins, main sequence binarieswith masses equal within 2%, are found exclusively amongspectroscopic binaries with periods less than 43 days; themedian period of the twins is 7 days. Accretion of highangular momentum material from a star forming cloudfavors the formation of more equal mass binary compo-nents. I speculate that this process went to completionfor the closest binaries at their earliest formation stages.

My curiosity about the twins followed from an interest inthe mass ratio distribution of binaries. Chad Bender stud-ied this in a large sample of known spectroscopic binariesin the Hyades for his thesis. Lisa Prato is determining themass ratio distribution in much younger SBs.

Q: You have used the CHARA interferometer to directly

measure the diameters of several young stars; how many

more are accessible with this technique?

A: The angular resolutions that will be available for theforeseeable future limit us to 10−50Myr old stars in nearbyyoung moving groups, and sensitivity limits us to theirbrightest and nearest members. I think that Russel White,Gail Schaefer, and I have picked off the stars that are mea-surable now in the northern sky. Russel and Gail measured3, and Gail and I have measured 3. The CHARA sensitiv-ity limits are improving. The prospects are good that ina few years we’ll reach some K and M members that JoshSchlieder identified in his thesis work.

Q: Of your 12 PhD students, 6 are women and 6 men.This is still unusual in our field. How did it come about?

A: It just happened, and I was unaware of the accu-rate census until I offered the champagne toast at JoshSchlieder’s thesis defense. I think it’s true to say that Iam gender-blind as regards scientific collaborators. Per-haps this is because my mother and father both earneddoctorates in physics at Charles University in Prague; asa kid I must have thought that was normal. But you’reright that the demographic is unusual and I’m remindedof Jeremy Bernstein’s observation. When asked to specu-late how many Einsteins mankind has missed, he replied“roughly a half”. As an example of how society and prej-udice change slowly, Bernstein goes on to observe thatthere were very few Jews in European and North Amer-ican universities before the 20th century; the Ivy Leagueschools were particularly slow to change. Currently, forwomen, academia (at least in physics and astronomy) stilllags behind industry and business, not that the situationis perfect there either.

Q: What advice would you give young people currently in-

terested in a career in astronomy?

A: Go for it if, with no self-deception, you believe that youcan compete with your peers. However, don’t have yourheart set on emulating your professor or continuing yourthesis work. There are many other ways to find happiness(as there are without a doctorate). Consider yourself awell-trained physical scientist and be flexible about whereyou might apply your abilities. My standard advice toyoung people is to do what you’re good at, that othersfind difficult, and that someone is willing to pay you for.

The funding problems we experience now are not unique toastronomy as the mindless sequester vividly demonstrates.

Q: Are you less involved in research post-retirement?

A: No; however, freed of formal teaching responsibilitiesand avoiding departmental hassles and meetings like theplague makes more time available for grandchildren, read-ing, and music. My spouse and I need cultural fellowshipsto New York City.

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My Favorite ObjectThe Carina Nebula Complex

Thomas Preibisch

Most stars form in rich stellar clusters or associations, andtherefore close to high-mass (M > 20M⊙) stars. Evenour solar system seems to have formed in such an envi-ronment, where nearby massive stars had an importantimpact on the early evolution of the solar nebula. The hotand luminous O-type stars in massive star-forming regionsprofoundly influence their environments by creating HIIregions, generating wind-blown bubbles, and exploding assupernovae. This feedback can disperse a large fractionof the original molecular clouds, out of which the starsformed, and thus may terminate the star formation pro-cess. On the other hand, cloud compression provided byionization fronts and expanding wind bubbles may alsotrigger the formation of new generations of stars in thecompressed clouds. The detailed balance of these two op-posing processes determines the global evolution, i.e. thestar formation history and the resulting star formation ef-ficiency. However, the involved physical processes are notyet well understood and it is still debated whether themassive star feedback is more or less important than theprimordial turbulence in the clouds, and how efficient thetriggering of star formation can actually be. These ques-tions are also of fundamental importance for understand-ing the star formation process in (extragalactic) starburstregions, where the number of very massive stars is (much)higher than in the largest Galactic star forming regions.

A major observational problem for studies of massive starfeedback results from the fact that the nearby star formingregions, which can be easily studied at high spatial resolu-tion, host (at most) very small numbers of high-mass stars;therefore, the level of feedback is orders of magnitudessmaller than in extragalactic starburst regions. Regionshosting significant numbers of very massive (M ≥ 50M⊙)stars (which dominate the feedback) are usually too faraway to allow detailed studies of small-scale cloud struc-tures or to detect their full stellar populations.

The Carina Nebula is an ideal target in this respect: ata moderate and well known distance of 2.3 kpc, it rep-resents the nearest southern region with a large enoughpopulation of massive stars (≥ 70 O-type and WR stars)to sample the top of the IMF. Most of the massive starsin the Carina Nebula reside in one of several loose clusterswith ages ranging from <1 to several Myr. The actionof the massive star feedback is impressively illustrated bythe famous Hubble Space Telescope and Spitzer images ofthe Carina Nebula, which show how the clouds are erodedand shaped by the stellar radiation and winds, giving riseto numerous evaporating globules and giant dust pillars.

A good summary of basic information about the CarinaNebula is given in Smith & Brooks (2008). As discussedin Smith et al. (2000), until about 15 years ago the CarinaNebula was generally assumed to be just an evolved HIIregion, without significant star formation activity. The de-tection of embedded infrared sources in some of the dustpillars started to change this view dramatically. Today weknow (partly based on the results described in this arti-cle) that the Carina Nebula Complex is one of the mostproductive star factories in our Galaxy. These propertiesmake the Carina Nebula the best site to study in detail thephysics of violent massive star formation and the resultingfeedback effects, cloud dispersal and triggering of star for-mation. It constitutes our best ”bridge” between nearbyregions with low levels of feedback like Orion, which canbe studied in great detail, and the much more massive andenergetic, but also much more distant extragalactic giantHII regions and starburst systems.

My interest in the Carina Nebula was sparked in 2007,when Leisa Townsley (Penn State University) invited meto join a team of X-ray astronomers planning a large-scaleX-ray survey of the Carina Nebula with the Chandra X-ray satellite. In the Chandra Carina Complex Project, a1.4 square-degree area was mapped with a mosaic of 22individual pointings, spending a total observing time of1.34 Megaseconds (15.5 days). An overview of the numer-ous results from this project can be found in Townsleyet al. (2011). The Chandra images revealed 14 368 in-dividual X-ray sources, and a sophisticated classificationscheme showed that 10 714 of these are most likely youngstars (Broos et al. 2011). This shows that the young stel-lar population in the Carina Nebula is much larger thanthought just a few years ago. Another major result wasthe finding that about half of the young stars are mem-bers in one of about 30 clusters, whereas the other 50%are widely distributed over the entire area of the complex(Feigelson et al. 2011).

While these Chandra data provided the first unbiased (al-though luminosity-limited) sample of the young stars inthe region, the X-ray data alone do not yield much infor-

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mation about stellar properties. Deep near-infrared dataare essential for a determination of individual stellar (andcircumstellar) parameters, but such data existed only fora few selected small parts in the inner Carina Nebula re-gion; a deep and comprehensive wide-field near-infraredsurvey was obviously missing.

When the Chandra Carina Complex Project was planned,the new near-infrared wide-field imager HAWK-I for theESO 8m Very Large Telescope was just being commis-sioned. From discussions with Hans Zinnecker and MarkMcCaughrean I realized that HAWK-I would be the per-fect instrument to obtain the required deep wide-field sur-vey data. Our proposal for observing time was successfuland in January 2008 a mosaic of 24 contiguous HAWK-I fields was observed as part of the scientific verificationprogram. Our HAWK-I survey of the Carina Nebula (seePreibisch et al. 2011c for a detailed description and theESO Photo Release1 for images) covered a total area of1280 square-arcminutes. All data were processed and cali-brated by the Cambridge Astronomical Survey Unit. Witha detection limit of J ∼ 23, H ∼ 22, and Ks ∼ 21our HAWK-I data represent the largest and deepest near-infrared survey of the Carina Nebula obtained so far. Morethan 600 000 point sources were detected, about 20 timesmore than the number of 2MASS sources in the same area.

Our HAWK-I images are deep enough to detect all starsin the Carina Nebula down to masses of 0.1M⊙ for agesup to 3 Myr and extinctions of AV = 15 mag. The verygood seeing conditions during our observations (FWHM∼ 0.5′′) and the 0.106′′ pixel scale of HAWK-I resulted ina superb image quality and revealed numerous interest-ing cloud structures in unprecedented detail. One partic-ularly notable detection was an embedded young stellarobject with a circumstellar disk seen almost edge-on (seeFig. 1). As described in Preibisch et al. (2011b), our ra-diative transfer modeling showed that the central youngstellar object must be rather massive, most likely in therange 10 − 15M⊙. The surrounding disk and envelope isvery large (with a diameter of about 7000 AU) and mas-sive (∼ 2M⊙), and constitutes an interesting target forfurther detailed studies. Our modeling of another pecu-liar nebulosity is described in Ngoumou et al. (2013).

Matching the HAWK-I point-sources to the Chandra X-ray source catalog yielded infrared counterparts for 6636X-ray sources. This strongly increased the number ofknown infrared counterparts to the Chandra sources (inthe common field-of-view), from just 33.9% based on 2MASSto 88.8% with HAWK-I. It provided the basis for a de-tailed characterization of the X-ray selected population ofyoung stars, as described in Preibisch et al. (2011a). Wefound that the number of X-ray detected low-mass starsis at least as high as expected from the number of known

1http://www.eso.org/public/news/eso1208/

Figure 1: RGB composite image of the disk object in theCarina Nebula, constructed from the Ks-, H-, and J-bandHAWK-I images. The bright bluish point-source left of thecenter is an unrelated (foreground?) star. See Preibischet al. (2011b) for further information.

high-mass stars and scaling by the field star IMF. Thisimplies that there is clearly no deficit of low-mass stars inthe Carina Nebula Complex. Our analysis of the K-bandluminosity function of the X-ray selected Carina membersalso showed that (at least down to the X-ray detectionlimit around 0.5M⊙) the shape of the IMF in the CarinaNebula is consistent with that in the field IMF. This is rel-evant because some observational studies of massive starforming or starburst regions (including earlier studies ofthe Carina Nebula) had claimed to see a truncated IMFand a corresponding deficit of low-mass stars; our datashow no indication of such an effect.

We also found that the fraction of near-infrared excesssources (i.e. a proxy of disk-bearing young stars) in theindividual clusters in the Carina Nebula is considerablylower than typical for nearby, less massive clusters of sim-ilar age. This suggests that the process of circumstellardisk dispersal proceeds on a faster timescale in the CarinaNebula than in the more quiescent regions, and is mostlikely the consequence of the very high level of massivestar feedback in the Carina Nebula.

Further important information about the young stars inthe Carina Nebula was obtained in the analysis of Spitzerobservations of the complex (Smith et al. 2010b; Povichet al. 2011). In combination, these X-ray, near-, and mid-infrared surveys have strongly boosted our knowledge ofthe young stellar populations in the Carina Nebula Com-plex (see also Preibisch 2011).

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In order to investigate the interaction of the stars and thesurrounding clouds, detailed information on the structureand the physical properties of the clouds is needed. Whilethe available Spitzer and MSX maps showed the surfacestructure of the clouds and traced the warm gas, the bulkof the cloud mass is inside denser and colder structures,and can only be observed at longer wavelengths. All far-infrared/sub-mm or radio data sets existing at that timehad either too poor angular resolution to reveal detailsin the cloud structure, or covered only small parts of thelarge Carina Nebula Complex. Therefore, we performedcomprehensive wide-field surveys of the clouds in the far-infrared and sub-mm regime as another major part of ourmulti-wavelength project.

As a first step to meaningfully complement the extraor-dinary quality of the recent X-ray, optical, and infrareddata sets, I started a collaboration with Karl Menten andFrederic Schuller from the Max Planck Institute for Ra-dio Astronomy in Bonn to obtain a deep wide-field sub-mm survey with LABOCA at the APEX telescope. Our1.2◦×1.2◦ LABOCA map provided an unprecedented viewof the cold, dense clouds in the Carina Nebula Complexat an angular resolution of 18′′, corresponding to phys-ical scales of 0.2 pc. An impressive comparison of thesub-mm and optical appearance of the cloud complex canbe seen in an ESO Photo Release2. Our analysis of theLABOCA data (see Preibisch et al. 2001d) showed thatthe cold dust in the complex is distributed in a wide va-riety of structures, from the very massive (∼ 15 000M⊙)and dense cloud to the west of the stellar cluster Tr 14,over several clumps of a few hundred solar masses, to nu-merous small clumps containing only a few solar massesof gas and dust. Most clouds show clear indications thattheir structure is shaped by the very strong ionizing radi-ation and possibly the stellar winds of the massive stars.The total mass of the dense clouds to which LABOCAis sensitive was found to be ∼ 60 000M⊙. There is thusclearly still a large reservoir of dense clouds available forfurther star formation. An analysis of the clump massspectra is described in Pekruhl et al. (2013).

While LABOCA was the perfect instrument to map thedense and cold cloud clumps, it is less sensitive to thesomewhat warmer and more diffuse gas at the surfaces ofthe irradiated clouds and in the inner regions of the Ca-rina Nebula, where the original clouds have already beenlargely destroyed by the feedback of the massive stars.The Herschel observatory is ideally suited to map thefar-infrared emission from this slightly warmer gas and toprovide a complete inventory of the cloud structures. Wetherefore used SPIRE and PACS onboard of Herschel tomap the full spatial extent (more than 5 square-degrees)of the entire Carina Nebula Complex at wavelengths be-

2http://www.eso.org/public/news/eso1145/

Figure 2: Color composite of a 2.5◦ × 2.7◦ re-gion of our Herschel 70µm (blue), 160µm (green),and 250µm (red) maps. This image was createdfor the ESA Science & Technology website releasesci.esa.int/science-e/www/object/index.cfm?fobjectid=50414.The bubble-like cloud complex in the upper right part isthe Gum 31 region.

tween 70µm and 500µm. Our Herschel maps (see Fig. 2)revealed the small-scale structure of the clouds in unprece-dented details and allowed us to determine the temper-atures and column densities (see Preibisch et al. 2012).A detailed study of the physical parameters of individ-ual cloud structures and the cloud mass budget was re-cently completed (Roccatagliata et al. 2013). We foundthat most clouds have temperatures ranging from about20 K (in the dense clumps) up to ∼ 35− 40 K (for cloudsclose to massive stars). The total cloud mass above theAV ≥ 1 mag threshold is about 500 000M⊙. Consideringthat the strong feedback from massive stars is dispersingthe cloud complex since several Myr, this a remarkablylarge value. We could also quantify the level of the ra-diative feedback from the hot stars and found that theintensity of the FUV irradiation at most cloud surfacesis at least about 1000 times stronger than the galacticaverage value (the so-called Habing field). This level ofirradiation is very similar to the observed FUV intensitiesin the 30 Dor region or in the starburst nucleus of M82.

The Herschel maps furthermore revealed over 600 point-like sources, most of which are embedded protostars. Ouranalysis (see Gaczkowski et al. 2013) of their luminosi-

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ties and masses (estimated from radiative transfer simula-tion of the observed spectral energy distributions) yieldedthe remarkable result that all these objects seem to below- or intermediate-mass protostars (M∗ ≤ 10− 15M⊙);no highly luminous (L∗ ≥ 104L⊙), i.e. high-mass (M∗ ≥20M⊙) young stellar objects are seen in our maps. Thisabsence of high-mass protostars is remarkable, given thepresence of large numbers (≥ 70) of high-mass stars in the(few Myr old) optically visible young stellar population inthe Carina Nebula.

Our analysis of the spatial distribution of the Herschel -detected protostars showed that they are strongly concen-trated along the edges of irradiated clouds. A very similarresult had been found in our previous investigation of jet-driving protostars (Ohlendorf et al. 2012). This suggeststhat the currently forming generation of stars in the Ca-rina Nebula Complex is predominantly triggered by thefeedback from the numerous massive stars in the severalMyr old generation. These findings provide strong obser-vational support for the model of triggered star formationin the irradiated pillars that was suggested by Smith etal. (2010b). The current star formation activity is thuslargely restricted to the surfaces of the numerous individ-ual pillars.

As the sample of Herschel detected protostars traces theyoungest generation of currently forming stars in the Ca-rina Nebula, we could also estimate the current star forma-tion rate in the complex. The value of ∼ 0.017M⊙/yearwe derived is very similar to the average star formationrate over the last few Myr, that was determined by Povichet al. (2011). This shows that the Carina Nebula Complexalone is responsible for as much as about 1 percent of thetotal star formation rate of our entire Galaxy, emphasizingonce again the importance of this star forming region.

Numerous further interesting aspects of the Carina NebulaComplex still remain to be explored. We have recently be-gun to extend our studies of the young stellar populationsto the Gum 31 HII region at the north-western edge of theCarina Nebula (see Fig. 2); first results are presented inOhlendorf et al. (2013). We also have performed new X-ray and infrared observations to improve the spatial com-pleteness of our studies of the young stellar population.

Detailed observations of the small-scale structure of indi-vidual cloud pillars constitute another current topic of ourongoing work. The direct comparison of these data withsophisticated numerical models (see, e.g., Gritschneder etal. 2010; Ercolano et al. 2012) will provide new insight intothe formation and evolution of pillars and their gravita-tional collapse into stars and stellar clusters. To conclude,the Carina Nebula will certainly keep us busy for the nextseveral years.

I would like to thank several colleagues for discussions andadvice that was important for the success of this project,particularly Hans Zinnecker, Mark McCaughrean, KarlMenten, Frederic Schuller, and Silvia Leurini. I also wouldlike to name the Postdocs, PhD- and Master-students inmy group at the University of Munich who have been(or are still) contributing to the different analysis steps:Thorsten Ratzka, Veronica Roccatagliata, Stephanie Pekruhl,Henrike Ohlendorf, Judith Ngoumou, Benjamin Gaczkowski,Max Mehlhorn, Peter Zeidler, Caroline Hebinck, TiagoGehring, and Benjamin Kuderna.

Finally, I want to acknowledge funding for various aspectsof this project by the German Science Foundation (DFGPR569/9-1). The analysis of the Herschel data was fundedby the German Federal Ministry of Economics and Tech-nology through the DLR grant number 50 OR 1109. Addi-tional support came from funds from the Munich Clusterof Excellence: “Origin and Structure of the Universe”.

References:

Broos, P., Townsley, L., Feigelson, E.D., et al. 2011, ApJS, 194, 2Ercolano, B., Dale, J. E., Gritschneder, M., et al. 2012, MNRAS,420, 141Feigelson, E.D., Getman, K.V., Townsley, L., et al. 2011, ApJS, 194,9Gaczkowski, B., Preibisch, T., Ratzka, T., Roccatagliata, V., Ohlen-dorf, H., Zinnecker, H., 2013, A&A, 549, A67Gritschneder, M., Burkert, A., Naab, T. et al. 2010, ApJ, 723, 971Ngoumou, J., Preibisch, T., Ratzka, T., Burkert, A., 2013, ApJ,submittedOhlendorf, H., Preibisch, H., Gaczkowski, B., Ratzka, T., Grell-mann, R., McLeod, A., 2012, A&A, 540, A81Ohlendorf, H., Preibisch, T., Gaczkowski, B., Ratzka, T., Ngoumou,J., Roccatagliata, V., Grellmann, R., 2013, A&A, 552, A14Pekruhl, S., Preibisch, T., Schuller, F., Menten, K., 2013, A&A, 550,A29Povich, M.S., Smith, N., Majewski, S.R., et al. 2011, ApJS 194, 14Preibisch, T., 2011, Reviews in Modern Astronomy, (ed. R. vonBerlepsch), Vol. 23, p. 223Preibisch, T., Hodgkin, S., Irwin, M., et al. 2011a, ApJS, 194, 10Preibisch, T., Ratzka, T., Gehring, T. et al. 2011b, A&A, 530, A40Preibisch, T., Ratzka, T., Kuderna, B., et al. 2011c, A&A, 530, A34Preibisch, T., Schuller, F., Ohlendorf, H., Pekruhl, S., Menten, K.M.,Zinnecker, H., 2011d, A&A, 525, A92Preibisch, T., Roccatagliata, V., Gaczkowski, B., Ratzka, T., 2012,A&A, 541, A133Roccatagliata, V., Preibisch, T., Ratzka, T., Gaczkowski, B., 2013,A&A, submitted (arXiv:1303.5201)Smith, N., & Brooks, K. J. 2008, Handbook of Star Forming Re-gions, (ed. B. Reipurth), Volume II, 138Smith, N. 2006, MNRAS, 367, 763Smith, N., Egan, M.P., Carey, s., et al. 2000, ApJ 532, L145Smith, N., Bally, J., & Walborn, N.R. 2010a, MNRAS, 405, 1153Smith, N., Povich, M. S., Whitney, B. A., et al. 2010b, MNRAS,406, 952Townsley, L., Broos, P., Corcoran, M.F., et al. 2011, ApJS, 194, 1

8

Perspective

The Birth Cluster of the Sunby Susanne Pfalzner

Our Sun resides in a sparsely populated region of the MilkyWay. The nearest massive young cluster3, the Orion Neb-ula Cluster, is more than 400 pc away, so one can easily getthe impression that such massive clusters have little rele-vance for our own Solar system. However, there are strongindications that the Sun might have formed as part of justsuch a dense stellar environment. Most of these clustersdissolve quickly after their formation, which is the reasonwhy we see no signs of the solar birth cluster nowadays:4.6 Gyr after the Sun formed the solar birth cluster haslargely dispersed (Portegies-Zwart 2009).

The indications for the cluster origin of the Solar systemcome from very diverse sources:The one which we are perhaps most unfamiliar with in thestar formation community comes from the chemical com-position in chondrites - meteorites which formed at thesame time and basically from the same material as theSun. It is the presence of precursors to the short-lived ra-dioactive isotopes 60Fe and 26Al in these chondrites, whichmakes them interesting for the determination of the his-tory of the Solar system (Gritschneider et al. 2012). Inparticular the isotope 60Fe is extremely difficult to pro-duce otherwise than by stellar nucleosynthesis (Williams& Gaidos 2007, Gounelle et al. 2009), making a super-nova the most likely source. A range of supernovae pro-genitor masses would match, but stars with a mass of ≈25 M⊙ provide the best fit (Adams 2010, and referencestherein). When the supernova exploded, the Sun shouldhave been fairly close (0.2 - 2 pc) for the protoplanetary

3In the following we call all these stellar groups ”cluster” regard-less of whether the stars remain bound for any length of time.

disc to become enriched to such a degree (for a discussion,see Adams 2010). As stars with masses in excess of 25 M⊙

usually form only in clusters with a fairly large number (>4000) of members (Lee et al. 2008), this is a strong cuethat the Sun formed in a fairly massive cluster.

The other two indications for the cluster origin of the Suncan be deduced from todays form of the Solar system.These are a) the sharp outer edge of our planetary sys-tem at 30-40 AU and b) the very high eccentricities ofthe Kuiper belt objects. The sharpness of the outer edgeis best illustrated by the low mass contained in the totalof the large number of Kuiper belt objects, which is only∼ 0.01 - 0.1 Earth masses (Bernstein et al. 2004). Theprotoplanetary disc from which the Solar system eventu-ally formed was most likely initially considerably larger.Possible processes that could have led to the truncation ofthe disc include gravitational interactions with other clus-ter members, photo-evaporation by nearby massive starsor the supernova explosion itself. Each of these scenar-ios requires a cluster environment of relatively high stellardensity.

The first of these options is favoured because such gravi-tational interactions lead not only to disc truncation butmove as well matter onto eccentric orbits as required forthe Kuiper belt objects (see Figure 1). The most promi-nent example of an eccentric Kuiper belt object is Sednawith a periastron of 76 AU, an apastron of 937 AU andan eccentricity of 0.8527. It is well beyond the reach ofthe gas giants and could not have been scattered intothis highly eccentric orbit from interactions with Neptunealone (Gomez et al. 2005). The most straightforward ex-planation for the high eccentricity would be some type ofdynamical interaction (Morbidelli & Levison 2004). It isa point of debate whether there is an encounter scenariothat can account for both features - disc cut-off and Sednaorbit - resulting from a single encounter, or whether twoseparate encounters are necessary.

Each of the observed features described above can be ac-counted for by alternative means. For example, gives theNice model an alternative explanation for origin of the lowmass in the Kuiper belt (Thommes et al. 2002). However,only the cluster origin scenario explains all three effects atthe same time.

The requirements on the mass of the supernova progenitorprovides a lower limit for the number of stars, N , in thesolar birth cluster, whereas the radiation field producedby the large number of massive stars gives an upper limit.It was found that the early solar nebula could survive inclusters with N < 105 (Scally & Clarke 2001, Mann &Williams 2009). Consistent results for the likely member-ship are obtained from estimates based on the likelihood ofan encounter that leads to a cut-off of the protoplanetarydisc at 30 AU (Adams 2010). Assuming that the average

9

Figure 1: Simulations of the effect of the fly-by of a star on the protoplanetary disc of the Sun.

mass of the cluster stars is 0.5 M⊙, this is equivalent to atotal cluster mass mcl in the range of 2000 M⊙ < mcl <5 × 104 M⊙.

The density of the Solar system birth cluster is constrainedby considering what types of encounters are necessary toresult in a Sedna-like orbit assuming an encounter with aperiastron in the range 100 - 1000 AU. It was found thatthe densities in the cluster centre must have been in therange 103 M⊙ pc−3 < ρc < 105 M⊙ pc−3 (Brasser et al.2006, Schwamb et al. 2010). Here the central density isgiven, because due to mass segregation the most massivestars are usually located close to the cluster centre. As theSolar system must have formed close to a supernova thathad a massive star as progenitor, the Sun most likely alsoresided close to the cluster centre. The requirements forthe central cluster density translate into a mean densityin the range of 10 M⊙ pc−3 ≤ ρm ≤ 104 M⊙ pc−3.

In summary, the presence of short-lived isotopes, the fall-off of the mass distribution of the Solar system, and the

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orbit of Sedna all combine to constrain the solar birthcluster to a membership of a few thousands to ten thou-sands of stars with a mean cluster density in the range of10 ≤ ρm ≤ 104 M⊙ pc−3 at the moment of the encounter.

The mass requirement puts the solar birth cluster in themassive cluster category. In the Milky Way such massiveyoung star clusters (tc < 20 Myr, mc > 103 M⊙) are ob-served to have mean densities ranging from less than 0.01to several 105 M⊙ pc−3 and radii from 0.1 pc to severaltens of pc. So, clusters with the required properties, interms of mass and density, for the Solar birth cluster existalso presently in the Milky Way.

Massive clusters seem to exist in two distinct groups ofwhich one is much more compact than the other (Hunter1999, Maiz-Apellaniz 2001) - strongly suggesting a bi-modal cluster formation. Each of these cluster groups ex-pands with age, leading to two well-defined density-radiustracks (see Figure 2) (Pfalzner 2009, Portegies Zwart etal. 2010).

The group of compact clusters develop from a radius Rc of∼ 0.1 pc at 1 Myr to about 1 - 3 pc at 20 Myr. Simultane-ously, the stellar density drops from initially≥ 105 M⊙ pc−3

to 103 M⊙ pc−3 during that timespan. Thus, these com-pact clusters simply diffuse while more or less retainingtheir mass. Typical members of this group are for exam-ple Arches, Quintuplet, and NGC 3606.

The other group of loose extended clusters are often clas-sified as OB associations. At an early age (2 Myr) theseclusters have approximately the same mass as compactclusters but spread out over much larger volumes. Typicalradii are ∼ 5 pc resulting in much lower mean cluster den-sities (< 1 - 103 M⊙ pc−3). They also expand with time,reaching a cluster size of about 20-25 pc at 20 Myr. Incontrast to compact clusters these extended clusters losearound 90% of their mass during the expansion process.For example, NGC 6611, NGC 2244, and U Sco belong tothis group.

This bi-modal classification of massive clusters immedi-ately imposes an additional constriction on the formationhistory of our solar system: The Solar system must have

10

developed either in a compact or a loose extended cluster.This reduces the scenarios of the solar birth cluster to onlytwo possible types of developmental paths. It only remainsto determine which of the two environments - compact orloose clusters - is the more likely origin of the Solar system.

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Figure 3: Density development of the two groups of mas-sive clusters as a function of cluster age. The box depictsthe density requirement for the solar birth cluster at themoment of the encounter (Pfalzner 2013).

The lines in Figure 3 track the typical development forclusters more massive than 104 M⊙ in the Milky Way.Using these paths to guide the choice of parameters onecan investigate the encounter history of the upper end ofthe range of cluster mass for the solar birth environment.

The compact clusters are likely to remain a bound entityfor at least 100 Myr - only afterwards might the Galactictidal field disrupt them. A statistical argument againstcompact clusters as solar birth hosts would be that prob-ably only ∼10% of all stars are born within systems thatremain gravitationally bound over such timescales (Adams& Myers 2001).

However, the strongest argument against compact clustersis their very high initial density in combination with thehigh number of massive stars. Pfalzner (2013) investigatedthe typical encounter history in both cluster environments.In Figure 3 the density requirement for the solar birthcluster is depicted by a green box. It can be seen that itoverlaps with the development of compact clusters at agestc > 4 Myr. Before this time, the cluster densities are toohigh: the cluster environment is extremely collisional andencounters closer than 100 AU very common. Such a veryclose encounter would lead to a truncation of the disc tordisc < 30 AU and deprive the disc of the material neces-sary to form the outer planets. Although some compactplanetary system might form, it would no longer resembleour Solar system.

Even if a solar-type planetary system managed againstall likelihood to form, at an age of 20 Myr the averagestellar density would still be several 100 M⊙ pc−3. Here,interactions with other cluster members would inevitablylead to disturbances, destroying the near circularity andco-planarity observed in the Solar system. Although onecannot completely exclude the possibility that the Solarsystem may have developed in a compact cluster environ-ment, in the light of these conclusions, it seems ratherunlikely, especially as photo-evaporation can lead to addi-tional disc destruction (Adams 2010).

It is much more probable that the Solar system developedin a loose extended massive cluster environment. The den-sity requirement for the solar birth cluster overlaps withthe development of loose clusters only for ages tc < 3 Myr(Figure 3), where the mean density is approximately a fewtimes 10 - 100 M⊙/pc

3. Owing to the rapid decrease indensity in the solar birth cluster, encounters played a rolein shaping the Solar system only very early on in the clus-ter development. In a loose cluster environment solar-typestars have a probability of ∼ 30% of experiencing a po-tentially solar-system-forming encounter during the first 2Myr after the on-set of cluster expansion. As the clusterdensity decreases with age, so does the encounter proba-bility and after 5 Myr of cluster development, encountersbelow 1000 AU become extremely rare. This also neatlysolves the seemingly contradictory situation that a densebirth cluster is required to provide for the nuclear enrich-ment and explain Sedna’s orbit, but at the same time, aless interactive environment is needed to avoid disruptivedynamical interactions with the newly formed Solar sys-tem.

Eventually, such a cluster disperses to a high degree overtimescales of ∼ 20 Myr leaving behind a cluster that onlycontains at most 10 - 20% (see Figure 2) of its initialmass. Even if the solar system was part of the remnantcluster after gas expulsion, the stellar density would be< 1 M⊙ pc−3, far too low to make further close encoun-ters likely.

What is probably the most surprising result in this con-text is that not only the encounter frequency changes insuch an expanding cluster, but as well the quality of theseencounters. Whereas early on (< 2 Myr) hyperbolic en-counters with low-mass stars dominate, it is parabolic en-counters with high-mass stars that take over this role atlater stages (2 - 4 Myr)(Olczak et al. 2010, Pfalzner 2013).This means that it is highly questionable that the per-turber which formed the shape of the Solar system was asolar-type star on a parabolic orbit (Dukes & Krumholz2012). The preference of encounters with low-mass stars(m2 < 0.8 M⊙) is simply due to them being the most com-mon cluster members. That these encounters are largelyof strongly hyperbolic nature means that they lead to con-

11

siderably less mass loss in the disc than that caused by theequivalent parabolic ones. The reason is that the interac-tion time for disc mass removal is much shorter (see, forexample, Pfalzner et al 2005, Olczak et al. 2010). Theconsiderable amount of encounters with the highest massstars (> 10 M⊙), despite their low number, is caused bygravitational focusing. Future investigations will have totake into account the entire mass spectrum and a muchwider eccentricity range to narrow down the encounterscenario that led to the formation of the Solar system. Itcould even be that the supernova progenitor itself mighthave been the encounter partner that led to the shape ofthe Solar system.

The above results can only be regarded as a first step. Onall fronts of this multi-disciplinary field open questions stillremain.

For the cluster development this means: In the above con-sidered clusters star formation has largely finished, the gashas been expelled and the cluster expands. There are cur-rently many unknowns about the state of the cluster beforecluster expansion. The time scales of the gas expulsion,the dynamical state - equilibrium, sub- or supervirial -before gas expulsion, and the degree to which early sub-structuring plays a role all need pinpointing via tighterconstraints from observations. Additional it is unknownwhat role binaries play for the encounter dynamics andto what extend they lead to additional cluster expansion.The big unknown is the encounter frequency in the phasewhen the cluster is still forming. Models that can describemassive cluster formation are rare and so are observationsof possible massive cluster precursors. Even though thedynamics of the expansion is now established for mostmassive clusters in the Galaxy (≥ 104 M⊙), the possiblecluster membership could be about a factor of five lowerthan investigated in Pfalzner (2013). How clusters, con-taining only a few thousand stars, develop with time iscompletely unknown, and even whether two types of clus-ters exist at this lower mass end is an open question.

In the past, the encounter dynamics has mostly been treatedin a very simplified way. Typically only encounters be-tween two Solar-type stars and/or parabolic orbits wereconsidered. Future work would have to consider hyper-bolic encounters and include the entire mass spectrum ofencounter partners.

Naturally the gaps are biggest where the different fieldsmeet. For example, it is currently unclear how the en-counter statistics changes in the early expansion phasewhere bound and unbound stars occupy the same space.All this calls for further research in these fields. Whatmakes this question of the origin of the Sun particularly in-teresting is the interdisciplinary approach that is required.Currently this is done by combining the results from dif-ferent fields. The ultimate aim should be a truely self-

consistent approach.

References:

Adams, F. C. 2010. ARAA 48, 47.Adams, F.C., Myers P.C., 2001 ApJ 533, 744.Bernstein, G. M., Trilling, D. E., Allen, R. L., Brown, M. E., Hol-man, M., Malhotra, R. 2004. AJ 128, 1364.Brasser, R., Duncan, M. J., Levison, H. F. 2006. Icarus 184, 59.Dukes, D., & Krumholz, M. R. 2012, ApJ, 754, 56.Gomes, R. S., Gallardo, T., Fernandez, J. A., Brunini, A. 2005. Ce-lestial Mechanics and Dynamical Astronomy 91, 109.Gounelle, M., Meibom, A., Hennebelle, P., & Inutsuka, S.-i. 2009,ApJ, 694, L1.Gritschneder, M., Lin, D. N. C., Murray, S. D., Yin, Q.-Z., & Gong,M.-N. 2012, ApJ, 745, 22.Hunter, D.A. 1999, Wolf-Rayet Phenomena in Massive Stars andStarburst Galaxies, IAU Symp. No.193, 418.Lee, J.E., Bergin, E. A., & Lyons, J. R. 2008, Meteoritics and Plan-etary Science, 43, 1351.Maiz Apellaniz, J., Walborn, N. R., Morrell, N. I., Niemela, V. S.,& Nelan, E. P. 2007, ApJ, 660, 1480.Mann, R. K., Williams, J. P. 2009. ApJ 694, L36.Morbidelli, A., Levison, H. F. 2004. AJ 128, Oey, M. S., & Clarke,C. J. 2005, ApJ, 620, L43.Olczak, C., Pfalzner, S., Eckart, A. 2010. A&A 509, A63.Pfalzner, S. 2009. A&A 498, L37.Pfalzner, S. 2013, A&A, 549, A82Pfalzner, S., Vogel, P., Scharwachter, J., & Olczak, C. 2005, A&A,437,967.Portegies Zwart, S. F. 2009. ApJ 696, L13.Portegies Zwart, S. F., McMillan, S. L. W., Gieles, M. 2010. ARAA48, 431.Scally, A., Clarke, C. 2001. MNRAS 325, 449.Schwamb, M. E., Brown, M. E., Rabinowitz, D. L., Ragozzine, D.2010. ApJ 720, 1691.Thommes, E. W., Duncan, M. J., Levison, H. F. 2002. AJ 123, 2862.Williams, J. P., Gaidos, E. 2007. ApJ 663, L33.

12

Abstracts of recently accepted papers

Formation and evolution of interstellar filaments; Hints from velocity dispersion mea-surements

D. Arzoumanian1,2, Ph. Andre1, N. Peretto1, and V. Konyves1,2

1 Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, IRFU/Service d’Astrophysique, C.E.A. Saclay, Ormedes Merisiers, 91191 Gif-sur-Yvette, France2 IAS, CNRS (UMR 8617), Universite Paris-Sud, Batiment 121, 91400 Orsay, France E-mail contact: doris.arzoumanianat ias.u-psud.fr or pandre at cea.fr

We investigate the gas velocity dispersions of a sample of filaments recently detected as part of the Herschel Gould BeltSurvey in the IC5146, Aquila, and Polaris interstellar clouds. To measure these velocity dispersions, we use 13CO, C18O,and N2H

+ line observations obtained with the IRAM 30m telescope. Correlating our velocity dispersion measurementswith the filament column densities derived from Herschel data, we show that interstellar filaments can be divided intotwo regimes: thermally subcritical filaments, which have transonic velocity dispersions (cs <∼ σtot < 2 cs) independentof column density, and are gravitationally unbound; and thermally supercritical filaments, which have higher velocitydispersions scaling roughly as the square root of column density (σtot ∝ Σ0

0.5), and are self-gravitating. The highervelocity dispersions of supercritical filaments may not directly arise from supersonic interstellar turbulence but maybe driven by gravitational contraction/accretion. Based on our observational results, we propose an evolutionaryscenario whereby supercritical filaments undergo gravitational contraction and increase in mass per unit length throughaccretion of backgroundmaterial while remaining in rough virial balance. We further suggest that this accretion processallows supercritical filaments to keep their approximately constant inner widths (∼ 0.1 pc) while contracting.

Accepted by Astronomy and Astrophysics

http://arxiv.org/pdf/1303.3024

Reverse dynamical evolution of Eta Chamaeleontis

Christophe Becker1, Estelle Moraux1, Gaspard Duchene1,2, Thomas Maschberger1 and Warrick Lawson3

1 UJF-Grenoble 1 / CNRS-INSU, Institut de Planetologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Greno-ble, F-38041, France2 Astronomy Department, University of California Berkeley, HFA B-20 3411, Berkeley CA 94720-3411, USA3 School of Physical, Environmental and Mathematical Sciences, University of New South Wales, Australian DefenceForce Academy, Canberra ACT 2600, Australia

E-mail contact: Christophe.Becker at obs.ujf-grenoble.fr

In the scope of the star formation process, it is unclear how the environment shapes the initial mass function (IMF).While observations of open clusters propose a universal picture for the IMF from the substellar domain up to a fewsolar masses, the young association η Chamaeleontis presents an apparent lack of low mass objects (m < 0.1 M⊙).Another unusual feature of this cluster is the absence of wide binaries with a separation > 50 AU. We aim to testwhether dynamical evolution alone can reproduce the peculiar properties of the association under the assumption of auniversal IMF. We use a pure N-body code to simulate the dynamical evolution of the cluster for 10 Myr, and comparethe results with observations. A wide range of values for the initial parameters are tested (number of systems, typicalradius of the density distribution and virial ratio) in order to identify the initial state that would most likely lead toobservations. In this context we also investigate the influence of the initial binary population on the dynamics andthe possibility of having a discontinuous single IMF near the transition to the brown dwarf regime. We consider asan extreme case an IMF with no low mass systems (m < 0.1 M⊙). The initial configurations cover a wide rangeof initial density, from 102 to 108 stars/pc3, in virialized, hot and cold dynamical state. We do not find any initialstate that would evolve from a universal single IMF to fit the observations. Only when starting with a truncated IMF

13

without any very low mass systems and no wide binaries, can we reproduce the cluster core properties with a successrate of 10% at best. Pure dynamical evolution alone cannot explain the observed properties of η Chamaeleontis fromuniversal initial conditions. The lack of brown dwarfs and very low mass stars, and the peculiar binary properties (lowbinary fraction and lack of wide binaries), are probably the result of the star formation process in this association.

Accepted by A&A


Physical properties of outflows:Comparing CO- and H2O-based parameters in Class 0 sources

P. Bjerkeli1, R. Liseau1, B. Nisini2, M. Tafalla3, P. Bergman4, G. Melnick5 and G. Rydbeck1

1 Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439 92Onsala, Sweden2 INAF - Osservatorio Astronomico di Roma, Via di Frascati 33, 00040 Monte Porzio Catone, Italy3 Observatorio Astronomico Nacional (IGN), Calle Alfonso XII,3. 28014, Madrid, Spain4 Onsala Space Observatory, Chalmers University of Technology, 439 92 Onsala, Sweden5 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

E-mail contact: per.bjerkeli at chalmers.se

Context: The observed physical properties of outflows from low-mass sources put constraints on possible ejectionmechanisms. Historically, these quantities have been derived from CO using ground-based observations. It is, therefore,important to investigate whether parameters such as momentum rate (thrust) and mechanical luminosity (power) arethe same when different molecular tracers are used.Aims: Our objective is to determine the outflow momentum, dynamical time-scale, thrust, energy, and power usingCO and H2O as tracers of outflow activity.Methods: Within the framework of the Water In Star-forming regions with Herschel (WISH) key program, threemolecular outflows from Class 0 sources have been mapped using the Heterodyne Instrument for the Far Infrared(HIFI) instrument aboard Herschel. We used these observations together with previously published H2 data to inferthe physical properties of the outflows. We compared the physical properties derived here with previous estimatesbased on CO observations.Results: Inspection of the spatial distribution of H2O and H2 confirms that these molecules are co-spatial. The mostprominent emission peaks in H2 coincide with strong H2O emission peaks and the estimated widths of the flows whenusing the two tracers are comparable.Conclusions: For the momentum rate and the mechanical luminosity, inferred values are not dependent on whichtracer is used, i.e. the values agree to within a factor of 4 and 3, respectively.

Accepted by A&A


X-Ray Determination of the Variable Rate of Mass Accretion onto TW Hydrae

N. S. Brickhouse1, S. R. Cranmer1, A. K. Dupree1, H. M. Guenther1, G. J. M. Luna2 and S. J. Wolk1

1 Harvard-Smithsonian Center for Astrophysics2 Instituto de Astronomia y Fisica del Espacio, (IAFE), Buenos Aires, Argentina

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

Diagnostics of electron temperature (Te), electron density (ne), and hydrogen column density (NH) from the ChandraHigh Energy Transmission Grating spectrum of He-like Ne IX in TW Hydrae (TW Hya), in conjunction with aclassical accretion model, allow us to infer the accretion rate onto the star directly from measurements of the accretingmaterial. The new method introduces the use of the absorption of NeIX lines as a measure of the column density ofthe intervening, accreting material. On average, the derived mass accretion rate for TW Hya is 1.5× 10−9 M⊙ yr−1,for a stellar magnetic field strength of 600 Gauss and a filling factor of 3.5%. Three individual Chandra exposuresshow statistically significant differences in the NeIV line ratios, indicating changes in NH , Te, and ne by factors of0.28, 1.6, and 1.3, respectively. In exposures separated by 2.7 days, the observations reported here suggest a five-fold

14

reduction in the accretion rate. This powerful new technique promises to substantially improve our understanding ofthe accretion process in young stars.

Accepted by Astrophysical Journal Letters (ApJ 760:L21)

arXiv:1211.1710

The Herbig Ae SB2 System HD 104237

C.R. Cowley1, F. Castelli2, and S. Hubrig3

1 Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1042, USA2 Istituto Nazionale di Astrosica, Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143, Trieste, Italy3 Leibniz-Institut fur Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482, Potsdam, Germany

E-mail contact: cowley at umich.edu

The double-lined spectroscopic binary HD 104237 (DX Cha) is part of a complex system of some half-dozen nearbyyoung stars. We report a significant change from an orbit for the SB2 system derived from 1999-2000 observations.We obtain abundances from the primary and secondary spectra. The abundance analysis uses both detailed spectralsynthesis and determinations based on equivalent widths of weak absorption lines with Wλ typically < 25 mA.Abundances are derived for 25 elements in the primary, and 17 elements in the secondary. Apart from lithium andzirconium, abundances do not depart significantly from solar. Lithium may be marginally enhanced with respect tothe meteoritic value in the primary. It somewhat depleted in the secondary. The emission-line spectrum is typical ofHerbig Ae stars. We compare and contrast the spectra of the HD 104237 primary and two other Herbig Ae stars withlow v · sin(i), HD 101412 and HD 190073.

Accepted by MNRAS


The Exciting Lives of Giant Molecular Clouds

C. L. Dobbs1 and J. E. Pringle2

1 University of Exeter, UK2 Institute of Astronomy, Cambridge, UK

E-mail contact: dobbs at astro.ex.ac.uk

We present a detailed study of the evolution of GMCs in a galactic disc simulation. We follow individual GMCs(defined in our simulations by a total column density criterion), including their level of star formation, from theirformation to dispersal. We find the evolution of GMCs is highly complex. GMCs often form from a combination ofsmaller clouds and ambient ISM, and similarly disperse by splitting into a number of smaller clouds and ambient ISM.However some clouds emerge as the result of the disruption of a more massive GMC, rather than from the assemblyof smaller clouds. Likewise in some cases, clouds accrete onto more massive clouds rather than disperse. Becauseof the difficulty of determining a precursor or successor of a given GMC, determining GMC histories and lifetimesis highly non-trivial. Using a definition relating to the continuous evolution of a cloud, we obtain lifetimes typicallyof 4-25 Myr for > 105 M⊙ GMCs, over which time the star formation efficiency is about 1 %. We also relate thelifetime of GMCs to their crossing time. We find that the crossing time is a reasonable measure of the actual lifetimeof the cloud, although there is considerable scatter. The scatter is found to be unavoidable because of the complexand varied shapes and dynamics of the clouds. We study cloud dispersal in detail and find both stellar feedback andshear contribute to cloud disruption. We also demonstrate that GMCs do not behave as ridge clouds, rather massivespiral arm GMCs evolve into smaller clouds in inter-arm spurs.

Accepted by MNRAS


Results of magnetic field measurements in young stars DO Tau, DR Tau, DS Tau

A.V. Dodin1, S.A. Lamzin1, and G.A. Chountonov2

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1 Sternberg Astronomical Institute of Moscow State University, Moscow, 119992, Russia2 Special Astrophysical Observatory of the Russian AS, Nizhnij Arkhyz 369167, Russia

E-mail contact: dodin nv at mail.ru

Results of measurements of the longitudinal magnetic field in a hot accretion spot in three classical T Tauri stars(CTTS) are presented. The magnetic field in the formation region of the narrow component of the emission line HeI5876 A was found for each star in our sample at a level of more than 2σ. In case of DS Tau we have found the field inthe narrow components of NaI D lines, which was equal to +0.8 ± 0.3 kG, i.e. it was equal to the field measured onthe narrow component of HeI 5876 A. Our results indicate that the magnetic field in the hot spots can be studied forCTTS down to 13m that allow in the future to double a number of CTTS with measured field in the accretion zone.

Accepted by Astrophysical Bulletin


Magnetospheric Accretion and Ejection of Matter in Resistive MHD Simulations

Miljenko Cemeljic1, Hsien Shang1 and Tzu-Yang Chiang1

1 Academia Sinica, Institute of Astronomy and Astrophysics and Theoretical Institute for Advanced Research inAstrophysics, P.O. Box 23-141, Taipei 106, Taiwan

E-mail contact: miki at tiara.sinica.edu.tw

The ejection of matter in the close vicinity of a young stellar object is investigated, treating the accretion disk asa gravitationally bound reservoir of matter. By solving the resistive MHD equations in 2D axisymmetry using ourversion of the Zeus-3D code with newly implemented resistivity, we study the effect of magnetic diffusivity in themagnetospheric accretion-ejection mechanism. Physical resistivity was included in the whole computational domainso that reconnection is enabled by the physical as well as the numerical resistivity. We show, for the first time, thatquasi-stationary fast ejecta of matter, which we call micro-ejections, of small mass and angular momentum fluxes,can be launched from a purely resistive magnetosphere. They are produced by a combination of pressure gradientand magnetic forces, in presence of ongoing magnetic reconnection along the boundary layer between the star and thedisk, where a current sheet is formed. Mass flux of micro-ejection increases with increasing magnetic field strengthand stellar rotation rate, and is not dependent on the disk to corona density ratio and amount of resistivity.

Accepted by ApJ


Crucial aspects of the initial mass function (I): The statistical correlation between thetotal mass of an ensemble of stars and its most massive star

M. Cervino1,2, Carlos Roman-Zuniga3, Valentina Luridiana2,4, Amelia Bayo5,6, Nestor Sanchez7 andEnrique Perez1

1 Instituto de Astrofisica de Andalucia (IAA-CSIC), Glorieta de la Astronomia s/n, 18008 Granada, Spain2 Instituto de Astrofisica de Canarias, c/ via Lactea s/n, 38205 La Laguna, Tenerife, Spain3 Instituto de Astronomia, Universidad Academica en Ensenada, Universidad Nacional Autonoma de Mexico, EnsenadaBC, 22860 Mexico4 Departamento de Astrofisica, Universidad de La Laguna (ULL), 38205 La Laguna, Tenerife, Spain5 European Southern Observatory, Casilla 19001, Santiago 19, Chile6 Max Planck Institut fur Astronomie, Konigstuhl 17, 69117, Heidelberg, Germany7 S. D. Astronomia y Geodesia, Fac. CC. Matematicas, Universidad Complutense de Madrid, 28040, Madrid, Spain

E-mail contact: mcs at iac.es

Context: Our understanding of stellar systems depends on the adopted interpretation of the initial mass function,IMF φ(m). Unfortunately, there is not a common interpretation of the IMF, which leads to different methodologiesand diverging analysis of observational data.Aims: We study the correlation between the most massive star that a cluster would host, mmax, and its total massinto stars, M, as an example where different views of the IMF lead to different results.

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Methods: We assume that the IMF is a probability distribution function and analyze the mmax−M correlation withinthis context. We also examine the meaning of the equation used to derive a theoretical M − mmax relationship,N ×

∫ mup

mmaxφ(m) dm = 1 with N the total number of stars in the system, according to different interpretations of the

IMF.Results: We find that only a probabilistic interpretation of the IMF, where stellar masses are identically independentdistributed random variables, provides a self-consistent result. Neither M nor the total number of stars in the cluster,N , can be used as IMF scaling factors. In addition, mmax is a characteristic maximum stellar mass in the cluster, butnot the actual maximum stellar mass. mmax will exist in the cluster. A 〈M〉 − mmax correlation is a natural resultof a probabilistic interpretation of the IMF; however, the distribution of observational data in the N (or M)−mmax

plane includes a dependence on the distribution of the total number of stars, N (and M), in the system, ΦN (N ),which is not usually taken into consideration.Conclusions: We conclude that a random sampling IMF is not in contradiction to a possible mmax − M physicallaw. However, such a law cannot be obtained from IMF algebraic manipulation or included analytically in the IMFfunctional form. The possible physical information that would be obtained from the N (or M) −mmax correlationis closely linked with the ΦM(M) and ΦN (N ) distributions; hence it depends on the star formation process and theassumed definition of stellar cluster.

Accepted by A&A


Crucial aspects of the initial mass function (II): The inference of total quantities frompartial information on a cluster

Miguel Cervino1,2, Carlos Roman-Zuniga3, Amelia Bayo4,5, Valentina Luridiana2,6, Nestor Sanchez7

and Enrique Perez1

1 Instituto de Astrofisica de Andalucia (IAA-CSIC), Glorieta de la Astronomia s/n, 18008 Granada, Spain2 Instituto de Astrofisica de Canarias, c/ via Lactea s/n, 38205 La Laguna, Tenerife, Spain3 Instituto de Astronomia, Universidad Academica en Ensenada, Universidad Nacional Autonoma de Mexico, EnsenadaBC, 22860 Mexico4 European Southern Observatory, Casilla 19001, Santiago 19, Chile5 Max Planck Institut fur Astronomie, Konigstuhl 17, 69117, Heidelberg, Germany6 Departamento de Astrofisica, Universidad de La Laguna (ULL), 38205 La Laguna, Tenerife, Spain7 S. D. Astronomia y Geodesia, Fac. CC. Matematicas, Universidad Complutense de Madrid, 28040, Madrid, Spain.

E-mail contact: mcs at iac.es

Context: In a probabilistic framework of the interpretation of the initial mass function (IMF), the IMF cannot bearbitrarily normalized to the total mass, M, or number of stars, N , of the system. Hence, the inference of M andN when partial information about the studied system is available must be revised. (i.e., the contribution to the totalquantity cannot be obtained by simple algebraic manipulations of the IMF).Aims: We study how to include constraints in the IMF to make inferences about different quantities characterizingstellar systems. It is expected that including any particular piece of information about a system would constrain therange of possible solutions. However, different pieces of information might be irrelevant depending on the quantity tobe inferred. In this work we want to characterize the relevance of the priors in the possible inferences.Methods: Assuming that the IMF is a probability distribution function, we derive the sampling distributions of Mand N of the system constrained to different types of information available.Results: We show that the value of M that would be inferred must be described as a probability distributionΦM[M;ma, Na,ΦN (N )] that depends on the completeness limit of the data, ma, the number of stars observed downto this limit, Na, and the prior hypothesis made on the distribution of the total number of stars in clusters, ΦN (N ).

Accepted by A&A


17

SMA Observations of Class 0 Protostars: A High-Angular Resolution Survey of Proto-stellar Binary Systems

Xuepeng Chen1,2, Hector G. Arce2, Qizhou Zhang3, Tyler L. Bourke3, Ralf Launhardt4, Jes K. Jørgensen5,Chin-Fei Lee6, Jonathan B. Foster7, Michael M. Dunham2, Jaime E. Pineda8,9 and Thomas Henning4

1 Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijing Road, Nanjing 210008, China; [email protected] Department of Astronomy, Yale University, Box 208101, New Haven, CT 06520-8101, USA; [email protected] Harvard-Smithsonian Center for Astrophysics, 60 Garden Street., Cambridge, MA 02138, USA4 Max Planck Institute for Astronomy, Konigstuhl 17, D-69117 Heidelberg, Germany5 Niels Bohr Institute and Centre for Star and Planet Formation, Copenhagen University, Juliane Maries Vej 30,DK-2100 Copenhagen Ø, Denmark6 Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan7 Institute for Astrophysical Research, Boston University, Boston, MA 02215, USA8 ESO, Karl Schwarzschild Str. 2, 85748 Garching bei Munchen, Germany9 Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester, M139PL, UK

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

We present high angular resolution 1.3mm and 850µm dust continuum data obtained with the Submillimeter Arraytoward 33 Class 0 protostars in nearby clouds (distance < 500pc), which represents so far the largest survey towardprotostellar binary/multiple systems. The median angular resolution in the survey is 2.5 arcsec, while the medianlinear resolution is approximately 600AU. Compact dust continuum emission is observed from all sources in the sample.Twenty-one sources in the sample show signatures of binarity/multiplicity, with separations ranging from 50AU to5000AU. The numbers of singles, binaries, triples, and quadruples in the sample are 12, 14, 5, and 2, respectively.The derived multiplicity frequency (MF) and companion star fraction (CSF) for Class 0 protostars are 0.64± 0.08and 0.91± 0.05, respectively, with no correction for completeness. The derived MF and CSF in this survey areapproximately two times higher than the values found in the binary surveys toward Class I young stellar objects, andapproximately three (for MF) and four (for CSF) times larger than the values found among main sequence stars, witha similar range of separations. Furthermore, the observed fraction of high order multiple systems to binary systems inClass 0 protostars (0.50± 0.09) is also larger than the fractions found in Class I young stellar objects (0.31± 0.07) andmain sequence stars (≤ 0.2). These results suggest that binary properties evolve as protostars evolve, as predicted bynumerical simulations. The distribution of separations for Class 0 protostellar binary/multiple systems shows a generaltrend in which companion star fraction increases with decreasing companion separation. We find that 67%± 8% ofthe protobinary systems have circumstellar mass ratios below 0.5, implying that unequal-mass systems are preferredin the process of binary star formation. We suggest an empirical sequential fragmentation picture for binary starformation, based on this work and existing lower resolution single-dish observations.

Accepted by The Astrophysical Journal


A Mechanism of Exciting Planetary Inclination and Eccentricity through a ResidualGas Disk

Yuan-Yuan Chen, Hui-Gen Liu, Gang Zhao, and Ji-Lin Zhou

School of Astronomy and Space Science & Key Laboratory of Modern Astronomy and Astrophysics in Ministry ofEducation, Nanjing University, Nanjing, China, 210093

E-mail contact: cyy198531 at nju.edu.cn

Accordling to the theory of Kozai resonance, the initial mutual inclination between a small body and a massive planetin an outer circular orbit is as high as ∼ 39.2◦ for pumping the eccentricity of the inner small body. Here we showthat, with the presence of a residual gas disk outside two planetary orbits, the inclination can be reduced as low asa few degrees. The presence of disk changes the nodal precession rates and directions of the planet orbits. At theplace where the two planets achieve the same nodal processing rate, vertical secular resonance would occur so thatmutual inclination of the two planets will be excited, which might trigger the Kozai resonance between the two planetsfurther. However, in order to pump an inner Jupiter-like planet, the conditions required for the disk and the outer

18

planet are relatively strict. We develop a set of evolution equations, which can fit the N-body simulation quite well butbe integrated within a much shorter time. By scanning the parameter spaces using the evolution equations, we findthat, a massive planet (10MJ) at 30AU with 6o inclined to a massive disk (50MJ) can finally enter the Kozai resonancewith an inner Jupiter around the snowline. And a 20◦ inclination of the outer planet is required for flipping the innerone to a retrograde orbit. In multiple planet systems, the mechanism can happen between two nonadjacent planets,or inspire a chain reaction among more than two planets. This mechanism could be the source of the observed giantplanets in moderate eccentric and inclined orbits, or hot-Jupiters in close-in, retrograde orbits after tidal damping.

Accepted by ApJ


On the temperature structure of the Galactic Centre cloud G0.253+0.016

Paul C. Clark1, Simon C. O. Glover1, Sarah E. Ragan2, Rahul Shetty1 and Ralf Klessen1

1 Universitat Heidelberg, Zentrum fur Astronomie, Institut fur Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120Heidelberg, Germany2 Max Planck Institut fur Astronomie, Konigstuhl 17, 69117 Heidelberg, Germany

E-mail contact: p.clark at uni-heidelberg.de

We present a series of smoothed particle hydrodynamical models of G0.253+0.016 (also known as “The Brick”), avery dense molecular cloud that lies close to the Galactic Centre. We explore how its gas and dust temperatures reactas we vary the strength of both the interstellar radiation field (ISRF) and the cosmic ray ionisation rate (CRIR). Thecloud has an extent in the plane of the sky of roughly 3.4 pc × 9.4 pc. As its size along the line-of-sight is unknown,we consider two cases. In our fiducial, high-density model, we adopt a depth along the line-of-sight of 3.4 pc, and inthe low-density model, we assume an extent along the line-of-sight of 17 pc. To recover the observed gas and dusttemperatures, we find that the ISRF must be around 1000 times the solar neighbourhood value, and the CRIR mustbe roughly 10−14 s−1, regardless of the geometries studied. For such high values of the CRIR, we find that coolingin the cloud’s interior is dominated by neutral oxygen, in contrast to standard molecular clouds, which at the samedensities are mainly cooled via CO. Our results suggest that the conditions near G0.253+0.016 are more extreme thanthose generally accepted for the inner 500 pc of the galaxy.

Accepted by Astrophysical Journal Letters


Direct imaging discovery of 12-14 Jupiter mass object orbiting a young binary systemof very low-mass stars

P. Delorme1, J. Gagne2, J.H. Girard3, A.M. Lagrange1, G. Chauvin1, M-E. Naud2, D. Lafreniere2, R.Doyon2, A. Riedel4, M. Bonnefoy5, and L. Malo2

1 UJF-Grenoble 1 / CNRS-INSU, Institut de Planetologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Greno-ble, F-38041, France2 Departement de physique and Observatoire du Mont Megantic, Universite de Montreal, C.P. 6128, Succursale Centre-Ville, Montreal, QC H3C 3J7, Canada3 European Southern Observatory, Alonso de Crdova 3107, Vitacura, Cassilla 19001, Santiago, Chile4 Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York,NY 10034, USA5 Max Planck Institute for Astronomy, Konigstuhl 17, D-69117 Heidelberg, Germany

E-mail contact: Philippe.Delorme at obs.ujf-grenoble.fr

Context. Though only a handful of extrasolar planets have been discovered via direct imaging, each of these discoverieshad tremendous impact on our understanding of planetary formation, stellar formation and cool atmosphere physics.Aims. Since many of these newly imaged giant planets orbit massive A or even B stars we investigated whether giantplanets could be found orbiting low-mass stars at large separations.Methods. We have been conducting an adaptive optic imaging survey to search for planetary-mass companions ofyoung M dwarfs of the solar neigbourhood, to probe different initial conditions of planetary formation.

19

Results. We report here the direct imaging discovery of 2MASS J01033563-5515561(AB)b, a 12-14 MJup companionat a projected separation of 84 AU from a pair of young late M stars, with which it shares proper motion. We alsodetected a Keplerian-compatible orbital motion. Conclusions. This young L-type object at planet/brown dwarf massboundary is the ?first ever imaged around a binary system at a separation compatible with formation in a disc.

Accepted by A&A Letters


Near-infrared variability in the star-forming region RCW38

Mathias Dorr1, Rolf Chini1,2, Martin Haas1, Roland Lemke1 and Dieter Nurnberger1

1 Astronomisches Institut, Ruhr–Universitat Bochum, Universitatsstraße 150, 44801 Bochum, Germany2 Instituto de Astronomıa, Universidad Catolica del Norte, Antofagasta, Chile

E-mail contact: chini at astro.rub.de

We present the results of a 3 month near-infrared monitoring campaign of the young cluster RCW38 using the 80 cmIRIS telescope near Cerro Armazones, Chile. Variability data with a median sampling of 1 day was gathered for 1026sources, while a total of 3433 sources in JHK could be studied in the co-added, deep images with a completeness limitof K < 15mag. 139 sources were identified as variable with amplitudes above 10% in H and K, respectively. 47% ofthese variables were classified as candidate young stars by previous X-ray and mid-infrared studies. While the majorityof the variable sources show no K-excess, their high extinction and concentration towards the cluster center togetherwith their irregular variability behaviour suggest that they are also candidate young stellar objects. Most of them arelikely low-mass sources with variability amplitudes typical for T Tauri stars. The majority of previously suggestedOB candidates appears to be intermediate-mass pre-main sequence sources on the basis of their JHK properties.

Accepted by Astronomy & Astrophysics

Disk-Related Bursts and Fades in Young Stars

Krzysztof Findeisen1, Lynne Hillenbrand1, Eran Ofek2, David Levitan1, Branimir Sesar1, Russ Laher3

and Jason Surace3

1 Cahill Center for Astronomy and Astrophysics, California Institute of Technology, MC 249-17, Pasadena, CA 91125,USA2 Benoziyo Center for Astrophysics, Department of Particle Physics and Astrophysics, Weizmann Institute of Science,Rehovot 76100, Israel3 Spitzer Science Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125, USA

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

We present first results from a new, multiyear, time domain survey of young stars in the North America Nebulacomplex using the Palomar Transient Factory. Our survey is providing an unprecedented view of aperiodic variabilityin young stars on timescales of days to years. The analyzed sample covers RPTF ≈ 13.5 − 18 and spans a rangeof mid-infrared color, with larger-amplitude optical variables (exceeding 0.4 mag root-mean-squared) more likely tohave mid-infrared evidence for circumstellar material. This paper characterizes infrared excess stars with distinctbursts above or fades below a baseline of lower-level variability, identifying 41 examples. The light curves exhibita remarkable diversity of amplitudes, timescales, and morphologies, with a continuum of behaviors that can not beclassified into distinct groups. Among the bursters, we identify three particularly promising sources that may representtheoretically predicted short-timescale accretion instabilities. Finally, we find that fading behavior is approximatelytwice as common as bursting behavior on timescales of days to years, although the bursting and fading duty cycle forindividual objects often varies from year to year.



20

Magnetically Active Stars in Taurus-Auriga: Photometric Variability and Basic PhysicalParameters

K.N. Grankin1

1 Crimean Astrophysical Observatory, Nauchny, Crimea 98409, Ukraine

E-mail contact: konstantin.grankin at rambler.ru

The paper presents an analysis of homogeneous long-term photometric observations of 28 well-known weak-line T Tauristars (WTTS) and 60 WTTS candidates detected by the ROSAT observatory in the direction of the Taurus-Aurigastar-forming region. 22 known WTTS and 39 WTTS candidates are shown to exhibit periodic light variations thatare attributable to the phenomenon of spotted rotational modulation. The rotation periods of these spotted stars liewithin the range from 0.5 to 10 days. Significant differences between the long-term photometric behaviors of knownWTTS and WTTS candidates have been found. We have calculated accurate luminosities, radii, masses, and ages for74 stars. About 33 percent of the sample of WTTS candidates have ages younger than 10 Myr. The mean distanceto 24 WTTS candidates with reliable estimates of their radii is shown to be 143+/-26 pc.

Accepted by Astronomy Letters


Mid-infrared observations of the circumstellar disks around PDS 66 and CRBR 2422.8-3423

C. Grafe and S. Wolf

University of Kiel, Institute for Theoretical Physics and Astrophysics, Leibnizstrasse 15, 24118 Kiel, Germany

E-mail contact: cgraefe at astrophysik.uni-kiel.de

Aims. We present mid-infrared observations and photometry of the circumstellar disks around PDS 66 and CRBR2422.8-3423, obtained with VISIR/VLT in the N band and for the latter also in the Q band. Our aim is to resolvethe inner regions of these protoplanetary disks, which carry potential signatures of intermediate or later stages of diskevolution and ongoing planet formation.Methods. We determined the radial brightness profiles of our target objects and the corresponding PSF referencethat were observed before and after our target objects. Background standard deviations, the standard errors, andthe seeing variations during the observations were considered. Adopting a simple radiative transfer model based onparameters taken from previous studies, we derived constraints on the inner-disk hole radius of the dust disk.Results. Neither of the circumstellar disks around our science targets are spatially resolved in our observations.However, we are able to constrain the inner-disk hole radius to < 15.0+0.5

−0.5 AU and < 10.5+0.5−1.0 AU for PDS 66 and

CRBR 2422.8-3423, respectively. The photometry we performed yields N-band flux densities of 599± 8 mJy for PDS66 and 130±14 mJy for CRBR 2422.8-3423, as well as a Q-band flux density of 858±109 mJy for CRBR 2422.8-3423.

Accepted by A&A


Cores, filaments, and bundles: hierarchical core formation in the L1495/B213 Taurusregion

A. Hacar1,2, M. Tafalla1, J. Kauffmann3, and A. Kovacs4

1 Observatorio Astronomico Nacional (IGN), Alfonso XII 3, E-28014 Madrid, Spain2 Institute for Astrophysics, University of Vienna, Turkenschanzstrasse 17, 1180 Vienna, Austria3 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA4 University of Minnesota, 116 Church St SE, Minneapolis, MN 55414, USA

E-mail contact: alvaro.hacar at univie.ac.at

Context. Core condensation is a critical step in the star-formation process, but is still poorly characterized observa-tionally.Aims. We have studied the 10 pc-long L1495/B213 complex in Taurus to investigate how dense cores have condensed

21

out of the lower-density cloud material.Results. From the N2H

+ emission, we identify 19 dense cores, some starless and some protostellar. They are notdistributed uniformly, but tend to cluster with relative separations on the order of 0.25 pc. From the C18O emission,we identify multiple velocity components in the gas. We have characterized them by fitting gaussians to the spectra,and by studying the distribution of the fits in position-position-velocity space. In this space, the C18O componentsappear as velocity-coherent structures, and we have identified them automatically using a dedicated algorithm (FIVe:Friends In Velocity). Using this algorithm, we have identified 35 filamentary components with typical lengths of 0.5pc, sonic internal velocity dispersions, and mass-per-unit-length close to the stability threshold of isothermal cylindersat 10 K. Core formation seems to have occurred inside the filamentary components via fragmentation, with a smallnumber of fertile components with larger mass-per-unit-length being responsible for most cores in the cloud. At largescales, the filamentary components appear grouped into families, which we refer to as bundles.Conclusions. Core formation in L1495/B213 has proceeded by hierarchical fragmentation. The cloud fragmented firstinto several pc-scale regions. Each of these regions later fragmented into velocity-coherent filaments of about 0.5 pcin length. Finally, a small number of these filaments fragmented quasi-statically and produced the individual densecores we see today.

Accepted by A&A


Assessing molecular line diagnostics of triggered star formation using synthetic obser-vations

Thomas J. Haworth1, Tim J. Harries1, David M. Acreman1, and David A. Rundle2

1 School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL2 Met Office, FitzRoy Road, Exeter, EX1 3PB

E-mail contact: haworth at astro.ex.ac.uk

We investigate observational signatures of triggered star formation in bright rimmed clouds (BRCs) by using molecularline transfer calculations based on radiation-hydrodynamic radiatively-driven-implosionmodels. We find that for BRCsthe separation in velocity between the line profile peak of an optically thick and an optically thin line is determined byboth the observer viewing angle and the density of the shell driving into the cloud. In agreement with observations,we find that most BRC line profiles are symmetric and that asymmetries can be either red or blue, in contrast to theblue-dominance expected for a collapsing cloud. Asymmetries in the line profiles arise when an optically thick line isdominated by the shell and an optically thin line is dominated by the cloud interior to the shell. The asymmetriesare red or blue depending on whether the shell is moving towards or away from the observer respectively. Using theknown motions of the molecular gas in our models we rule out the envelope expansion with core collapse mechanism asthe cause of the lack of blue-asymmetry in our simulated observations. We show that the absence of a strong photondominated region (PDR) around a BRC may not rule out the presence of triggered star formation: if the BRC lineprofile has a strong blue component then the shell is expected to be driving towards the observer, suggesting that thecloud is being viewed from behind and the PDR is obstructed. This could explain why BRCs such as SFO 80, 81 and86 have a blue secondary peak and only a weak PDR inferred at 8 microns. Finally we also test the use of 12CO, 13COand C18O as diagnostics of cloud mass, temperature and column density. We find that the inferred conditions are inreasonable agreement with those from the models.

Accepted by MNRAS


Probability Distribution Functions of 12CO(J=1-0) Brightness and Integrated Intensityin M51: The PAWS View

Annie Hughes1, Sharon E. Meidt1, Eva Schinnerer1, Dario Colombo1, Jerome Pety1,2, Adam K. Leroy4,Clare L. Dobbs5, Santiago Garcıa-Burillo6, Todd A. Thompson7,8, Gaelle Dumas2, Karl F. Schuster2

and Carsten Kramer9

1 Max Planck Institute for Astronomy, Konigstuhl 17, 69117 Heidelberg, Germany

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2 Institut de Radioastronomie Millimetrique, 300 Rue de la Piscine, F-38406 Saint Martin d’Heres, France3 Observatoire de Paris, 61 Avenue de l’Observatoire, F-75014 Paris, France.4 National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA5 School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, UK6 Observatorio Astronomico Nacional - OAN, Observatorio de Madrid Alfonso XII, 3, 28014 - Madrid, Spain7 Department of Astronomy, The Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA8 Center for Cosmology and AstroParticle Physics, The Ohio State University, 191 W. Woodruff Ave., Columbus, OH43210, USA9 Instituto Radioastronomıa Milimetrica, Av. Divina Pastora 7, Nucleo Central, 18012 Granada, Spain

E-mail contact: hughes at mpia.de

We analyse the distribution of CO brightness temperature and integrated intensity in M51 at ∼ 40 pc resolution usingnew 12CO(J = 1 → 0) data from the Plateau de Bure Arcsecond Whirlpool Survey (PAWS). We present probabilitydistribution functions (PDFs) of the CO emission within the PAWS field-of-view, which covers the inner ∼ 11× 7 kpcof M51. We find clear variations in the shape of CO PDFs both within different M51 environments, defined accordingto dynamical criteria, and between M51 and two nearby low-mass galaxies, M33 and the Large Magellanic Cloud.Globally, the PDFs for the inner disk of M51 can be represented by narrow lognormal functions that cover ∼ 1 to 2orders of magnitude in CO brightness and integrated intensity. The PDFs for M33 and the LMC are narrower andpeak at lower CO intensities, consistent with their lower gas surface densities. However, the CO PDFs for differentdynamical environments within the PAWS field depart significantly from the shape of the global distribution. ThePDFs for the interarm region are approximately lognormal, but in the spiral arms and central region of M51, theyexhibit diverse shapes with a significant excess of bright CO emission. The observed environmental dependence onthe shape of the CO PDFs is qualitatively consistent with changes that would be expected if molecular gas in thespiral arms is characterised by a larger range of average densities, gas temperatures and velocity fluctuations, thoughfurther work is required to disentangle the relative importance of large-scale dynamical effects versus star formationfeedback in regulating these properties. We show that the shape of the CO PDFs for different M51 environments isonly weakly related to global properties of the CO emission, e.g. the total CO luminosity, but is strongly correlatedwith properties of the local giant molecular cloud (GMC) and young stellar cluster populations, including the shape oftheir mass distributions. For galaxies with strong spiral structure such as M51, our results indicate that galactic-scaledynamical processes play a significant role in the formation and evolution of GMCs and stellar clusters.

Accepted by ApJ


Accretion Rates for T Tauri Stars Using Nearly Simultaneous Ultraviolet and OpticalSpectra

Laura Ingleby1, Nuria Calvet1, Gregory Herczeg2, Alex Blaty1, Frederick Walter3, David Ardila4,Richard Alexander5, Suzan Edwards6, Catherine Espaillat7, Scott G Gregory8,9, Lynne Hillenbrand8

and Alexander Brown10

1 University of Michigan, USA2 KIAA, Peking University, China3 Stony Brook University, USA4 NASA Herschel Science Center, USA5 University of Leicester, UK6 Smith College, USA7 NASA Sagan Postdoctoral Fellow, CfA8 California Institute of Technology, USA9 University of St. Andrews, UK10 Center for Astrophysics and Space Astronomy, USA

E-mail contact: lingleby at umich.edu

We analyze the accretion properties of 21 low mass T Tauri stars using a dataset of contemporaneous near ultraviolet(NUV) through optical observations obtained with the Hubble Space Telescope Imaging Spectrograph (STIS) andthe ground based Small and Medium Aperture Research Telescope System (SMARTS), a unique dataset because

23

of the nearly simultaneous broad wavelength coverage. Our dataset includes accreting T Tauri stars (CTTS) inTaurus, Chamaeleon I, η Chamaeleon and the TW Hydra Association. For each source we calculate the accretion rate(M) by fitting the NUV and optical excesses above the photosphere, produced in the accretion shock, introducingmultiple accretion components characterized by a range in energy flux (or density) for the first time. This treatmentis motivated by models of the magnetospheric geometry and accretion footprints, which predict that high density,low filling factor accretion spots co-exist with low density, high filling factor spots. By fitting the UV and opticalspectra with multiple accretion components, we can explain excesses which have been observed in the near infrared.Comparing our estimates of M to previous estimates, we find some discrepancies; however, they may be accounted forwhen considering assumptions for the amount of extinction and variability in optical spectra. Therefore, we confirmmany previous estimates of the accretion rate. Finally, we measure emission line luminosities from the same spectraused for the M estimates, to produce correlations between accretion indicators (Hβ, Ca II K, C II] and Mg II) andaccretion properties obtained simultaneously.

Accepted by ApJ


A Compound Model for the Origin of Earth’s Water

A. Izidoro1, K. de Souza Torres2, O. C. Winter1 and N. Haghighipour3

1 UNESP, Universidade Estadual Paulista, Grupo de Dinamica Orbital & Planetologia, Guaratingueta, CEP 12.516-410, Sao Paulo, Brazil2 UTFPR, Universidade Tecnologica Federal do Parana, Brazil3 Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii-Manoa, Honolulu, HI 96822, USA

E-mail contact: ocwinter at pq.cnpq.br

One of the most important subjects of debate in the formation of the solar system is the origin of Earth’s water. Cometshave long been considered as the most likely source of the delivery of water to Earth. However, elemental and isotopicarguments suggest a very small contribution from these objects. Other sources have also been proposed, among whichlocal adsorption of water vapor onto dust grains in the primordial nebula and delivery through planetesimals andplanetary embryos have become more prominent. However, no sole source of water provides a satisfactory explanationfor Earth’s water as a whole. In view of that, using numerical simulations, we have developed a compound modelincorporating both the principal endogenous and exogenous theories, and investigating their implications for terrestrialplanet formation and water delivery. Comets are also considered in the final analysis, as it is likely that at least someof Earth’s water has cometary origin. We analyze our results comparing two different water distribution models, andcomplement our study using the D/H ratio, finding possible relative contributions from each source and focusing onplanets formed in the habitable zone. We find that the compound model plays an important role by showing greateradvantage in the amount and time of water delivery in Earth-like planets.

Accepted by Astrophysical Journal (Vol 767:A54)


Kinetic Scheme for Solving M1 Model of Radiative Transfer

Yuji Kanno1, Tetsuya Harada1 and Tomoyuki Hanawa1

1 Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

E-mail contact: hanawa at cfs.chiba-u.ac.jp

We show a numerical scheme to solve the moment equations of the radiative transfer, i.e., M1 model which followsthe evolution of the energy density, E, and the energy flux, F . In our scheme we reconstruct the intensity from E andF so that it is consistent with the closure relation, relation, χ = (3 + 4f2)/(5 + 2

√

4− 3f2). Here the symbols, χ,f = |F |/(cE), and c, denote the Eddington factor, the reduced flux, and the speed of light, respectively. We evaluatethe numerical flux across the cell surface from the kinetically reconstructed intensity. It is an explicit function of Eand F in the neighboring cells across the surface considered. We include absorption and reemission within a numericalcell in the evaluation of the numerical flux. The numerical flux approaches to the diffusion approximation when thenumerical cell itself is optically thick. Our numerical flux gives a stable solution even when some regions computed

24

are very optically thick. We show the advantages of the numerical flux with examples. They include flash of beamedphotons and irradiated protoplanetary disks.

Accepted by Publ. Astron. Soc. Japan


Static compression of porous dust aggregates

Akimasa Kataoka1, Hidekazu Tanaka2, Satoshi Okuzumi3 and Koji Wada4

1 National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan2 Institute of Low Temperature Science, Hokkaido University, Kita, Sapporo 060-0819, Japan3 Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo, 152-8551, Japan4 Planetary Exploration Research Center, Chiba Institute of Technology, Narashino, Chiba, 275-0016, Japan

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

Context: In protoplanetary disks, dust grains coagulate with each other and grow to form aggregates. As these ag-gregates grow by coagulation, their filling factor φ decreases down to φ ≪ 1. However, comets, the remnants of theseearly planetesimals, have φ ∼ 0.1. Thus, static compression of porous dust aggregates is important in planetesimalformation. However, the static compression strength has been investigated only for relatively high density aggregates(φ > 0.1).Aims: We investigate and find the compression strength of highly porous aggregates (φ ≪ 1). Methods: We performthree dimensional N -body simulations of aggregate compression with a particle-particle interaction model. We intro-duce a new method of static compression: the periodic boundary condition is adopted and the boundaries move withlow speed to get closer. The dust aggregate is compressed uniformly and isotropically by themselves over the periodicboundaries.Results: We empirically derive a formula of the compression strength of highly porous aggregates (φ ≪ 1). We checkthe validity of the compression strength formula for wide ranges of numerical parameters, such as the size of initialaggregates, the boundary speed, the normal damping force, and material. We also compare our results to the previousstudies of static compression in the relatively high density region (φ > 0.1) and confirm that our results consistentlyconnect to those in the high density region. The compression strength formula is also derived analytically.

Accepted by A&A


Star-forming regions of the Aquila rift cloud complex. I. NH3 tracers of dense molecularcores

S.A. Levshakov1,2,3, C. Henkel4,5, D. Reimers1, M. Wang6, R. Mao6, H. Wang6, and Y. Xu6

1 Hamburger Sternwarte, Universitat Hamburg, Gojenbergsweg 112, D-21029 Hamburg, Germany2 Io?e Physical-Technical Institute, Polytekhnicheskaya Str. 26, 194021 St. Petersburg, Russia3 St. Petersburg Electrotechnical University ’LETI’, Prof. Popov Str. 5, 197376 St. Petersburg, Russia4 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, D-53121 Bonn, Germany5 Astronomy Department, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia6 Purple Mountain Observatory, Academia Sinica, Nanjing 210008, P. R. China

E-mail contact: lev at astro.ioffe.rssi.ru

Aims. In the present part of our survey we search for ammonia emitters in the Aquila rift complex which trace thedensest regions of molecular clouds.Methods. From a CO survey carried out with the Delingha 14-m telescope we selected ∼ 150 targets for observationsin other molecular lines. Here we describe the mapping observations in the NH3(1,1) and (2,2) inversion lines of thefirst 49 sources performed with the Effelsberg 100-m telescope.Results. The NH3(1,1) and (2,2) emission lines are detected in 12 and 7 sources, respectively. Among the newlydiscovered NH3 sources, our sample includes the following well-known clouds: the starless core L694-2, the Serpenscloud Cluster B, the Serpens dark cloud L572, the filamentary dark cloud L673, the isolated protostellar source B335,and the complex star-forming region Serpens South. Angular sizes between 40′′ and 80′′ (∼ 0.04−0.08 pc) are observed

25

for compact starless cores but as large as 9′ (∼ 0.5 pc) for filamentary dark clouds. The measured kinetic temperaturesof the clouds lie between 9 K and 18 K. From NH3 excitation temperatures of 3− 8K we determine H2 densities withtypical values of ∼ (0.4− 4)× 104 cm−3. The masses of the mapped cores range between ∼ 0.05 and ∼ 0.5 M⊙. Therelative ammonia abundance, X = [NH3]/[H2], varies from 1×10−7 to 5×10−7 with the mean 〈X〉 = (2.7±0.6)×10−7

(estimated from spatially resolved cores assuming the filling factor η = 1). In two clouds, we observe kinematicallysplit NH3 profiles separated by ∼ 1 km s−1. The splitting is most likely due to bipolar molecular outflows for one ofwhich we determine an acceleration of <∼0.03 km s−1 yr−1. A starless core with significant rotational energy is foundto have a higher kinetic temperature than the other ones which is probably caused by magnetic energy dissipation.

Accepted by A&A


Characterizing the Stellar Photospheres and Near-infrared Excesses in Accreting TTauri Systems

M. K. McClure1, N. Calvet1, C. Espaillat2, L. Hartmann1, J. Hernandez3, L. Ingleby1, K. L. Luhman4,P. D’Alessio5 and B. Sargent6

1 The University of Michigan, 500 Church St., 830 Dennison Bldg., Ann Arbor, MI 48109, USA2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA3 Centro de Investigaciones de Astronomia (CIDA), Merida 5101-A, Venezuela4 The Pennsylvania State University, University Park, PA 16802, USA5 Centro de Radioastronomia y Astrofisica, Universidad Nacional Autonoma de Mexico, 58089 Morelia, Michoacan,Mexico6 Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623, USA

E-mail contact: melisma at umich.edu

Using NASA IRTF SpeX data from 0.8 to 4.5 µm, we determine self-consistently the stellar properties and excessemission above the photosphere for a sample of classical T Tauri stars (CTTS) in the Taurus molecular cloud withvarying degrees of accretion. This process uses a combination of techniques from the recent literature as well asobservations of weak-line T Tauri stars (WTTS) to account for the differences in surface gravity and chromosphericactivity between the TTS and dwarfs, which are typically used as photospheric templates for CTTS. Our improvedveiling and extinction estimates for our targets allow us to extract flux-calibrated spectra of the excess in the near-infrared. We find that we are able to produce an acceptable parametric fit to the near-infrared excesses using acombination of up to three blackbodies. In half of our sample, two blackbodies at temperatures of 8000 K and 1600 Ksuffice. These temperatures and the corresponding solid angles are consistent with emission from the accretion shockon the stellar surface and the inner dust sublimation rim of the disk, respectively. In contrast, the other half requiresthree blackbodies at 8000, 1800, and 800 K, to describe the excess. We interpret the combined two cooler blackbodiesas the dust sublimation wall with either a contribution from the disk surface beyond the wall or curvature of the wallitself, neither of which should have single-temperature blackbody emission. In these fits, we find no evidence of acontribution from optically thick gas inside the inner dust rim.

Accepted by ApJ


SABOCA 350-µm and LABOCA 870-µm dust continuum imaging of IRAS 05399-0121:mapping the dust properties of a pre- and protostellar core system

Oskari Miettinen1 and Stella S. R. Offner2

1 Department of Physics, University of Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland2 Department of Astronomy, Yale University, New Haven, CT 06511, USA

E-mail contact: oskari.miettinen at helsinki.fi

Context. Thermal emission from dust provides a valuable tool to determine important physical properties of densestructures within molecular clouds.Aims. We attempt to map the distributions of dust temperature and H2 column density of IRAS 05399-0121/SMM

26

1, which is a dense double-core system in Orion B9. We also search for substructures within the cores through high-resolution submillimetre imaging.Methods. The source was mapped with APEX/SABOCA at 350 µm. We combine these data with our previousLABOCA 870-µm data. The spatial resolution of the new SABOCA image, ∼ 3 400 AU, is about 2.6 times betterthan provided by LABOCA, and is therefore well-suited for the purpose of the present study. We also make use ofthe Spitzer infrared observations to characterise the star-formation activity in the source.Results. The filamentary source remains a double-core system on the 3 400 AU scale probed here, and the projectedseparation between IRAS 05399 and SMM 1 is 0.14 pc. The temperature map reveals warm spots towards IRAS 05399and the southeastern tip of the source. Both IRAS 05399 and SMM 1 stand out as peaks in the column density map.

A simple analysis suggests that the density profile is of the form ∼ r−(2.3+2.2

−0.9), as determined at the position of SMM

1. The broadband spectral energy distribution of IRAS 05399 suggests that it is near the Stage 0/I borderline. Avisual inspection of the Spitzer/IRAC images provides hints of a quadrupolar-like jet morphology around IRAS 05399,supporting the possibility that it is a binary system.Conclusions. The source splitting into two subcores along the long axis can be explained by cylindrical Jeans-typefragmentation but the steepness of the density profile is shallower than what is expected for an isothermal cylinder.The difference between the evolutionary stages of IRAS 05399 (protostellar) and SMM 1 (starless) suggests that theformer has experienced a phase of rapid mass accretion, supported by the very long outflow it drives. The protostellarjet from IRAS 05399 might have influenced the nearby core SMM 1. In particular, the temperature map features arelikely to be imprints of protostellar or shock heating, while external heating could be provided by the nearby high-massstar-forming region NGC 2024.

Accepted by Astronomy and Astrophysics


Cloud formation in colliding flows: influence of the choice of cooling function

Milica Micic1,2,4, Simon C.O. Glover1, Robi Banerjee3, and Ralf S. Klessen1

1 Universitat Heidelberg, Zentrum fur Astronomie, Institut fur Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120Heidelberg2 Member of the International Max Planck Research School for Astronomy and Cosmic Physics at the University ofHeidelberg (IMPRS-HD) and the Heidelberg Graduate School of Fundamental Physics (HGSFP)3 Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany4 Astronomical Observatory, Volgina 7, 11060 Belgrade, Republic of Serbia

E-mail contact: milica at aob.rs

We study the influence of the choice of cooling function on the formation of molecular clouds in high-resolution three-dimensional simulations of converging flows. We directly compare the results obtained using the simple, parametrizedcooling function introduced by Koyama & Inutsuka (2002) and used by a number of converging flow studies with theresults of the detailed calculation of the non-equilibrium chemistry and thermal balance of the gas. We find that anumber of the cloud properties, such as the mass and volume filling fractions of cold gas, are relatively insensitiveto the choice of cooling function. On the other hand, the cloud morphology and the large-scale velocity distributionof the gas do strongly depend on the cooling function. We show that the differences that we see can largely beexplained by differences in the way that Lyman-α cooling is treated in the two complementary approaches, and thata proper non-equilibrium treatment of the ionisation and recombination of the gas is necessary in order to model thehigh-temperature cooling correctly. We also investigate the properties of the dense clumps formed within the cloud.In agreement with previous models, we find that the majority of these clumps are not self-gravitating, suggesting thatsome form of large-scale collapse of the cloud may be required in order to produce gravitationally unstable clumpsand hence stars. Overall, the physical properties of the dense clumps are similar in both simulations, suggesting thatthey do not depend strongly on the choice of cooling function. However, we do find a systematic difference of around10 K in the mean temperatures of the clumps produced by the two models.

Accepted by MNRAS


27

The HCN-Water Ratio in the Planet Formation Region of Disks

Joan Najita1, John Carr2, Klaus Pontoppidan3, Colette Salyk1, Ewine van Dishoeck4 and Geoff Blake5

1 NOAO, 950 N. Cherry Ave, Tucson, AZ 85719, USA2 Naval Research Lab, Code 7211, Washington, DC 20375, USA3 STScI, 3700 San Martin Drive, Baltimore, MD 21218, USA4 NOAO, 950 N. Cherry Ave, Tucson, AZ 85719, USA5 Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, Netherlands6 Caltech, Division of Geological & Planetary Sciences, Mail Stop 150-21, Pasadena, CA 91125, USA

E-mail contact: najita at noao.edu

We find a trend between the mid-infrared HCN/H2O flux ratio and submillimeter disk mass among T Tauri stars inTaurus. While it may seem puzzling that the molecular emission properties of the inner disk (< few AU) are relatedto the properties of the outer disk (beyond ∼ 20AU) probed by the submillimeter continuum, an interesting possibleinterpretation is that the trend is a result of planetesimal and protoplanet formation. Because objects this large aredecoupled from the accretion flow, when they form, they can lock up water (and oxygen) beyond the snow line, therebyenhancing the C/O ratio in the inner disk and altering the molecular abundances there. We discuss the assumptionsthat underlie this interpretation, a possible alternative explanation, and related open questions that motivate futurework. Whatever its origin, understanding the meaning of the relation between the HCN/H2O ratio and disk mass isof interest as trends like this among T Tauri disk properties are relatively rare.

Accepted by ApJ (766:A134)


A Sample of OB Stars That Formed in the Field

M.S. Oey1, J.B. Lamb1, C.T. Kushner1, E.W. Pellegrini2, and A.S. Graus3

1 Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI,48109-10422 Present address: Department of Physics and Astronomy, University of Toledo, 2801 W. Bancroft, Toledo, OH 436063 Present address: Department of Physics and Astronomy, University of California, Irvine, CA 92697

E-mail contact: msoey at umich.edu

We present a sample of 14 OB stars in the Small Magellanic Cloud that meet strong criteria for having formed underextremely sparse star-forming conditions in the field. These stars are a minimum of 28 pc in projection from other OBstars, and they are centered within symmetric, round HII regions. They show no evidence of bow shocks, implyingthat the targets are not transverse runaway stars. Their radial velocities relative to local HI also indicate that theyare not line-of-sight runaway stars. A friends-of-friends analysis shows that 9 of the objects present a few low-masscompanion stars, with typical mass ratios for the two highest-mass stars of around 0.1. This further substantiatesthat these OB stars formed in place, and that they can and do form in extremely sparse conditions. This poses strongconstraints on theories of star formation and challenges proposed relations between cluster mass and maximum stellarmass.

Accepted by ApJ


Imprints of feedback in young gasless clusters?

Richard J. Parker1 and James E. Dale2

1 Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland2 Excellence Cluster ‘Universe’, Boltzmannstraße 2, 85748 Garching, Germany

E-mail contact: rparker at phys.ethz.ch

We present the results ofN -body simulations in which we take the masses, positions and velocities of sink particles fromfive pairs of hydrodynamical simulations of star formation by Dale et al. (2012, 2013) and evolve them for a further

28

10Myr. We compare the dynamical evolution of star clusters that formed under the influence of mass–loss drivenby photoionization feedback, to the evolution of clusters that formed without feedback. We remove any remaininggas and follow the evolution of structure in the clusters (measured by the Q–parameter), half-mass radius, centraldensity, surface density and the fraction of bound stars. There is little discernible difference in the evolution of clustersthat formed with feedback compared to those that formed without. The only clear trend is that all clusters whichform without feedback in the hydrodynamical simulations lose any initial structure over 10Myr, whereas some of theclusters which form with feedback retain structure for the duration of the subsequent N -body simulation. This isdue to lower initial densities (and hence longer relaxation times) in the clusters from Dale et al. (2012, 2013) whichformed with feedback, which prevents dynamical mixing from erasing substructure. However, several other conditions(such as supervirial initial velocities) also preserve substructure, so at a given epoch one would require knowledge ofthe initial density and virial state of the cluster in order to determine whether star formation in a cluster has beenstrongly influenced by feedback.

Accepted by MNRAS


Spatial distribution of small hydrocarbons in the neighborhood of the Ultra CompactHII region Monoceros R2

P. Pilleri1,2,3, S. Trevino-Morales4, A. Fuente2, C. Joblin5,6, J. Cernicharo1, M. Gerin7, S. Viti8,O. Berne5,6, J.R. Goicoechea1, J. Pety9, M. Gonzalez-Garcıa4, J. Montillaud10, V. Ossenkopf11, C. Kramer4,S. Garcıa-Burillo2, F. Le Petit12, J. Le Bourlot12

1 Centro de Astrobiologıa (INTA-CSIC), Ctra. M-108, km. 4, E-28850 Torrejon de Ardoz, Spain2 Observatorio Astronomico Nacional, Apdo. 112, E-28803 Alcala de Henares (Madrid), Spain3 Los Alamos National Laboratory, Los Alamos, NM 87545, USA4 Instituto de Radio Astronomıa Milimetrica (IRAM), Avenida Divina Pastora 7, Local 20, 18012 Granada, Spain5 Universite de Toulouse; UPS-OMP; IRAP; Toulouse, France6 CNRS; IRAP; 9 Av. colonel Roche, BP 44346, F-31028 Toulouse cedex 4, France7 LERMA, Observatoire de Paris, 61 Av. de l’Observatoire, 75014 Paris, France8 Dept. of Physics and Astronomy, UCL, Gower Place, London WC1E6BT, UK9 Institut de Radioastronomie Millimetrique, 300 Rue de la Piscine, 38406 Saint Martin d’Heres, France10 Department of Physics, P.O.Box 64, FI-00014, University of Helsinki, Finland11 I. Physikalisches Institut der Universitat zu Koln, Zulpicher Straße 77, 50937 Koln, Germany12 Observatoire de Paris, LUTH and Universite Denis Diderot, Place J. Janssen, 92190 Meudon, France

E-mail contact: ppilleri at oan.es

Context: We study the chemistry of small hydrocarbons in the photon-dominated regions (PDRs) associated with theultra-compact HII region (UCHII) Mon R2.Aims Our goal is to determine the variations of the abundance of small hydrocarbons in a high-UV irradiated PDRand investigate the chemistry of these species.Methods: We present an observational study of the small hydrocarbons CH, CCH and c-C3H2 in Mon R2 combiningspectral mapping data obtained with the IRAM-30m telescope and the Herschel space observatory. We determine thecolumn densities of these species, and compare their spatial distributions with that of polycyclic aromatic hydrocarbon(PAH), which trace the PDR. We compare the observational results with different chemical models to explore therelative importance of gas-phase, grain-surface and time-dependent chemistry in these environments.Results: The emission of the small hydrocarbons show different spatial patterns. The CCH emission is extended whileCH and c-C3H2 are concentrated towards the more illuminated layers of the PDR. The ratio of the column densitiesof c-C3H2 and CCH shows spatial variations up to a factor of a few, increasing from N(c-C3H2)/N(CCH)≈ 0.004 inthe envelope to a maximum of ≈ 0.015− 0.029 towards the 8µm emission peak. Comparing these results with othergalactic PDRs, we find that the abundance of CCH is quite constant over a wide range of G0, whereas the abundanceof c-C3H2 is higher in low-UV PDRs, with the N(c-C3H2)/N(CCH) ratio ranging ≈0.008-0.08 from high to low UVPDRs. In Mon R2, the gas-phase steady-state chemistry can account relatively well for the abundances of CH andCCH in the most exposed layers of the PDR, but falls short by a factor of 10 to reproduce c-C3H2. In the low-density molecular envelope, time-dependent effects and grain surface chemistry play a dominant role in determining

29

the hydrocarbons abundances.Conclusions: Our study shows that the small hydrocarbons CCH and c-C3H2 present a complex chemistry in whichUV photons, grain-surface chemistry and time dependent effects contribute to determine their abundances. Each ofthese effects may be dominant depending on the local physical conditions, and the superposition of different regionsalong the line of sight leads to the variety of measured abundances.

Accepted by A&A

hyyp://arxiv.org/pdf/1303.4984

An X-rays Survey of the Young Stellar Population of the Lynds 1641 and Iota OrionisRegions

I. Pillitteri1, S.J. Wolk1, S.T. Megeath2, L. Allen3, J. Bally4, Marc Gagne5, R.A. Gutermuth6, L.Hartman7, G. Micela8, P. Myers1, J.M. Oliveira9, S. Sciortino8, F. Walter1, L. Rebull10, and J. Stauffer10

1 SAO Harvard Center for Astrophysics, 60 Garden St, Cambridge MA 02138 USA2 Department of Physics & Astronomy, University of Toledo, OH USA3 National Optical Astronomy Observatory USA4 University of Colorado, Boulder, CO USA5 Department of Geology & Astronomy, West Chester University, West Chester, PA USA6 Dept. of Astronomy, University of Massachusetts, Amherst, MA 01003 USA7 University of Michigan, Ann Arbor, MI USA8 INAF - Osservatorio Astronomico di Palermo Italy9 School of Physical & Geographical Sciences, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BGUK10 CALTECH, Pasadena, CA, 91125 USA

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

We present an XMM-Newton survey of the part of Orion A cloud south of the Orion Nebula. This survey includesthe Lynds 1641 (L1641) dark cloud, a region of the Orion A cloud with very few massive stars and hence a relativelylow ambient UV flux, and the region around the O9 III star ι Orionis. In addition to proprietary data, we usedarchival XMM data of the Orion Nebula Cluster (ONC) to extend our analysis to a major fraction of the Orion Acloud. We have detected 1060 X-ray sources in L1641 and Iota Ori region. About 94% of the sources have 2MASS& Spitzer counterparts, 204 and 23 being Class II and Class I or protostars objects, respectively. In addition, wehave identified 489 X-ray sources as counterparts to Class III candidates, given they are bright in X-rays and appearas normal photospheres at mid-IR wavelengths. The remaining 205 X-ray sources are likely distant AGNs or othergalactic sources not related to Orion A. We find that Class III candidates appear more concentrated in two mainclusters in L1641. The first cluster of Class III stars is found toward the northern part of L1641, concentrated aroundIota Ori. The stars in this cluster are more evolved than those in the Orion Nebula. We estimate a distance of 300-320pc for this cluster and thus it is closer than the Orion A cloud. Another cluster rich in Class III stars is located inL1641 South and appears to be a slightly older cluster embedded in the Orion A cloud. Furthermore, other evolvedClass III stars are found north of the ONC toward NGC 1977.

Accepted by ApJ


Identification of transitional disks in Chamaeleon with Herschel

A. Ribas1,2,3, B. Merın4, H. Bouy2, C. Alves de Oliveira1, D.R. Ardila5, E. Puga4, A. Kospal6, L.Spezzi7, N.L.J. Cox8, T. Prusti6, G.L. Pilbratt6, Ph. Andre9, L. Matra10, and R. Vavrek4

1 ESAC-ESA, P.O. Box, 78, 28691 Villanueva de la Caada, Madrid, Spain2 Centro de Astrobiologıa, INTA-CSIC, P.O. Box - Apdo. de correos 78, Villanueva de la Canada Madrid 28691, Spain3 Ingenierıa y Servicios Aeroespaciales-ESAC, P.O. Box, 78, 28691 Villanueva de la Canada, Madrid, Spain4 Herschel Science Centre, ESAC-ESA, P.O. Box, 78, 28691 Villanueva de la Caada, Madrid, Spain5 NASA Herschel Science Center, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125,

30

USA6 Research and Scientic Support Department, ESTEC-ESA, PO Box 299, 2200 AG, Noordwijk, The Netherlands7 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748, Garching bei Munchen, Germany 8 Instituutvoor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, B-3001, Leuven, Belgium9 Laboratoire AIM Paris Saclay, CEA/DSM CNRS Universite Paris Diderot, IRFU, Service dAstrophysique, Centred’Etudes de Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette, France10 School of Physics, Trinity College Dublin, Dublin 2, Ireland

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

Transitional disks are circumstellar disks with inner holes that in some cases are produced by planets and/or sub-stellar companions in these systems. For this reason, these disks are extremely important for the study of planetarysystem formation. The Herschel Space Observatory provides an unique opportunity for studying the outer regions ofprotoplanetary disks. In this work we update previous knowledge on the transitional disks in the Chamaeleon I and IIregions with data from the Herschel Gould Belt Survey. We propose a new method for transitional disk classificationbased on the WISE 12 micron-PACS 70 micron color, together with inspection of the Herschel images. We applied thismethod to the population of Class II sources in the Chamaeleon region and studied the spectral energy distributionsof the transitional disks in the sample. We also built the median spectral energy distribution of Class II objects inthese regions for comparison with transitional disks. The proposed method allows a clear separation of the knowntransitional disks from the Class II sources. We find 6 transitional disks, all previously known, and identify 5 objectspreviously thought to be transitional as possibly non-transitional. We find higher fluxes at the PACS wavelengthsin the sample of transitional disks than those of Class II objects. We show the Herschel 70 micron band to be anefficient tool for transitional disk identification. The sensitivity and spatial resolution of Herschel reveals a significantcontamination level among the previously identified transitional disk candidates for the two regions, which calls for arevision of previous samples of transitional disks in other regions. The systematic excess found at the PACS bandscould be a result of the mechanism that produces the transitional phase, or an indication of different evolutionarypaths for transitional disks and Class II sources.

Accepted by A&A


Herschel far-infrared observations of the Carina Nebula Complex. III: Detailed cloudstructure and feedback effects

V. Roccatagliata1, T. Preibisch1, T. Ratzka1 and B. Gaczkowski1

1 Universitats-Sternwarte Munchen, Ludwig-Maximilians-Universitat, Scheinerstr. 1, 81679 Munchen, Germany

E-mail contact: vrocca at usm.uni-muenchen.de

Context. The star formation process in large clusters/associations can be strongly influenced by the feedback fromhigh-mass stars. Whether the resulting net effect of the feedback is predominantly negative (cloud dispersal) or positive(triggering of star formation due to cloud compression) is still an open question.Aims. The Carina Nebula complex (CNC) represents one of the most massive star-forming regions in our Galaxy.We use our Herschel far-infrared observations to study the properties of the clouds over the entire area of the CNC(with a diameter of ≈ 3.2◦, which corresponds to ≈ 125 pc at a distance of 2.3 kpc). The good angular resolution(10′′−36′′) of the Herschel maps corresponds to physical scales of 0.1 – 0.4 pc, and allows us to analyze the small-scale(i.e. , clump-size) structures of the clouds.Methods. The full extent of the CNC was mapped with PACS and SPIRE in the 70, 160, 250, 350, and 500µm bands.We determined temperatures and column densities at each point in these maps by modeling the observed far-infraredspectral energy distributions. We also derived a map showing the strength of the UV radiation field. We investigatedthe relation between the cloud properties and the spatial distribution of the high-mass stars and computed total cloudmasses for different density thresholds.Results. Our Herschel maps resolve for the first time the small-scale structure of the dense clouds over the entirespatial extent of the CNC. Several particularly interesting regions, including the prominent pillars south of η Car, areanalyzed in detail. We compare the cloud masses derived from the Herschel data with previous mass estimates basedon sub-mm and molecular line data. Our maps also reveal a peculiar wave-like pattern in the northern part of theCarina Nebula. Finally, we characterize two prominent cloud complexes at the periphery of our Herschel maps, which

31

are probably molecular clouds in the Galactic background.Conclusions. We find that the density and temperature structure of the clouds in most parts of the CNC is dominatedby the strong feedback from the numerous massive stars, and not by random turbulence. Comparing the cloud massand the star formation rate derived for the CNC with other Galactic star-forming regions suggests that the CNCis forming stars in a particularly efficient way. We suggest this to be a consequence of triggered star formation byradiative cloud compression.

Accepted by Astronomy & Astrophysics


High-quality preprints can be obtained from:http://www.usm.uni-muenchen.de/people/preibisch/publications.html

Star formation in the massive ”starless” infrared dark cloud G0.253+0.016

Luis F. Rodrıguez1,2 and Luis Zapata1

1 Centro de Radioastronomıa y Astrofısica, UNAM, A. P. 3-72, (Xangari), 58089 Morelia, Michoacan, Mexico2 Astronomy Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia

E-mail contact: l.rodriguez at crya.unam.mx

G0.253+0.016 is a remarkable massive infrared dark cloud located within ∼100 pc of the galactic center. With a highmass of 1.3× 105 M⊙, a compact average radius of ∼2.8 pc and a low dust temperature of 23 K, it has been believedto be a yet starless precursor to a massive Arches-like stellar cluster. We present sensitive JVLA 1.3 and 5.6 cmradio continuum observations that reveal the presence on three compact thermal radio sources projected against thiscloud. These radio sources are interpreted as HII regions powered by ∼B0.5 ZAMS stars. We conclude that althoughG0.253+0.016 does not show evidence of O-type star formation, there are certainly early B-type stars embedded in it.We detect three more sources in the periphery of G0.253+0.016 with non-thermal spectral indices. We suggest thatthese sources may be related to the galactic center region and deserve further study.

Accepted by The Astrophysical Journal (Letters)


The Herschel and JCMT Gould Belt Surveys: Constraining Dust Properties in thePerseus B1 Clump with PACS, SPIRE, and SCUBA-2

S. I. Sadavoy1,2, J. Di Francesco1,2, D. Johnstone1,2,3, M. J. Currie3, E. Drabek4, J. Hatchell4, D.Nutter5, Ph. Andre6, D. Arzoumanian7, M. Benedettini8, J.-P. Bernard9,10, A. Duarte-Cabral11,12,C. Fallscheer1,2, R. Friesen13, J. Greaves14, M. Hennemann6, T. Hill6, T. Jenness3, V. Konyves6,7,B. Matthews1,2, J. C. Mottram15, S. Pezzuto8, A. Roy6, K. Rygl8, N. Schneider-Bontemps11,12, L.Spinoglio8, L. Testi16, N. Tothill17, D. Ward-Thompson18 and G. White19

1Department of Physics & Astronomy, University of Victoria, Victoria, BC, Canada2National Research Council Canada, Victoria, BC, Canada3Joint Astronomy Centre, Hilo, Hawaii, USA4School of Physics, University of Exeter, Exeter, U.K.5School of Physics and Astronomy, Cardiff University, Cardiff, UK6Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, IRFU/Service d’Astrophysique, Saclay, France7IAS, CNRS (UMR 8617), Universite Paris-Sud 11, Orsay, France8Istituto di Astrofisica e Planetologia Spaziali, Rome, Italy9CNRS, IRAP, 9 Av. colonel Roche, Toulouse Cedex 4, France10Universite de Toulouse, UPS-OMP, IRAP,Toulouse Cedex 4, France11Universite de Bordeaux, LAB, Floirac, France12CNRS, LAB, Floirac, France13Dunlap Institute, University of Toronto, Toronto, ON, Canada14School of Physics and Astronomy, University of St. Andrews, St. Andrews, UK15Leiden University, 506 Huygens Laboratory, Leiden, Netherlands

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16ESO, Garching bei Munchen, Germany17University of Western Sydney, Penrith, Australia18Jeremiah Horrocks Institute, University of Central Lancashire, Preston, Lancashire, UK19The Open University, Department of Physics and Astronomy, Milton Keynes, UK

E-mail contact: ssadavoy at uvic.ca

We present Herschel observations from the Herschel Gould Belt Survey and SCUBA-2 science verification observationsfrom the JCMT Gould Belt Survey of the B1 clump in the Perseus molecular cloud. We determined the dust emissivityindex using four different techniques to combine the Herschel PACS+SPIRE data at 160−500 µm with the SCUBA-2data at 450 µm and 850 µm. Of our four techniques, we found that the most robust method was to filter-out thelarge-scale emission in the Herschel bands to match the spatial scales recovered by the SCUBA-2 reduction pipeline.Using this method, we find β ≈ 2 toward the filament region and moderately dense material and lower β values(β >∼ 1.6) toward the dense protostellar cores, possibly due to dust grain growth. We find that β and temperatureare more robust with the inclusion of the SCUBA-2 data, improving estimates from Herschel data alone by factors of∼ 2 for β and by ∼ 40% for temperature. Furthermore, we find core mass differences of <∼30% compared to Herschel -only estimates with an adopted β = 2, highlighting the necessity of long-wavelength submillimeter data for derivingaccurate masses of prestellar and protostellar cores.

Accepted by ApJ


A candidate circumbinary Keplerian disk in G35.20-0.74 N: A study with ALMA

A. Sanchez-Monge1, R. Cesaroni1, M.T. Beltran1, M.S.N. Kumar2, T. Stanke3, H. Zinnecker4, S.Etoka5,6, D. Galli1, C.A. Hummel3, L. Moscadelli1, T. Preibisch7, T. Ratzka7, F.F.S. van der Tak8,9, S.Vig10, C.M. Walmsley1,11 and K.-S. Wang12

1 Osservatorio Astrofisico di Arcetri, INAF, Largo Enrico Fermi 5, I-50125, Firenze, Italy2 Centro de Astrofisica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal3 ESO, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Munchen, Germany4 SOFIA Science Center, NASA Ames Research Center, Mailstop 232-12, Moffett Field, CA 94035, USA5 Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester M139PL, UK6 Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany7 Universitats-Sterwarte Munchen, Ludwig-Maximilians-Universitat, Scheinerstrasse 1, 81679 Munchen, Germany8 SRON Netherlands Institute for Space Research, P.O. Box 800, 9700 AV, Groningen, The Netherlands9 Kapteyn Astronomical Institute, University of Groningen, The Netherlands10 Department of Earth and Space Science, Indian Institute of Space Science and Technology, Thiruvananthapuram,India11 Dublin Institute for Advanced Studies (DIAS), 31 Fitzwilliam Place, Dublin 2, Ireland12 Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

E-mail contact: asanchez at arcetri.astro.it

We report on ALMA observations of continuum and molecular line emission with 0.4 arcsec resolution towards thehigh-mass star-forming region G35.20–0.74N. Two dense cores are detected in typical hot-core tracers (e.g., CH3CN)which reveal velocity gradients. In one of these cores, the velocity field can be fitted with an almost edge-on Kepleriandisk rotating about a central mass of ∼18 M⊙. This finding is consistent with the results of a recent study of theCO first overtone bandhead emission at 2.3 µm towards G35.20–0.74N. The disk radius and mass are >∼2500 au and∼3 M⊙. To reconcile the observed bolometric luminosity (∼3 × 104 L⊙) with the estimated stellar mass of 18 M⊙,we propose that the latter is the total mass of a binary system.

Accepted by Astronomy and Astrophysics Letters


33

Photometric variability in FU Ori and Z CMa as observed by MOST

Michal Siwak1, Slavek M. Rucinski2, Jaymie M. Matthews3, Rainer Kuschnig3,8, David B. Guenther4,Anthony F.J. Moffat5, Jason F. Rowe6, Dimitar Sasselov7, and Werner W. Weiss8

1 Mount Suhora Astronomical Observatory, Cracov Pedagogical University, ul. Podchorazych 2, 30-084 Krakow,Poland2 Deparntment of Astronomy and Astrophysics, University of Toronto, 50 St. George St., Toronto, Ontario, M5S 3H4,Canada3 Department of Physics & Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, B.C.,V6T 1Z1, Canada4 Institute for Computational Astrophysics, Department of Astronomy and Physics, Saint Marys University, Halifax,N.S., B3H 3C3, Canada5 Department de Physique, Universite de Montreal, C.P.6128, Succursale: Centre-Ville, Montreal, QC, H3C 3J7,Canada6 NASA Ames Research Center, Mo?ett Field, CA 94035, USA7 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA8 Universitat Wien, Institut fur Astronomie, Turkenschanzstrasse 17, A-1180 Wien, Austria

E-mail contact: siwak at oa.uj.edu.pl

Photometric observations obtained by the MOST satellite were used to characterize optical small scale variability ofthe young stars FU Ori and Z CMa. Wavelet analysis for FU Ori reveals the possible existence of several 2 − 9 dquasi-periodic features occurring nearly simultaneously; they may be interpreted as plasma parcels or other localizeddisc heterogeneities revolving at different Keplerian radii in the accretion disc. Their periods may shorten slowly whichmay be due to spiralling in of individual parcels toward the inner disc radius, estimated at 4.8± 0.2 R⊙. Analysis ofadditional multicolour data confirms the previously obtained relation between variations in the B − V colour indexand the V magnitude. In contrast to the FU Ori results, the oscillation spectrum of Z CMa does not reveal anyperiodicities with the wavelet spectrum possibly dominated by outburst of the Herbig Be component.

Accepted by MNRAS


The 69 micron forsterite band in spectra of protoplanetary disks - Results from theHerschel DIGIT programme

B. Sturm1, J. Bouwman1, Th. Henning1, N.J. Evans II2, L.B.F.M. Waters3,8,11, E.F. van Dishoeck4,6,J.D. Green2, J. Olofsson1, G. Meeus5, K. Maaskant3, C. Dominik3, J.C. Augereau7, G.D. Mulders3,11,B. Acke8, B. Merin9, G.J. Herczeg6,10, and The DIGIT team

1 Max Planck Institute for Astronomy, Konigstuhl 17, D-69117 Heidelberg, Germany2 The University of Texas at Austin, Department of Astronomy, 2515 Speedway, Stop C1400 Austin, TX 78712-1205,USA3 Astronomical Institute Anton Pannekoek, University of Amsterdam, PO Box 94249, 1090 GE Amsterdam, TheNetherlands4 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands 5 Dep. de Fısica Teorica,Fac. de Ciencias Universidad Autonoma de Madrid, Campus Cantoblanco 28049 Madrid, Spain6 Max Planck Institute for extraterrestrial Physics, Garching, Germany7 UJF-Grenoble 1 /CNRS-INSU, Institut de Planetologie et d’Astrophysique de Grenoble (IPAG), UMR 5274, Greno-ble, F-38041, France8 Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Heverlee, Belgium9 ESAC, Madrid, Spain10 Kavli Institute for Astronomy and Astrophysics, Ye He Yuan Lu 5, Beijing, 100871, P.R. China11 SRON Netherlands Institute for Space Research, P.O. Box 800, 9700 AV Groningen, The Netherlands

E-mail contact: : sturm at mpia.de

Context. We have analysed Herschel-PACS spectra of 32 circumstellar disks around Herbig Ae/Be and T-Tauri starsobtained within the Herschel key programme DIGIT. In this paper we focus on the 69 µm emission band of the

34

crystalline silicate forsterite.Aims. This work provides an overview of the 69 µm forsterite bands in the DIGIT sample. We aim to derive thetemperature and composition of the forsterite grains. With this information, constraints can be placed on the spatialdistribution of the forsterite in the disk and its formation history.Methods. Position and shape of the 69 µm band are used to derive the temperature and composition of the dust bycomparison to laboratory spectra of that band. We combine our data with existing Spitzer IRS spectra to comparethe presence and strength of the 69 µm band to the forsterite bands at shorter wavelengths.Results: A total of 32 sources have been observed, 8 of them show a 69 µm emission band that can be attributed toforsterite. With the exception of the T-Tauri star AS205, all of the detections are for disks associated with HerbigAe/Be stars. Most of the forsterite grains that give rise to the 69 µm bands are warm (∼ 100− 200 K) and iron-poor(less than ∼ 2% iron). Only AB-Aur requires approximately 3− 4% of iron.Conclusions. Our findings support the hypothesis that the forsterite grains form through an equilibrium condensationprocess at high temperatures. The connection between the strength of the 69 and 33 µm bands shows that at leastpart of the emission in these bands originates from the same dust grains. Further, any model that explains the PACSand the Spitzer IRS observations must take the effects of a wavelength dependent optical depth into account. We findindications of a correlation of the detection rate of the 69mu band with the spectral type of the host stars. However,our sample is too small to obtain a definitive result.

Accepted by A&A


HH 114 MMS: a new chemically active outflow

M. Tafalla1 and A. Hacar1,2

1 Observatorio Astronomico Nacional (IGN), Alfonso XII 3, E-28014 Madrid, Spain2 Institute for Astrophysics, University of Vienna, Turkenschanzstrasse 17, A-1180 Vienna, Austria

E-mail contact: m.tafalla at oan.es

Context. A small group of bipolar protostellar outflows display strong emission from shock-tracer molecules such asSiO and CH3OH, and are generally referred to as “chemically active.” The best-studied outflow from this group isthe one in L 1157.Aims. We study the molecular emission from the bipolar outflow powered by the very young stellar objectHH 114 MMS and compare its chemical composition with that of the L 1157 outflow.Methods. We have used the IRAM 30m radio telescope to observe a number of transitions from CO, SiO, CH3OH,SO, CS, HCN, and HCO+ toward the HH 114 MMS outflow. The observations consist of maps and a two-positionmolecular survey.Results. The HH 114 MMS outflow presents strong emission from a number of shock-tracer molecules that dominatethe appearance of the maps around the central source. The abundance of these molecules is comparable to the abun-dance in L 1157.Conclusions. The outflow from HH 114 MMS is a spectacular new case of a chemically active outflow.

Accepted by Astronomy and Astrophysics (A&A 552:L9)

http://adsabs.harvard.edu/abs/2013A\&A...552L...9T


The HIFI spectral survey of AFGL2591 (CHESS). I. Highly excited linear rotor moleculesin the high-mass protostellar envelope

M.H.D. van der Wiel1,2,3, L. Pagani4, F.F.S. van der Tak2,1, M. Kazmierczak2 and C. Ceccarelli5

1 Kapteyn Astronomical Institute, U of Groningen, NL2 SRON Netherlands Institute for Space Research, Groningen, NL3 Institute for Space Imaging Science, U of Lethbridge, AB, Canada4 LERMA, Observatoire de Paris, France5 LAOG, U Joseph Fourier, Grenoble, France

35

E-mail contact: matthijs.vanderwiel at uleth.ca

Context. Linear rotor molecules such as CO, HCO+ and HCN are important probes of star-forming gas. Forthese species, temperatures of <∼50K are sufficient to produce emission lines that are observable from the groundat (sub)millimeter wavelengths. Molecular gas in the environment of massive protostellar objects, however, is knownto reach temperatures of several hundred K. To probe this, space-based far-infrared observations are required.Aims. We aim to reveal the gas energetics in the circumstellar environment of the prototypical high-mass protostellarobject AFGL2591.Methods. Rotational spectral line signatures of CO species, HCO+, CS, HCN and HNC from a 490–1240GHz surveywith Herschel/HIFI, complemented by ground-based JCMT and IRAM 30m spectra, cover transitions in the energyrange (Eup/k) between 5K and ∼300K. Selected frequency settings in the highest frequency HIFI bands (up to1850GHz) extend this range to 750K for 12C16O. The resolved spectral line profiles are used to separate and studyvarious kinematic components. Observed line intensities are compared with a numerical model that calculates excita-tion balance and radiative transfer based on spherical geometry.Results. The line profiles show two emission components, the widest and bluest of which is attributed to an approachingoutflow and the other to the envelope. We find evidence for progressively more redshifted and wider line profiles fromthe envelope gas with increasing energy level. This trend is qualitatively explained by residual outflow contributionpicked up in the systematically decreasing beam size. Integrated line intensities for each species decrease as Eup/kincreases from <∼50 to ∼700K. The H2 density and temperature of the outflow gas are constrained to ∼105–106 cm−3

and 60–200K. In addition, we derive a temperature between 9 and 17K and N(H2) ∼ 3×1021 cm−2 for a knownforeground cloud seen in absorption, and N(H2) <∼ 1019 cm−2 for a second foreground component.Conclusions. Our spherical envelope model systematically underproduces observed line emission at Eup/k > 150Kfor all species. This indicates that warm gas should be added to the model and that the model’s geometry shouldprovide low optical depth pathways for line emission from this warm gas to escape, for example in the form of UVheated outflow cavity walls viewed at a favorable inclination angle. Physical and chemical conditions derived for theoutflow gas are similar to those in the protostellar envelope, possibly indicating that the modest velocity (<10 km s−1)outflow component consists of recently swept-up gas.

Accepted by A&A


Hot water in the inner 100 AU of the Class 0 protostar NGC1333 IRAS2A

Ruud Visser1, Jes K. Jørgensen2,3, Lars E. Kristensen4,5, Ewine F. van Dishoeck4,6 and Edwin A.Bergin1

1 Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA2 Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark3 Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, ØsterVoldgade 5-7, 1350 Copenhagen K, Denmark4 Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, the Netherlands5 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA6 Max-Planck-Institut fur Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany

E-mail contact: visserr at umich.edu

Evaporation of water ice above 100 K in the inner few 100 AU of low-mass embedded protostars (the so-called hotcore) should produce quiescent water vapor abundances of ∼10−4 relative to H2. Observational evidence so far pointsat abundances of only a few 10−6. However, these values are based on spherical models, which are known frominterferometric studies to be inaccurate on the relevant spatial scales. Are hot cores really that much drier thanexpected, or are the low abundances an artifact of the inaccurate physical models? We present deep velocity-resolvedHerschel-HIFI spectra of the 312–303 lines of H16

2 O and H182 O (1097 GHz, Eu/k = 249 K) in the low-mass Class

0 protostar NGC1333 IRAS2A. A spherical radiative transfer model with a power-law density profile is unable toreproduce both the HIFI data and existing interferometric data on the H18

2 O 313–220 line (203 GHz, Eu/k = 204 K).Instead, the HIFI spectra likely show optically thick emission from a hot core with a radius of about 100 AU. Themass of the hot core is estimated from the C18O J = 9–8 and 10–9 lines. We derive a lower limit to the hot waterabundance of 2× 10−5, consistent with the theoretical predictions of ∼10−4. The revised HDO/H2O abundance ratio

36

is 1× 10−3, an order of magnitude lower than previously estimated.

Accepted by ApJ


The Burst Mode of Accretion in Primordial Protostars

Eduard Vorobyov1,2, Alexander DeSouza3 and Shantanu Basu3

1 University of Vienna, Institute of Astrophysics, Vienna, 1180, Austria2 Research Institute of Physics, Southern Federal University, Stachki 194, Rostov-on-Don, 344090, Russia3 Department of Physics and Astronomy, University of Western Ontario, London, Ontario, N6A 3K7, Canada

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

We study the formation and long-term evolution of primordial protostellar disks harbored by first stars using numericalhydrodynamics simulations in the thin-disk limit. The initial conditions are specified by pre-stellar cores with distinctmass, angular momentum, and temperature. This allows us to probe several tens of thousand years of the disk’s initialevolution, during which we observe multiple episodes of fragmentation leading to the formation of gravitationallybound gaseous clumps within spiral arms. These fragments are torqued inward due to gravitational interaction withthe spiral arms on timescales of 103 - 104 yr and accreted onto the growing protostar, giving rise to accretion andluminosity bursts. The burst phenomenon is fueled by continuing accretion of material falling onto the disk from thecollapsing parent core, which replenishes the mass lost by the disk due to accretion, and triggers repetitive episodes ofdisk fragmentation. We show that the burst phenomenon is expected to occur for a wide spectrum of initial conditionsin primordial pre-stellar cores and speculate on how the intense luminosities (∼ 107 L⊙) produced by this mechanismmay have important consequences for the disk evolution and subsequent growth of the protostar.



Molecular line emission from a protoplanetary disk irradiated externally by a nearbymassive star

Catherine Walsh1,2, T. J. Millar1 and Hideko Nomura3

1 Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, University Road,Belfast BT7 1NN, UK2 Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands3 Department of Astronomy, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan

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

Star formation often occurs within or nearby stellar clusters. Irradiation by nearby massive stars can photoevaporateprotoplanetary disks around young stars (so-called proplyds) which raises questions regarding the ability of planetformation to take place in these environments. We investigate the two-dimensional physical and chemical structure ofa protoplanetary disk surrounding a low-mass (T Tauri) star which is irradiated by a nearby massive O-type star todetermine the survivability and observability of molecules in proplyds. Compared with an isolated star-disk system,the gas temperature ranges from a factor of a few (in the disk midplane) to around two orders of magnitude (in thedisk surface) higher in the irradiated disk. Although the UV flux in the outer disk, in particular, is several orders ofmagnitude higher, the surface density of the disk is sufficient for effective shielding of the disk midplane so that thedisk remains predominantly molecular in nature. We also find that non-volatile molecules, such as HCN and H2O,are able to freeze out onto dust grains in the disk midplane so that the formation of icy planetesimals, e.g., comets,may also be possible in proplyds. We have calculated the molecular line emission from the disk assuming LTE anddetermined that multiple transitions of atomic carbon, CO (and isotopologues, 13CO and C18O), HCO+, CN, andHCN may be observable with ALMA, allowing characterization of the gas column density, temperature, and opticaldepth in proplyds at the distance of Orion (≈400 pc).

Accepted by The Astrophysical Journal Letters

http://iopscience.iop.org/2041-8205/766/2/L23/

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Dramatic Evolution of the Disk-Shaped Secondary in the Orion Trapezium Star θ1 OriB1 (BM Ori): MOST Satellite Observations

Diana Windemuth1, William Herbst1, Evan Tingle1, Rachel Fuechsl1, Roy Kilgard1, Melanie Pinette2,Matthew Templeton3 and Arne Henden3

1 Astronomy Department, Wesleyan University, Middletown, CT 06459, USA2 Department of Physics and Astronomy, Bowdoin College, USA3 American Association of Variable Star Observers, Cambridge, MA 02138, USA

E-mail contact: dwindemuth at wesleyan.edu

The eclipsing binary θ1 Orionis B1 , variable star designation BM Ori, is the faintest of the four well-known Trapeziumstars at the heart of the Orion Nebula. The primary is a B3 star (∼6M⊙) but the nature of the secondary (∼2M⊙)has long been mysterious, since the duration and shape of primary eclipse are inappropriate for ordinary stars. Herewe report nearly continuous photometric observations obtained with the MOST satellite over ∼4 cycles of the 6.47dbinary period. The light curve is of unprecedented quality, revealing a deep, symmetric primary eclipse as well as aclear reflection effect and secondary eclipse. In addition, there are other small disturbances, some of which repeat atthe same phase over the four cycles monitored. The shape of the primary light curve has clearly evolved significantlyover the past 40 yr. While its overall duration and depth have remained roughly constant, the slopes of the descentand ascent phases are significantly shallower now than in the past and its distinctive flat-bottomed ”pseudo-totality”is much less obvious or even absent in the most recent data. We further demonstrate that the primary eclipse wasdetected at X-ray wavelengths during the Chandra COUP study. The light curve continues to be well modeled bya self-luminous and reflective disk-shaped object seen nearly edge-on orbiting the primary. The dramatic changein shape over four decades is modeled as an opacity variation in a tenuous outer envelope or disk of the secondaryobject. We presume that the secondary is an extremely young protostar at an earlier evolutionary phase than canbe commonly observed elsewhere in the Galaxy and that the opacity variations observed are related to its digestionof some accreted matter over the last 50-100 yr. Indeed, this object deserves continued observational and theoreticalattention as the youngest known eclipsing binary system.



The Progression of Star Formation in the Rosette Molecular Cloud

Jason E. Ybarra1, Elizabeth A. Lada1, Carlos G. Roman-Zuniga2, Zoltan Balog3, Junfeng Wang4 andEric D. Feigelson5

1 Department of Astronomy, University of Florida, Gainesville, FL 32605, USA2 Instituto de Astronomıa, Universidad Nacional Autonoma de Mexico, Unidad Academica de Ensenada, Apdo. Postal22860, Ensenada, B. C., Mexico3 Max-Planck-Institut fur Astronomie, Heidelberg, Germany4 Department of Physics and Astronomy & Center for Interdisciplinary Exploration and Research in Astrophysics(CIERA), Northwestern University, 2131 Tech Dr, Evanston, IL 60208, USA5 The Pennsylvania State University, University Park, PA 16802, USA

E-mail contact: jybarra at astro.ufl.edu

Using Spitzer Space Telescope and Chandra X-ray Observatory data, we identify YSOs in the Rosette MolecularCloud (RMC). By being able to select cluster members and classify them into YSO types, we are able to track theprogression of star formation locally within the cluster environments and globally within the cloud. We employ nearestneighbor method (NNM) analysis to explore the density structure of the clusters and YSO ratio mapping to studyage progressions in the cloud. We find a relationship between the YSO ratios and extinction which suggests starformation occurs preferentially in the densest parts of the cloud and that the column density of gas rapidly decreasesas the region evolves. This suggests rapid removal of gas may account for the low star formation efficiencies observedin molecular clouds. We find that the overall age spread across the RMC is small. Our analysis suggests that star

38

formation started throughout the complex around the same time. Age gradients in the cloud appear to be localizedand any effect the HII region has on the star formation history is secondary to that of the primordial collapse of thecloud.



Line Emission from Radiation-Pressurized HII Regions I: Internal Structure and LineRatios

Sherry C.C. Yeh1, Silvia Verdolini2, Mark R. Krumholz3, Christopher D. Matzner1, and AlexanderG.G.M. Tielens2

1 Department of Astronomy & Astrophysics, University of Toronto, 50 St. George St., Toronto, ON M5S 3H4, Canada2 Leiden Observatory, University of Leiden, P. O. Box 9513, 2300 RA Leiden, Netherlands3 Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064

E-mail contact: yeh at astro.utoronto.ca

The emission line ratios [OIII]λ5007/Hβ and [NII]λ6584/Hα have been adopted as an empirical way to distinguish be-tween the fundamentally different mechanisms of ionization in emission-line galaxies. However, detailed interpretationof these diagnostics requires calculations of the internal structure of the emitting HII regions, and these calculationsdepend on the assumptions one makes about the relative importance of radiation pressure and stellar winds. In thispaper we construct a grid of quasi-static HII region models to explore how choices about these parameters alter HIIregions’ emission line ratios. We find that, when radiation pressure is included in our models, HII regions reach asaturation point beyond which further increases in the luminosity of the driving stars does not produce any furtherincrease in effective ionization parameter, and thus does not yield any further alteration in an HII region’s line ratio.We also show that, if stellar winds are assumed to be strong, the maximum possible ionization parameter is quite low.As a result of this effect, it is inconsistent to simultaneously assume that HII regions are wind-blown bubbles and thatthey have high ionization parameters; some popular HII region models suffer from this inconsistency. Our work inthis paper provides a foundation for a companion paper in which we embed the model grids we compute here withina population synthesis code that enables us to compute the integrated line emission from galactic populations of HIIregions.

Accepted by ApJ


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Abstracts of recently accepted major reviews

Three-Dimensional Dust Radiative Transfer

Jurgen Steinacker1,2, Maarten Baes3 and Karl Gordon4,3

1 Institut de Planetologie et d’Astrophysique de Grenoble (UMR 5274), BP 53, F-38041 Grenoble, Cedex 9, France2 Max-Planck-Institut fur Astronomie, Konigstuhl 17, D-69117 Heidelberg, Germany3 Sterrenkundig Observatorium UGent, Krijgslaan 281 S9, B-9000 Gent, Belgium4 Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA

E-mail contact: stein at mpia.de

Cosmic dust is present in many astrophysical objects, and recent observations across the electromagnetic spectrumhave revealed that the dust distribution is often strongly three-dimensional. Dust grains are effective in absorbingand scattering UV/optical radiation, and re-emit the absorbed energy at infrared wavelengths. Understanding theintrinsic properties of these objects, including the dust itself, therefore requires 3D dust radiative transfer calculations.Unfortunately, the 3D dust radiative transfer problem is non-local and non-linear, which makes it one of the hardestchallenges in computational astrophysics. Nevertheless, significant progress has been made in the last decade, withan increasing number of codes capable of dealing with the complete 3D dust radiative transfer problem. We discussthe complexity of this problem, describe the two most successful solution techniques (Ray-Tracing and Monte Carlo),and discuss the state of the art in modeling observational data using 3D dust radiative transfer codes. We end withan outlook on the bright future of this field.

Accepted by Annual Reviews of Astronomy and Astrophysics, 51


Stellar Multiplicity

G. Duchene1,2 and A. Kraus3

1 University of California, Berkeley, USA2 Institut de Planetologie et d’Astrophysique de Grenoble, France3 Harvard-Smithsonian Center for Astrophysics, Cambridge, USA

E-mail contact: gduchene at berkeley.edu

Stellar multiplicity is an ubiquitous outcome of the star formation process. The frequency and main characteristicsof multiple systems, and their dependence on primary mass and environment, therefore are powerful tools to probethis process. While early attempts were fraught with selection biases and limited completeness, instrumentationbreakthroughs in the last two decades now enable robust statistical analyses. In this review, we summarize currentempirical knowledge of stellar multiplicity for Main Sequence stars and brown dwarfs, as well as among populationsof Pre-Main Sequence stars and embedded protostars. Among field objects, the multiplicity rate and breadth of theorbital period distribution are steep functions of the primary mass, whereas the mass ratio distribution is essentiallyflat for most populations besides the lowest mass objects. The time-variation of the frequency of visual companionsfollows two parallel, constant tracks corresponding to loose and dense stellar populations, although current observationsdo not yet distinguish whether initial multiplicity properties are universal or dependent on the physical conditions ofthe parent cloud. Nonetheless, these quantitative trends provide a rich comparison basis for numerical and analyticalmodels of star formation.

Accepted by ARA&A (vol. 51)

http://arviv.org/pdf/1303.3028

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Dissertation Abstracts

Chemical and physical characterization of the first stages ofprotoplanetary disk formation

Ugo Hincelin

Laboratory of Astrophysics of Bordeaux, University of Bordeaux, France

Chemistry Department, University of Virginia, McCormick Road, PO Box 400319 Charlottesville, VA 22904, USA

Electronic mail: ugo.hincelin at virginia.edu

Ph.D dissertation directed by: Valentine Wakelam and Stephane Guilloteau

Ph.D degree awarded: October 2012

Low mass stars, like our Sun, are born from the collapse of a molecular cloud. The matter falls in the center of thecloud, creating a protoplanetary disk surrounding a protostar. Planets and other Solar System bodies will be formedin the disk. The chemical composition of the interstellar matter and its evolution during the formation of the disk areimportant to better understand the formation process of these objects.

I studied the chemical and physical evolution of this matter, from the cloud to the disk, using the chemical gas-graincode Nautilus.

A sensitivity study to some parameters of the code (such as elemental abundances and parameters of grain surfacechemistry) has been done. More particularly, the updates of rate coefficients and branching ratios of the reactions ofour chemical network showed their importance, such as on the abundances of some chemical species, and on the codesensitivity to others parameters.

Several physical models of collapsing dense core have also been considered. The more complex and solid approach hasbeen to interface our chemical code with the radiation-magneto-hydrodynamic model of stellar formation RAMSES, inorder to model in three dimensions the physical and chemical evolution of a young disk formation. Our study showedthat the disk keeps imprints of the past history of the matter, and so its chemical composition is sensitive to the initialconditions.

http://www.theses.fr/en/2012BOR14603

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New Jobs

Postdoctoral Position in Star Formation and Astrochemistry

The Institut de Planetologie et d’Astrophysique de Grenoble (IPAG) is seeking applications for a Postdoctoral positionin star formation and astrochemistry. The successful applicant will work with Sebastien Maret (IPAG) and BenoıtCommercon (LERMA, Paris) on the modeling of an extensive set of observations of young solar type protostarsobtained with the Plateau de Bure interferometer (PdBI) as part of an IRAM large program (PI Philippe Andre).The postdoctoral researcher will lead the development of a numerical model that couples the result of state-of-the-artMHD simulations of pre- and proto-stellar core dynamical evolution with a complete chemistry network. He/she willalso contribute to analyze and interpret the PdBI observations, as well as follow-up observations that we plan onobtaining with ALMA and NOEMA.

Applicants should have a PhD in astronomy and a strong background in numerical modeling of the dynamics, chemistryand/or radiative transfer of star forming regions. Knowledge of millimeter or sub-millimeter interferometry is an asset.Good English communication skills and ability to work in a team are essential (note that knowledge of the Frenchlanguage is not required). Regular travels between Grenoble and Paris are expected.

The postdoctoral researcher will be appointed for an initial period of two years with the possibility of renewal forone year, with an attractive salary that commensurate with experience. The appointment is expected to start onSeptember 1st, 2013. A full working environment, including a laptop, a linux server and an access to a 352-cores gridcomputer, will be provided. Travel funds are also available upon prior agreement with the postdoc supervisor.

Applicants should send a curriculum vitae, a publication list, and a statement of research experience and interests byemail to Sebastien Maret ([email protected]). They should also arrange for three reference letters(to be sent directly by the referees by email). Deadline for applications is June 1st 2013.

Lecturer position at the University of Exeter

Contact: Isabelle Baraffe ([email protected])

The Astrophysics group at the University of Exeter (http://emps.exeter.ac.uk/physics-astronomy/research/astrophysics/) invites applications for an appointment as a Lecturer in the College of Engineering, Mathematicsand Physical Sciences (Reference of the post P44302).

This post aims to expand current research performed in the Astrophysics group at the University of Exeter, in areasrelated or complementary to extrasolar planets, planetary atmospheres, stellar and planetary structures, star andplanet formation and the interstellar medium. Candidates in observational or theoretical astrophysics and in otherinterdisciplinary fields related to astrophysics are encouraged to apply. The group has strong links with AppliedMathematics at the University of Exeter and with the Met Office (based in Exeter). Suitable candidates will bringresearch that will expand and strengthen astrophysics at the University.

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The successful applicant will hold a PhD in Physics, Astrophysics or a related area and have an internationally-recognised research programme in an active field of astrophysics research related or complementary to existing Exeterstrengths.

We are looking for innovative researchers with an international reputation and with a strong track record of researchfunding and international quality publications. The successful candidate will have the ability to attract postgraduateresearch students and will contribute to relevant areas of teaching as appropriate.

Appointments will be made in the salary range £32,267 - £36,298 per annum dependent on qualifications and expe-rience.

Informal enquiries can be made to Prof Isabelle Baraffe (tel +44 (0)1392 725123; email: [email protected]).

For further details and to apply on line visit www.exeter.ac.uk/jobs, searching under reference number P44302.

The closing date for completed applications is May 15 2013.

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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Meetings of Possible Interest

StarBench: A Workshop for the Benchmarking of Star Formation Codes8 - 11 April 2013 University of Exeter, UKhttp://www.astro.ex.ac.uk/people/haworth/workshop_bench/index.html

Transformational Science with ALMA: From Dust to Rocks to Planets - Formation and Evolution ofPlanetary Systems8 - 12 April 2013 Hilton Waikoloa Village, The Big Island of Hawaii, USAhttp://www.cv.nrao.edu/rocks/index.html

International Young Astronomer School on Exploiting the Herschel and Planck data15 - 19 April 2013 Meudon, Francehttp://ufe.obspm.fr/rubrique344.html

Habitable Worlds Across Time and Space29 April - 2 May 2013 Space Telescope Science Institute, Baltimore, USAhttp://www.stsci.edu/institute/conference/habitable-worlds

Ice and Planet Formation15 - 17 May 2013 Lund Observatory, Swedenhttp://www.astro.lu.se/~anders/IPF2013/

IAU Symposium 297: The Diffuse Interstellar Bands20 - 24 May 2013 Noordwijkerhout, The Netherlandshttp://iau297.nl/

Brown Dwarfs come of Age20 - 24 May 2013 Fuerteventura, Canary Islands, Spainhttp://bdofage.tng.iac.es/

The Origins of Stellar Clustering - from Fragmenting Clouds to the Build-up of Galaxies26 May 2013 - 16 June 2013 Aspen, Colorado, USAhttp://www.mpa-garching.mpg.de/~diederik/aspen2013

IAU Symposium 299: Exploring the Formation and Evolution of Planetary Systems2 - 7 June 2013 Victoria, BC, Canadahttp://www.iaus299.org

Massive Stars: From alpha to Omega10 - 14 June 2013 Rhodes, Greecehttp://a2omega.astro.noa.gr

Lin-Shu Symposium: Celebrating the 50th Anniversary of the Density-Wave Theory24 - 28 June 2013 Beijing, Chinahttp://events.asiaa.sinica.edu.tw/conference/20130624/

Physics at the Magnetospheric Boundary25 - 28 June 2013 Geneva, Switzerlandhttp://www.isdc.unige.ch/magbound/

Protostars and Planets VI15 - 20 July 2013 Heidelberg, Germanyhttp://www.ppvi.org

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Dust Growth in Star & Planet Formation 201322 - 25 July 2013 MPIA, Heidelberg, Germanyno web site yet

2013 Sagan Summer Workshop: Imaging Planets and Disks29 July - 2 August 2013 Pasadena, CA, USAhttp://nexsci.caltech.edu/workshop/2013/

IAUS 302 - Magnetic Fields Throughout Stellar Evolution26 - 30 August 2013 Biarritz, Francehttp://iaus302.sciencesconf.org

Meteoroids 2013. An International Conference on Minor Bodies in the Solar System26 - 30 August 2013 Dep. of Physics, A.M. University, Poznan, Polandhttp://www.astro.amu.edu.pl/Meteoroids2013/index.php

Exoplanets and Brown Dwarfs2 - 5 September 2013 de Havilland, University of Hertfordshire, Hatfield, Nr. London, UKno web site yet

400 Years of Stellar Rotation17 - 22 November 2013, Natal, Brazilhttp://www.dfte.ufrn.br/400rotation/

The Life Cycle of Dust in the Universe: Observations, Theory, and Laboratory Experiments18 - 22 November 2013 Taipei, Taiwanhttp://events.asiaa.sinica.edu.tw/meeting/20131118/

The 18th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun9 - 13 June 2014 Flagstaff, Arizona, USAhttp://www2.lowell.edu/workshops/coolstars18/

Living Together: Planets, Stellar Binaries and Stars with Planets8 - 12 September 2014 Litomysl Castle, Litomysl, Czech Republichttp://astro.physics.muni.cz/kopal2014/

Towards Other Earths II. The Star-Planet Connection15 - 19 September 2014 Portugalhttp://www.astro.up.pt/toe2014

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

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