a searchforw idecompanionstotheextrasolarplanetary...
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Subm itted to ApJ April24,2009
A Search for W ide C om panions to the Extrasolar Planetary
System H R 8799
Laird M .Closeand Jared R.M ales
Steward Observatory,University ofArizona,Tucson,AZ 85721
A B ST R A C T
The extrasolar planetary system around HR 8799 is the �rst m ultiplanet
system everim aged.Itisalso,by a wide m argin,the highestm asssystem with
> 27 Jupitersofplanetary m asspast25 AU.Thisisa rem arkable system with
no analogue with any other known planetary system . In the �rst part ofthis
paper we investigate the nature oftwo faint objects im aged near the system .
Theseobjectsareconsiderably fainter(H=20.4,and 21.6 m ag)and m oredistant
(projected separations of 612, and 534 AU) than the three known planetary
com panionsb,c,and d (68-24 AU).Itispossible thatthese two objectscould
be lower m ass planets (ofm ass � 5 and � 3 M Jup) that have been scattered
to widerorbits. W e m ake the �rstdirectcom parison ofnewly reduced archival
Gem iniadaptiveopticsim agestoarchivalHST/NICM OS im ages.W ith nearly a
decadebetween theseepochswecan accurately assesstheproperm otion nature
ofeach candidate com panion. W e �nd that both objects are unbound to HR
8799 and are background. W e estim ate that HR 8799 has no com panions of
H< 22 from � 5� 1500.Any scattered giantplanetsin the HR 8799 system are
> 600 AU or less than 3 M Jup in m ass. In the second part ofthis paper we
carry outa search forwidercom m on properm otion objects. W hile we identify
nobound com panionstoHR 8799,oursearch yields16objectswithin 1degreein
the NOM AD catalog and POSS DSS im ageswith sim ilar(�20 m as/yr)proper
m otionsto HR 8799,threeofwhich warrantfollow-up observations.
Subjectheadings:planetary system s,stars:individual:HR 8799
1. Introduction
Therehavebeen severalsurveystodirectly im ageextrasolarplanetsfortheground with
adaptiveoptics(AO)and from spacewith HST.Untilvery recently allsurveysreturned null
{ 2 {
results,and soitwasgenerally assum ed thatwide,m assive,extrasolarplanetswould berare
(atleastaround Sun-likestars)past20 AU (Lafreniereetal.2007a;Nielsen etal.2008 and
referenceswithin).However,in Novem ber2008 M aroisetal.2008 announced thediscovery
of3 planets orbiting the A5V star HR 8799,based on Near-IR im aging at the Keck and
Gem initelescopes.Using data from Keck in 2004-2008 and Gem iniin 2007-2008,they were
ableto establish com m on-properm otions(assum ing thenon-com m on m otion com ponentof
� 25 m as/yr forb and c was due to orbitalm otion ofthe planets around the star). The
three planets,HR 8799b,c,and d orbit at approxim ately 68,38 and 24 AU respectively.
M aroisetal.2008 estim ate e�ective tem peratures of870,1090,and 1090K for the three
planets,and arrive atestim atesform assof7,10,and 10 M Jup.These estim atesarebased
ontheestim ated 30-160M yrageofHR 8799andhybridtheoreticalcoolingtracks(lum inosity
vs.age)forgiantplanets(M aroisetal.2008).
Itispossible thatadditionalcom panionscould be discovered during a search atwider
separations.Thebinary fraction oflateA starsisatleast70% (Bateetal.2009).Recently,
(Verasetal.2009) have predicted a population ofgiant planets at large separations (100
AU -10,000AU)from starshosting relatively close-in planets,wherethedistantobjectsare
dynam ically scattered/pum ped to largeseparationsaftersystem assem bly.Such e�ectsm ay
explain theverywide,low m ass,com panionsGQ Lup b at> 100AU (Neuhauseretal.2005)
and/orAB Pic B at> 250 AU (Chauvin etal.2005). There is certainly the possible ex-
istence oflow m ass,reddened,stellar com panions that have not yet been detected. It is
even possiblethatHR 8799hasasm all,com m on-properm otion group,around it.Given the
uniquenatureoftheHR 8799system ,asearch forwide(> 100AU)com panionsisim portant
and m otivated thispaper.
2. O bservations & R eductions
On Oct. 30 1998 UT HST/NICM OS observed HR 8799 with its coronagraph,and 2
candidate com panionswere identi�ed (Lowranceetal.2005)in the rollsubtracted im ages.
Thesefaintpointsourceswherereported at13.700and 15.700(540AU and 619AU)with H m ag-
nitudesof21.6and 20.4,respectively.Thesearem uch wideseparationsthan the3con�rm ed
planetswhich werenotdiscovered in theNICM OS dataatthetim e(Lafreniereetal.2009).
Figure1 showsourown rollsubtraction oftheotherwisealready pipelinereduced NICM OS
datawith the2objectsidenti�ed.HR 8799’shigh galacticlatitude(b= �35o)indicatesthat
there isa �nite chance one (orboth)are notbackground objects(see Fig2). However,we
need todeterm ineifthesearerealcom m on properm otion com panionsorsim ply background
objects.Forlack ofa betternom enclaturewehaveelected to calltheclosestcandidate\HR
{ 3 {
8799B" and the fartherone \HR 8799C",however,the use ofthese labelsdoesnotim ply
they arephysicalcom panions.
In October25,2007(M aroisetal.2008)obtained 118x30sAngularDi�erentialIm aging
(ADI;(M aroisetal.2006)) dataset ofHR 8799 on the Gem ini-North telescope with the
AltairAO system and NIRINIR cam era.Typically an ADIdatasetwould notbetheideal
m ethod ofim aging faintcom panionsat13.700and 15.700sincetherewillbea risk ofrotational
blurring ofthe im ages in the azim uthaldirection. However,in this HR 8799 dataset the
integrationsof30swere shortenough thatonly m inim alazim uthalblurring occurred {and
only then in the fastest rotating im ages neartransit. Therefore,we were able to create a
new custom \ADI-like" IRAF pipeline to produce \W ide Field" ADIim ages (W iFiADI)
to im age faint com panions at the very edge of ADI datasets. Since the focus of W iFi
ADIiswide com panionsthere isno need to use m ore advanced ADIreductionslike LOCI
(Lafreniereetal.2007b).
OurW iFiADIpipelineisvery sim ilartostandard ADIreduction and runsin astandard
IRAF environm ent.In ADIthetelescoperotatorisdisabled and sothem edian oftheim ages
givesan estim ateofthem asterPSF without\contam ination" from realobjectson thesky.
Then one m ustsubtractthe m asterPSF o� each individualfram e aftera crosscorrelation
alignm entofeach fram easin Closeetal.2002.Oncethefram eshavethePSF rem oved they
need toberotated bytheparallacticangleand m edian com bined (thesubroutinetocalculate
the rotation angle isa custom scriptdeveloped forGem inidata in Closeetal.2003). One
way thattheW iFiADIpipelinedi�ersfrom thestandard isthatitisoptim ized to preserve
any faint o�-axis objects that m ight fallpast the edge ofthe IR array in the m ajority of
the individualADI fram es. For exam ple,the code accurately m asks m any bad pixels in
thecornersoftheNIRIarray and usesa �nalm edian com bineofall118 re-rotated (m aster
PSF subtracted)im ageswith no pixelclipping orrejection (so even thecornerpixelsofthe
individualfram esareutilized in the �nalW iFiim age).W e also carefully o�seteach im age
by the m ode ofthe outerregion ofeach im age,thisallowsthe �nalm edian com bine to be
m ostsensitive in theouterregionsoftheim age.
OurW iFiADIpipeline when used with theNIRIdetectorwith its0.0219"/pixelscale
isthen capable ofcreating a round W iFiADIFOV of31.7100in diam eterwhen there isat
least90 degreesof�eld rotation during the ADIobservation,and the objectiscentered in
the detector. In the case ofthe Oct. 25 2007 Gem iniHR 8799 data ofM aroisetal.2008
the above assum ptionsare alltrue and ourpipeline produced a �nalim age (see Fig.3)of
allH < 22 objectswithin � 5� 1500ofHR 8799.
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3. A nalysis
Asisclearfrom �gure1 and 3 therearetwo faintobjectsnearHR 8799.Based on de-
tailed search oftheliteratureand theVLT/Gem ini/Subaru/HST archiveswehaveconcluded
thattherehasnotbeen any published attem ptto recover\B" or\C" untilnow.HR 8799A
hasa totalproperm otion of119 m as/yearso therecovery ofthetwo candidatecom panions
atthesam eseparationsasin 1988wrtHR 8799A would bean unam biguouscon�rm ation of
theirphysicalassociation.Theseobjectsareboth fainterthan theHD8799b-d planets(they
would havem assesof3and 5M jup on the0.1Gyr(Bara�eetal.2002)COND tracks;which
predict reasonable lum inosities at these ages for higher m ass objects;Closeetal.2007b),
consistentwith being scattered by theheavier,close-in,planets.
In Figure 4 and 5 the 2007 positions ofthese two faint com panions are shown. In
both cases the current positions are m uch closer to the locations calculated for distant
background objectsratherthan physicalcom panions.Therefore,ourastrom etry provesthat
the NICM OS com panions ofLowranceetal.2005 appear to be faint background objects
unrelated to HR 8799A (seeTable1 fora detailed listofourastrom etricm easurem ents).
3.1. D oes H R 8799b Show any Parallax M otion ofa B ackground O bject?
In the direction ofPegasus m ostnearby stars appear to be m oving towards the East
South East.Thisisdueto theSun’sm otion in theoppositedirection wrttheLSR.In fact,
theSun’sspacem otion causesa stationary object(wrtLSR)at39.9 pcto havea m easured
properm otion of95.51 m as/yrto theEastand 38.51 m as/yrto theSouth {based on values
forthe Solarm otion given by Jaschek & Valbousquet1993. W hile itisclear thatplanets
HR 8799b and HR 8799chavesim ilarproperm otionson thesky to HR 8799A (seeleftside
ofFig.6),once we subtracttheSolarm otion there islessagreem ent(see rightside ofFig.
6).However,thislack ofcom m on properm otion can beexplained by increased velocity due
to orbitalm otion ofb and caround A (M aroisetal.2008).
FortheplanetHR 8799b (which hasthelargesttim elineofobservations),thereappears
to besom e\scatter" in itsm easured position from A from thenearly straightlineexpected
forb’slong period orbit. The exactsolution fora stable orbitofthe m assive planetsb,c,
and d isstillsom ewhatuncertain (Fabrycky & M urray-Clay 2008).
In Fig.7 weconsiderthequestion whatwould this\scatter" resem bleifb wasactually
a background objectat100 pc thathad sim ilar properm otions,by chance,to HR 8799A
(ata distance of100 pcHR 8799b would roughly havethenorm allum inosity and colorsof
a background L dwarf). In thism odelb’sposition should show a \reverse" parallax w.r.t.
{ 5 {
HR 8799A with an am plitude of60% thatofHR 8799A’sparallax. W e calculate parallax
ofHR8799 in theusualm anner(Biller& Close2007)and then m ultiply by -0.6 to calculate
\reverse" parallax.
In Fig. 7 we show two m odels for the nature ofHR 8799b m otion: a background
objectat100 pc;and a sim ple \linear" planetary arc.The sm alltrianglesin Fig.7 denote
tim e stam ps in the 100 pc m odelto each observation date over the 9.885 yr period since
the detection ofb in a LOCI analysis ofthe NICM OS dataset by Lafreniereetal.2009.
W e note how neither the slightly curving \linear" orbit or the 100 pc background m odel
�t alldata points sim ultaneously inside the 1� errorbars. The \linear" orbit is a sim pler
m odelwith a better �t,but it certainly is not perfect since the reduced of�2� � 2 gives
an � 8% chance that it is the correct m odel{assum ing no unknown system atic errors in
the astrom etry. On the otherhand,a background source at100 pc m odelcan be rejected
with 99.95% con�dence(�2� � 4:4).W hilethereisstillsigni�cantscatterin thelinearorbit
�t for b,we cannot reject it (we also do not,at this tim e,know what orbit to �t it to
(Fabrycky & M urray-Clay 2008)). However,we can rejectthe hypothesis thatthisscatter
in HR 8799b’s position is reverse parallax due to it being a background object at 100pc
(assum ing,ofcourse,thereported astrom etricvaluesand errorsarecorrect).
3.2. A Search For O ther C om m on Proper M otion C om panions to H R 8799
Even though the\B"and \C"objectsareclearlybackground,thereexiststhepossibility
ofotherwidercom panionstoHR 8799A thatm ightbefound by searchingnearby forsim ilar
proper m otion. W e searched 12875 objects within �1o ofHR 8799 in the the US Naval
Observatory M erged Astrom etric Dataset (NOM AD) catalog (Zachariasetal.2004) with
non-zero proper m otions. See Figure 8 for a plot ofthe resulting proper m otion vectors.
M ost objects inside 1o ofHR 8799 are background and so do not have as large a proper
m otion asHR 8799,which isdom inated by theSun’sm otion w.r.ttheLSR.In Figure8 we
havehighlighted thoseobjectswhich haveproperm otion vectorswithin a circleofradius20
m as/yraround HR8799’sproperm otion.Thisyieldsa listof15 objects,two ofwhich m ay
warrantfollow up observations.W efurtherdiscusstheseobjectsbelow.
To increase oursensitivity to fainterobjectsthatm ighthave been m issed by previous
surveyswem anuallyexam ined thePalom arOpticalSkySurvey(POSS)POSS1(1951August
12 08:12:00 UT)and POSS2 (1991 October02 05:47:00 UT)Red DSS im agesto search for
objectswithin 1squaredegreeofHR 8799A with sim ilarproperm otions.ThePOSS1 im age
hasa platescaleof1:700perpixel,whereasPOSS2 has1:000perpixel.W e�rstm agni�ed the
POSS1 im ageto m atch thePOSS2 platescale.Next25background starswereselected,and
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theirpositionsm easured by centroiding in each im age. W e then com pared theirpositions
on the two im ages to determ ine the optim um rotation (� 0:7 degrees) to apply to the
POSS1 im age. W e then selected an additional25 background starsfora totalof50 stars
spread acrosstheim agesto build a background reference fram e.Properm otionswerethen
m easured forindividualstarsby determ ining the average relative change in o�setfrom the
50 background starsbetween the2 im ages
A di�erent sam ple of30 background stars was selected to test our technique. These
were each com pared to the 50 reference starsin each fram e,and theirproperm otionswere
calculated from the average change in o�setfrom the reference stars. The overallaverage
ofthesem easurem entswas�R A = 0:81� 3:50 m as/yrand �D E C = 4:92� 3:04 m as/yr.W e
subtracttheseo�setsfrom theproperm otion m easurem entsm adeforindividualstars.
Forbrightstarsthere isa �0:3 pixeluncertainty in centroid position (estim ated from
FW H M =p
SN R),and forthefaintestobjectsthatweconsidered a�0:95pixeluncertainty.
Given the 40.139 yearbaseline between thetwo positionsthisam ountsto �10:6 m as/yrof
properm otion uncertainty forbrightstars,and �33:5 m as/yrforfaintobjects.W ecom bine
these in quadrature with the standard error ofour reference stars estim ated from the 30
teststarsabove to obtain an estim ated uncertainty of� �11 m as/yrand � �34 m as/yr.
Thebrightstarcasecom paresfavorably with otherPOSS based properm otion surveys,e.g.
Lepine& Shara 2005 with � �8 m as/yr.
The1o X 1o areaofsky centered on HR8799wassearched m anually by blinkingbetween
the registered POSS1 and POSS2 im ages. In order to com pensate for subtle changes in
m agni�cation and �eld distortion,theim agewasre-centered on convenientbackground stars
in each sm allarea being searched. W hen a proper m otion candidate was identi�ed, its
position wasm easured by centroiding and then itsaverage change in o�setrelative to the
50 referencebackground starswascalculated.
Asa check on ourm easurem ents,wecom pared ourm easurem entsofproperm otion for
2 brighthigh properm otion starsin the �eld,NLTT 55870 and NLTT 55853,with POSS
based proper m otion m easurem ents (Lepine& Shara 2005). W e m easured (�R A;�D E C ) =
(184.7,-43.5)and (178.2,-61.4)respectively com pared to thevaluesof(185,-44)and (164,
-63)reported by Lepine& Shara 2005.These m easurem entsareconsistentwith each other
within ourbrightstaruncertainty of� �11 m as/yr.
W enotethatwearecom paring m easurem entsofproperm otion relativeto a sam pleof
background stars,which isnotthetrueabsoluteproperm otion.Lepine& Shara 2005discuss
thissystem atic e�ectand attribute itto bulk m otion ofthe reference stars. Taking NLTT
55870 and NLTT 55853 asan exam ple,they apply correction o�setsof��R A = +4 m as/yr
{ 7 {
and ��D E C = �7m as/yrtodeterm inetheabsolutem otion.W ehavenotdeterm ined o�sets
forourown sam pleofreferencestars,butgiven theagreem entofourrelativem easurem ents
with Lepine& Shara 2005 we apply the sam e o�sets. The only de�nitive way to overcom e
thissystem atice�ectforourpurposeswould betosim ultaneouslym easuretheproperm otion
ofHR 8799 itself(which hasaccurate Hipparcosm otions),howeveritisbadly saturated in
the POSS im ages rendering m easurem ents ofits position uncertain to severalpixels. W e
attem pted to m easuretheproperm otion ofHR 8799 by determ ining best�tintersection of
thehorizontalandverticaldi�ractionspikes,obtainingaveryuncertainestim ate(�R A;�D E C )
= (110,-43). This is close to the Hipparcos value ofHR 8799’s m otion: (�R A;�D E C ) =
(107:88� 0:75,�50:08� 0:64)m as/yr(Perrym an etal.1997).
Though we did identify severalfaint candidate objects on the POSS im ages with no
obvious counterparts in NOM AD,only one appears worthy offurther investigation with
respect to the goals ofthis paper. This object is ata separation of4.60 from HR 8799A,
with properm otionsof(�R A;�D E C )= (105� 34;�6� 34).Itisavery faintobject,detected
in the POSS im ageswith SN R � 10. In the Sloan DigitalSky Survey (SDSS)database it
isdesignated J230716.69+210509.1.Through theSDSS we also located itin theUSNO-B1
catalog (M onetetal.2003). In USNO-B1 it is not given a proper m otion m easurem ent.
Itquite clearly m ovesbetween POSS im agesrelative to nearby background stars,and itis
closeto NLTT 55870 (discussed above),which givescon�dencethatourdetection ofm otion
isnotdue to a localdata reduction artifact. It’s�D E C is1:3� from the expected value of
a com m on properm otion com panion ofHR 8799A,howeveritsproxim ity warrantsfurther
attention.W ediscussthisobjectin m oredetailbelow in section 4.1.
4. D iscussion
Thelargem assofthethreeplanetscom bined im pliesa very largeinitialstellarnebula,
andtheirlargeorbitalradiipresentchallengesforboththecoreaccretion(Fortney etal.2008)
and thegravitationalinstability theoriesofplanetform ation (Boss1997).Thissystem could
perhaps be our best evidence for a new \non-core-accretion" m ode ofplanet form ation {
hence the detection ofany additionalcom panions (planetary or higher in m ass) is very
im portant.
The observations ofM arois et al. raise severalinteresting questions. The photom -
etry shows a conspicuous lack of absorption by M ethane redwards of 1.6 �m , which is
expected for such relatively cool(Teff � 870 K) objects like HR 8799b {by allthe \hot-
start" (Bara�eetal.2002; Burrowsetal.2003) or \core-accretion" (Fortney etal.2008)
synthetic spectra m odels. Having perform ed photom etry atseveralbands,they attem pted
{ 8 {
to�tspectralenergydistributions(SEDs)generated byahybrid atm osphericm odelingcode.
Thebest�tSEDsproduced e�ectivetem peraturesover1400K ((M aroisetal.2008)on-line
supplem ent). The authorsargue thatsuch high tem peraturescannotbe supported by the
observed low lum inositiesunlessthe objectsare unreasonably sm alloreach hassigni�cant
dustextinction and reddening.They claim 3edge-on dustdisks{which would bem isaligned
with the plane oftheirorbits(which isnearly face-on){ could explain such reddening,and
so they rejected thisdustreddening idea.
W e �nd thatHR 8799 appearsto be reddened by no m ore than AH � 0:3 m ag (from
2M ASS colorsin (M aroisetal.2008)com pared to a ZAM S A5),m aking itim possiblethat
line ofsight extinction to HR 8799A alone is the cause. However,the lack ofa \reverse"
parallax in theastrom etricresidualsofb’sseparation from A (seeFig.7)o�ersstrong proof
that HR8799b is a physicalcom panion ofA.Hence,it is unclear why HR8799b appears
underlum inousforitsbest�tm odeltem peratures. Perhapsstrongly non-LTE e�ectssup-
pressCH 4 in theouteratm osphere(M aroisetal.2008).In any case,thediscovery ofother
wide reddened (or underlum inous) com panions would be very interesting in this system .
Thereforeweneed to investigate thepropertiesofeach properm otion candidate.
4.1. IndividualO bjects w ith Sim ilar Proper M otion to H R 8799
TheNOM AD databasecontains15objectswith sim ilar(�20m as/yr)properm otion to
HR 8799A.NOM AD # 1115-0634383(seeTable2)hasawide480separation from HR 8799A.
Itisred,with V = 16.64 and B-V colorof1.61 from the NOM AD m agnitudes. NOM AD
# 1108-0634609 isa Tycho 2 star,TYC 1717-1120-1. Itisnoteworthy due to itsrelatively
bright V = 10.62. Though very likely not gravitationally bound to HR 8799A (since at
projected separations > 1x105 AU from HR 8799A they would be wider than the widest
known binaries (Closeetal.1990;Closeetal.2007a)),these objects m ay warrant further
study to determ ine ifthey are co-m oving with the HR 8799 system . The otherobjects in
Table 2 appearto be a com bination oftoo faintand too widely separated to warrantsuch
speculation.
Our 1 square degree m anualsearch ofthe POSS im ages around HR8799 discovered
one nearby object within 1:3� ofHR8799. W e willbrie y discus this \com m on proper
m otion" candidate(SDSS J230716.69+210509.1)noted in Table3.W econverted theSDSS
photom etry using the relationsgiven by Jordietal.2006,obtaining V = 20:83� 0:12 m ag
and B � V = 1:78� 0:10 m ag.Itisnotin the2M ASS pointsource catalog,howeverthere
are� 4� detectionsjustabovethenon-Gaussian noisein theJ and Ks2M ASS im ages.
{ 9 {
Though our m easurem ent ofits proper m otion is m arginally sim ilar to HR 8799,it
appearstobetoofaint/bluetohaveaphysicalassociation {basedonitscolorsandm agnitude
itm ay bem oredistantthan 39.9 pc.W eby no m eansclaim thatthisisde�nitive,ascolor
based parallaxesare very uncertain. Due to itsrelative proxim ity to HR8799 and the high
interestin thissystem ,furthere�ortto con�rm ourproperm otion m easurem ent,obtain IR
photom etry,and perhapsobtain a radialvelocity iswarranted.
In sum m ary,a cursory inspection ofthe properm otionsand available photom etry for
theseobjectsyieldsnostrongcandidatesforaboundstellarcom paniontoHR 8799.Nonethe-
less,given the im portance ofthe HR 8799 system and the m any astrophysicalpuzzles it
presents,atleastthese3 objectswarrantfurtherscrutiny.
Thereisstillaneed forfuturework in thesearch forwidecom panionstoHR 8799.Due
tothebrightnessofHR 8799onsurveyim agesthereexistsanannulusfrom � 1500< r<� 6000
which has not been adequately explored in this paper for stellar com panions {let alone
planetary m assobjects.Thediscovery ofany such objectsin thisannuluscould providenew
insightsinto theplanetary com panionsofHR 8799.
5. C onclusions
W ehavem adethe�rstdirectcom parison ofnewly W iFiADIreduced archivalGem ini
AO im agesto archivalHST/NICM OS coronagraphic im ages. W ith 9 years between these
epochs we can accurately assess the proper m otion nature ofeach com panion. W e �nd
thatboth objects are unbound to HR 8799 and are background. In this paperourm ajor
conclusionsare:
1.W eestim atethatno bound com panionsofH< 22 m ag existfrom � 5� 1500from HR
8799A.
2.Any unseen scattered giantextrasolarplanetsin theHR 8799 system are> 600 AU
and/orlessthan � 3M Jup in m ass.
3. The residuals in the currentpublished astrom etry ofHR 8799b’sorbitare notex-
plained by forcing HR 8799b to bea background objectat> 100 pc.
4.W hileweidentify no clearly bound com panionsto HR 8799A in ourim ages(beyond
theextrasolarplanetHR 8799b),oursearch yields16 objectswithin 1 degreein theUSNO
catalog orPOSS plateswith sim ilar(�20 m as/yr)properm otionsto HR 8799A.Three of
which m eritfollow-up observations.
{ 10 {
Theauthorswould liketothankGlenn SchneiderforhelpfuldiscussionsaboutNICM OS
coronagraphic data and Andy Skem er for helpfuldiscussions about the LSR.This paper
utilized data from the HST and Gem iniarchives. This paper extensively used IRAF,the
DSS,2M ASS,SDSS and Sim bad databases.LM C issupported by an NSF CAREER award
and JRM issupported by the2008 Steward Observatory GraduateFellowship.
Facilities:Gem m ini,HST (NICM OS).
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{ 11 {
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{ 12 {
Fig. 1.| Rollsubtracted NICM OS F160W im age from 1998, showing the 2 candidate
com panions\C"(totheleft)and \B"(totheright)�rstidenti�ed by (Lowranceetal.2005)
{ each iscircled in white.Each wasvisible in only one roll.The red circle around the star
showsthe 1.700radiusofHR 8799b. The NE com passiscorrectforthe positive im age (HD
8799B),however for HR 8799C (negative im age) the com pass should be rotated by 30o
counterclockwise
{ 13 {
Fig. 2.| Histogram ofthe H > 20 point source detections m ade by the HST/NICM OS
survey (Lowranceetal.2005) and Gem iniDeep Planet Survey (Lafreniereetal.2007a),
com bined,binned by galactic latitude. These results dem onstrate the low density ofsuch
background objectsaway from thegalacticplane.W enotethatHR 8799’s\overdensity" of
such com panionshintsthattherem ightbeaco-m oving group (oratleastarealcom panion)
around HR 8799. The insetshowsthe totalnum berofstarsobserved in each latitude bin
by thetwo surveys.
{ 14 {
Fig. 3.| Our W iFiADI reduction ofthe Oct 25,2007 Gem iniAltair/NIRI dataset of
(M aroisetal.2008). Note the locations oftwo very faint \B" (PA = 13o;Sep=13.7800)
and \C" (PA = 115o;Sep=14.8600)sources. North is up East to the left. Also there isa
detection oftheplanetHR 8799b which islocated nearitsnom inalposition reported in Keck
AO im ages(M aroisetal.2008).Forclarity we have inserted a zoom ed in box centered on
HR 8799b,the otherplanets(c & d)were too close and faintto be clearly detected in this
W iFiADIreduction.
{ 15 {
Fig.4.| A 1.5x1.200section ofourreduced W iFiim ageoftheGem ini2007 Oct25 dataset.
NotethattheH=21.6 object\B" detected by HST/NICM OS isclearly notcom m on proper
m otion with HR 8799A.The size ofthe errorcircles is dom inated by 0.5% platescale un-
certaintiesacrossthe�eld.North up Eastleft,0:0219� 0:000100/pix.Theobjectisslightly
elongated due to the signi�cant �eld rotation 14.1500o� axis during these exposures near
transit.
{ 16 {
Fig. 5.| Sam e as�g4 butforthe H=20.4 object \C".Aswith \B" the \C" object also
appearsto bebackground aswell.Notethatthebrightsm allpixels\clum ps" arebad pixels
atthevery edgeofthearray,thereisonly onerealobjectin theim age(noted by thearrow).
{ 17 {
Fig. 6.| Left: The properm otions ofHR 8799A,and extrasolar planets candidates HR
8799b and HR 8799cplotted overa 6.14 yrperiod {norm alized to a com m on starting point
in 2002ofthe(Fukagawa etal.2009)observation.R ight:Sam eastotheLeftbuttheSolar
re ex m otion of95.51m as/yrin RA and -38.51m as/yrDEC atthe position ofHR 8799A
(d=39.9pc)hasbeen rem oved. Hence,thisisa plotofthe true m otionsofHR 8799A,and
extrasolarplanetscandidatesHR 8799b and HR 8799c(allwrttheLSR).Itisinteresting to
notethatHR 8799A,b,and cappeartohaveclearly di�erentproperm otionsoncetheSolar
m otion issubtracted.Thesedi�erencesin m otion arem ostlikely dueto orbitalm otion ofb
and caround A (M aroisetal.2008).
{ 18 {
Fig. 7.| Here we plot 1� errors often years ofHR 8799b relative astrom etry ofb wrt
A from Fukagawa etal.2009 (Subaru AO;largesterrors),Lafreniereetal.2009 (NICM OS;
Oct30 1998 top data point),and therestofthedata pointsfrom M aroisetal.2008 (Keck
AO).Thedotted linetracesthe\reverse" parallax thatshould beobserved ifHR 8799b isa
background objectat100 pc with a sim ilarproperm otion to A.The trianglesdenote tim e
stam ps to each observation date over the 9.885 yr period since the NICM OS observation.
Note how neithera slightly curving \linear" orbitorthe 100 pc background objectm odel
�tsalldata pointssim ultaneously inside the 1� errorbars. However,the �tforthe 100 pc
m odelisquite poor,hence,we can rejectthe hypothesisthatthis\scatter" in HR 8799b’s
position wrtHR 8799A isdueto thereverseparallax ofa background objectat100 pc.W e
do notplotournew Gem iniOct17,2007 position forb sincethereareunknown system atic
errors in the data atthe �44 m as level,hence little statisticalweight would be added by
such a data point.
{ 19 {
Fig.8.| Properm otionsof12875 objectswithin 2 squaredegreescentered on HR 8799A.
The NOM AD database was searched to recover allobjects in this �eld with proper m o-
tion m easurem ents. Diam ondshighlightthe 15 objectswith properm otion vectorswithin
�20m as/yrofHR 8799’svector(seeTable2).W ealsoblinked thePOSS1(1951)and POSS2
(1991)red im agesto search forstarswith properm otions,yielding 1 interesting object(tri-
angle)with no properm otion m easurem entin NOM AD (seeTable3).Theerrorbarsshow
our�34 m as/yruncertainty forthatonePOSS objectsom e28000from HR 8799A.
{ 20 {
Table1:RelativeAstrom etry ofthe1400Com panionsw.r.t.HR 8799A
Com p. Epoch H �RA �D E C Sep. P.A. ref.
nam e (UT) m ag (arcsec) (arcsec) (arcsec) (deg)
\B" Oct.30,1998 21.6 3:756� 0:09 13:19� 0:09 13:71� 0:08a 15:9� 0:1 low05b
\B" Oct.25,2007 NA 3:24� 0:02 13:78� 0:07 14:15� 0:07 13:24� 0:07 newc
\C" Oct.30,1998 20.4 14:29� 0:09 �6:45� 0:09 15:68� 0:08a 114:3� 0:1 low05b
\C" Oct.25,2007 NA 13:42� 0:07 �6:40� 0:03 14:86� 0:07 115:5� 0:1 newc
aThe HR 8799A to B (or C) separation is as given by (Lowranceetal.2005),the errors are as given by
(Lowranceetal.2005).
bdata from (Lowranceetal.2005).
cdata from ourW iFiADIreduction,astrom etricerrorsdom inated by 0.5% platescaleerrorsacrossthe �eld.
{ 21 {
Table 2:NOM AD Objectswithin �1o W ith Sim ilar(�20 m as/yr)ProperM otionsto HR
8799
NOM AD ID SEP �R A �D E C B V R
(0) m as/yr m as/yr m ag m ag m ag
1113-0634282 33.4 112.0 -64.0 20.41 ... 19.61
1104-0645427 42.8 106.0 -52.5 18.35 17.97 ...
1115-0633369 43.0 120.0 -46.0 21.53 ... 19.50
1111-0630350 43.4 124.0 -58.0 19.87 ... 19.76
1104-0645407 43.9 90.0 -56.0 22.00 ... ...
1107-0632334 44.6 104.0 -34.0 18.25 17.62 16.87
1104-0645709 45.2 116.0 -54.0 21.46 ... 20.25
1115-0634383a 48.4 108.0 -60.0 18.25 16.64 15.91
1118-0648887 48.7 96.0 -50.0 21.01 ... 19.93
1119-0648440 53.7 94.0 -50.0 17.94 ... 19.71
1117-0654704 55.2 120.0 -54.0 21.81 ... 20.13
1114-0630617 56.5 96.0 -52.0 20.95 ... 20.09
1111-0631888 57.9 96.0 -50.0 21.12 ... 19.37
1103-0652623 58.9 108.0 -50.0 20.92 ... 19.86
1108-0634609a b 59.2 124.4 -51.4 11.61 10.62 10.02
Note.| Table2:V and R m agnitudesarenotalwaysgiven in NO M AD.Theproperm otion ofHR 8799
is107.88 and -50.08 m as/yr.
aW e discussthisobjectin section 4.1.
bAlso known asTYC 1717-1120-1.
{ 22 {
Table3:FaintObject28000from A with Sim ilarProperM otionsFrom POSS
SDSS # SEP �R A �D E C V B-V
(0) m as/yr m as/yr m ag m ag
J230716.69+210509.1a 4.6 105�34 m as/yr -6�34 m as/yr 20:83� 0:12 1:78� 0:10
Note. | Table 3: Proper m otion vector as m easured from PO SS plates in this work. V m agnitude,
B-V color, and associated uncertainties were derived from the SDSS photom etry using the form ulas of
Jordietal.2006.The properm otion ofHR 8799 is107.88 and -50.08 m as/yr.
aAlso known asUSNO -B1 1110-0590705.
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