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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

{ 6 {

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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Thispreprintwasprepared with the AAS LATEX m acrosv5.2.

{ 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.