DRAFT VERSION JULY 10, 2012 Preprint typeset uaing JllIEX style emulateapj v. 5/2/ll

DIRECT DETECTION AND ORBIT ANALYSIS OF THE EXOPLANETS HR 8799 bed FROM ARCmVAL 2005 KECK/NIRC2 DATA 1 2 3 THAYNE CURRIE , MlSATO FuKAGAWA , CHRISTIAN THALMANN , SOKO· MATSUMURA

Dmft uer6ion Jul" 101 2012 ABSTRACT We present previously unpublished July 2005 H-band coronagraphic data of the young, planet­ hostmg star HR 8799 from the newly-released Keck/NIRC2 archive. Despite poor observing condi­ tions, we detect three of the planets (HR 8799 bed), two of them (HR 8799 bc) without advanced image processing. Comparing these data with previously published 1998-2011 astrometry and that from rI>-reduced October 2010 Keck data constrains the orbits of the planets. Analyzing the planets' astrom~t'?' ",;parately! HR 8799 d'~ orbit is likely hlclined ~t leaat 25° from face-on and the others may be on In Inclined orbIts. For SemlIDaJor BXlS ratios conSIstent Wlth a 4:2:1 mean-motion resonance our analysis yields precise values for HR 8799 bcd's orbital parameters and strictly constrains th~ planets' eccentricities to be less than 0.18-1).3. However, we find no acceptable orbital801utions with this resonance that place the planets in face-on orbits; HR 8799 d shows the largest deviation from such orbits. Moreover, few orbits make HR 8799 d coplanar with b and c, whereas dynamical stability analyses used to constrain the planets' masses typically assume coplanar and/or fare.on orbits. This paper illustrates the significant science gain enabled with the release of the NmC2 archive. Subject headings: planetary systems, stars: early-type, stars: individual: HR 8799

1. INTRODUCTION Currie et a1. 2011a, see also Fabrycky and Murray­ The nearby, young A-type star HR 8799 (d = 39.4 Clay 2010). However, Soummer et al. (2011) show that circular I fa.ce-Qn, and coplanar orbits are incon­ pc, Rj 30 Myr; Zuckerman et a1. 2011) harbors the first independently confirmed, directly imaged exoplan­ sistent with 1998 HST astrometry, identifying a best­ etary system and the only imaged multi-planet system fit orbit for HR 8799 d of i = 28° and e = 0.115. (Marois et a1. 2008). After the discovery of HR 8799 Generally, more eccentric orbits destabiliie the system. The system stability depends on the (mutual) indin... bcd (T"oj '" 24, 38, and 68 AU) reported in Novem­ ber 2008 (Marois et a1. 2008), other studies identified at tions of the planets (Fabrycky and Murray-Clay 2010; least one of these planets ·in archival data taken prior Sudol and Haghighipour 2012). Thus, the HR 8799 plan­ to 2008 (Lafreniere et al. 2009; Fukagawa et al. 2009; ets' true mass limits derived from dynarrrical stability Metchevet al. 2009; Soummer et a1. 2011). arguments may slightly differ from those previously re­ HR 8799 planet astrometry derived from both pre ported. and post-discovery images can help constrain .the sys­ Well-sampled HR 8799 d astrometry could help clarify tem', dynamical stability and, in turn, the planets' phys­ whet~er HR 8799 d's orbit must be inclined, eccentric, ical properties. At least two of the HR 8799 plan­ and/or coplanar with the other planets. However until ets are likely locked in a mean motion resonance, oth­ now there is a ~ 9-year gap between the 1998 HST detec­ erwise the system would quickly become dynamically tion and the next one (2007; Metchev et a1. 2009). New unstable (Fabrycky and Murray-Clay 2010). The re­ astrometry for HR 8799 bee in between 1998 and 2007 cently discovered fourth companion at ~ 15 AU, HR could also help constrain· those planets' orbits. By bet­ 8799 e, generally makes dynamical stability less likely ter determining the HR 8799 planets' orbital properties, (Marois et al. 201Oa; Currie et al. 2011a), favoring lower we can more conclusively investigate system dynamical mas....--es of Mb,cde < 7, 10 MJI an important constraint stability and thus better clarify the range of allowable given the uncertainties in deriving masses frotp. planet planet masses. coolmg and atmosphere models (Spiegel and Burrows In this Letter, we report the detection of HR 8799 bed 2012: Madhusudhan et a1. 2011). from unpublished, now-public Keck/NIRC2 data taken Studies focused on fitting the planets' orbits and/or in 2005 supplemented with a re-reduction of published testing dynamical stability typically assume that the October 2010 data from Marois et aI. (2010a). We use planets are a) in resonance (4:2:1 for HR 8799 bed these data to better constrain the orbital properties of or 2:1 for HR 8799 cd), b) in circular, face-on orbits, HR 8799 bcd. c) and/or in coplanar orbits (e.g. Marois et al. 2010a; 2. OBSERVATIONS AND DATA REDUCTION

1 NASA-Goddard Space Flight Center 2.1. July 2005 Data 20SW University We downloaded HR 8799 data taken on July 15, 3 Astronomical Institute Anton Pa.nne~oek, University of Am­ swdam 2005 from the newly-available Keck/NffiC2 data archive 4 Department of Astronomy, University of Maryland-College (Program ID H53BN2, P.I. Michael Liu). The data Pari< were taken in H band with the narroW camera (9.952 6 NExScl, California Institute of 'Thchnology mas/pixel; Yelda et a1. 2010) with the ~'6 diameter cora- 2 nagraphic spot and the uincirclell pupil plane mask. lffi final image". 8799 was observed in lOs exposures in "vertical angle" Figure 1 (right panel) shows our final image displaying or angular differential imaging mode (Marois et al. 2006) hi~her signal-to-noise detections of HR 8799 b (SNR - through transit (Hour Angle = [-0.20,0.55]) with a total 38) and c (SNR - 18) and new detection of d (SNR - 5), field rotation of 147.1'. During these observations, the using algorithm parameters of 6 2: 0.74, NA = 245, g = seeing condition.s fluctuated and the observers periodi­ 0.95 ; dT = 6, and Teorr ~ 0.315, though similar settings cally recentered the star behind the mask, changing the yield nearly identical results (i.e. 6 .2: 0.73-0.8, r.",.,. 2: intensity profile of the stellar halo (and thus the quasi­ 0.31-0.36). We achieve contrast galna of up to - 80% static speckle pattern). During a few frames ·near transit (for HR 8799 d) over our best LOCI reduction. the star did not properly center at all behind the coron­ For flux calibration, we perform aperture photome­ agraph. We identify '" 11 minutes of science-grade data. tryon HR 8799 bed and on the nearby star GJ 616.2 Basic image processing followed standard steps previ­ observed just prior to HR 8799. We use fake point ously used to process NIRC2 data (Currie et al. 2012). sources to further correct for LOCI-based photometric For a first-order reduction) we perform a simple uclas­ biases (i.e. LafrerJere et al. 2007; Currie et al. 2011a,b) sical" ADI-based PSF subtraction (e.g. Marois et al. and find m(H) = 18.05 ± 0.09 mag for HR 8799 b, m(H) 2006). Figure 1 shows this reduction, clearly reveal­ = 17.06 ± 0.13 for HR 8799 c, and m(H) = 16.71 ± 0.24 ing HR 8799 b (SNR - 12) and identifying HR 8799 for HR 8799 d. The magnitude differences between HR c, albeit at low SNR (- 4). With the LOCI approach 8799 c and d appear slightly discrepant compared to bet­ (Lafreniere et al. 2007) as implemented and modified in ter calibrated NIRC2 measurements from Marois et al. pre,1ous work (Currie et al. 2010, 2011a,b), we easily de­ (2008), although the individual measurements are con­ tect HR 8799 band c and obtain a marginal detection of sistent to within ~ 1

2008; Metchev et a1. 2009; Galicher et al .. 2011, this the observed planet position within the orbit (i.e., the work), VLT/ 2009 (Currie et a1. 2011a), and LBT/Pisces anomaly)8. The most likely orbit is then the one orbit (Es;>osito et al: 2012). Fbr the Pisces data, we in­ that maximizes the measure of likelihood," C(nMLO ) = cluce the substantial north position angle uncertainty. InaXn 'c(n). BecaUSe of the highly skewed distribution of We furthermore modify the Keck/ NIRC2 astrometry re­ some parameters from the best-fit orbits, in particular ported in Marois et al. (2008) and Metchev et al. (2009) log a, the MLO parameters can differ significantly from to reflect the updated NIRC2 astrometric calibration the weighted median parameters. (Yelda et a1. 2010) accuracy, rescaling the position by a factor of 9.952/9.963, and putting in a PAno,'h,n.w­ 3.2. Result. PAnorth,old = 0.13° clockwise rota.tion. Table 1 summa.rizes our results, a.cd Figure 2 displays Th separately determine the range of allowable HR the orbits in a/i/e space (left), the histogram distribu­ 8799 bcd orbits, we follow our previously-adopted tion of i (middle) , and the histogram distribution of tbe Moote Carlo-based approach (Thalmann et at 2009; longitude of the ascending node, 0 (right). The top pan­ Currie et a1. 2OHb), comparing the HR 8799 planet as­ eIs display properties for HR 8799 b, tbe middle for HR "trometry to predictions from ra.ndomly-selected orbits. 8799 c, and the bottom for HR 8799 d. Assuming a X' In e first set of "conservative" simulations, we con­ cutoff of X~i9 + 1, the observations well constrain the sider the orbits separately. Dynamical stability analy­ HR 8799 d oroit - a ~ 24-32 AU, i ~ 32-42°, e ~ 0.03-- sis mggests that HR 8799 bed are likely in resonance 0.23, and n ~ 43-63°. They limit t he HR 8.799 c's most (Fabrycky and Murray-Clay 2010); the 4:2:1 resonance plausible orbital parameters to a ~ 36-42 AU, i ~ 13-- is particularly adept at stabilizing the system. To focus 26°, and e ~ 0.03-0.13. A8 expected, the parameters for on dynamically stable orbits we then select the subset of HR 8799 b are the most poorly oonstrained, showing the best-fitting orbits that preclude the planets from cross­ widest dispersion and the largest differences between the ing,orbits and are consistent with a. 4:2:1 resonance. Here median parameter value and that from the MLO. we define !(resonance" broadly, including orbits with ra­ Our analysis clearly disfavors face-on orbits for all tios of periods between 1.9 and 2.1 for consecutive pairs three planets, especially for HR 8799 c and d. Addition­ of planets since, at least in some circumstances, exact a!ly, the inclination distributions for HR 8799 be appear period ratios may be rare (e.g. Fabrycky et al. 2012) 7. systematically skewed towards values lower than those 2 Fbr all our sim.ulations, the minimum X for the bJ for d. Formally, though, the set of a.cceptab!y-fitting or­ c, and d planets are 20.8, 13.8, and 14.8, for reduced bits HR 8799 bed include some that make the planets X~ ,alues of 1.04, 0.86, and 1.24. Following Currie et a1. copla!lar. (2011b), we choose a cutoff of X2 $ X~in + 1 to represent Assuming a 4:2:1 mean-motion resonance oonfigurar the family of best-fitting orbits. Formally, this cutoff tion, we place far stronger limits on nearly all of the HR admits only an average additional deviation per ea.ch x 8799 bed orbital properties (Figure 3). This assumption or y measurement of '" 1/2Nob. (i.e. '" 1/20 for HR 8799 explicitly rules out e > 0.18 for HR 8799 be and e > 0.3 b; '" 1/14 for HR 8799 d) beyond the best-fit models for HR 8799 d. Likewise, we identify a very narrow range which themselves imply typical deviations of '" 1-(7 per of planet semimajor axes: a = 67.5- 70.8 AU, 42.1-44.4 each x or y measurement (since the minimum reduced AU, and 26.4--28.1 AU for HR 8799 b, c, and d. The 68% X~ values are R:: 1). However, we obtain nearly identical confidence interval in 0 for HR 8799 d further narrows results for more relaxed cutoffs (see below) . From the set to 46°-62°. of models passing our X2 cutoff, including the subset in For this oonfiguration, HR 8799 d (c) must be in an reso:lance, we determine the weighted median value and orbit viewed more than 25° (15°) from face-on while HR tbe weighted 68% confidence interval about tbe median 8799 b is likely inclined by at least 5°. Furthermore, for each model parameter from amongst the set of best­ the inclinat ion distributions between HR 8799 d and HR fitting orbits. 8799 be are even more dissimilar, implying that HR 8799 Furthermore, we report a "most likely orbit" (MLO) d is most likely inclined relative to c by at least", 7° simply defined as follows. First, over the best-fitting and b by more than'" 21°. While our analyses cannot family of orbits, we calculate histograms for the follow­ conclusively rule out coplanar orbits in a 4:2:1 mean­ ing parameters: logarithm of the semi-major axis (hlo~ .), . motion resonance, they suggest that few such orbits are eccentricity (h.), inclination (h,), longitude of ascending compatible with 12 years of HR 8799 planet astrometry. node (hn), and argument of periastron (hw). Fbr each To confirm that we are fully sampling the subset of orbit n in the best-fitting ensemble, we then define the orbital parameters covering the ~2 minima., we run our measure of likelihood C(n) as simulations with a more relaxed X cutoff of X2 ~ X~ l n + [5, 5, 3.:;) for HR 8799 b, c, and d, whiCh formally admit C(n) = hlo •• (lOgan) .h.(en)· h,(in)· hn(On)' hw(wn)· W; an additional average deviation from the data of '" 0.3- . (1) (7 for each measurement. With this cutoff, we obtain Le., the product of all histograms values in the bins in nearly identical results (second set of rows in Table 1). which the orbit n lies, representing the individual like­ Considering the planets' orbits separately, we find a ~ lihood of each measured orbital param~er , as well as 23-31 AU, i ~ 27-41°', e ~ 0.01-0.31, and 0 ~ 41-63° for the statistical weight, W , representing the likelihood of HR 8799d. We find similar ranges in orbital parameters for HR 8799 c and (for the resonance case) HR 8799 7 Dynamica.l simulations identify stable solutions for at least some planet masses where only HR 8799 c and d Me in resonance, 8 Here, the statistical weight W is defined as the mean orbital so our oonclnsioIlS from this set of astrometric analyses may be less velocity for the com!SJ)Onding orbit divided by the orbital velocity appllcab:'e for HR 8799 b . at the observed epoch, W := (tI )orblt / tI (toba). 4 h. Likev..ise, the planets' range of inclinations exclude astrometric monitoring ofHR 8799 (i.e. Konopacky et a1. face.on orbits. HR 8799 d's inclination distribution is 2011) will better clarify the planets' orbital properties. skewed to systematically higher values, expected if it is Limits on the planets' dynamical masses will provide cru­ non ~ coplanar with b and c, although here there are more cial input for planet cooling models and even more firmly orbit combinations that could make the planets coplanar. establish HR 8799 as a benchmark system to understand the properties of young, self-luminous planets. 4. DISCUSSION Finally, this work and other recent studies of From analyzing HR 8799 bed astrometry from our new HR 8799 (Soummer et a1. 2011; Lafreniere et al. 2009; "pre-discovery" image and other da.ta, we provide new Fukagawa et a1. 2009) clearly demonstrate the value of constraints ·on the planets' orbital properties. Treating publicly archiving data on advanced telescopes. III our the three planets separately, we narrowly constrain three case, detecting at least two HR 8799 planets (HR 8799 major orbital parameters (a/i/e) for HR 8799 c and d. bc) was rather straightforward and did not require ad­ None of the planets are likely to be orbiting face-on and vanced image processing techniques developed well after the inclinations for acceptably-fitting orbits are system­ the data were taken . .As data for Keck and many other atic.lly higher for HR 8799 d than for HR 8799 b and 8-10 m class telescopes are now archived, they proTIde·an c. indispensible resource with which to confirm and charac­ If HR 8799 bed have semimajor e.xes consistent with terize directly imaged planets like HR 8799's and other a 4:2:1 resonance, our analysis strongly constrains the substellar companions. major orbital properties for all three planets. The three planets (especially c and d) tlien even more obviously have inclined orbits. Most acceptable solutions for HR 8799 d place the planet on an orbit inclined by more than We thank Christian Marois, Scott Kenyon, and the 7' (21') relative to HR 8799 b(c)'s orbit: few orbital so­ anonymous referee for helpful comments. This research lutions consistent with the astrometry also place them has made use of the Keck Observatory Archive (KOA) , on coplanar orbits. Adopting a less restrictive defini­ which is operated by the W. M. Keck Obeervatory and tion for "acceptably-fitting" orbits does not undo any of the NASA Exoplanet Science Institute (NExScI), un­ these trends, although there are more orbit combinations der contract with the N ationa! Aeronautics and Space making the planets coplanar. Adopting the median pa­ Administration. We are extremely grateful to the rameter value or MLO instead of the more conservative NExScI/KOA staff for developing and maintaining the 68% confidence interval likewise does not change these NIRC2 archive. TC is supported by a NASA Postdoc­ results. toral Fellowship; 8M is supported by an Astronomy Cen­ These results provide valuable ir.put for constraining ter for Theory and Computation Prize Fellowship at the the :n... of the HR 8799 planetary system. Longer-term University of Maryland.

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TABLE 1 HR 8799 PLANET PHOTOMETRlC/ ASTROMETRlC PROPERTIF13

HR8799b HR 8799 c HR8799 d Parameter Measured Photometry m(H) on 2005-07-15 18.05± 0.09 17.06 ± 0.13 16.71 ± 0.24 Astrometf\! 2005-07-15 (iE,NI)" 1.(96, 0.856 (± 0.005) -0.713,0.630 (± 0.005) -0.OS7, -0.578 (± 0.010) 2010..10-30 «(E,N )" 1.546,0.748 (± 0.005) -0.598, 0.737 (± 0.005) -0.283, -0.567 (± 0.005) Derived MLO, m<4. ,[68% C.I.J

~l~T.~·+1) 71.0, 109.9 169.7,164.9J 37.2, 38.0 35.5,42 .0 26.2, 27.3 24.4,31.5 " 4:2:1 resonance 68.1,68.8 67.5,70.8'1 42.5,43.2 42.1,44.4 27.3, 27.3 26.4,28.1 i (0), full 14.1, 34.9 12.3,43.0 21. 7, 19.9 12.5,25.8 37.1, 37.9 31.6,41.6 II 4:2:1 resonance 8.5, 9.5 14.9,14.8J 25.8, 27.6 25.2,28.8 38.1, 37.9 36.0,39.1 e, full 0.02, 0.27 10.02,0.49J 0.01, 0.08 0.03,0.13 0.04, 0.09 0.03,0.23 /I 4:2:1 resonance 0.01, 0.02Io.0,0.03J 0.12,0.14Io.11,0.17J 0.03, 0.04 0.01,0.08 J n (0), fuU 149.7, 141.0 40.9,161.4J 128.8, 122.2 J62.0,152.4J 56.8, 53.5 43.3,63.0 " 4:2:1 re600ance 163.2, 87.1 122.9,158.9J 147.4, 131.9, 1104.8,158.5J 56.9, 54.3 46.0,60.2 J

II 4:2:1 resonance 0.01, 0.03 O.Ql,O.06 j 0.02, 0.09 0.02,0.14J 0.0, 0.05 10.01,0.11] n (0), full 142.7, 119.5 132.4,I60.5J 124.7, 86.8 137.1,142.5J 52.5, 58.4141.0,98.51 " 4:2:1 resonance 142.1,78.2 12 1.9,154.3J 61.1, 70. ~ 142.2,140.5J 60.9,55.7 44.1,67.2 NOTE. - Measured parameters - Our photometric uncertainties consider both the signa.l·to-noise of our detections and the a.bsolute flux calibrat.ion uncerta.inties; astrometric uncertainties consider the SNR, astro­ metric calibration uncertainty (e.g. 0.5 pixels in x and y, see Sect. 2), etc. Derived parameters - The three colwnn entries are MLO (the «most likely orbit" (see §3), med. (the median parameter value), and /68% C. I.J (the 68% confidence inte.v&l).

FIG. 1.- HR 8799 images processed with "classical" PSF subtraction (left) and A-LOCI (right) showing the detections of HR 8799 b, c, and d (circled). 6

1.0 'l-n-cl:-;n-o"tio-n-:("'(d~.-g7)--~~" o 45 90 •• 0.8 r==w::w..-- .. ; 20 ~ 30 I' .0 .~ • b .~ :;; "5 i 0,6 S ~ 15 '0 20 ~ • u 0.4 ~ I 10 .!l E , ~ 10 c 0.2 5

O.OL-__~~~ I ___...... J '0 '00 '000 o 50 100 150 Semimojor oxis CI (AU) long. of osc. node {) (deg) 1.0 'l:-nc":U:':no":t7""",:;.o:,(;'("d"eg~)~-',.C;!...""" 25r-~~~~~~~~ o 45 90 0.8 - M+_ 20 •• •c .S • c • ~ 40 ]! .~ 0.6 iI 15 .g • ~ , 10.4 } 10 • E, I c 0.2 I I! II O~~~ __~ ______~ 0.0 O~ __~~ __~-L~~~ 10 '00 1000 0 45 90 o 50 100 150 Semimojor axis Q. (AU) Inclination i (deg) Long. of osc. node {) (dog) 1.0 r-~=-.~:;"(.,r;,:)",;:"=,--",, 80r---~~~~~~---. .Or-~~:~,~~~~~~~ Inclinotlon" deg . ,r, o 45 90 ~ Ii 0.8 r=1' • : I· • ~ 60 o I! d ,• !, JO I! • I ~ 0.6 ,• i "2 • . 40 '0 20 ~ I ] 0.4 ~ ! " , E ~ 20 0.2 E '0 H. . O.O'--~~_~~l __....J 10 100 1000 0 4S 90 0 50 100 150 Semi'mojor oxis CI (AU) Inclinotion i (deg) Long. of osc. node 0 (deg) FIG. 2.- ABtrometric a.nalysis results for HR 8799 b (tOp), HR 8799 c (middle), and HR 8199 d (bottom) considering the full range of orbilB satisfying the criterion ~ < X~ m i n +1. The panels show the orbits in a/eli space (left) and hlstogro.m distributions of !.he orbital inclina.tion i (middle panels) and longitude of e.scending node (right panels). In the left panels, the lX' Identifies parameters e and Ill' :rom the 'Jest-fit orbital solution; the 'plus' sign denotes the weighted median value (or the same parameters. For the middle and right panels, the vertical blue dashed line identifies the MLO, the vertical red dashed line identifies the median parameter value, and the vertical red dotted lines bracket the 68% confidence interval. 7

0.' Inclination" (deg) 80 0 '5 90 f O.J - •c c• 60 .!l • b ~, ;; .~ ;; u • i ·c 0.2 40 C .. .. • • t 8 S> ~ ... E, I: 0.1 ,. c ~c 20 i 0.0 0 10 100 1000 90 0 50 100 150 Semimojor axis a. (AU) LOn(~ . of osc. node 0 (deg) 140 0.' Inclination" (deg) 0C"""!iiP 45__ 90 120 O.J • • ,gc 100 • C • , ~ i 80 0.2 f! :Sc .. 60 •u .ll ~ E, 40 0.1 c f 20 • O . O'--_~~~ ___-" 0 10 100 1000 90 0 50 100 150 Semimojor axis IS (AU) Long. of osc. node Q Cdeg) 0.' r--'n-c':!in':a-t-;a-n;;':"''''(~d.'-g-:):'''';:'-',.-'''-....., 400 o 45 90 O.J • d

i 0.2 .0 400 '0 200 "I; .... Ij ! l x ! Ii. 0.1 i ~ 200 h ~ 100 :i: 0.0'----lj;....._...:.. __~_..J 0 i!1 OL...... Jr'...;i"':"-i:"...~_~~...... J to 100 1000 0 45 90 0 50 100 150 Semimajo( axis a. (AU) Inclination i (deg) Long. of OSC. node 0 (deg) FIG. 3.- Se.me as Figure 2 except only for non-crossing orbits consistent with a 4:2:1 mean-motion reson8.tlce between HR 8799 b, c, and d, 8. :onflgural;;lon which promotes orbital stability (e.g Fabrycky and Murray-Clay 2010). Note the lack of high-eccentricity orbits and the nri.rrower range in acceptable orbital parameters) especialo/ for HR 8799 c and d .