Near-Infrared Detection and Characterization of the Exoplanet HD 95086 b with the Gemini Planet Imager
Raphael Galicher, Julien Rameau, Mickael Bonnefoy, Jean-Loup Baudino, Thayne Currie, Anthony Boccaletti, Gael Chauvin, Anne-Marie Lagrange, Christian Marois
AAstronomy & Astrophysics manuscript no. ms_v9_twocol c (cid:13)
ESO 2018October 8, 2018
Letter to the Editor
Near-infrared detection and characterization of the exoplanetHD 95086 b with the Gemini Planet Imager (cid:63)
R. Galicher , J. Rameau , M. Bonnefoy , J.-L. Baudino , T. Currie , A. Boccaletti , G. Chauvin , A.-M.Lagrange , C. Marois LESIA, CNRS, Observatoire de Paris, Univ. Paris Diderot, UPMC, 5 place Jules Janssen, 92190 Meudon, Francee-mail: [email protected] UJF-Grenoble 1 / CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Greno-ble, F-38041, France Department of Astronomy and Astrophysics, Univ. of Toronto, 50 St. George St., Toronto, ON, M5S 1A1, Canada National Research Council of Canada Herzberg, 5071 West Saanich Road, Victoria, BC, V9E 2E7, Canada
ABSTRACT
HD 95086 is an intermediate-mass debris-disk-bearing star.VLT/NaCo . µm observations revealed it hosts a ± Jup companion (HD 95086 b) at (cid:39) AU. Follow-up observations at 1.66 and 2.18 µm yielded a null detection, suggestingextremely red colors for the planet and the need for deeper direct-imaging data. In this Letter, we report H- ( . µm ) and K - ( . µm ) band detections of HD 95086 b from Gemini Planet Imager (GPI) commissioning observations taken bythe GPI team. The planet position in both spectral channels is consistent with the NaCo measurements and we confirmit to be comoving. Our photometry yields colors of H-L ’= . ± . mag and K -L ’= . ± . mag, consistent withpreviously reported 5- σ upper limits in H and Ks. The photometry of HD 95086 b best matches that of 2M 1207 b andHR 8799 cde. Comparing its spectral energy distribution with the BT-SETTL and LESIA planet atmospheric modelsyields T eff ∼ ∼ ± M Jup . Warm-start modelsreproduce the combined absolute fluxes of the object for M=4-14 M
Jup for a wide range of plausible initial conditions(S init =8-13 k B /baryon). The color-magnitude diagram location of HD 95086 b and its estimated T eff and log g suggestthat the planet is a peculiar L-T transition object with an enhanced amount of photospheric dust. Key words. instrumentation: adaptive optics - planets and satellites: detection - Planets and satellites: atmospheres -stars: individual (HD95086)
1. Introduction
HD 95086 b is a directly imaged planet ( ± M J , a proj = 55.7 ± AU ) discovered by Rameau et al. (2013a) inL (cid:48) (3.8 µm ) with VLT/NaCo (Lenzen et al. 2003; Rous-set et al. 2003) orbiting the young A8 star HD 95086 (M ∼ (cid:12) ), a member of the Lower Centaurus Crux subgroup( ± Myr, Pecaut et al. 2012; Meshkat et al. 2013). Ad-ditional L (cid:48) images taken later in 2013 confirmed that theobject is comoving with its star (Rameau et al. 2013b).NaCo Ks ( . µ m) and NICI (Chun et al. 2008) H-band( . µ m) observations failed to reveal the planet (Rameauet al. 2013a; Meshkat et al. 2013). However, σ lower limitsof Ks-L (cid:48) = 1 . ± . mag and H-L (cid:48) = 3 . ± . mag suggestthat the planet may have extremely red colors, similar tothe young planets HR 8799 bcde and 2M 1207 b (Chauvinet al. 2004; Marois et al. 2008; Marois et al. 2010a), whichhave very dusty/cloudy atmospheres (Barman et al. 2011;Currie et al. 2011). Higher contrast near-IR data able todetect HD 95086 b can provide better comparisons withthese objects and better constrain its atmosphere.In this Letter, we present detections of HD 95086 b withthe recently installed Gemini Planet Imager (GPI, Macin- (cid:63) based on public data taken at the GPI commissioning. tosh et al. 2014) on Gemini South from public data as a partof GPI commissioning observations (Perrin et al. 2014). Thedata (acquired and reduced by the GPI team), their analy-sis, and the detections are presented in § 2. In § 3, we com-bine GPI H and K photometry with NaCo L (cid:48) photometryto constrain the physical properties of HD 95086 b.
2. Observations and data reduction
The GPI is a new instrument for imaging and character-izing planets around young nearby bright stars, combiningan extreme adaptive optics system, coronagraphs, and anintegrated field spectrograph (IFS). The IFS platescale is . ± . . px − for a . (cid:48)(cid:48) field-of-view (FOV) and thetrue North position angle is given within 1 deg .The HD 95086 spectral data were obtained at H ( . − . µ m, R= − ) and K ( . − . µ m, R= − ) in2013 December using apodized Lyot coronagraphs (Tab. 1)and angular differential imaging (ADI, Marois et al. 2006a).Conditions were good: 0.43 (cid:48)(cid:48) and 0.6 (cid:48)(cid:48) DIMM seeing, airmasses of . and . , and coherence times of ms and ms, respectively. The GPI commissioning team used theirpipeline for bad-pixel removal, destriping, non-linearity http://planetimager.org/ Article number, page 1 of 4 a r X i v : . [ a s t r o - ph . S R ] A p r &A proofs: manuscript no. ms_v9_twocol Table 1.
Observing log of HD 95086 with GPI
Date Filter Coro mask diam (mas) DIT(s) × NDITS × Nb λ Nb images FOV rotation ( ◦ ) / /
10 K -coro 306 . × ×
17 11.7 / / H-coro 246 . × ×
21 15.0
Notes.
Date, filter, occulting mask diameter, exposure, numbers of coadds, of spectral channels, of images, and FOV rotation. and persistence corrections, flat-fielding, wavelength cali-bration, and converting the data into spectral data cubes.We used the data cubes relying on the GPI pipeline quality.The data are made of and spectral cubes at H and K bands, respectively, consisting of spectral channels each.To further process the data, we registered each slice ofthe spectral cubes using the barycenter of the four satellitespots (attenuated replica of the central star PSF induced bya grid placed in a pupil plane, Marois et al. 2006b). Then,we minimized the speckle noise in each slice using inde-pendent pipelines each adopting various methods (Maroiset al. 2006a; Lafrenière et al. 2007; Lagrange et al. 2010;Boccaletti et al. 2012; Chauvin et al. 2012; Soummer etal. 2012; Currie et al. 2013; Marois et al. 2014) used forADI and spectral differential imaging (SSDI, Racine et al.1999). Finally, all slices were mean-combined to yield an in-tegrated broad-band image to maximize the signal-to-noiseratio (S/N) of any off-axis source. Binning images in wave-length and suppressing the speckles (ADI), or suppressingthe speckles in each spectral channel (ADI/ADI+SSDI) andbinning images give similar results, and all our pipelinesrecover HD 95086 b, which is the sole bright spot at the ex-pected separation. Thus, we provide the first detections atH and K bands (Fig. 1) with an S/N of ∼ Fig. 1.
Final images of the HD 95086 system at H (top) and K (bottom) bands from two of our pipelines. The planet (arrow)is detected in all images. The bright speckles are masked up to500 mas from the central star. To estimate the planet flux and position, we needed un-saturated GPI PSFs. As GPI cannot acquire off-axis obser- vations of the star, we calibrated photometry and astrom-etry using the satellite spots, which are expected to havesame shape and brightness for a given filter. In the labora-tory the spot-to-central-star flux ratios were . × − (9.23 mag) and . × − (8.92 mag) at H and K bands .To check these values, we compared H and K photometryof HD 8049 B (VLT/NACO-SINFONI, Zurlo et al. 2013)with our measurements derived from public GPI HD 8049data. Assuming that the object is not photometrically vari-able with time and considering the laboratory spot con-trasts, GPI and VLT photometry are consistent within (cid:15) = 0 . mag, which we take as the error on the ratios.From these ratios, we assessed biases induced by our pro-cessing by injecting fake point-sources (i.e., unsaturatedPSFs) into the data before applying speckle-suppressiontechniques (Lagrange et al. 2010; Marois et al. 2010b; Chau-vin et al. 2012; Galicher et al. 2012). We obtained templatesof the planet image. Adjusting the flux of the templates, wefound the planet photometry and the fitting error (cid:15) , whichdepends on the detection quality. (cid:15) is 0.8 mag and 0.3 magat H and K . Finally, we estimated the variation (cid:15) of stel-lar flux over the sequence with the variation of spot flux. (cid:15) is . mag and . mag over the H and K sequences includ-ing the variations between spots. The resulting photometricerror is the quadratic error, which is dominated by the lowS/N at H and is a mix of all errors at K .For the astrometric error, we considered uncertainties inthe centroiding accuracy of individual slices ( ≤ . pixel),the plate scale ( . pixel), the planet template fit ( . pixelat H, . pixel at K ), and the North position angle (1 deg).The error is dominated by the low S/N of the detectionsand the generic GPI calibrations. The current precision isgood enough to assess the comoving status of the com-panion (Fig. 2). We tried to use the astrometric standardHD 8049 B in GPI data to better constrain the North ori-entation. We did not succeed because of the high orbitalmotion of HD 8049 B and because there is no contemporaryobservation from other instruments.Final measurements are presented in Tab. 2. We includerevised 2012 NaCo L (cid:48) photometry obtained by 1) bettercalibrating the planet signal (as in Currie et al. 2013)and 2) precisely deriving the L (cid:48) neutral density (ND) filterthroughput (used to flux-calibrate HD 95086) by comparingND and unsaturated β Pic data.
3. Characterization
Absolute magnitudes were derived from the contrast ratios(Tab. 2): M H = 15 . ± . mag, M K = 14 . ± . mag,and M L (cid:48) = 11 . ± . mag using the 2MASS and WISEW1 (Cutri et al. 2003, 2012) photometry of the star . Correction factors from the GPI/NaCo and 2MASS/WISEphotometry, derived from the spectrum of an A7III star in thePickles et al. (1998) library, are negligible.Article number, page 2 of 4alicher et al.: HD 95086 GPI follow-up
400 380 360 340 320 300 280 260 ∆α (mas)−640−620−600−580−560−540−520−500 ∆ δ ( m a s ) Fig. 2.
HD 95086 b positions from its star in RA ( ∆ α ) andDEC ( ∆ δ ). GPI and NaCo measurements are marked in blueand expected positions of a background object in yellow. Table 2.
HD 95086 b photometry and astrometry at H and K (GPI data) and L (cid:48) (Rameau et al. 2013a,b, and revision*). Date Filter Sep (mas) PA( o ) ∆ m ±
17 150 . ± . . ± . K ±
15 151 . ± . . ± . (cid:48) . ± . . ± . . ± . (cid:48) . ± . . ± . . ± . (cid:48) . ± . . ± . . ± . ∗ Fig. 3.
Color-magnitude diagram using the new H-band pho-tometry of HD 95086 b (yellow star) and data from Bonnefoy etal. (2013), Bonnefoy et al. (2014), and Currie et al. (2014).
Combining the H band GPI data with revised NaCo L (cid:48) data, we compared the L (cid:48) /H-L (cid:48) color-magnitude diagramposition of HD 95086 b with that of young companions, fielddwarfs (Leggett et al. 2010, 2013), and LYON evolutionarytracks (Chabrier et al. 2000; Baraffe et al. 2003) generatedfor the GPI/NaCo passbands . We converted the GPI mea-surements into H photometry by applying correction factors http://phoenix.ens-lyon.fr/simulator/index.faces Table 3.
Physical parameters predicted by hot-start evolution-ary models for the observed absolute magnitudes.
SED L’Model BT-SETTL Lesia Dusty Cond T eff (K) 1050 +450 − +300 − +43 − +66 − log g (dex) 4 . +0 . − . . +1 . − . . +0 . − . . +0 . − . M ( M Jup ) – – . +1 − . +1 . − . derived from published spectra, the filter transmissions, anda spectrum of Vega. HD 95086 b lies at the L-T transitionin this diagram, similar to other young (8-30 Myr) planetslike HR 8799 cde (Marois et al. 2008; Marois et al. 2010a)and 2M1207 b (Chauvin et al. 2004). Its red H-L (cid:48) colorcompared with the sequence of field dwarf objects (Leggettet al. 2010, 2013) suggests a high content of photosphericdust (Barman et al. 2011; Currie et al. 2011), owing toreduced surface gravity (e.g. Fig. 11 of Marley et al. 2012).We built the 1.5-4.8 µ m spectral energy distribution(SED) of the planet following Bonnefoy et al. (2013) bycombining the GPI photometry with the L (cid:48) one. The nor-malized SED (at L (cid:48) ) is best compatible with the young ex-oplanets HR 8799 bcde and 2M1207 b, but is redder. Its col-ors are also ∼ (cid:48) . The BT-SETTL grid covers
400 K ≤ T eff ≤ with 50 to100 K increments, − . ≤ log g ≤ . dex with 0.5 dex in-crements, and M/H=0.0 or +0.5 dex. The BT-SETTLmodels that reproduce the photometry of HD 95086 bhave
600 K ≤ T eff ≤ and . ≤ log g ≤ . .The three LESIA grids assume
700 K ≤ T eff ≤ , . ≤ log g ≤ . dex, and solar abundances: one withoutclouds and two with clouds of Fe and Mg SiO particles.For each LESIA model, we selected the planet radius thatminimizes χ between the observed and calculated apparentmagnitudes. We only kept models with a radius in a realisticrange derived from evolution models (0.6 to 2 Jupiter radii,Mordasini et al. 2012). All LESIA models that reproducedthe HD 950866 b photometry have
900 K ≤ T eff ≤ and . ≤ log g ≤ . .The planet mass cannot be derived from the atmo-sphere models, and evolutionary models are needed. Com-paring the planet’s L (cid:48) luminosity with hot-start DUSTYand COND models for an age of ± Myr, we find aplanet mass of M= ± M Jup (Tab. 3). We did not use theH and K photometries because they are poorly reproducedby the models for an object at the L-T transition (larger un-certainties than for L’). The models predict T eff and log g,in agreement with those derived from the SED fit.Alternatively, we used the warm-start models(Spiegel&Burrows 2012) to account for possible dif-ferent initial conditions for the planet (parameterized bythe initial entropy between 8 and 13 k B /baryon). Themodels assume solar metallicity and atmospheres enrichedby a factor of 3 with/without dust clouds as boundaryconditions. Synthetic SEDs are generated from predicted Article number, page 3 of 4 &A proofs: manuscript no. ms_v9_twocol
Jup ]8910111213 S i n i t [ k B / ba r y on ] No modelcf3shy1shy3s2 4 6 8 10 12 14Mass [M
Jup ]8910111213 S i n i t [ k B / ba r y on ] Fig. 4.
Combination of initial entropies ( S init ) and masses(shaded areas) for which the planet 1.6-4.8 µ m photometriesare reproduced by the warm-start models of Spiegel&Burrows(2012) withing 1 σ . Three boundary conditions are considered:with (hy) and without (cf) cloudy atmospheres, at solar (1s)and 3x solar (3s) metallicity. Initial entropies for the cold-start(filled circles) and hot-start (open circles) models of Marley etal. (2007) are overlaid. spectra of planets . For the full range of initial entropieswe considered, models assuming masses of −
14 M
Jup match the SED of HD 95086 b (Fig. 4). For much of thisrange ( S init = 9 . − ) a mass of Jup is favored.
4. Conclusions
We reported the near-IR detections of HD 95086 b from GPIpublic commissioning data. We confirmed that the com-panion is comoving with HD 95086 and derived the firstestimates of its magnitudes with respect to its star: H = . ± . and K = . ± . .While the mid-IR luminosity of HD 95086 b is best con-sistent with an L-T transition object, it has redder near-IRcolors than other young, imaged planet-mass companions.This is consistent with a very dusty and low surface gravityatmosphere.Comparison with atmosphere models provide
600 K ≤ T eff ≤ and . ≤ log g ≤ . .Evolutionary models are consistent with a mass of ± M Jup . However, the models are affected by systematicerrors that are difficult to quantify because of the lack ofyoung objects at the L/T transition.More higher precision spectroscopic and photometricdata for HD 95086 b are required to refine the planetproperties.
Acknowledgments: we thank the consortium who built theGPI instrument and the data analysis team for developing re-duction tools. We are grateful to Dave Spiegel and Adam Bur-rows for making the warm-start models publicly avaliable. JR,MB, GC, and AML acknowledge financial support from the ∼ adam/browndwarfs/spexprism. JLBPhD is funded by the LabEx “Exploration Spatiale des Environ-nements Planétaires” (ESEP) References
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