Near-infrared integral-field spectra of the planet/brown dwarf companion AB Pictoris b

Context. We have already imaged a co-moving companion at a projected separation of ∼260 AU from the young star AB Pic A. Evolutionary model predictions based on JHK photometry of AB Pic b suggest a mass of ∼13−14 MJup, placing the object at the deuterium-burning boundary. Aims. We aim to determine the spectral type, the surface gravity, and the effective temperature of AB Pic b. From the comparison of our absolute photometry to surface fluxes generated by atmospheric models, we also aim at deriving mass and radius estimates that are independent of evolutionary model predictions to test and refine them. Methods. We used the adaptive-optics-fed integral field spectrograph SINFONI to obtain high-quality, medium-resolution spectra of AB Pic b (Rλ = 1500−2000) over the 1.1−2.5 μm range. Our analysis relie on comparing our spectra to young standard templates and to the latest libraries of synthetic spectra developed by the Lyon group. Results. AB Pic b is confirmed as a young early-L dwarf companion. We derive a spectral type L0–L1 and find several features indicative of an intermediate gravity atmosphere. A comparison to synthetic spectra yields Teff = 2000 +100 −300 K and log(g) = 4 ± 0. 5d ex. Determination of the derived atmospheric parameters of AB Pic b is limited by an imperfect match of current atmosphere spectra with our near-infrared observations of AB Pic b. The current treatment of dust settling and the missing molecular opacity lines in the atmosphere models could be responsible. By combining the observed photometry, the surface fluxes from atmosphere models and the known distance of the system, we derive new mass, luminosity, and radius estimates of AB Pic b. They independently confirm the evolutionary model predictions. We finally review the current methods used for characterizing planetary mass companions and discuss them in the perspective of future planet deep-imaging surveys that will be faced with the same limitations.

[1]  N. Santos,et al.  Search for associations containing young stars (SACY) - II. Chemical abundances of stars in 11 young associations in the solar neighborhood , 2009, 0904.1221.

[2]  L. Hillenbrand,et al.  MEASURING TINY MASS ACCRETION RATES ONTO YOUNG BROWN DWARFS , 2009, 0901.3684.

[3]  Kaspar von Braun,et al.  DIRECTLY DETERMINED LINEAR RADII AND EFFECTIVE TEMPERATURES OF EXOPLANET HOST STARS , 2009, 0901.1206.

[4]  David Lafreniere,et al.  Direct Imaging and Spectroscopy of a Planetary-Mass Candidate Companion to a Young Solar Analog , 2008, 0809.1424.

[5]  U. Toronto,et al.  Lithium Depletion of Nearby Young Stellar Associations , 2008, 0808.3584.

[6]  Germano R. Quast,et al.  Young Nearby Loose Associations , 2008, 0808.3362.

[7]  D. Saumon,et al.  The Evolution of L and T Dwarfs in Color-Magnitude Diagrams , 2008, 0808.2611.

[8]  France.,et al.  The extrasolar planet atmosphere and exosphere: Emission and transmission spectroscopy , 2008, Proceedings of the International Astronomical Union.

[9]  Michael C. Liu,et al.  HN Peg B: A Test of Models of the L to T Dwarf Transition , 2008, 0804.1386.

[10]  R. F. Jameson,et al.  Near‐infrared cross‐dispersed spectroscopy of brown dwarf candidates in the Upper Sco association★ , 2007, 0711.1109.

[11]  L. Hartmann,et al.  Hubble and Spitzer Observations of an Edge-on Circumstellar Disk around a Brown Dwarf , 2007, 0706.0279.

[12]  R. Jayawardhana,et al.  Rotation and Activity of Pre-Main-Sequence Stars , 2007, 0704.3266.

[13]  V. Makarov.  Unraveling the Origins of Nearby Young Stars , 2007 .

[14]  Michael C. Liu,et al.  Characterizing Young Brown Dwarfs Using Low-Resolution Near-Infrared Spectra , 2006, astro-ph/0611408.

[15]  Eric Mamajek,et al.  The Planetary Mass Companion 2MASS 1207–3932B: Temperature, Mass, and Evidence for an Edge-on Disk , 2006, astro-ph/0610550.

[16]  M. Marley,et al.  On the Luminosity of Young Jupiters , 2006, astro-ph/0609739.

[17]  M. Sterzik,et al.  Search for associations containing young stars (SACY). I. Sample and searching method , 2006, astro-ph/0609258.

[18]  C. Fabron,et al.  SPHERE: a planet finder instrument for the VLT , 2006, Astronomical Telescopes + Instrumentation.

[19]  Stefan Gillessen,et al.  SINFONI data reduction software , 2006 .

[20]  T. Barman,et al.  Discovery of a Very Young Field L Dwarf, 2MASS J01415823–4633574 , 2005, astro-ph/0511462.

[21]  J. Davy Kirkpatrick,et al.  New spectral types L and T , 2005 .

[22]  D. Mouillet,et al.  Giant Planet Companion to 2MASSW J1207334-393254 , 2005, astro-ph/0504659.

[23]  D. Mouillet,et al.  A companion to AB Pic at the planet/brown dwarf boundary , 2005, astro-ph/0504658.

[24]  John T. Rayner,et al.  An Infrared Spectroscopic Sequence of M, L, and T Dwarfs , 2004, astro-ph/0412313.

[25]  S. Megeath,et al.  Spectroscopic Confirmation of the Least Massive Known Brown Dwarf in Chamaeleon , 2004, astro-ph/0411445.

[26]  D. Mouillet,et al.  A giant planet candidate near a young brown dwarf - Direct VLT/NACO observations using IR wavefront sensing , 2004, astro-ph/0409323.

[27]  Bernard Delabre,et al.  First light of SINFONI at the VLT , 2004 .

[28]  Ben Zuckerman,et al.  Young Stars Near the Sun , 2004 .

[29]  E. H. Olsen,et al.  The Geneva-Copenhagen survey of the Solar neighbourhood - Ages, metallicities, and kinematic properties of ~14 000 F and G dwarfs , 2004, astro-ph/0405198.

[30]  L. Hillenbrand,et al.  The Spectroscopically Determined Substellar Mass Function of the Orion Nebula Cluster , 2004, astro-ph/0404292.

[31]  F. Allard,et al.  Measuring Fundamental Parameters of Substellar Objects. I. Surface Gravities , 2004, astro-ph/0403265.

[32]  J. Brinkmann,et al.  L′ and M′ Photometry of Ultracool Dwarfs , 2004, astro-ph/0402475.

[33]  G. H'ebrard,et al.  Detection of Oxygen and Carbon in the Hydrodynamically Escaping Atmosphere of the Extrasolar Planet HD 209458b , 2004, astro-ph/0401457.

[34]  Michael S. Bessell,et al.  New Members of the TW Hydrae Association, β Pictoris Moving Group, and Tucana/Horologium Association , 2003 .

[35]  Adam J. Burgasser,et al.  The NIRSPEC Brown Dwarf Spectroscopic Survey. I. Low-Resolution Near-Infrared Spectra , 2003, astro-ph/0309257.

[36]  George H. Rieke,et al.  Gravity Indicators in the Near-Infrared Spectra of Brown Dwarfs , 2003, astro-ph/0305147.

[37]  G. Rieke,et al.  A Census of the Young Cluster IC 348 , 2003, astro-ph/0304409.

[38]  T. Fusco,et al.  Adaptive optics imaging survey of the Tucana-Horologium association , 2003, astro-ph/0304116.

[39]  F. Allard,et al.  Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 209458 , 2003, astro-ph/0302293.

[40]  Berkeley,et al.  FeH Absorption in the Near-Infrared Spectra of Late M and L Dwarfs , 2002, astro-ph/0209083.

[41]  L. Wallace,et al.  Detection of the 1.6 μm E 4Π-A 4Π FeH System in Sunspot and Cool Star Spectra , 2001 .

[42]  F. Allard,et al.  Infrared Spectroscopy of Substellar Objects in Orion , 2001, astro-ph/0105154.

[43]  F. Allard,et al.  The Limiting Effects of Dust in Brown Dwarf Model Atmospheres , 2001, astro-ph/0104256.

[44]  P. H. Hauschildt,et al.  Infrared Spectra and Spectral Energy Distributions of Late M and L Dwarfs , 2000, astro-ph/0010174.

[45]  C. Torres,et al.  A New Association of Post-T Tauri Stars near the Sun , 2000, astro-ph/0005579.

[46]  F. Allard,et al.  Evolutionary Models for Very Low-Mass Stars and Brown Dwarfs with Dusty Atmospheres , 2000, astro-ph/0005557.

[47]  Bradford A. Smith,et al.  A Candidate Substellar Companion to HR 7329 , 2000, astro-ph/0005047.

[48]  B. Zuckerman,et al.  Identification of a Nearby Stellar Association in theHipparcos Catalog: Implications for Recent, Local Star Formation , 2000, astro-ph/0002461.

[49]  Rodger I. Thompson,et al.  A Candidate Substellar Companion to CD –33°7795 (TWA 5) , 1998, astro-ph/9812187.

[50]  N. Kobayashi,et al.  K-Band Spectra and Narrowband Photometry of DENIS Field Brown Dwarfs , 1998, astro-ph/9811352.

[51]  T. Forveille,et al.  X-ray and molecular emission from the nearest region of recent star formation. , 1997, Science.

[52]  T. Guillot,et al.  A Nongray Theory of Extrasolar Giant Planets and Brown Dwarfs , 1997, astro-ph/9705201.

[53]  Bradford A. Smith,et al.  A Circumstellar Disk Around β Pictoris , 1984, Science.

[54]  D. Mouillet,et al.  Deep imaging survey of young, nearby austral stars - VLT/NACO near-infrared Lyot-coronographic observations , 2010 .

[55]  Peter L. Wizinowich,et al.  Adaptive Optical System Technologies II , 1998 .