Abstract
Chauvin et al. 2005 imaged a co-moving companion at ~260 AU from the young star AB Pic A. Evolutionary models predictions based on J H K photometry of AB Pic b suggested a mass of ~13 - 14 MJup, placing the object at the deuterium-burning boundary. We used the adaptive-optics-fed integral field spectrograph SINFONI to obtain high quality medium-resolution spectra of AB Pic b (R = 1500-2000) over the 1.1 - 2.5 microns range. Our analysis relies on the comparison of our spectra to young standard templates and to the latest libraries of synthetic spectra developed by the Lyon's Group. AB Pic b is confirmed to be a young early-L dwarf companion. We derive a spectral type L0-L1 and find several features indicative of intermediate gravity atmosphere. A comparison to synthetic spectra yields Teff = 2000+100-300 K and log(g) = 4 +- 0.5 dex. The determination of the derived atmospheric parameters of AB Pic b is limited by a non-perfect match of current atmosphere spectra with our near-infrared observations of AB Pic b. The current treatment of dust settling and 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 confirm independently the evolutionary model predictions. We finally review the current methods used to characterize planetary mass companions and discuss them in the perspective of future planet deep imaging surveys.
Highlights
Understanding how planets form and evolve and which physical processes affect their atmospheric chemistry remains a major challenge in exoplanetary science, ever since the first glimpse of planetary formation revealed by the discovery of the β Pictoris star debris disk (Smith & Terrile 1984)
We present here high-quality near-infrared spectra of the AB Pic b companion
We obtained high-quality 1.1−2.5 μm medium-resolution spectra of the young very low-mass companion AB Pic b, whose evolutionary models place it on the planet/brown-dwarf boundary
Summary
Understanding how planets form and evolve and which physical processes affect their atmospheric chemistry remains a major challenge in exoplanetary science, ever since the first glimpse of planetary formation revealed by the discovery of the β Pictoris star debris disk (Smith & Terrile 1984). At the age of the association (∼30 Myr, see Torres et al 2000; Stelzer & Neuhäuser 2000; Zuckerman & Webb 2000; Zuckerman et al 2001; Torres et al 2001; Scholz et al 2007; Mentuch et al 2008), several evolutionary models predict a companion mass of 13–14 MJup, in agreement with the L0–L3 spectral type derived from NACO K-band spectroscopy. This places AB Pic b at the planetary mass boundary (∼13.6 MJup). Respective limitations in the perspective of a future deep-imaging search for giant planets
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