  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.
