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

TL;DR

This study provides detailed near-infrared spectra of AB Pic b, confirming its status as a young early-L dwarf with specific atmospheric properties, and compares observations with models to refine its physical parameters.

Contribution

First high-quality medium-resolution spectra of AB Pic b obtained and analyzed, improving understanding of its atmospheric characteristics and confirming evolutionary model predictions.

Findings

AB Pic b is a young early-L dwarf with spectral type L0-L1.

Derived atmospheric parameters: Teff ≈ 2000 K, log(g) ≈ 4.

Spectral features indicate intermediate gravity atmosphere.

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.