Infrared and kinematic properties of the substellar object G196-3B

Abstract

We report unusual near- and mid-infrared photometric properties of G196-3B, the young substellar companion at 16″ from the active M2.5-type star G196-3A, using data taken with the IRAC and MIPS instruments onboard Spitzer. G196-3B shows markedly redder colors at all wavelengths from 1.6 up to 24 μm than expected for its spectral type, which is determined at L3 from optical and near-infrared spectra. We discuss various physical scenarios to account for its reddish nature and conclude that a low-gravity atmosphere with enshrouded upper atmospheric layers and/or a warm dusty disk/envelope provides the most likely explanations, the two of them consistent with an age in the interval 20-300Myr. We also present new and accurate separate proper motion measurements for G196-3A and B confirming that both objects are gravitationally linked and share the same motion within a few masyr-1. After integration of the combined spectrophotometric spectral energy distributions, we obtain the result that the difference in the bolometric magnitudes of G196-3A and B is 6.15 ± 0.10mag. Kinematic consideration of the Galactic space motions of the system for distances in the interval 15-30pc suggests that the pair is a likely member of the Local Association and that it lies near the past positions of young star clusters like α Persei less than 85Myr ago, where the binary might have originated. At these young ages, the mass of G196-3B would be in the range 12-25M Jup, close to the frontier between planets and brown dwarfs. © 2010. The American Astronomical Society. All rights reserved.