Medium-resolution infrared integral field spectroscopy of the brown dwarf TWA 5 B.

We obtained medium-resolution infrared K-band integral field spectroscopy with VLT/Sinfoni for the brown dwarf TWA 5 B, a companion to the weak-line T Tauri star TWA 5 in the TW Hya association. We compare the final spectrum with theoretical model atmospheres from DRIFT-PHOENIX (Dehn et al. 2007, Helling et al. 2008 ab, Witte 2008) for temperature from 2000 to 3100 K, gravity log g = 3.0, 3.5, and 4.0 (g in cm/s2) and metallicity -0.5, 0.0 (solar), and 0.5; we also varried the extinction towards TWA 5 B while searching for the best-fit model between Av = 0.0 and 15 mag. The best-fitting model spectrum yields the following parameters for TWA 5 B: Effective temperature Teff≃2800 K, metallicity [M/H]≃-0.5 (for metal content M), surface gravity log g≃4.0, and extinction Av = 0.0 mag. From these parameters and the distance towards TWA (∼65 pc), we can compute the mass of the brown dwarf to be roughly 25 Jupiter masses, but with large error bars including massive planets and low-mass stars. Given its projected separation from the primary star, ∼123 AU, it has certainly more likely formed star-like, i.e. being a brown dwarf companion. [ABSTRACT FROM AUTHOR]