High-Resolution Infrared Spectroscopy of the Brown Dwarf ϵ Indi Ba

We report on the analysis of high-resolution infrared spectra of the newly discovered brown dwarf ϵ Ind Ba. This is the closest known brown dwarf to the solar system, with a distance of 3.626 pc. Spectra covering the ranges of λλ2.308-2.317 μm and λλ1.553-1.559 μm were observed at a resolution of λ/Δλ = R = 50,000. The physical parameters of effective temperature and surface gravity are derived for ϵ Ind Ba by comparison with model spectra calculated from atmospheres computed using unified cloudy models. The results are Teff = 1500 ± 100 K, log g = 5.2 ± 0.3 (in units of cm s-2), placing it in the critical boundary between the late L and early T dwarfs. The high spectral resolution also allows us to measure an accurate projected rotational velocity, with v sin i = 28 ± 3 km s-1. Combined with a published luminosity for ϵ Ind Ba [with log(L/L☉) = -4.71], the derived parameters result in a "spectroscopic" mass estimate of ~30MJ, a radius of ~0.062 R☉, and a maximum rotational period of ~3.0 hr. A compilation and comparison of effective temperatures derived from spectroscopy using model atmospheres versus those derived from luminosities and theoretical Mbol-radius relations reveal a systematic disagreement in the Teff scale. The source of this disagreement is unknown.