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/Δ;λ = 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 T_eff = 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 ∼30M_J, 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 M_bol-radius relations reveal a systematic disagreement in the T_eff scale. The source of this disagreement is unknown.