Abstract
We report on the analysis of high-resolution infrared spectra of the newly discovered brown dwarf 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 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 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.
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