The Physical Properties of HD 3651B: An Extrasolar Nemesis?

I present detailed analysis of the near infrared spectrum of HD 3651B, afaint, co-moving wide companion to the nearby planet-hosting star HD 3651.These data confirm the companion as a brown dwarf with spectral type T8,consistent with the analysis of Luhman et al. Application of the semi-empiricaltechnique of Burgasser, Burrows & Kirkpatrick indicates that HD 3651B has Teff= 790+/-30 K and log g = 5.0+/-0.3 for a metallicity of [M/H] = 0.12+/-0.04,consistent with a mass M = 0.033+/-0.013 M_sun and an age of 0.7-4.7 Gyr. Thesurface gravity, mass and age estimates of this source are all highly sensitiveto the assumed metallicity; however, a supersolar metallicity is deduced bydirect comparison of spectral models to the observed absolute fluxes. The ageof HD 3651B is somewhat better constrained than that of the primary, withestimates for the latter ranging over ~2 Gyr to >12 Gyr. As a widely orbitingmassive object to a known planetary system that could potentially harborterrestrial planets in its habitable zone, HD 3651B may play the role ofNemesis in this system.Comment: 16 pages, 3 figures, accepted to ApJ Part 1; note that this article supersedes astro-ph/060955