  We have derived a new age estimate for the nearby young star AB Dor and have
investigated the resulting implications for testing theoretical evolutionary
models with the data reported by Close and coworkers for the low-mass companion
AB Dor C. Using color-magnitude diagrams, we find that the AB Dor moving group
is roughly coeval with the Pleiades (100-125 Myr) and is clearly older than IC
2391 (35-50 Myr). In fact, based on a comparison of the kinematics of AB Dor
and the Pleiades, we suggest that the stars identified by Zuckerman and
coworkers as members of a moving group with AB Dor are remnants of the large
scale star-formation event that formed the Pleiades. Using the age of 50+50/-20
Myr adopted by Close, the luminosity predicted by the models of Chabrier and
Baraffe for AB Dor C is larger than the value reported by Close, but is still
within the quoted uncertainties. Meanwhile, the agreement is good when our age
estimate for AB Dor C is adopted. Thus, we find no evidence in the data
presented by Close for AB Dor C to suggest that previous studies using the
models of Chabrier and Baraffe and bolometric luminosity as the mass indicator
have significantly underestimated the masses of young low-mass stars and brown
dwarfs.
