A NEW VIEW OF VEGA'S COMPOSITION, MASS, AND AGE

We present estimates of Vega's composition, mass, and age based on a simultaneous fit of high-resolution metal line profiles, the wings of the Balmer lines, the absolute visible/near-IR fluxes, and high angular resolution triple phase data from the Navy Prototype Optical Interferometer to gravity-darkened Roche models. This substantially expands our earlier analysis. We determine that Vega has a much lower mass, 2.135 +/- 0.074M(circle dot), than generally assumed. This strongly supports the contention that Vega is metal-poor throughout (Z similar to 0.008), suggesting it was formed that way. Assuming a uniform composition equal to that derived for the surface, and the luminosity and radius obtained here, we derive a best estimate of Vega's age, 455 +/- 13 Myr, and mass, 2.157 +/- 0.017M(circle dot), by fitting to standard isochrones. We continue to argue that Vega is much too old to be coeval with other members of the Castor moving group and is thus unlikely to be a member. The updated chemical abundances continue to support the conclusion that Vega is a lambda Boo star.