Bayesian Ages for Early-Type Stars From Isochrones Including Rotation, and a Possible Old Age for the Hyades

We combine recently computed models of stellar evolution using a new treatment of rotation with a Bayesian statistical framework to constrain the ages and other properties of early-type stars. We find good agreement for early-type stars and clusters with known young ages, including Pictoris, the Pleiades, and the Ursa Majoris moving group. However, we derive a substantially older age for the Hyades open cluster (750 100 Myr compared to 625 50 Myr). This older age results from both the increase in main-sequence lifetime with stellar rotation and from the fact that rotating models near the main-sequence turnoff are more luminous, overlapping with slightly more massive (and shorter-lived) nonrotating ones. Our method uses a large grid of nonrotating models to interpolate between a much sparser rotating grid, and also includes a detailed calculation of synthetic magnitudes as a function of orientation. We provide a web interface at http://www.bayesianstellarparameters.info, where the results of our analysis may be downloaded for individual early-type (B V 0.25 -) Hipparcos stars. The web interface accepts user-supplied parameters for a Gaussian metallicity prior and returns posterior probability distributions on mass, age, and orientation.