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

Timothy D. Brandt, Chelsea X. Huang

Published 2015-01-19Version 1

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 beta Pictoris and the Pleiades. However, we derive a slightly older age for the Ursa Majoris moving group (600+/-100 Myr compared to 500+/-100 Myr), and a much older age for the Hyades open cluster (950+/-100 Myr compared to 625+/-50 Myr). These older ages result 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. The dramatically older age inferred for the Hyades requires a major reevaluation either of the cluster age or of the rotating stellar models. 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 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.