HST/GHRS Observations of the beta Pictoris System: Basic Parameters of the Age of the System

Abstract

We have reevaluated the basic parameters and age of the A5 IV--V star, beta Pictoris, making use of new observations obtained by the Goddard High-Resolution Spectrograph aboard the Hubble Space Telescope and using modern methods of atmospheric modeling and spectral synthesis. We derive stellar parameters appropriate to its spectral type (Teff = 8200 +/- 150 K, log g = 4.25 +/- 0.1) including a normal (solar) metallicity. When dated by comparison with current evolutionary tracks, we find that (1) the star is apparently "underluminous"---a situation we attribute to (gray) extinction by the disk---and (2) the star is either a pre--main-sequence (PMS) star nearing the zero-age main sequence (ZAMS), or it is a main-sequence star older than 0.3 Gyr. Given the apparent youth of the disk as inferred from its high density, we judge the PMS interpretation as most likely.