Testing Seismic Models of Hot B Subdwarfs with Gaia Data

Abstract

We report the results of a study designed to test further the basic validity of the seismic models of hot pulsating B subdwarfs that have been developed over the last two decades. Given estimates of the effective temperature, surface gravity, and mass as obtained from a seismic analysis, and given an estimate of the He/H ratio as available from independent spectroscopy, it is possible to compute a "seismic distance" that is suitably corrected for interstellar reddening from a model atmosphere calculation in conjunction with two-band photometry. The test consists of comparing such a distance with that obtained directly from the high-accuracy Gaia parallax measurements that have become available through Data Release 2. Using observed magnitudes in the Gaia G BP, G RP bandpasses as well as ground-based photometry in the Johnson B, V, Strömgren b, y, and SDSS g, r filters, we find that all of our seismic estimates fall within 1σ of their parallax counterparts. In addition, the derived reddening for our target stars is shown to be generally consistent with Galactic dust reddening and extinction maps. These results apply to a sample of 14 pulsating hot B subdwarfs for which seismic models were published in the past. We also derive useful constraints on the distances to two more pulsators that belong to unresolved binary systems. The excellent agreement found between seismic and parallax distances for the bulk of the sample adds further credibility to the seismic models that have been calculated for pulsators of this type.