A preliminary look at the empirical mass distribution of hot B subdwarf stars

¹ Département de Physique, Université de Montréal, Succ. Centre-Ville, CP 6128, Montréal, QC, H3C 3J7, Canada
e-mail: fontaine@astro.umontreal.ca
² Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
³ CNRS, IRAP, 14 Av. E. Belin, 31400 Toulouse, France
⁴ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
⁵ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
⁶ Institut d’Astrophysique et de Géophysique de l’Université de Liège, Allée du 6 Août 17, 4000 Liège, Belgium
⁷ FNRS, rue d’Egmont 5, 1000 Bruxelles, Belgium

Received: 7 October 2011
Accepted: 12 December 2011

Abstract

We present the results of about a decade of efforts toward building an empirical mass distribution for hot B subdwarf stars on the basis of asteroseismology. So far, our group has published detailed analyses pertaining to 16 pulsating B subdwarfs, including estimates of the masses of these pulsators. Given that measurements of the masses of B subdwarfs through more classical methods (such as full orbital solutions in binary stars) have remained far and few, asteroseismology has proven a tool of choice in this endeavor. On the basis of a first sample of 15 pulsators, we find a relatively sharp mass distribution with a mean mass of 0.470 M_⊙, a median value of 0.470 M_⊙, and a narrow range 0.441−0.499 M_⊙ containing some 68.3% of the stars. We augmented our sample with the addition of seven stars (components of eclipsing binaries) with masses reliably established through light curve modeling and spectroscopy. The new distribution is very similar to the former one with a mean mass of 0.470 M_⊙, a median value of 0.471 M_⊙, and a slightly wider range 0.439−0.501 M_⊙ containing some 68.3% of the stars. Although still based on small-number statistics, our derived empirical mass distribution compares qualitatively very well with the expectations of stellar evolution theory.