Fundamental properties of nearby single early B-type stars

Abstract

Fundamental parameters of a sample of 26 apparently slowly-rotating single early B-type stars in the solar neighbourhood are presented and compared to high-precision data from detached eclipsing binaries (DEBs). The data are used to discuss the evolutionary status of the stars in context of the most recent Geneva grid of models. Evolutionary masses plus radii and luminosities are determined to better than typically 5%, 10%, and 20% uncertainty, respectively, facilitating the mass-radius and mass-luminosity relationships to be recovered with a similar precision as derived from DEBs. Good agreement between evolutionary and spectroscopic masses is found. Absolute visual and bolometric magnitudes are derived to typically 0.15-0.20mag uncertainty. Metallicities are constrained to better than 15-20% uncertainty and tight constraints on evolutionary ages of the stars are provided. Signatures of mixing with CN-cycled material are found in 1/3 of the sample stars. Typically, these are consistent with the amount predicted by the new Geneva models with rotation. A few objects are possibly the product of binary evolution. In particular, the unusual characteristics of tau Sco point to a blue straggler nature, due to a binary merger. The accuracy and precision achieved in the determination of fundamental stellar parameters from the quantitative spectroscopy of single early B-type stars comes close (within a factor 2-4) to data derived from DEBs. However, significant systematic differences with data from the astrophysical reference literature are found. Masses are about 10-20% and radii about 25% lower then the recommended values for luminosity class V, resulting in the stars being systematically fainter than assumed usually, by about 0.5mag in absolute visual and bolometric magnitude. (abstract abridged)