A chemically peculiar Be-shell star in a sub-solar metallicity solution for the post-mass-transfer eclipsing binary V658 Car

Abstract

V658 Car (HD 92406) is a newborn resp. rejuvenated shell star binary system at the age of only 1 Myr after the end of mass transfer. In this renewed study the peculiarities of the Be star are at first by-passed by the determination of the properties of the contracting hot subdwarf precursor, but finally resolved by combining photometric data and radial velocity results with existing stellar models. For the effective temperatures, radii and masses we get about 12900 K, 1.92/2.20 Rsun and 4.49 Msun for the Be star, and about 18400 K, 1.87 Rsun and 0.56 Msun for its companion star. The Be star has a rotational velocity of 336 km/s and is surrounded and dimmed in our view by a large and luminous equatorial decretion disk having a radius of ~ 42 Rsun. According to stellar models these results fit to a surprisingly low metallicity Z of 0.003 and a Teff ~ 5400 K higher than observational expectations for the Be star, which hence should belong to the chemically peculiar stars, in spite of its rapid rotation.