Parameters of the two helium-rich subdwarfs in the short period binary PG1544+488

Details Parameters of the two helium-rich subdwarfs in the short period binary PG1544+488 Parameters of the two helium-rich subdwarfs in the short period binary PG1544+488

Aug 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007iaus..240..129a&link_type=abstract

Binary Stars as Critical Tools and Tests in Contemporary Astrophysics, International Astronomical Union. Symposium no. 240, he

Astronomy and Astrophysics

Astrophysics

Scientific paper

Helium-rich subdwarf B (He-sdB) stars form a small group of chemically peculiar, early-type, low-mass stellar remnants. They are thought to be formed either as a result of mergers of white dwarfs or by convective mixing of a helium white dwarf envelope after a late helium flash. PG1544+488 is the prototype of the He-sdB stars. It was serendipitously found to be short period binary (P ~ 0.5 day) comprising two helium-rich subdwarfs. In this poster we report physical parameters and orbital solution for the two helium-rich subdwarfs in PG1544+488 from optical spectra obtained over a period of three years. The physical parameters - effective temperature, surface gravity and helium abundances (by number) - for both subdwarfs were measured by fitting the observed spectra with LTE models using a chi-squared minimization procedure. The orbital solutions were obtained using radial velocities measured from the optical spectra. We also briefly discuss the implications of the discovery that PG1544+488 is a binary on our current understanding of the evolution of helium-rich subdwarf B stars and the possibility of a third formation channel for these stars involving a common-envelope in a close binary.

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