Summary: Astronomy & Astrophysics manuscript no. H4215 March 26, 2003
(DOI: will be inserted by hand later)
Physical parameters of helium­rich subdwarf B stars from
medium resolution optical spectroscopy #
A. Ahmad and C. S. Je#ery
Armagh Observatory, College Hill, Armagh BT61 9DG. N. Ireland, UK
Received 24 December 2002 / Accepted 13 February 2003
Abstract. Most subdwarf B (sdB) stars have spectra that show helium (He) abundances depleted to a lesser or greater extent.
This has been attributed to di#usion and gravitational settling. However a small but significant number of stars with similar
temperatures and gravities show relatively strong helium spectra. The question is how these helium­rich sdB (He­sdB) stars are
related to their He­deficient counterparts. We present physical parameters for sample of He­sdB stars using line­blanketed LTE
models. From the analysis we show that the He­sdB stars are quite distinct from the He­poor sdB. We also explore the idea of
a possible link between some extreme helium (EHe) stars and He­rich subdwarf O (He­sdO) stars.
Key words. stars: chemically peculiar ­ stars: early­type ­ subdwarfs ­ stars: atmospheres ­ stars: fundamental parameters ­
stars: evolution
1. Introduction
The vast numbers of faint blue stars in our own Galaxy (Green
et al. 1986) and in giant elliptical galaxies (Brown et al. 1997)
are dominated by a population of subluminous B stars. These
so­called subdwarf B (sdB) stars are core­helium burning stars

Source: Armagh Observatory

Collections: Physics