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Physical parameters of helium-rich subdwarf B stars from medium resolution optical spectroscopy
 

Summary: Physical parameters of helium-rich subdwarf B stars from
medium resolution optical spectroscopy
A. Ahmad and C. S. Jeffery
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 diffusion 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 helium-rich sdB (He-sdB) stars are
related to their He-deficient counterparts. We present physical parameters for sample of He-sdB stars using line-blanketed LTE
models. From the analysis we show that the He-sdB stars are quite distinct from the He-poor sdB. We also explore the idea of
a possible link between some extreme helium (EHe) stars and He-rich subdwarf O (He-sdO) stars.
Key words. stars: chemically peculiar - stars: early-type - 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
so-called subdwarf B (sdB) stars are core-helium burning stars
of 0.5 M with a thin hydrogen envelope. Their surfaces are
predominantly weak in helium as a consequence of elemen-

  

Source: Armagh Observatory

 

Collections: Physics