Summary: Physical parameters of helium-rich subdwarf B stars from
spectral energy distributions
A. Ahmad and C. S. Jeffery
Armagh Observatory, College Hill, Armagh BT61 9DG. N. Ireland. UK
Received 15 July 2003 / Accepted 02 October 2003
Abstract. We present effective temperatures and angular radii for eleven helium-rich subdwarf B stars. These are measured
using spectral energy distributions from archival IUE spectra and existing optical and infrared photometry. The data have been
analysed using a grid of high-gravity helium-rich LTE model atmospheres and a 2
-minimization procedure. The parameters
derived here allow for independent verification of the parameters derived from the analysis of optical spectra.
Key words. stars: chemically peculiar - stars: early-type - subdwarfs - stars: atmospheres - stars: fundamental parameters
Helium-rich subdwarf B stars (He-sdB) stars are rare faint blue
stars first identified as sdOD stars in the Palomar-Green (PG)
survey of faint blue objects (Green et al. 1986). They are found
both in our Galaxy (PG survey) as well as in globular clus-
ters (Moehler et al. 1997; 2002). The optical spectra of He-sdB
stars, by definition show strong HeI and in some cases HeII ab-
sorption lines. Some of them also show strong carbon lines.
The evolution of these stars has been under much debate.