Subluminous B stars come in a variety of flavours including single stars, close and wide binaries, and pulsating and non-pulsating variables.
We present a fine analysis of the bright intermediate helium sdB star CPD-20d1123 which shows it to be cool, for a hot subdwarf, with Teff = 23000 K and with a surface helium abundance ~17 percent by number. Other elements do not show extraordinary anomalies; in common with majority sdB stars, carbon and oxygen are substantially depleted, whilst nitrogen is enriched. Magnesium through sulphur appear to be depleted by ~0.5 dex, but chlorine and argon are substantially enhanced.
We also present a series of radial velocity measurements which show the star to be a close binary with an orbital period of 2.3 d, suggesting it to be a post-common-envelope system.
The discovery of an intermediate helium rich sdB star in a close binary in addition to kjnown and apparently single exemplars supports the view that these are very young sdB stars in which radiatively driven stratification of the photosphere is incomplete
- stars: abundances binaries,
- chemically peculiar stars,
- stars: evolution,
- stars: horizontal branch,
- stars: subdwarf
Available at: http://works.bepress.com/vincent_woolf/1/