Helium, Carbon and Silicon Abundances in the HW VIR Eclipsing Binary Subdwarf-B Primary

Abstract

Light curve solutions show HW Vir and PG 1336-018 to be remarkably similar eclipsing binaries. The subdwarf-B (sdB) primary of PG 1336-018 is a pulsator but pulsation is not detected in the sdB primary of HW Vir. Ultraviolet spectra were used to obtain carbon and silicon abundances in the sdB primary of HW Vir; in due course these should be compared with those in the sdB primary of PG 1336-018 to see if pulsation in the latter could be explained by the κ -mechanism, arising from higher metal abundances and microscopic diffusion.