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Paper: A New Determination of Abundances for the Subdwarf B Star HD 4539
Volume: 392, Hot Subdwarf Stars and Related Objects
Page: 109
Authors: Sale, S.E.; Schoenaers, C.; Lynas-Gray, A.E.
Abstract: Abundance patterns in sdB stars, and how these differ between pulsators and non-pulsators, are not yet understood. With the recent discovery of non-radial pulsation in HD 4539, and the availability of flux calibrated ultraviolet spectra to supplement optical spectra obtained for pulsation studies, a further study of abundances in this bright sdB star was identified as a requirement for more sophisticated future pulsation models. Neutral and molecular hydrogen column densities, and three-dimensional galactic extinction models, were used to estimate EB−V = 0.04 ± 0.01 as the interstellar extinction along the line-of-sight to HD 4539. The energy distribution then gave Teff = 26000 ± 500K; log g = 5.2 ± 0.1 and [He/H] = −1.25 ± 0.05 were then obtained from fits to Balmer and He I lines. An over-abundance of nitrogen and an under-abundance of oxygen was confirmed but in other details derived abundances were discordant with those in the literature. In particular, carbon and silicon were found to be more depleted by nearly one order of magnitude.
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