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Paper: Metal Abundances in sdBs from UV Spectroscopy
Volume: 334, 14th European Workshop on White Dwarfs
Page: 315
Authors: O'Toole, S.J.
Abstract: We report on a study of high-resolution (R = 45,800) UV HST/STIS spectroscopy of sdB stars. These observations are part of a project to measure the abundance of iron-group elements in pulsating and non-pulsating sdBs, as well as to study diffusion in these stars. We find that for two of the nonpulsating sdBs (Ton S-227 and Feige 66), which are closest in spectral parameters to one of the pulsators (PG 1219+534), the iron abundance is about a factor of 4-5 below the solar value. For both of the pulsators studied (PG 1219+534 and Feige 48) the abundance of iron is approximately solar, or even slightly above, as found in previous studies. Another star (CPD−64°481) shows an approximately solar iron abundance, however its pulsation status is unclear. The abundances of other iron-group elements vary, although they are almost always supersolar. Elements beyond the iron group are also discussed, and provide challenges for the theories of diffusion and radiative levitation in hot subdwarfs. Finally, we have analysed very high-resolution (R = 114,000) STIS spectra of two sdBs, and find that many of the problems with continuum definition are substantially reduced. Also, at this resolution isotopic shifts in the Pb IV 1313 Å resonance line are at least partially resolved.
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