Elemental Abundances in Normal Late B-Stars and Hgmn-Stars from Co-Added IUE Spectra - Part Two - Magnesium Aluminium and Silicon

Details Elemental Abundances in Normal Late B-Stars and Hgmn-Stars from Co-Added IUE Spectra - Part Two - Magnesium Aluminium and Silicon Elemental Abundances in Normal Late B-Stars and Hgmn-Stars from Co-Added IUE Spectra - Part Two - Magnesium Aluminium and Silicon

Sep 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...276..393s&link_type=abstract

Astronomy and Astrophysics, Vol.276, NO. 2/SEPII, P. 393, 1993

Astronomy and Astrophysics

Astrophysics

34

Stars: Abundances, Stars: Atmospheres, Stars: Chemically Peculiar, Stars: Early-Type, Ultraviolet: Stars

Scientific paper

Atmospheric abundances of magnesium, aluminium, and silicon are derived for a sample of forty normal, superficially normal, and HgMn-type main-sequence late-B stars by spectrum-synthesis analysis of co-added high-resolution International Ultraviolet Explorer (lUE) spectra. In the normal and superficially normal stars, the abundances of these elements are found to be approximately solar, with the notable exception of α Lyr which is underabundant by typically 0.3-0.5 dex. In the HgMn stars, magnesium exhibits a broad range of abundances from near-solar values to pronounced deficiencies (˜1 dex). Aluminium is deficient in essentially all HgMn stars, and becomes increasingly underabundant at higher effective temperatures. Silicon shows a narrow but significant spread of abundances in the HgMn stars, and is in general mildly underabundant when compared with normal stars of similar effective temperature. The correlation between aluminium underabundances and effective temperature is the first of its type detected in HgMn stars.
Published radiative diffusion calculations for magnesium and silicon in non-magnetic stellar atmospheres are shown to be broadly consistent with these observations, although the predicted correlation with Teff for the former is opposite to that observed. Evidence is presented for the existence of a sub-group of hot, mild HgMn stars exemplified by objects such as 46 Aql and distinguished primarily by the following properties: (1) effective temperatures in the narrow interval 13000-14000K; (2) low surface gravities (typically log g ˜ 3.5) in most, but not all, cases; (3) underabundances of carbon, silicon, and magnesium; (4) overabundances of iron; and (5) relatively mild enhancements of manganese compared with other HgMn stars of similar Teff.

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