NLTE analyses of sdB stars: progress and prospects
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We report on preliminary results of a hybrid non-LTE analysis of high-resolution, high-S/N spectra of the helium-rich subdwarf B star Feige49 and the helium-poor sdB HD205805. Non-LTE effects are found to have a notable impact on the stellar parameter and abundance determination. In particular the HeI lines show significant deviations from detailed balance, with the computed equivalent widths strengthened by up to ~35%. Non-LTE abundance corrections for the metals (C, N, O, Mg, S) are of the order ~0.05-0.25 dex on the mean, while corrections of up to ~0.7 dex are derived for individual transitions. The non-LTE approach reduces systematic trends and the statistical uncertainties in the abundance determination. Consequently, non-LTE analyses of a larger sample of objects have the potential to put much tighter constraints on the formation history of the different sdB populations than currently discussed.
8 pages, 5 figures; to appear in: Baltic Astronomy, Proceedings of the Second Meeting on Hot Subdwarf Stars an Related Objects, La Palma, June 2005
8 pages, 5 figures; to appear in: Baltic Astronomy, Proceedings of the Second Meeting on Hot Subdwarf Stars an Related Objects, La Palma, June 2005