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Context. Hot subdwarf B stars (sdBs) are considered to be core helium-burning stars with very thin hydrogen envelopes situated on or near the extreme horizontal branch. The formation of sdBs is still unclear as well as the chemical composition of their atmospheres. The observed helium depletion is attributed to atmospheric diffusion. Metal abundances have been determined for about a dozen sdBs only resulting in puzzling patterns with enrichment of heavy metals and depletion of lighter ones.
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S. Geier (2012) studied this question.
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