Astronomy and Astrophysics – Astrophysics
Scientific paper
2004-05-21
Astronomy and Astrophysics
Astrophysics
To appear in "Extreme Horizontal Branch Stars and Related Objects", Astrophysics and Space Science, Kluver Academic Publishers
Scientific paper
10.1023/B:ASTR.0000044342.79287.
We summarize recent results of quantitative spectral analyses using NLTE and metal line-blanketed LTE model atmospheres. Temperatures and gravities derived for hundreds of sdB stars are now available and allow us to investigate systematic uncertainties of teff, log g scales and to test the theory of stellar evolution and pulsations. Surface abundance patterns of about two dozen sdB stars are surprisingly homogenous. In particular the iron abundance is almost solar for most sdBs. We highlight one iron deficient and three super metal-rich sdBs, a challenge to diffusion theory. SdB stars are slowly rotating stars unless they are in close binary systems which is hard to understand if the sdB stars were formed in merger events. The only exception is the pulsator PG 1605+072 rotating at v sin i = 39km/s. Signatures of stellar winds from sdB stars have possibly been found.
Edelmannn H.
Heber Uli
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