Subdwarf O Stars from SDSS and SPY
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We present the results of quantitative spectral analysis of sdOs from the SDSS database. Fitting the Balmer, HeI and HeII lines to non-LTE model spectra, we derived their effective temperatures, surface gravities and helium abundances. We find the helium-enriched sdO stars to rally in a small intervall of Teff = 40,000K to 50,000K and log(g) = 5.5 to 6.0. We conclude, that the sdB stars are linked with the helium-deficient sdO stars, i.e. the sdBs are predecessors for the helium-deficient sdOs. To explain the helium-enriched sdO stars in their entirety, we regard two scenarios as most promising: The merging of two helium-core white dwarfs and the late hot flashers.
to appear in "Hot Subdwarf Stars and Related Objects", ASPC Volume Nr. 392 p.175
to appear in "Hot Subdwarf Stars and Related Objects", ASPC Volume Nr. 392 p.175