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.
@article{arxiv.0804.3698,
title = {Subdwarf O Stars from SDSS and SPY},
author = {H. A. Hirsch and U. Heber and S. J. O'Toole},
journal= {arXiv preprint arXiv:0804.3698},
year = {2008}
}
Comments
to appear in "Hot Subdwarf Stars and Related Objects", ASPC Volume Nr. 392 p.175