Computer Science
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aipc.1314...79h&link_type=abstract
INTERNATIONAL CONFERENCE ON BINARIES: In celebration of Ron Webbink's 65th Birthday. AIP Conference Proceedings, Volume 1314, p
Computer Science
1
Dwarf Stars, White Dwarfs, Brightness, Galactic Centre, Stellar Evolution, Giant And Subgiant Stars, Faint Blue Stars, White Dwarfs, Degenerate Stars, Nuclei Of Planetary Nebulae, Luminosities, Magnitudes, Effective Temperatures, Colors, And Spectral Classification, Galactic Center, Bar, Circumnuclear Matter, And Bulge, Hertzsprung-Russell, Color-Magnitude, And Color-Color Diagrams
Scientific paper
Amongst the hot subdwarf stars, the helium enriched sdOs still remain a mystery. Rivalling scenarios for their origin include mergers of He white dwarfs, first proposed by Ron Webbink, and the so-called ``late hot flasher'' where a star undergoes a delayed helium flash long after leaving the RGB. Recent NLTE spectral analyses revealed that an evolutionary link between sdO stars and their cooler cousins, the sdB stars, is plausible only for the helium-deficient sdO stars, i.e. they are the likely successors to sdB stars. A large sample of sdO stars has recently been analysed using NLTE model atmospheres to derive carbon and nitrogen abundances. The stars are generally speaking either C-rich or N-rich-a few are both. The N-rich stars are on average significantly cooler than the C-rich, whereas both subsample have the same mean surface gravity. The surface composition of N-rich He-sdOs are best explained by the merger of two helium white dwarfs or of a helium white dwarf with a post-sdB star. Only the late flasher model seems to be capable to explain the C-rich sdO stars. Closer inspection, however, reveals problems for both scenarios to explain the distribution of the stars in the (Teff, log g)-plane as well as the rotational properties. A hyper-velocity sdO star moving so fast that it is unbound to the Galaxy possibly has been ejected by the super-massive black hole in the Galactic centre.
Heber Ulrich
Hirsch Heiko
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