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2006ApJ...638..454P - Astrophys. J., 638, 454-471 (2006/February-2)
An analysis of ultraviolet spectra of extreme helium stars and new clues to their origins.
PANDEY G., LAMBERT D.L., JEFFERY C.S. and RAO N.K.
Abstract (from CDS):
The initial metallicity of an EHe is indicated by the abundance of elements from Al to Ni; Fe is adopted to be the representative of initial metallicity. Iron abundances range from approximately solar to about 1/100 solar. Clues to EHe evolution are contained within the H, He, C, N, O, Y, and Zr abundances. Two novel results are (1) the O abundance for some stars is close to the predicted initial abundance yet the N abundance indicates almost complete conversion of initial C, N, and O to N by the CNO cycles; and (2) three of the seven stars with UV spectra show a strong enhancement of Y and Zr attributable to an s-process.
The observed compositions are discussed in light of expectations from accretion of an He white dwarf by a C-O white dwarf. Qualitative agreement seems likely except that a problem may be presented by those stars in which the O abundance is close to the initial O abundance.
Abstract Copyright: ∼
Journal keyword(s): Stars: Abundances - Stars: Chemically Peculiar - Stars: Evolution
Simbad objects: 19
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