Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984nascp2349..289b&link_type=abstract
In NASA. Goddard Space Flight Center Future of Ultraviolet Astronomy Based on Six Years of IUE Res. p 289-292 (SEE N85-20961 1
Astronomy and Astrophysics
Astronomy
13
Companion Stars, Subgiant Stars, White Dwarf Stars, Carbon Stars, Iue, Stellar Evolution, Stellar Luminosity
Scientific paper
Subgiant CH stars are F- and G-type subgiants and dwarfs showing enhanced carbon and s-process abundances at their surfaces. Their low luminosities are difficult to understand in the context of standard stellar-evolution theory. One possible hypothesis is that subgiant CH stars are the former secondary components of binary systems in which processed material was transferred from a red-giant carbon-star primary; the former primary would now be an optically invisible white dwarf. However, IUE spectra of 21 subgiant CH stars failed to reveal any of the predicted white-dwarf companions. Together with the distribution of these objects in the HR diagrams, the observations suggest that subgiant CH stars are former red giants that, evolving as single stars, underwent violent mixing events that returned them to the vicinity of the main sequence. Nevertheless, many subgiant CH stars (and their probable descendants, the barium and CH stars) are long-period spectroscopic binaries. Results are compatible with the conclusion that the unseen companions are generally unevolved red dwarfs. Apparently the primary components of such wide binaries are, for some as yet unknown reason, prediposed toward violent mixing.
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