Physics
Scientific paper
Jun 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982a%26a...110..215o&link_type=abstract
Astronomy and Astrophysics, vol. 110, no. 2, June 1982, p. 215-224.
Physics
12
Binary Stars, Stellar Atmospheres, Stellar Evolution, Stellar Models, Stellar Temperature, Visual Observation, Abundance, Acceleration (Physics), Astronomical Photometry, Dwarf Stars, Giant Stars, Stellar Color
Scientific paper
For a sample of t4 physical binaries with late type giant primaries uvbyβ photometry is combined with available calculated colours for stellar atmosphere models to derive Te, g, [Fe/H], B.C., and Mbol for both components. The accuracy and reliability of the derived quantities are estimated. It is concluded that g values for giants are not reliably determined in this way for individual stars. For the F type dwarf companions some derived g values also appear unreliable, while [Fe/H] determined from an empirical calibration is superior to the value derived from the models of Kurucz (1979).
About one third of the giant primaries seem to be more metal rich than their secondaries. Three possible explanations are discussed. 1. There may still be systematic differences between spectroscopic abundance determinations for giants and dwarfs. 2. Use of a grid of atmosphere models with a suitable nitrogen enrichment will remove some of the discrepancy, but this effect has been taken into account by the method used in deriving the abundances. 3. Some unknown type of mixing process may occur in normal single giants, may be at the beginning of their asymptotic giant branch evolution.
Comparisons with available isochrones indicate that the mixing length parameter should be allowed to decrease by more than 0.5 as the models evolve from the ZAMS to the giant branch. Also, the position of the giant primaries may indicate that mass loss occurs during the subgiant or early giant phase, but this indirect evidence is arguable.
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