The role of convection in stellar atmospheres. II. Cool main-sequencestars and metal-deficient subdwarfs.

Abstract

view Abstract Citations (11) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The role of convection in stellar atmospheres. II. Cool main-sequence stars and metal-deficient subdwarfs. Travis, L. D. ; Matsushima, S. Abstract On the basis of Spiegel's improved theory of convection, a grid of model atmospheres has been constructed for effective temperatures between 60000 and 4500 K with changing metal content and other atmospheric parameters. Significant effects of the nonlocal flux from a deeper convective zone are seen to change the atmospheric structure in such a way that it reduces the temperature gradient and the gas pressure near the surface, as compared to those resulting from the pure radiative or the traditional treatment of the mixing-length theory. The result of these changes is a reddening of the UB V colors, which is more enhanced as the metal content decreases up to about of the solar value. The line-free colors predicted by the models appear to define the upper envelope of observed colors of extreme subdwarfs in the (U - B, B - V)- or (U - B, R - I)diagram, indicating the extreme limit of the ultraviolet excess. The effective-temperature scales determined for G and K stars from these models are found to be several hundred degrees higher than some of the earlier estimates. The results appear to offer limited support to the recent view that many, if not all, of the extreme subdwarfs have luminosities definitely lower than the mainsequence stars. Subject headings: atmospheres, stellar - convection - late-type stars - subdwarfs Publication: The Astrophysical Journal Pub Date: May 1973 DOI: 10.1086/152130 Bibcode: 1973ApJ...182..189T full text sources ADS | data products SIMBAD (20)