Spectroscopic analyses of metal-poor stars. 1: Basic data and stellar parameters

Details Spectroscopic analyses of metal-poor stars. 1: Basic data and stellar parameters Spectroscopic analyses of metal-poor stars. 1: Basic data and stellar parameters

Nov 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...291..895a&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 291, no. 3, p. 895-909

Astronomy and Astrophysics

Astrophysics

70

Abundance, Dwarf Stars, Metallicity, Spectroscopic Analysis, Stellar Evolution, Stellar Models, Subgiant Stars, Atmospheric Models, Data Reduction, Galactic Evolution, Line Spectra, Stellar Atmospheres, Stellar Temperature

Scientific paper

Accurate stellar parameters have been obtained from the analyses of more than thousand spectra of 115 metal-poor dwarfs and subgiants with visual magnitudes brighter than V approximately equal to 12. The stellar sample was selected mainly by high proper motion, with additional restrictions from B-V colors and U-B excesses. The effective temperatures cover a range from 5000 to 6500 K while abundances are found between (M/H) = -0.1 and -0.3 dex. Based on homogeneous ODF blanketed model atmospheres in local thermodynamic equilibrium (LTE) and working differentially with respect to the Sun we derive a consistent set of stellar parameters, effective temperature, surface gravity, metal abundance and microturbulence velocity. Individual profile synthesis is applied to a number of spectral lines for each star, which has led as a rule to accuracies in Teff of better than 100 K, in log g of better than 0.15, and in (Fe/H) of better than 0.1 dex. Because of the consistent treatment with only one type of model atmosphere, this sample provides an oppurtunity to examine the individual parameters statistically and investigate in detail their relation to the formation and evolution of the Galaxy. One aspect of this analysis is a general shift to higher iron abundances for the most metal-poor stars. Along with the recently preferred meteoritic solar iron abundance and effective temperatures from conistent Balmer line profile fits that tend to be 100-200 K hotter than found from photometric calibrations, discrepancies of up to 0.5 dex in (Fe/H) can be explained in comparison with other abundance analyses. The most important results refer to the evolutionary status of the bona fide subdwarf sample. Irrespective of the different effective temperatures found here, there exists a severe problem when comparing post main sequence evolutionary models of cool stars with our observed parameters. Even more interesting is the fact, demonstrated by the results of a consistent analysis of the iron ionization equilibrium, that roughly half of the subdwarfs are subgiants, some of them having nearly reached the bottom of the giant branch.

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