SPECTROSCOPIC ANALYSES OF METAL-POOR STARS .1. BASIC DATA AND STELLARPARAMETERS

Accurate stellar parameters have been obtained from the analyses of mo re than thousand spectra of 115 metal-poor dwarfs and subgiants with v isual magnitudes brighter than V approximate to 12. The stellar sample was selected mainly by high proper motion, with additional restrictio ns from B-V colours and U-B excesses. The effective temperatures cover a range from 5000 to 6500 K while metal abundances are found between [M/H] = -0.1 and -3.0 dex. For the first time a representative number of unevolved cool metal-poor stars has been analysed individually usin g purely spectroscopic methods. Based on homogeneous ODF blanketed mod el atmospheres in LTE and working differ entially with respect to the Sun we derive a consistent set of stellar parameters, effective temper ature, 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 T-eff of bette r than 100 K, in log g of better than 0.15, and in [Fe/H] of better th an 0.1 dex. Because of the consistent treatment with only one type of model atmosphere, this sample provides an opportunity to examine the i ndividual parameters statistically and investigate in detail their rel ation to the formation and evolution of the Galaxy. One aspect of this analysis is a general shift to higher iron abundances for the most me tal-poor stars. Along with the recently preferred meteoritic solar iro n abundance and effective temperatures from consistent Balmer line pro file fits that tend to be 100 - 200 K hotter than found from photometr ic calibrations, discrepancies of up to 0.5 dex in [Fe/H] can be expla ined in comparison with other abundance analyses. The most important r esults refer to the evolutionary status of the bona fide subdwarf samp le. Irrespective of the different effective temperatures found here, t here exists a severe problem when comparing post main sequence evoluti onary models of cool stars with our observed parameters. Even more int eresting is the fact, demonstrated by the results of a consistent anal ysis of the iron ionization equilibrium, that roughly half of the subd warfs are subgiants, some of them having nearly reached the bottom of the giant branch.