RELATIVE ABUNDANCE DETERMINATIONS IN EXTREMELY METAL POOR GIANTS .2. TRANSITION-PROBABILITIES AND THE ABUNDANCE DETERMINATIONS

This paper determines the abundances of iron and other elements for one star of intermediate metallicity and for nine extremely metal poor stars, including two members of the globular cluster M92 as well as CD -38°245, the most metal poor star known. In the process, we evaluate the accuracy of transition probabilities for Fe I and other elements. Our determination of the iron abundance for M92 is [Fe/H] = -2.5 ± 0.2, lower than the values of -2.0 or -2.2 adopted recently. We suggest that errors in solar gf-values may have caused overestimates of the iron abundances for the most metal poor stars in globular clusters. Our revised M92 iron abundance increases by somewhat less than 3 Gyr the age of M92 inferred by Stetson and Harris from more metal rich isochrones, and brings the oxygen-to-iron ratios and overall metallicities of extremely metal poor cluster giants into agreement with those of the field dwarfs of lowest metallicity. The distribution of the abundances of other elements with respect to iron is the same in most cases for all stars included here. At all low metallicities the light even-Z elements oxygen, magnesium, silicon, calcium, and titanium are somewhat overabundant, while the odd-Z elements are deficient relative to the adjacent even-Z elements. Manganese is the only element which shows a different relative abundance in the extremely metal poor star: it is more than a factor of 10 more deficient with respect to iron in this star than in the others.