Abundances of 30 Elements in 23 Metal‐Poor Stars

We report the abundances of 30 elements in 23 metal-poor ([Fe/H] <-1.7)giants. These are based on 7774 equivalent widths and spectral synthesis of 229additional lines. Hyperfine splitting is taken into account when appropriate.Our choice of model atmospheres has the most influence on the accuracy of ourabundances. We consider the effect of different model atmospheres on ourresults. In addition to the random errors in Teff, log g, and microturbulentvelocity, there are several sources of systematic error. These include usingTeff determined from FeI lines rather than colors, ignoring NLTE effects on theFeI/FeII ionization balance, using models with solar [alpha/Fe] ratios andusing Kurucz models with overshooting. Of these, only the use of models withsolar [alpha/Fe] ratios had a negligible effect. However, while the absoluteabundances can change by > 0.10 dex, the relative abundances, especiallybetween closely allied atoms such as the rare earth group, often show onlysmall (<0.03 dex) changes. We found that some strong lines of FeI, MnI and CrIconsistently gave lower abundances by ~0.2 dex, a number larger than the quotederrors in the gf values. After considering a model with depth-dependentmicroturbulent velocity and a model with hotter temperatures in the upperlayers, we conclude that the latter did a better job of resolving the problemand agreeing with observational evidence for the structure of stars. The erroranalysis includes the effects of correlation of Teff, log g, and microturbulentvelocity errors, which is crucial for certain element ratios, such as [Mg/Fe].The abundances presented here are being analyzed and discussed in a separateseries of papers.Comment: 27 pages, 9 figures, Table 2 included separately, to published in ApJ