Abundances in Stars from the Red Giant Branch Tip to near the Main-Sequence Turnoff in M5

We present the iron abundance and abundance ratios for 18 elements withrespect to Fe in a sample of stars with a wide range in luminosity fromluminous giants to stars near the turnoff in the globular cluster M5. Theanalyzed spectra, obtained with HIRES at the Keck Observatory, are of highdispersion (R=35,000). We find that the neutron capture, the iron peak and thealpha-element abundance ratios show no trend with Teff, and low scatter aroundthe mean between the top of the RGB and near the main sequence turnoff Towithin the precision of the measurements (~0.1 dex), gravitationally inducedheavy element diffusion does not appear to be present among the stars near themain sequence turnoff studied here. Our work and other recent studies suggestthat heavy element diffusion is inhibited in the surface layers of metal poorstars. Differences in the Na abundance from star to star which extend to themain sequence turnoff are detected in our sample in M5. The anti-correlationbetween O and Na abundances, observed in other metal poor globular clusters, isnot detected in our sample, but it may be hidden among stars with only upperlimits for their O abundances. Overall the abundance ratios of M5 appear verysimilar to those of M71, with the possible exception of the neutron captureelement Ba, where we argue that the apparent difference may be due todifficulties in the analysis. As in M71, the alpha-elements Mg, Ca, Si and Tiare overabundant relative to Fe. The results of our abundance analysis of 25stars in M5 provide further evidence of abundance variations among specificlight elements at unexpectedly low luminosities, which cannot be explained byour current understanding of stellar evolution.Comment: 56 pages, 14 figures, AJ in press (Jan 2003