Outer Versus Inner Halo Globular Clusters: NGC 7492 Abundances

We have carried out a detailed abundance analysis for 21 elements in a sampleof four RGB stars in the outer halo globular cluster NGC 7492 (R{GC} 25 kpc);we find [Fe/H] = -1.82 dex inferred from FeI lines (-1.79 from FeII) using highdispersion (R=35,000) spectra obtained with HIRES at the Keck Observatory. Mostelements show no sign of star-to-star variation within our limited sample. Wehave, however, detected an anti-correlation between O and Na abundances similarto that seen in our previous analyses of inner halo GCs as well as in studiesof relatively nearby GCs by others. We compare the abundance ratios in NGC 7492 with those we previouslydetermined for the much closer old halo GCs M3 and M13. After makingcorrections for trends of abundance ratio with metallicity characteristic ofhalo stars, we find that for for these three GCs for each of the elements incommon we deduce identical abundance ratios with respect to Fe to within theprobable measurement uncertainties. Thus, the chemical history of the outerhalo as exemplified by the metal-poor outer halo globular cluster NGC 7492 isindistinguishable from that of the inner halo, exemplified by M3 and M13, atleast through the epoch of formation of these old globular clusters. Thisapplies to the neutron capture processes as well.Comment: Accepted to the A