Elemental Abundances in Five Stars in M54, A Globular Cluster Associated with the Sagittarius Galaxy

Abstract

Chemical abundances in five stars in M54, a globular cluster associated with the Sagittarius dwarf galaxy, have been determined using high-resolution echelle spectra. We find the cluster to have [Fe/H] = -1.55 and possibly halo-normal abundance patterns, although the [O/Fe] and [α/Fe] ratios lie between solar and the normal halo values. One star shows the combination of low oxygen and enhanced Na and Al, symptomatic of deep mixing of ON-cycle and other proton-capture products; a second star shows a lesser degree of O depletion unaccompanied by Na and Al excesses. In the cluster Eu is also enhanced, indicating that about 30% of the Ba in the cluster is due to the r-process. In general, M54 is similar to globulars of comparable metallicity in the inner Galactic halo, despite its clear association with the Sagittarius dwarf spheroidal.