Neutron-Capture Element Abundances in the Globular Cluster M15

Abstract

High-resolution, high signal-to-noise ratio, blue–violet spectra of three red giant branch tip stars in M15 have been obtained with the Keck I High-Resolution Echelle Spectrograph. These spectra have been analyzed to determine the abundances of several neutron-capture elements, including the radioactive chronometer element thorium. There are two principal results of this study. First, the abundances of the heavier () elements for Z ≥ 56 each of the three stars is well matched by a scaled solar system r-process abundance distribution. Second, a weighted mean–observed Th/Eu ratio for the stars implies an age for the neutron-capture material in M15 stars of Gyr, in reasonable agreement with other recent age estimates for Galactic globular clusters. 14 ‫ע‬ 3