Chemical Abundances of Bright Giants in the Mildly Metal-Poor Globular Cluster M4

Abstract

We present a chemical composition analysis of three dozen giant stars in the nearby ``CN-bimodal&#39;&#39; mildly metal-poor (<[Fe/H]> = -1.18) globular cluster M4. The analysis combined traditional spectroscopic abundance methods with modifications to the line-depth ratio technique pioneered by Gray (1994). Silicon and aluminum are found to be primordially overabundant by factors exceeding the mild overabundances usually seen in alpha- and light odd elements among halo field and globular cluster giants of comparable metallicity. In addition, barium is found to be overabundant by a factor of about four. Superimposed on the primordial abundance distribution in M4, there is evidence for the existence of proton-capture synthesis of C, O, Ne, and Mg.