The Mildly Metal-Poor Globular Cluster M4: Star-to-Star Abundance Variations in 20 Giants

We present a chemical composition analysis of a sample of 20 giant branch stars in the "CN-bimodal" globular cluster M4 observed using high resolution echelle spectrographs at Lick & McDonald Observatories. M4, a mildly metal-poor ([Fe/H] ~ -1.1) globular cluster, is the nearest, brightest, and one of the most accessible targets to study the CN-bimodal phenomena. The abundance analysis includes elements Fe, Si, Ca, Sc, Ti, V, and Ni as well as elements that are diagnostics of proton-capture nucleosynthesis, O, Na, Mg, and Al, in addition to r-process and s-process elements, Eu and Ba.