Chemical abundances in globular cluster turn-off stars from Keck/HIRES observations

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Abstract
Spectroscopic observations at high spectral resolution of unevolved stars in globular clusters have only been possible since the 1993 advent of the Keck-I 10-meter telescope and its high-resolution spectrometer. Our program of deriving chemical abundances of lithium and several other elements in some unevolved, but identical, stars in three globular clusters is described. For M13 we have found a spread in Li abundances of a factor of five in four very similar stars. For six stars in M92 the range is a factor of three and for five in M71 the range is a factor of two. The stars with the highest abundances of Li show values that are a factor of two above the field halo star Li plateau. The abundances of several other species - Na, Mg, Si, Ca, Ti, Cr, Ni, Fe, Y, and Ba - show no such star-to-star variations. These abundances are compared with those of halo field stars which were derived from Keck HIRES spectra.

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