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A. M. Boesgaard (U. Hawaii), A. M. Cody (Harvard U.), C. P. Deliyannis (Indiana U.), J. R. King (UNLV), A. Stephens (U. Hawaii)
It is important to determine the composition of unevolved stars in globular clusters in order to learn the original composition of the cluster and to learn about stellar evolution and the chemical history of the Galactic halo. We have made observations of five stars at the turn-off in M 71 with the Keck I 10-m telescope and HIRES at a spectral resolution of 45,000. Such stars have not undergone any mixing with the interior layers and can provide benchmark abundances to interpret the abundance results found in red giants and other evolved stars. These stars have V = 17.7 and integration times of 2.5-5 hours were needed to obtain signal-to-noise ratios of 50-60. We have determined abundances of Li, Na, the Fe-peak elements: Fe, Cr, Ni, alpha-fusion elements: Mg, Si, Ca, Ti, and neutron capture elements: Y and Ba. Except for Li, we have found no star-to-star abundance variations and derive [Fe/H] = -0.80 ±0.02. The alpha elements are enhanced with [<\alpha>/Fe] = 0.24. Both Y and Ba are enhanced relative to Fe also. We compare our results with those from giant stars in M71, with turn-off stars in the globular clusters M13 and M92, and with halo field stars.
This work has been supported by the National Science Foundation.