Study of the Main Sequence Turnoff Stars in M13 and M71

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ABSTRACTCohen, JudithThis project investigates the chemical abundances of evolving stars in the galactic clusters M13 and M71. Using the Keck Observatory data archive and new spectra taken at the Palomar Observatory, a search is being conducted to identify chemical abundance variations, if any, among ~75 main sequence stars in each cluster by measuring the strengths of atomic lines and molecular features. Scatter larger than the expected measurement errors is used to detect abundance variations in the sample. For a subset of these stars, a second phase of the project may be undertaken. Detailed atmospheric models will be used to derive effective temperatures and surface gravities. Combining these results with distance estimates provided by Hipparcos and other projects, the masses of the stars can be estimated and the importance of mixing during various evolutionary phases of near solar-mass stars can be investigated. The results may help to resolve the discrepancy between the age estimates for globular clusters and determinations of the Hubble constant.