Study of the Main Sequence Turnoff Stars in M13 and M71

这个项目研究了星系团M13和M71中演化恒星的化学丰度。利用凯克天文台的数据档案和在帕洛玛天文台拍摄的新光谱，通过测量原子谱线的强度和分子特征，正在进行一项搜索，以确定每个星团中约75颗主序星的化学丰度变化，如果有的话。大于预期测量误差的散点用于检测样品中的丰度变化。对于这些恒星的一部分，可以进行项目的第二阶段。详细的大气模型将用于推导有效温度和表面重力。将这些结果与Hipparcos和其他项目提供的距离估计相结合，可以估计恒星的质量，并可以研究近太阳质量恒星在不同演化阶段混合的重要性。这一结果可能有助于解决球状星团年龄估计与哈勃常数测定之间的差异。

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.