Studies of Very Metal Poor Stars

20多年前，人们发现，在一些银河系球状星团的巨大分支的尖端，居住着C、N和O丰度变化很大的恒星。随后，在同一颗恒星中检测到Na、Al和Mg的变化，虽然不那么强烈，但仍然是真实的。该项目的目标是确定贫金属恒星中元素丰度的变化，首先集中在球状星团上，作为光度和进化状态的函数。我们解释和重现这种变化的能力是对我们对恒星演化的许多方面以及银河系早期化学历史的理解的严格考验。这是一个我们有时会失败的测试。在先前的工作中，在球状星团M71中发现了O和Na的反相关变化。此外，CH和CN的大反相关变化也被发现与恒星演化理论的预测相反。目前的项目将继续并将这项工作扩展到更多的金属贫乏的球状星团，在那里，由疏浚引起的恒星间丰度变化与原始变化之间的区别应该更加清晰。此外，该研究将扩展到更多的金属贫星团，在CH和CN波段上的工作，以尽可能低的光度。在一个相关的主要项目中，我们正在研究银河系中最缺乏金属的恒星（那些[Fe/H] =.3.0指数的恒星）的丰度分布和散射

PI CohenMore than 20 years ago it was discovered that the tip of the giant branch in some galactic globular clusters is populated by stars which show wide variations in C, N, and O abundances. Subsequently less strong, but still real, variations in Na, Al and Mg were detected among the same stars. The goal of this project is to determine the variations of abundances of elements in metal poor stars, concentrating first on globular clusters, as a function of luminosity and evolutionary state. Our ability to explain and reproduce such variations is a stringent test of our understanding of many aspects of stellar evolution as well as of the early chemical history of the Galaxy. It is a test we sometimes fail. In previous work anticorrelated variations of O and Na were found in the globular cluster M71. Furthermore large anticorrelated variations in CH and CN also were found contrary to predictions by stellar evolution theory. The present project will continue and expand this work to more metal poor globular clusters, where the distinction between star-to-star abundance variations arising from dredge up versus primordial variations should be clearer. In addition, the study will extend to more metal poor clusters the work on the CH and CN bands to as low a luminosity as possible. In a related major program the abundance distributions and scatter among the most metal poor stars in the Galaxy, those with [Fe/H] =.3.0 dex, are being studied.***