The Evolution of Massive Stars as a Function of Metallicity: Closing the Loop in the Local Group

这个项目将描述附近的大质量恒星群，本星系群的恒星形成星系，以便为恒星演化理论提供关键的测试。目前的模型，虽然在某些领域是成功的，但严重高估了高金属丰度（“金属”指元素周期表中氦以上的元素）下最巨大的黄色超巨星的寿命。这个项目将检查几个本星系群的大质量恒星，这些星系的金属丰度相差20倍。一个关键的目标是测量质量损失率，看看损失率是如何取决于金属丰度的。质量损失在很大程度上控制着大质量恒星的演化，决定了一颗质量为太阳40倍的恒星（例如）是否会演化为黄超巨星、红超巨星和/或沃尔夫-拉叶星。这里获得的数据将允许对最新的进化模型进行关键测试和改进。来自北亚利桑那大学和韦尔斯利学院的本科生将有机会作为该项目的一部分进行研究。最后，在本提案中获得的光谱将提供给其他研究人员，以使研究（例如）这些星系中的星际气体成为可能。

This project will characterize the massive star population of the nearby, star-forming galaxies of the Local Group in order to provide critical tests of stellar evolutionary theory. Current models, while successful in some areas, severely overestimate the lifetimes of the most massive yellow supergiants at high metal abundance ("metal" refers to elements above helium in the periodic table). This project will examine massive stars in several Local Group galaxies, where metallicities differ by a factor of 20. A key goal is to measure mass-loss rates to see how the rates depend upon metallicity. Mass loss largely controls the evolution of massive stars, determining whether a star of 40 solar masses (for example) evolves to a yellow supergiant, red supergiant, and/or a Wolf-Rayet star. The data obtained here will permit critical tests and improvement of the latest evolutionary models. Undergraduate students from Northern Arizona University and Wellesley College will have the opportunity to undertake research as part of this project. Finally, spectra obtained in the present proposal will be made available to other researchers, to enable studies of (for example) the interstellar gas in these galaxies.