Collaborative Research: On the Origin of Abundance Inhomogeneities in Globular Clusters

在这个合作项目中，Michael Briley博士（威斯康星大学奥什科什分校）和Graeme Smith博士（加州大学圣克鲁斯分校）将对球状星团恒星中各种元素的丰度进行详细的研究。人们早就知道，在单个星团中的恒星都具有相同丰度的铁和其他重元素，但在少量轻元素（如碳、氮、氧、钠、镁和铝）中具有不均匀的丰度。天文学家现在认识到，这些变化是在红巨星分支上升过程中发生的丰度变化过程（即，标准恒星模型中缺失的某种形式的深度混合）与恒星形成时代的原始变化叠加在一起的结果。研究小组将获得紫色光谱区CH和CN吸收带的光谱，以及可见红色波长的钠、镁和铝的吸收线。该项目有三个主要目标：检查混合引起的碳消耗的开始和程度作为铁丰度的函数；测量cn增强恒星的比例与星团质量和表观形状的关系，从而探索环境对原始丰度变化的影响；并扩大了研究轻元素变化的球状星团的范围。该项目将直接支持UCSC的研究生和UW Oshkosh（本科研究机构）的本科生的培训，他们将直接参与项目的各个方面。公众宣传和教育将通过在学校、俱乐部和民间组织的公开演讲，以及为利克3米望远镜的访客画廊制作演示文稿来实现，该演示文稿将描述如何使用光谱学来确定恒星的化学丰度，以及为什么球状星团特别产生了星系化学演化的天文化石记录。

In this collaborative program, Dr. Michael Briley (University of Wisconsin - Oshkosh) and Dr. Graeme Smith (University of California - Santa Cruz) will undertake a detailed study of the abundances of various elements in globular cluster stars. It has long been known that stars in an individual cluster all have the same abundance of iron and other heavier elements, but have inhomogeneous abundances in a handful of light elements such as carbon, nitrogen, oxygen, sodium, magnesium, and aluminum. Astronomers now realize that these variations result from an abundance altering process which operates during red giant branch ascent (i.e., some form of deep mixing missing from canonical stellar models) superimposed on primordial variations from the era of star formation. The research team will obtain spectra of CH and CN absorption bands in the violet spectral region, as well as absorption lines from sodium, magnesium, and aluminum at visible-red wavelengths. There are three main goals to the project: to examine the onset and extent of mixing-induced carbon depletion as a function of iron abundance; to measure the fraction of CN-enhanced stars as a function of cluster mass and apparent shape, thereby probing the effects of environment on primordial abundance variations; and to broaden the range of globular clusters in which light element variations have been studied. This project will directly support the training of a graduate student at UCSC and undergraduate students at UW Oshkosh (an undergraduate research institution), who will be directly involved in all aspects of the project. Public outreach and education will be enabled through public talks to schools, clubs, and civic organizations, as well as the development of a presentation for the visitor's gallery of the Lick 3-m telescope that will describe how spectroscopy is used to determine the chemical abundances of stars, and why globular clusters in particular yield an astronomical fossil record of the chemical evolution of galaxies.