Collaborative Research: Fundamental Stellar Physics from Large-sample Globular Cluster Photometry

合作研究：大样本球状星团光度学的基础恒星物理

• 批准号: 0098696
• 负责人: Eric Sandquist
• 金额: $ 17.06万
• 依托单位: San Diego State University Foundation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-07-01 至 2005-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0098696&HistoricalAwards=false
• 关键词: Collaborative; Research; Fundamental; Stellar; Physics

AST 0098696SandquistIn a collaborative research project, Dr. Eric Sandquist at San Diego State University and Dr. Michael Bolte at the University of California at Santa Cruz will use photometric observations of large numbers (tens of thousands) of evolved low-mass stars in globular clusters to probe the physical conditions found inside the stars. Because the observable properties of a star evolve quickly once it finishes consuming its core hydrogen and because a star's lifetime is primarily determined by its mass, stars of very slightly different masses can be in very different phases of their lives. By simply counting the numbers of stars present as a function of luminosity and temperature, these researchers can estimate how quickly stars of approximately 80% of the mass of the Sun change under the influence of internal processes.The investigators will pursue a number of definite tests of stellar physics that can be conducted with these kinds of observations. In several metal-poor clusters, a surplus of stars has been observed in the subgiant evolutionary phase, which is an indication that there may be an unusually efficient means of transporting energy away from the cores of those stars. The red giant bump has long been known to test how deeply convective motions penetrate into giant branch stars, and the investigators will test mixing processes that this feature and counts of red giant stars at all luminosities can provide. They also describe several new diagnostics that can be applied to the helium fusion phases of a star's life ( the horizontal branch and asymptotic giant branch). The asymptotic giant branch in particular has been difficult to study because of its short duration. The diagnostics provide practical methods of testing whether helium-burning stars evolve in ways predicted by theory. Finally, they describe the constraints that can be placed on the dynamical evolution of entire clusters by observations of blue straggler stars -a population that appears to be created by collisions of stars or the evolution of binary stars.The study will involve the analysis of CCD data already collected from a number of heavily-populated globular clusters, followed by thorough study of the incompleteness of the photometry -- a computationally intensive step that has been responsible for the small number of large-sample studies to date. To derive robust star counts, what is needed is detailed understanding of the probability that cluster stars were lost in the light of other stars or in noise as a function of stellar brightness and distance from the cluster center. Photometric studies of this kind are very important stepping stones toward new tests of our understanding of stellar physics and stellar populations.***

AST 0098696 Sandquist在一个合作研究项目中，圣地亚哥州立大学的Eric Sandquist博士和圣克鲁斯的加州大学的Michael Bolte博士将使用大量（数万）球状星团中演化的低质量恒星的光度观测来探测恒星内部的物理条件。由于星星的可观测性质在消耗完核心氢后会迅速演变，而且星星的寿命主要由其质量决定，因此质量略有不同的恒星可能处于非常不同的生命阶段。通过简单地计算恒星的数量作为光度和温度的函数，这些研究人员可以估计大约80%太阳质量的恒星在内部过程的影响下变化的速度。研究人员将进行一些可以通过这些观测进行的恒星物理学的明确测试。在几个贫金属的星团中，在亚巨星演化阶段观察到了过剩的恒星，这表明可能有一种异常有效的方式将能量从这些恒星的核心转移出去。红巨星撞击长期以来一直被认为可以测试深对流运动如何渗透到巨大的分支恒星中，研究人员将测试混合过程，这种特征和红巨星在所有光度下的计数可以提供。他们还描述了几种新的诊断方法，可以应用于星星生命的氦聚变阶段（水平分支和渐近巨星分支）。特别是渐近巨分支，由于持续时间短，一直难以研究。诊断提供了测试氦燃烧恒星是否以理论预测的方式演化的实用方法。最后，他们描述了通过观测蓝离散星--一种似乎是由恒星碰撞或双星演化产生的群体--可以对整个星团的动力学演化施加的限制。这项研究将涉及分析从一些人口稠密的球状星团收集的CCD数据，随后对光度测定法的不完整性进行了彻底研究-这是一个计算量很大的步骤，是迄今为止大样本研究数量很少的原因。为了得到可靠的星星计数，需要详细了解星团恒星在其他恒星的光线或噪声中丢失的概率，作为恒星亮度和距星团中心距离的函数。 这类光度学研究是非常重要的垫脚石，有助于我们对恒星物理学和恒星种群的理解进行新的检验。