Alternative Pathways of Stellar Evolution in Open Clusters

我们对单个恒星生命周期的理解是上个世纪最伟大的智力成就之一。然而，像我们的太阳这样的恒星有一半是在轨道上与伴星一起形成的。仅仅了解单个恒星就像研究人类生活而不包括夫妇。这项研究的目标是通过跟踪在数千颗恒星组成的星团中出生、生活和死亡的恒星，来了解这些另类的恒星生命故事。当两颗恒星的轨道彼此靠近时，就会产生不同的生命路径。它们的生命故事可以包括它们之间的物质交换，两个慢慢合并为一个，甚至是猛烈的恒星碰撞。将对单个恒星的研究与对星团中恒星的新理解相结合，将产生一个关于所有恒星生命的完整画面。这项工作也将增加在STEM中代表性不足的学生的参与。研究小组将为威斯康星州麦迪逊社区中心的学生开发课后项目。这些项目以天文学视频游戏为基础，激发和培养对STEM的兴趣。该团队还将在威斯康星州大学和麦迪逊学院的天文学和物理学课程中增加基于游戏的学习。最后，该团队将为代表性不足的本科生和研究生提供和指导研究经验。这项研究试图通过包括星团中恒星的相互作用来改变我们对恒星生命周期的看法。计划中的研究基于NSF资助的WIYN开放星团研究，该研究全面定义了6个丰富的老（1.6 Gyr t 8 Gyr）开放星团中的替代恒星演化产物以及它们形成的近距离双星种群。第一个目标是在理论上再现所有6个星团内的恒星演化路径，使用两个数值模拟代码，称为梅萨和TWIN。特别是，蓝离散与检测白矮星同伴将允许直接，详细的建模从祖双星到当前蓝离散双星的传质演化。第二个目标是模拟星团中恒星的旋转分布，作为有效温度的函数。主序星的自转趋势并不成立，实际的自转分布也不清楚。第三个目标是将角动量变化作为质量的函数进行建模。他们将使用恒星当前自旋下降速率的模型来限制恒星形成事件中自旋上升事件的大小。

Our understanding of the life cycle of individual stars is one of the great intellectual accomplishments of the past century. However, half of stars like our Sun form in orbit with companion stars. Going no further than understanding individual stars would be like studying human lives without including people who are in couples. The goal of this research is to understand these alternative stellar life stories, by following stars that are born, live and die in clusters of thousands of stars. The alternative life paths result when two stars orbit near each other. Their life stories can include exchanging material between them, the two slowly merging into one, or even violent stellar collisions. Combining the studies single stars with new understanding of stars in clusters will yield a complete picture of lives of all stars.This work also will increase participation of students underrepresented in STEM. The research team will develop after-school programs for students at community centers in Madison WI. These programs build on astronomy video games to excite and nurture interest in STEM. The team also will add game-based learning to astronomy and physics classes at the University of Wisconsin and at Madison College. Finally, the team will provide and mentor research experiences for underrepresented undergraduate and graduate students. This research seeks to transform our view of stellar life cycles by including the interactions of stars in clusters. The planned research rests upon NSF-funded WIYN Open Cluster Study research that comprehensively defines alternative stellar evolution products, and the close binary populations from which they form, in 6 rich older (1.6 Gyr t 8 Gyr) open clusters. The first objective is to theoretically reproduce alternative stellar evolution pathways within all 6 clusters using two numerical modeling codes, called MESA and TWIN. In particular, blue stragglers with detected white-dwarf companions will permit direct, detailed modeling of mass-transfer evolution from progenitor binaries to current blue-straggler binaries. The second objective is to simulate the rotation distributions of stars in clusters, as a function of effective temperature. The rotation trends of main-sequence single stars do not hold, and the actual rotation distributions of not yet known. The third objective is to model angular momentum changes as a function of mass. They will use models of current spin-down rates of stars to constrain the magnitude of spin-up events in stellar formation events.