Alternative Pathways of Stellar Evolution in Open Clusters

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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.