Most stars exist in “binary systems”, where two stars orbit one another, rather than as single stars like the Sun. If the two stars in a binary system have different masses, over time the higher mass star will expand into a giant star before the lower mass star. This often results in a short phase where the lower mass star orbits within the larger star, resulting in a dramatic exchange of energy and ejection of mass. The process results in the two stars coming closer together with only the core of the high mass star remaining. The phase is poorly understood and has never been observed in real-time. For this project, the investigators will use telescopes and computer simulations to study the process. The investigators will also provide research and training opportunities for undergraduate and graduate students.

The investigators will observationally determine the mapping between the initial and final conditions of common envelope (CE) evolution by characterizing a benchmark set of detached post-common envelope binaries located in stellar clusters. They recently completed a systematic search for post-CE white dwarf and main-sequence binary systems in 299 Milky Way open star clusters, yielding 52 high-probability post-CE systems, three of which they classify as confirmed. The researchers will characterize and model these 52 high-probability systems, thereby creating a unique set of benchmarks where the initial and final conditions of common envelope evolution are known. Directly relating post-CE systems to their pre-CE binary parameters will provide critical constraints on stellar evolution and population synthesis models.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.