Exploring the Origins of Unusual Binary Star Merger Products
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Date
2023-05
Authors
Moats, Cassandra
Journal Title
Journal ISSN
Volume Title
Publisher
The Ohio State University
Abstract
Whether a massive star explodes at the end of its life depends on the structure of its core. This structure can be significantly changed due to interaction with a close, gravitationally bound stellar companion. These stars and their companions can merge, and the nature of explosions of these merger products differs greatly. In a large population study, I identified a set of stars with unusual core structures. The majority of these stars had merged with their companion. These anomalous stars had an unusual combination of carbon oxygen (CO) core mass and core carbon mass fraction. I extracted key properties from these cases when the merger occurred. I used random forest regression and classification to look for the features most indicative of the core carbon mass fraction and the final state of the binary. I found that the core carbon mass fraction was best indicated by oxygen mass fraction and CO core mass and that mass ratio and orbital period were the most impactful features for the final state of the binary. I ran stellar evolution models in MESA and found that the unusual stars experienced one of two distinct evolutionary pathways. I found that for many of the stars, they began interacting with their companion close to the end of the main sequence and that in many, though not all, of these binaries, the secondary star had also evolved significantly, including a group of secondary stars that evolved off of the main sequence.
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Keywords
Stellar Evolution, Binary Stars, Massive Stars, Modules for Experiments in Stellar Astrophysics, Machine Learning, Astronomy