RUI: The Hydrodynamics and Observational Signatures of Binary Mergers

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A large variety of interesting astrophysical objects and systems are thought to pass through a contact or semidetached binary stage. The ultimate outcomes of such evolution include exotica such as binary neutron stars, planetary nebulae with double degenerate cores, ultracompact X-ray binaries, and blue stragglers. In a contact binary system, the two components orbit within a larger common envelope and maintain physical contact, while in a semidetached binary, one star gradually accretes mass from a companion overflowing its Roche lobe. In either case, one or both binary components can expand on a stellar evolution timescale, often causing the binary to become unstable and merge. If the binary components have degenerate cores, the cores can separately survive the merger to form systems with binary compact objects. Regardless of the parent stars, the merger of a binary can result in so-called mergebursts, characterized by a sudden and drastic observed increase in luminosity and by ejecta streaming away from the merger product. Making use of a smoothed particle hydrodynamics (SPH) code, Starsmasher, we will perform a parameter sweep covering such scenarios, varying both the evolutionary state of the parent stars and the mass ratio. We will determine the conditions under which a binary merges, and we will study carefully the dynamics and observable characteristics of the merger and merger product, including its light curve, continuum spectrum, and outflow velocity. Our results will complement binary stellar evolution and population synthesis calculations, they will assist in the interpretation of observations, and they will help explain the formation channels of numerous exotic objects, including specific examples such as V1309 Sco.This project represents an opportunity to foster a connection between researchers at Allegheny College and RIT. The proposed project will provide a valuable research focus for undergraduates at Allegheny. Undergraduates, often grappling with career plans, certainly will benefit from early exposure to intercollegiate collaboration and from building a solid foundation in computational methods, an area with broad applications. Based on his experience with Allegheny College students and their career trajectories, the PI expects that this project will equip them well for success in graduate school and in technically oriented careers. In addition, through the PI's teaching and outreach efforts, the project proposed here has the potential to reach a wide range of people and raise the scientific literacy of both local and national audiences.