RUI: The Hydrodynamics and Observational Signatures of Binary Mergers

许多有趣的天体物理对象和系统被认为是通过接触或半分离的双星阶段。这种演化的最终结果包括奇异的天体，如双中子星、双简并核心的行星状星云、超紧凑x射线双星和蓝离散星。在接触式双星系统中，两个组成部分在一个更大的共同包层内运行并保持物理接触，而在半分离式双星系统中，一颗恒星逐渐从一颗伴星那里吸积质量，使其罗氏叶溢出。在任何一种情况下，双星的一个或两个组成部分都会在恒星演化的时间尺度上膨胀，经常导致双星变得不稳定并合并。如果二元成分具有简并核，则这些核可以独立地在合并中幸存下来，形成具有二元紧致对象的系统。无论母星是什么，双星的合并都会导致所谓的合并爆发，其特征是亮度突然急剧增加，并从合并产物中喷出大量物质。利用平滑粒子流体动力学（SPH）代码Starsmasher，我们将执行覆盖这些场景的参数扫描，同时改变母星的演化状态和质量比。我们将确定双星合并的条件，我们将仔细研究合并和合并产物的动力学和可观察特征，包括其光曲线，连续光谱和流出速度。我们的结果将补充双星演化和星族合成计算，它们将有助于解释观测结果，并有助于解释许多外来物体的形成渠道，包括V1309 Sco等具体例子。这个项目为阿勒格尼学院和RIT的研究人员之间建立联系提供了一个机会。拟议的项目将为阿勒格尼大学的本科生提供一个有价值的研究重点。经常纠结于职业规划的大学生，肯定会从早期接触校际合作和在计算方法这一应用广泛的领域建立坚实的基础中受益。根据他与阿勒格尼学院学生的经验和他们的职业轨迹，PI希望这个项目能让他们在研究生院和技术导向的职业生涯中取得成功。此外，通过PI的教学和推广工作，这里提出的项目有可能触及更广泛的人群，提高当地和全国受众的科学素养。

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.