Marriages Made in Heaven: the Origin of Multiple Star Systems

上下文大多数高质量和中等质量的恒星都处于稳定的多星系统中，通常是双星系统，其中两颗恒星相互围绕椭圆轨道运行，但通常是涉及三颗或更多恒星的高阶多星系统。这些系统必须作为星星形成过程的一部分来创建（在它们形成之后，很难让两颗恒星在一起）。事实上，观测证据表明，几乎所有的恒星都是在多个系统中形成的，但随后一些更脆弱的系统被外部潮汐力或内在不稳定性所摧毁。因此，形成具有观测系统的统计特性的多个系统是星星形成理论的主要挑战之一。该项目将使用数值模拟来探索多个系统的形成动力学，稳定性和轨道参数（质量比，分离和偏心率），从最新的高分辨率观测所告知的最小条件开始;我们将特别关注在已经凝聚出细丝的核心中形成的多个系统。大多数没有形成多个星系的恒星质量都很低，该项目还将探索这些天体是如何形成的，以及为什么它们最终倾向于形成单一星系。一种可能性是，它们形成了星周圆盘，但随后未能获得足够的质量，并通过与更大质量的兄弟相互作用而从圆盘中弹出。另一种可能性是，它们形成于将物质汇集成形成星星团的细丝中。第三种可能性是，它们是从异常致密的低质量核心孤立形成的。我们将确定这些方案中哪一个是最可行的，以及为什么。学生将成为星星形成气体中的数值流体力学、磁、热、化学和辐射过程以及将观测结果转换为模拟初始条件的统计技术方面的专家

Context. Most high- and intermediate-mass stars are in stable multiple systems, usually binarysystems where the two stars pursue elliptical orbits round each other, but quite often higher-ordermultiples involving three or more stars. These systems must be created as part of the star formationprocess (it is very hard to get two stars together, after they have formed). Indeed, the observationalevidence suggests that almost all stars form in multiple systems, but then some of the more fragilesystems are destroyed by external tidal forces or intrinsic instability. Forming multiple systems withthe statistical properties of observed systems is therefore one of the main challenges of star formationtheory.Project. This project will use numerical simulations to explore the formation dynamics, stabilityand orbital parameters (mass ratios, separations and eccentricities) of multiple systems, starting frominitial conditions that are informed by the latest high-resolution observations; we will be particularlyconcerned with multiple systems forming in cores that have condensed out of filaments. The majorityof stars that do not end up in multiple systems have low-mass and the project will also explorehow these objects form and why they tend to end up single. One possibility is that they form incircumstellar discs, but then fail to acquire enough mass and are ejected from the disc by interactionwith more massive siblings. An alternative possibility is that they form in the filaments that funnelmatter into forming star clusters. A third possibility is that they form in isolation, from exceptionallydense low-mass cores. We will determine which of these scenarios is most viable and why.Skills. The student will become expert in numerical hydrodynamics, magnetic, thermal, chemicaland radiative processes in star forming gas, and statistical techniques for converting observationsinto initial conditions for simulations