标题： 关于星团中造父变星多重性的动力学演化及其对诞生时B型星多重性的影响 显示英文标题

标题： On the dynamical evolution of Cepheid multiplicity in star clusters and its implications for B-star multiplicity at birth

摘要： 经典造父变星为在数十到数百百万年期间对中等质量恒星的双星演化提供了一个独特的探测手段。 我们研究了造父变星的双星和多星特性，假设所有中B型恒星都在星团内部以双星形式形成。 这些双星既经历了恒星演化，又经历了与星团中其他恒星的动力学相遇。 动力学星团环境导致留在星团中的造父变星（$\approx 60$%）的双星比例高于逃逸到场中的造父变星（$\approx 35$%）。 在星团中，双星、三合星和多星的比例随着星团质量的增加而减少。 质量更大的星团中的双星轨道周期比低质量星团和场中的造父变星更短。 合并非常普遍，有$\approx 30$% 的中B型恒星由于与伴星的相互作用未能演化成造父变星。 大约$40$% 的造父变星与其伴星发生了合并，合并事件会影响恒星演化；从质量上预期的造父变星年龄可能与其宿主星团的年龄不同。 我们的模型预测，五分之一的造父变星是质量低于造父变星下限的恒星之间的合并结果；在星团中，这些天体出现的时间明显晚于其质量所预期的时间。 大约$3$到$5$% 的所有造父变星都有一个致密伴星（$\approx 0.15$% 的所有造父变星都由一个黑洞伴星伴随）。 从我们的模拟中得出的双星比例（42%）比观测到的双星造父变星比例低约两倍。 这表明，B型恒星在诞生时的多重性比例可能远大于一，因此中B型恒星可能通常形成于三合星及更高阶的系统中。 显示英文摘要

摘要： Classical Cepheid variable stars provide a unique probe to binary evolution in intermediate-mass stars over the course of several tens to hundreds of Myr. We studied the binary and multiple properties of Cepheids, assuming that all mid-B stars form in binaries inside star clusters. The binaries were subjected both to stellar evolution and dynamical encounters with other stars in the cluster. The dynamical cluster environment results in a higher binary fraction among the Cepheids that remain in star clusters ($\approx 60$%) than among the Cepheids which have escaped to the field ($\approx 35$%). In clusters, the binary, triple, and multiple fraction decreases with increasing cluster mass. More massive clusters have binaries of shorter orbital periods than lower mass clusters and field Cepheids. Mergers are very common with $\approx 30$% of mid-B stars not evolving to Cepheids because of the interaction with their companion. Approximately $40$ % of Cepheids have merged with their companion, and the merger event impacts stellar evolution; the age of Cepheids expected from their mass can differ from the age of their host cluster. Our models predict that one in five Cepheids is the result of a merger between stars with mass below the lower mass limit for Cepheids; in clusters, these objects occur substantially later than expected from their mass. Approximately $3$ to $5$ % of all Cepheids have a compact companion ($\approx 0.15$ % of all Cepheids are accompanied by a black hole). The binary fraction derived from our simulations (42%) underestimates the observed binary Cepheid fraction by approximately a factor of 2. This suggests that the true multiplicity fraction of B-stars at birth could be substantially larger than unity and, thus, that mid-B stars may typically form in triple and higher order systems.