Department of Astronomy, University of Wisconsin-Madison, Wisconsin 53706, USA.
Nature. 2011 Oct 19;478(7369):356-9. doi: 10.1038/nature10512.
In open star clusters, where all members formed at about the same time, blue straggler stars are typically observed to be brighter and bluer than hydrogen-burning main-sequence stars, and therefore should already have evolved into giant stars and stellar remnants. Correlations between blue straggler frequency and cluster binary star fraction, core mass and radial position suggest that mass transfer or mergers in binary stars dominates the production of blue stragglers in open clusters. Analytic models, detailed observations and sophisticated N-body simulations, however, argue in favour of stellar collisions. Here we report that the blue stragglers in long-period binaries in the old (7 × 10(9)-year) open cluster NGC 188 have companions with masses of about half a solar mass, with a surprisingly narrow mass distribution. This conclusively rules out a collisional origin, as the collision hypothesis predicts a companion mass distribution with significantly higher masses. Mergers in hierarchical triple stars are marginally permitted by the data, but the observations do not favour this hypothesis. The data are highly consistent with a mass transfer origin for the long-period blue straggler binaries in NGC 188, in which the companions would be white dwarfs of about half a solar mass.
在开放星团中，所有成员几乎同时形成，通常会观察到蓝色余迹星比氢燃烧主序星更亮、更蓝，因此它们应该已经演变成巨星和恒星残骸。蓝色余迹星的频率与星团双星分数、核心质量和径向位置之间的相关性表明，双星中的物质转移或合并主导了开放星团中蓝色余迹星的产生。然而，解析模型、详细观测和复杂的 N 体模拟都支持恒星碰撞的观点。在这里，我们报告称，在古老（7×10(9)-年）开放星团 NGC 188 的长周期双星中，蓝色余迹星的伴星质量约为太阳质量的一半，具有令人惊讶的窄质量分布。这确凿地排除了碰撞起源，因为碰撞假说预测的伴星质量分布具有显著更高的质量。数据勉强允许层次三重星的合并，但观测结果并不支持这一假设。这些数据与 NGC 188 中长周期蓝色余迹双星的物质转移起源高度一致，其中伴星将是大约半太阳质量的白矮星。
