Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, Wisconsin 53706, USA.
Nature. 2009 Dec 24;462(7276):1032-5. doi: 10.1038/nature08568.
Blue straggler stars lie on or near the main sequences of star clusters (all members of which formed around the same time), but typically are more luminous than the turn-off stars and therefore long ago should have evolved off the main sequence to become giants and white dwarfs. They are thought to derive from normal main-sequence stars that have undergone a recent increase in mass. Statistical evidence indicates that in globular star clusters the blue stragglers probably form from binary stars. The specific formation processes, such as mass transfer, mergers or stellar collisions during dynamical encounters of binary stars, remain unresolved. Here we report that 16 of the 21 blue stragglers (76 per cent) in the old (7-Gyr; ref. 2) open cluster NGC 188 are currently in binary systems, a frequency three times that found among normal solar-type main-sequence stars. These blue straggler binaries have a remarkable period-eccentricity distribution, with all but three having orbital periods of approximately 1,000 days. Moreover, these stars are rotating faster than normal main-sequence stars of the same surface temperatures. These data show that most, and possibly all, blue stragglers derive from multiple-star systems, and indicate that the several formation processes operate simultaneously. We suggest that rapid rotation of blue stragglers may place upper limits on their ages.
蓝离散星位于星团的主序带上或附近（所有成员都是在大致相同的时间形成的），但通常比熄火星更亮，因此很久以前就应该从主序带上演化为巨星和白矮星。它们被认为是由经历了最近质量增加的正常主序星形成的。统计证据表明，在球状星团中，蓝离散星可能是由双星形成的。具体的形成过程，如双星在动态相互作用期间的物质转移、合并或恒星碰撞，仍然没有得到解决。在这里，我们报告说，在古老的（7 亿年；参考文献 2）开放星团 NGC 188 中，21 颗蓝离散星中有 16 颗（76%）目前处于双星系统中，这一频率是正常太阳型主序星的三倍。这些蓝离散星双星具有显著的周期偏心率分布，除了三个之外，所有双星的轨道周期都约为 1000 天。此外，这些恒星的自转速度比具有相同表面温度的正常主序星快。这些数据表明，大多数（如果不是全部的话）蓝离散星都源自多星系统，并表明几种形成过程同时发生。我们认为，蓝离散星的快速自转可能对它们的年龄施加了上限。
