工厂与蜂巢I Praesepe低质量恒星的自转周期
The Factory and The Beehive I. Rotation Periods For Low-Mass Stars in Praesepe
摘要：
从单年龄种群测量的恒星自转周期对于研究恒星角动量含量如何随时间演变，这种演变如何取决于质量，以及自转如何影响恒星发电机和磁加热色球和日冕至关重要。我们报告的旋转周期为40晚K到中M恒星成员附近，丰富的，中期年龄（~ 6亿年）疏散星团Praesepe。这些旋转周期来自于2010年2月至5月Palomar Transient Factory对四个星团场进行的约200次观测。我们的测量结果表明，Praesepe的质量周期关系从一个定义良好的奇异关系过渡到一个更分散的分布在0.6 Msun的快速和慢速旋转。这一转变的位置与基于对年轻星团观测的预期以及恒星自旋下降是影响6亿年角动量演化的主要机制的假设大致一致。然而，与最近发表的毕宿星团（假设与Praesepe同时代）的数据进行比较，表明奇异质量-周期关系的分歧发生在不同的特征质量上，加强了Praesepe是两个星团中较年轻的发现。我们还使用以前公布的关系描述的旋转周期的演变作为颜色和质量的函数，以发展样本的Praesepe期间的时间。将所得预测与M35和NGC 2516（~ 1.5亿年）测量的周期以及运动学选择的年轻和年老场恒星种群进行比较，表明恒星自旋下降的进展可能比这些关系所描述的要慢。
英文摘要：
Stellar rotation periods measured from single-age populations are critical for investigating how stellar angular momentum content evolves over time, how that evolution depends on mass, and how rotation influences the stellar dynamo and the magnetically heated chromosphere and corona. We report rotation periods for 40 late-K to mid-M stars members of the nearby, rich, intermediate-age (~600 Myr) open cluster Praesepe. These rotation periods were derived from ~200 observations taken by the Palomar Transient Factory of four cluster fields from 2010 February to May. Our measurements indicate that Praesepe's mass-period relation transitions from a well-defined singular relation to a more scattered distribution of both fast and slow rotators at ~0.6 Msun. The location of this transition is broadly consistent with expectations based on observations of younger clusters and the assumption that stellar-spin down is the dominant mechanism influencing angular momentum evolution at 600 Myr. However, a comparison to data recently published for the Hyades, assumed to be coeval to Praesepe, indicates that the divergence from a singular mass-period relation occurs at different characteristic masses, strengthening the finding that Praesepe is the younger of the two clusters. We also use previously published relations describing the evolution of rotation periods as a function of color and mass to evolve the sample of Praesepe periods in time. Comparing the resulting predictions to periods measured in M35 and NGC 2516 (~150 Myr) and for kinematically selected young and old field star populations suggests that stellar spin-down may progress more slowly than described by these relations.
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