A New Look at an Old Cluster: The Membership, Rotation, and Magnetic Activity of Low-mass Stars in the 1.3 Gyr Old Open Cluster NGC 752
A New Look at an Old Cluster: The Membership, Rotation, and Magnetic Activity of Low-mass Stars in the 1.3 Gyr Old Open Cluster NGC 752
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旧星团的新视角：1.3 吉里旧疏散星团 NGC 752 中低质量恒星的成员资格、旋转和磁活动
作者：
M. Agueros;E. Bowsher;J. Bochanski;P. Cargile;K. Covey;S. Douglas;A. Kraus;A. Kundert;N. Law;A. Ahmadi;H. Arce
附近的疏散星团NGC 752提供了一个研究年龄>1 Gyr的恒星性质的难得机会。然而，为它构建一个成员目录是具有挑战性的;大多数调查仅限于确定其巨星和矮星成员早于中K。我们补充过去的成员目录与候选人选择更新的光度和适当的运动标准，产生一个列表的258名成员，一个>50%，比以前的目录增加。利用贝叶斯框架，将梅萨等时线和星迹演化模型与文献测光和59个星团成员的Tycho-Gaia天体测量解数据进行拟合，推断出NGC 752的年龄和距离为1.34 ± 0.06 Gyr和pc。我们还报告了我们的光学监测的集群使用Palomar瞬态工厂的结果。我们获得了12个K和M星团成员的旋转周期，这是对年龄>1 Gyr的低质量恒星测量的第一个周期。我们比较这些新的时期，从年轻的集群Praesepe和NGC 6811的数据，和角动量损失的理论模型，研究恒星自旋下降的低质量恒星在其第一个1.3 Gyr。虽然平均而言，NGC 752恒星的旋转速度比年轻的恒星慢，但差异并不显著。最后，我们使用光谱观测来测量星团恒星的Hα，发现早于M2的成员是磁不活跃的，正如在这个年龄所预期的那样。即将到来的盖亚数据应该巩固和扩大NGC 752的成员资格，以更低的质量，从而增加其对低质量恒星研究的重要性。
The nearby open cluster NGC 752 presents a rare opportunity to study stellar properties at ages >1 Gyr. However, constructing a membership catalog for it is challenging; most surveys have been limited to identifying its giants and dwarf members earlier than mid-K. We supplement past membership catalogs with candidates selected with updated photometric and proper-motion criteria, generating a list of 258 members, a >50% increase over previous catalogs. Using a Bayesian framework to fit MESA Isochrones & Stellar Tracks evolutionary models to literature photometry and the Tycho-Gaia Astrometric Solution data available for 59 cluster members, we infer the age of and distance to NGC 752: 1.34 ± 0.06 Gyr and pc. We also report the results of our optical monitoring of the cluster using the Palomar Transient Factory. We obtain rotation periods for 12 K and M cluster members, the first periods measured for such low-mass stars with a well-constrained age >1 Gyr. We compare these new periods to data from the younger clusters Praesepe and NGC 6811, and to a theoretical model for angular momentum loss, to examine stellar spin-down for low-mass stars over their first 1.3 Gyr. While on average NGC 752 stars are rotating more slowly than their younger counterparts, the difference is not significant. Finally, we use our spectroscopic observations to measure Hα for cluster stars, finding that members earlier than ≈M2 are magnetically inactive, as expected at this age. Forthcoming Gaia data should solidify and extend the membership of NGC 752 to lower masses, thereby increasing its importance for studies of low-mass stars.