年轻恒星哈勃4的径向速度监测：从轨道运动中解开星点寿命
Radial Velocity Monitoring of the Young Star Hubble 4: Disentangling Starspot Lifetimes from Orbital Motion
摘要：
我们研究了弱线金牛座T星哈勃4号，一个已知的长周期双星，和它的星点现象。我们使用了麦克唐纳天文台2.7米Harlan J. Smith望远镜在14年（2004-2010，2017-2019）内拍摄的光学径向速度（RV）数据和HST/WFC 3仪器的单历元成像。观察到的和明显的RV变化显示的贡献，分别从二进制的运动，以及从一个大的点组的恒星之一，被认为是主要的。通过拟合和去除RV的轨道信号，我们发现之前在恒星表面发现的大斑点群的寿命下限至少为5.1年。$\sim5$年下限是单个现货组的较长但并非前所未有的持续时间。后期的数据表明，发生了显着的斑点演变，将上限的斑点组寿命为12年。我们发现，前主序演化模型的金牛座（$\sim2$ MYR）的年龄，结合从文献中的组件质量估计，允许我们重现的HST相对光度和二进制引起的贡献明显的RV变化。我们在哈勃4号上发现的长寿命恒星斑点对年轻恒星的发电机模型有着重要的意义，因为它为磁场拓扑结构的长寿命提供了证据。对于年轻恒星系外行星的搜索也有重要意义，因为长寿命的相干RV信号可能是由点引起的，而不是行星运动的结果。(This本文包括德克萨斯大学奥斯汀分校麦克唐纳天文台的数据。
英文摘要：
We studied the weak-lined T Tauri star Hubble 4, a known long-period binary, and its starspot phenomena. We used optical radial velocity (RV) data taken over a span of 14 years (2004-2010, 2017-2019) at the McDonald Observatory 2.7m Harlan J. Smith telescope and single epoch imaging from the HST/WFC3 instrument. The observed and apparent RV variations show contributions, respectively, from the binary motion as well as from a large spot group on one of the stars, presumed to be the primary. Fitting and removing the orbital signal from the RVs, we found the lower bound on the lifetime of a previously identified large spot group on the surface of the star to be at least 5.1 years. A $\sim5$ year lower limit is a long, but not unprecedented, duration for a single spot group. The later epoch data indicate significant spot evolution has occurred, placing an upper bound on the spot group lifetime at 12 years. We find that pre-main sequence evolutionary models for the age of Taurus ($\sim2$ Myr), combined with component mass estimates from the literature, permit us to reproduce the HST relative photometry and the binary-induced contribution to the apparent RV variations. The long-lived star spot we find on Hubble 4 has significant implications for dynamo models in young stars, as it adds evidence for long lifetimes of magnetic field topologies. There are also significant implications for young star exoplanet searches as long-lived coherent RV signals may be spot-induced and not the result of planetary motion. (This paper includes data taken at The McDonald Observatory of The University of Texas at Austin.)
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