The Evolution of Rotation and Magnetic Activity in 94 Aqr Aa from Asteroseismology with TESS
The Evolution of Rotation and Magnetic Activity in 94 Aqr Aa from Asteroseismology with TESS
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DOI：
10.3847/1538-4357/aba963
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发表时间：
2020-07
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影响因子：
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通讯作者：
T. Metcalfe;J. V. van Saders;S. Basu;D. Buzasi;W. Chaplin;R. Egeland;R. García;P. Gaulme;D. Hub
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作者：
T. Metcalfe;J. V. van Saders;S. Basu;D. Buzasi;W. Chaplin;R. Egeland;R. García;P. Gaulme;D. Hub
以前大多数校准旋转和磁活动如何依赖于恒星年龄和质量的努力都依赖于对星团的观测，其中来自恒星演化模型的等时线被用来确定集合的性质。星震学采用类似的模型，通过匹配恒星的正常振荡模式来测量单个恒星的特性，从而高精度地得出恒星的年龄和质量。我们使用凌日系外行星测量卫星27天的光度测量来表征94 Aqr三重系统G8亚巨星的类太阳振荡。由此产生的恒星特性，结合对威尔森山HK项目35年活动测量的重新分析，使我们能够探测系统中旋转和磁活动的演变。亚巨星的星震年龄与恒星等时拟合一致，但旋转周期比角动量演化的标准模型所预期的要短得多。我们得出的结论是，可能需要减弱磁制动来重现恒星特性，而在氢壳燃烧阶段进化的亚巨星可以重新激活大规模的发电机作用，并在上升到红巨星分支之前短暂地维持磁活动周期。
Most previous efforts to calibrate how rotation and magnetic activity depend on stellar age and mass have relied on observations of clusters, where isochrones from stellar evolution models are used to determine the properties of the ensemble. Asteroseismology employs similar models to measure the properties of an individual star by matching its normal modes of oscillation, yielding the stellar age and mass with high precision. We use 27 days of photometry from the Transiting Exoplanet Survey Satellite to characterize solar-like oscillations in the G8 subgiant of the 94 Aqr triple system. The resulting stellar properties, when combined with a reanalysis of 35 yr of activity measurements from the Mount Wilson HK project, allow us to probe the evolution of rotation and magnetic activity in the system. The asteroseismic age of the subgiant agrees with a stellar isochrone fit, but the rotation period is much shorter than expected from standard models of angular momentum evolution. We conclude that weakened magnetic braking may be needed to reproduce the stellar properties, and that evolved subgiants in the hydrogen shell-burning phase can reinvigorate large-scale dynamo action and briefly sustain magnetic activity cycles before ascending the red giant branch.