Lifetimes and Emergence/Decay Rates of Star Spots on Solar-type Stars Estimated by Kepler Data in Comparison with Those of Sunspots
Lifetimes and Emergence/Decay Rates of Star Spots on Solar-type Stars Estimated by Kepler Data in Comparison with Those of Sunspots
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DOI：
10.3847/1538-4357/aaf471
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发表时间：
2019-02-01
影响因子：
4.9
通讯作者：
Shibata, Kazunari
中科院分区：
文献类型：
--
作者：
Namekata, Kosuke;Maehara, Hiroyuki;Shibata, Kazunari
活动太阳型恒星由于恒星自转而伴随着星星黑子的出现和衰减而表现出大的准周期亮度变化。开普勒观测数据适用于研究星星黑子的出现和衰变过程，这对理解恒星发电机和恒星耀斑的基本机制具有重要意义。在这项研究中，我们测量的时间演化的恒星黑子面积与开普勒数据跟踪的光变曲线的局部极小值。在这项分析中，我们提取的时间演化的星星斑点显示清晰的出现和衰减，而不受恒星的差异旋转。我们将该方法应用于开普勒观测到的5356颗活动太阳型恒星，得到了56个独立星星黑子的时间演化。我们计算了星星斑点的寿命和出现/衰变率从所获得的斑点面积的时间演化。结果表明，当黑子面积（A）为太阳半球面积的0.1%~ 2.3%时，星星黑子的寿命（T）在10 ~ 350天之间。我们还将它们与太阳黑子的寿命进行了比较，发现星星黑子的寿命比从太阳黑子的经验关系（T与A成正比）推断的寿命短得多，同时与其他关于恒星黑子寿命的研究一致。星星黑子的出现和衰减速率通常为5 x 10（20）Mx hr（-1）（8 MSH hr（-1）），面积为太阳半球的0.1%-2.3%，与太阳黑子的预期基本一致，这可能表明相同的基本过程。
Active solar-type stars show large quasi-periodic brightness variations caused by stellar rotation with star spots, and the amplitude changes as the spots emerge and decay. The Kepler data are suitable for investigations of the emergence and decay processes of star spots, which are important to understand the underlying stellar dynamo and stellar flares. In this study, we measured the temporal evolution of the star-spot area with Kepler data by tracing the local minima of the light curves. In this analysis, we extracted the temporal evolution of star spots showing clear emergence and decay without being disturbed by stellar differential rotation. We applied this method to 5356 active solar-type stars observed by Kepler and obtained temporal evolution of 56 individual star spots. We calculated the lifetimes and emergence/decay rates of the star spots from the obtained temporal evolution of the spot area. As a result, we found that the lifetimes (T) of star spots range from 10 to 350 days when the spot areas (A) are 0.1%-2.3% of the solar hemisphere. We also compared them with sunspot lifetimes and found that the lifetimes of star spots are much shorter than those extrapolated from an empirical relation of sunspots (T proportional to A), while being consistent with other research on star-spot lifetimes. The emergence and decay rates of star spots are typically 5 x 10(20) Mx hr(-1) (8 MSH hr(-1)) with an area of 0.1%-2.3% of the solar hemisphere and mostly consistent with those expected from sunspots, which may indicate the same underlying processes.