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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書誌事項

公開日
2019-01-30
資源種別
journal article
権利情報
  • https://iopscience.iop.org/page/copyright
  • https://iopscience.iop.org/info/page/text-and-data-mining
DOI
  • 10.3847/1538-4357/aaf471
  • 10.48550/arxiv.1811.10782
公開者
American Astronomical Society

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<jats:title>Abstract</jats:title> <jats:p>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 <jats:italic>Kepler</jats:italic> 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 <jats:italic>Kepler</jats:italic> 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 <jats:italic>Kepler</jats:italic> 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 (<jats:italic>T</jats:italic>) of star spots range from 10 to 350 days when the spot areas (<jats:italic>A</jats:italic>) 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 (<jats:italic>T</jats:italic> ∝ <jats:italic>A</jats:italic>), while being consistent with other research on star-spot lifetimes. The emergence and decay rates of star spots are typically 5 × 10<jats:sup>20</jats:sup> Mx hr<jats:sup>−1</jats:sup> (8 MSH hr<jats:sup>−1</jats:sup>) 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.</jats:p>

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