A comparative study of the magnetic activities of low-mass stars from G-type to M-type

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题名:	A comparative study of the magnetic activities of low-mass stars from G-type to M-type
作者:	林家龍;Lin, Chia-Lung
贡献者:	天文研究所
关键词:	閃焰;低質量恆星;系外行星;適居性;Flares;low-mass stars;Exoplanets;Habitability
日期:	2018-08-06
上传时间:	2018-08-31 11:33:21 (UTC+8)
出版者:	國立中央大學
摘要:	系外行星的適居可否在天文學與天文生物學都是很熱門的主題。由於許多因素，在適居帶的超級地球的大氣以及表面環境會因為其母星的物理狀態而大受影響。例如，強大的恆星風雨磁暴會剝離行星的大氣而限制生物圈的維持與發展。Maehara et al. (2013)的開創性研究中表示克普勒望遠鏡的高精確度使它收集的資料非常適合尋找特級或超級閃焰的工作，他們在148個G型主序星找到365個超級閃焰事件。特級與超級閃焰通常比目前歷史紀錄的最強太陽閃焰(1859年，Carrington 事件)還要強幾十至幾百倍。Shibayama et al. (2013)發現更多有閃焰事件的太陽型恆星，他們在279 G型主序星中偵測到1547個超級閃焰事件。Wu et al. (2015)以及Chang et al. (2017)利用克普勒望遠鏡的資料，完成了G與M型主序星的閃焰研究。他們發現一顆星的閃焰發生頻率與強度與其自轉速度(年齡)有極大的關係。年輕與自轉週期小於10天的星通常會發生能量較強的閃焰，且閃焰發生頻率也會偏高，這也代表著有較活躍的磁場活動。在這次的工作中，我們在K2 long cadence 數據中尋找有閃焰事件的M，K型主序星，尤其是一直以來被忽略的K型星。我們在548個M型星上找到3589個閃焰以及343個K型星上找到1647個閃焰事件，我們將這些閃焰與Shibayama et al. (2013)所找到的G型星閃焰做比較研究。;The habitability of exoplanets is a hot topic in both astronomy and astrobiology. Among many factors, the atmospheric and surface environments of the habitable super-Earths could be significantly influenced by the physical conditions of the central stars. For example, robust stellar winds and magnetic storms could lead to stripping away of the planetary atmospheres thus limiting the sustainability of any biospheres. The pioneering work of Maehara et al. (2012) demonstrated that the high-precision measurements of the Kepler space telescope are ideal for the investigations of superflares with energy far beyond the maximal level of solar flare events (i.e., the Carrington event in 1859); they have found 365 flares on 148 G dwarfs. Shibayama et al. (2013) explored more flaring solar-type stars; they have detected 1547 superflares on 279 G dwarfs. At NCU, Wu et al. (2015) and Chang et al. (2017) carried out the statistical studies of the "Kepler" flare activities of the G-type and M-type dwarf stars, respectively. They found that the flare occurrence frequencies and strengths regarding the flare energy have the strong dependencies on the rotation periods and hence the ages of the stars. Those younger and faster-rotating (with rotation periods < 10 days) tend to have stronger magnetic activities. In this work, we report on the results of a comprehensive study of the flare effects covering the temperature range from M dwarfs to the solar-type stars thus bridging the gap of the K-type stars. We have detected 3589 flares on 584 M dwarfs, 1647 flares on 343 K dwarfs by analyzing the K2 long cadence data. We compared the M, K dwarfs’ flares we found with G dwarfs’ flares from Shibayama et al. (2013).
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