Statistical Signatures of Nanoflare Activity. II. A Nanoflare Explanation for Periodic Brightenings in Flare Stars Observed by NGTS
Statistical Signatures of Nanoflare Activity. II. A Nanoflare Explanation for Periodic Brightenings in Flare Stars Observed by NGTS
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DOI：
10.3847/1538-4357/abbfa8
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发表时间：
2020-10
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通讯作者：
Chris J. Dillon;D. Jess;Michail Mathioudakis;C. A. Watson;J. Jackman;P. Wheatley;M. R. Goad;S. Casewell;D. R. Anderson;M. Burleigh;L. Raynard;R. West
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作者：
Chris J. Dillon;D. Jess;Michail Mathioudakis;C. A. Watson;J. Jackman;P. Wheatley;M. R. Goad;S. Casewell;D. R. Anderson;M. Burleigh;L. Raynard;R. West
一些研究已经记录了来自dMe耀斑星和其他恒星源的时间序列的周期性和准周期性信号。在静止阶段（即，没有较大规模的微耀斑或耀斑活动），周期范围从1秒到1000秒，因此暂时与星星对流层中产生的普遍存在的p模式振荡有关。因此，大多数的解释所观察到的周期性已被框在磁流体动力学波的行为。然而，我们提出，一系列连续的纳米片，基于幂律分布，可以在相关的时间序列中提供类似的周期性信号。适应以前的统计分析太阳nanoflare信号，我们发现的第一个统计证据恒星nanoflare信号嵌入在噪声包络的M型恒星光变曲线。利用下一代凌日巡天（NGTS）收集的数据，我们发现了恒星纳米耀斑活动的证据，表明耀斑幂律指数为3.25 ± 0.20，衰变时间为200 ± 100 s。我们还发现，合成的时间序列，一致的观测dMe耀斑星星光变曲线，能够产生准周期信号在相同的频率范围内的p模式信号，尽管纯粹由脉冲签名。传统上被认为是波动行为的结果的现象可以用一些高频但离散的纳米耀斑能量事件来描述。这种新的物理解释提出了一种新的诊断能力，通过将观察到的周期性信号与给定的纳米耀斑模型条件联系起来。
Several studies have documented periodic and quasi-periodic signals from the time series of dMe flare stars and other stellar sources. Such periodic signals, observed within quiescent phases (i.e., devoid of larger-scale microflare or flare activity), range in a period from 1 to 1000 s and hence have been tentatively linked to ubiquitous p-mode oscillations generated in the convective layers of the star. As such, most interpretations for the observed periodicities have been framed in terms of magnetohydrodynamic wave behavior. However, we propose that a series of continuous nanoflares, based upon a power-law distribution, can provide a similar periodic signal in the associated time series. Adapting previous statistical analyses of solar nanoflare signals, we find the first statistical evidence for stellar nanoflare signals embedded within the noise envelope of M-type stellar lightcurves. Employing data collected by the Next Generation Transit Survey (NGTS), we find evidence for stellar nanoflare activity demonstrating a flaring power-law index of 3.25 ± 0.20, alongside a decay timescale of 200 ± 100 s. We also find that synthetic time series, consistent with the observations of dMe flare star lightcurves, are capable of producing quasi-periodic signals in the same frequency range as p-mode signals, despite being purely composed of impulsive signatures. Phenomena traditionally considered a consequence of wave behavior may be described by a number of high-frequency but discrete nanoflare energy events. This new physical interpretation presents a novel diagnostic capability, by linking observed periodic signals to given nanoflare model conditions.