The Flaring Activity of M Dwarfs in the Kepler Field

Journal Article · Wed Nov 01 04:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA8EA2· OSTI ID:22875645

Yang, Huiqin; Liu, Jifeng; Gao, Qing; Cao, Zihuang ^[1]; Fang, Xuan ^[2]; Guo, Jincheng ^[3]; Zhang, Yong; Hou, Yonghui; Wang, Yuefei ^[4]

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1. Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)
2. Laboratory for Space Research, University of Hong Kong, Pokfulam, Hong Kong (China)
3. Department of Astronomy, Peking University, Beijing 100871 (China)
4. Nanjing Institute of Astronomical Optics and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042 (China)

Flare events are mainly due to magnetic reconnection and thus are indicative of stellar activity. The Kepler Space Observatory records numerous stellar activities with unprecedented high photometric precision in flux measurements. It is perfectly suitable for carrying out a statistical study of flares. Here we present 540 M dwarfs with flare events discovered using Kepler long-cadence data. The normalized flare energy, as defined by the ratio to bolometric stellar luminosity, L{sub flare}/L{sub bol}, is used to indicate the flare activity. We find that, similar to the X-ray luminosity relation, the L{sub flare}/L{sub bol} versus P{sub rot} relation can also be described with three phases, supersaturation, saturation, and exponential decay, corresponding to an ultra-short period, a short period, and a long period. The flare activity and the number fraction of flaring stars in M dwarfs rise steeply near M4, which is consistent with the prediction of a turbulent dynamo. The size of starspots are positively correlated with flare activity. The L{sub flare}/L{sub bol} ratio has a power-law dependence on L{sub Hα}/L{sub bol}, a parameter indicative of stellar chromosphere activity. According to this relation, a small enhancement in chromosphere activity may cause a huge rise in flare energy, which suggests that superflares or hyperflares may not need an extra excitation mechanism. Through a comparison study, we suggest that flare activity is a more suitable indicator for stellar activity, especially in the boundary region. However, contrary to what is expected, some M dwarfs with strong flares do not show any light variation caused by starspots. Follow-up observations are needed to investigate this problem.

• OSTI ID: 22875645
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 849; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BOLOMETERS
CHROMOSPHERE
COMPARATIVE EVALUATIONS
EXCITATION
FORECASTING
LUMINOSITY
MAGNETIC RECONNECTION
SPACE
STARSPOTS
STATISTICS