Investigating the rotational phase of stellar flares on M dwarfs using K2 short cadence data

Lauren Doyle, Gavin Ramsay, John Gerard Doyle, Kinwah Wu, Eamon Scullion

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22 Citations (Scopus)
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Abstract

We present an analysis of K2 short cadence data of 34 M dwarfs which have spectral types in the range M0-L1. Of these stars, 31 showed flares with a duration between ˜10 and 90min. Using distances obtained from Gaia DR2 parallaxes, we determined the energy of the flares to be in the range ˜1.2 × 1029-6 × 1034 erg. In agreement with previous studies we find rapidly rotating stars tend to show more flares, with evidence for a decline in activity in stars with rotation periods longer than ˜10 d. The rotational modulation seen in M dwarf stars is widely considered to result from a starspot which rotates in and out of view. Flux minimum is therefore the rotation phase where we view the main starspot close to the stellar disc centre. Surprisingly, having determined the rotational phase of each flare in our study we find none show any preference for rotational phase. We outline three scenarios which could account for this unexpected finding. The relationship between rotation phase and flare rate will be explored further using data from wide surveys such as NGTS and TESS.
Original languageEnglish
Pages (from-to)2153-2164
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Volume480
Issue number2
Early online date24 Jul 2018
DOIs
Publication statusPublished - 21 Oct 2018

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