K2 Ultracool Dwarfs Survey – V. High superflare rates on rapidly rotating late-M dwarfs

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https://academic.oup.com/mnras/article/486/1/1438/5427921

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https://doi.org/10.1093/mnras/stz886
 http://hdl.handle.net/11603/24158

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UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)

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https://orcid.org/0000-0002-8090-3570

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2019-04-04

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journal articles
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R R Paudel, J E Gizis, D J Mullan, S J Schmidt, A J Burgasser, P K G Williams, A Youngblood, K G Stassun, K2 Ultracool Dwarfs Survey – V. High superflare rates on rapidly rotating late-M dwarfs, Monthly Notices of the Royal Astronomical Society, Volume 486, Issue 1, June 2019, Pages 1438–1447, https://doi.org/10.1093/mnras/stz886

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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract

We observed strong superflares (defined as flares with energy in excess of 10³³ erg) on three late-M dwarfs: 2MASS J08315742+2042213 (hereafter 2M0831+2042; M7 V), 2MASS J08371832+2050349 (hereafter 2M0837+2050; M8 V), and 2MASS J08312608+2244586 (hereafter 2M0831+2244; M9 V). 2M0831+2042 and 2M0837+2050 are members of the young (∼700 Myr) open cluster Praesepe. The strong superflare on 2M0831+2042 has an equivalent duration (ED) of 13.7 h and an estimated energy of 1.3 × 1035 erg. We observed five superflares on 2M0837+2050, on which the strongest superflare has an ED of 46.4 h and an estimated energy of 3.5 × 10³⁵ erg. This energy is larger by 2.7 orders of magnitude than the largest flare observed on the older (7.6 Gyr) planet-hosting M8 dwarf TRAPPIST-1. Furthermore, we also observed five superflares on 2M0831+2244 which is probably a field star. The estimated energy of the strongest superflare on 2M0831+2244 is 6.1 × 10³⁴ erg. 2M0831+2042, 2M0837+2050, and 2M0831+2244 have rotation periods of 0.556 ± 0.002, 0.193 ± 0.000, and 0.292 ± 0.001 d, respectively, which we measured by using K2 light curves. We compare the flares of younger targets with those of TRAPPIST-1 and discuss the possible impacts of such flares on planets in the habitable zone of late-M dwarfs.