K2 Ultracool Dwarfs Survey. III. White Light Flares Are Ubiquitous in M6-L0 Dwarfs

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1803.07708.pdf (1.24 MB)

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https://iopscience.iop.org/article/10.3847/1538-4357/aab8fe

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https://arxiv.org/ct?url=https%3A%2F%2Fdx.doi.org%2F10.3847%2F1538-4357%2Faab8fe&v=e2eb9d3a
 http://hdl.handle.net/11603/24156

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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

Date

2018-05-04

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journal articles
preprints
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Citation of Original Publication

Paudel, Rishi R. et al. K2 Ultracool Dwarfs Survey. III. White Light Flares Are Ubiquitous in M6-L0 Dwarfs. The Astrophysical Journal 858 (May 4, 2018), no. 1. https://doi.org/10.3847/1538-4357/aab8fe.

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© 2017. The American Astronomical Society. All rights reserved

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Abstract

We report the white light are rates for 10 ultracool dwarfs (UCDs) using Kepler K2 short cadence data. Among our sample stars, two have spectral type M6, three are M7, three are M8 and two are L0. Most of our targets are old low mass stars. We identify a total of 283 flares in all of the stars in our sample, with Kepler energies in the range log Eᴋₚ ~(29 - 33.5) erg. Using the maximum-likelihood method of line fi tting, we fi nd that the flare frequency distribution (FFD) for each star in our sample follows a power law with slope -𝛼 in range -(1.3-2.0). We fi nd that cooler objects tend to have shallower slopes. For some of our targets, the FFD follows either a broken power law, or a power law with an exponential cutoff. For the L0 dwarf 2MASS J12321827-0951502, we find a very shallow slope (-𝛼 = -1.3) in the Kepler energy range (0.82-130)✕10³⁰ erg: this L0 dwarf has flare rates which are comparable to the rates of high energy flares in stars of earlier spectral types. In addition, we report photometry of two super flares: one on the L0 dwarf 2MASS J12321827-0951502 and another on the M7 dwarf 2MASS+J08352366+1029318. In case of 2MASS J12321827-0951502, we report a flare brightening by a factor of ~144 relative to the quiescent photospheric level. Likewise, for 2MASS J08352366+1029318, we report a flare brightening by a factor of ~60 relative to the quiescent photospheric level. These two super flares have bolometric (UV/optical/infrared) energies 3.6 ✕10³³ erg and 8.9 ✕10³³ erg respectively, while the FWHM time scales are very short, ~2 minutes. We fi nd that the M8 star TRAPPIST-1 is more active than the M8.5 dwarf: 2M03264453+1919309, but less active than another M8 dwarf (2M12215066-0843197).