K2 Ultracool Dwarfs Survey. II. The White Light Flare Rate of Young Brown Dwarfs
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Author/Creator ORCID
Date
2017-08-09
Type of Work
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Citation of Original Publication
Gizis, John E. Et al. K2 Ultracool Dwarfs Survey. II. The White Light Flare Rate of Young Brown Dwarfs. The Astrophysical Journal 845 (Aug. 9, 2017), no. 1. https://doi.org/10.3847/1538-4357/aa7da0.
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© 2017. The American Astronomical Society. All rights reserved
Subjects
Abstract
We use Kepler K2 Campaign 4 short-cadence (one-minute) photometry to measure white light flares
in the young, moving group brown dwarfs 2MASS J03350208+2342356 (2M0335+23) and 2MASS
J03552337+1133437 (2M0355+11), and report on long-cadence (thirty-minute) photometry of a superflare in the Pleiades M8 brown dwarf CFHT-PL-17. The rotation period (5.24 hr) and projected rotational velocity (45 km s⁻¹) confirm 2M0335+23 is inflated (R ≥ 0.20R☉ ) as predicted for a 0.06M☉ ,
26-Myr old brown dwarf βPic moving group member. We detect 22 white light flares on 2M0335+23.
The flare frequency distribution follows a power-law distribution with slope −α = −1.8 ± 0.2 over
the range 10³¹ to 10³³ erg. This slope is similar to that observed in the Sun and warmer flare stars,
and is consistent with lower energy flares in previous work on M6-M8 very-low-mass stars; taken the
two datasets together, the flare frequency distribution for ultracool dwarfs is a power law over 4.3
orders of magnitude. The superflare (2.6 × 10³⁴ erg) on CFHT-PL-17 shows higher energy flares are
possible. We detect no flares down to a limit of 2 ×10³⁰ erg in the nearby L5γ AB Dor Moving Group
brown dwarf 2M0355+11, consistent with the view that fast magnetic reconnection is suppressed in
cool atmospheres. We discuss two multi-peaked flares observed in 2M0335+23, and argue that these
complex flares can be understood as sympathetic flares, in which a fast-mode MHD waves similar to
EUV waves in the Sun trigger magnetic reconnection in different active regions.