Characterizing a Dramatic $\Delta V\sim -9$ Flare on an Ultracool Dwarf Found by the ASAS-SN Survey

Abstract

We analyze a $\Delta V\sim -9$ magnitude flare on the newly identified M8 dwarf SDSS J022116.84+194020.4 (hereafter SDSSJ0221) detected as part of the All-Sky Automated Survey for Supernovae (ASAS-SN). Using infrared and optical spectra, we confirm that SDSSJ0221 is a relatively nearby (d$\sim$76 pc) M8 dwarf with strong quiescent H$\alpha$ emission. Based on kinematics and the absence of features consistent with low-gravity (young) ultracool dwarfs, we place a lower limit of 200 Myr on the age of SDSSJ0221. When modeled with a simple, classical flare light-curve, this flare is consistent with a total $U$-band flare energy $E_U\sim$ 10${}^{34}$ erg, confirming that the most dramatic flares are not limited to warmer, more massive stars. Scaled to include a rough estimate of the emission line contribution to the $V$ band, we estimate a blackbody filling factor of $\sim$$10-30\%$ during the flare peak and $\sim$$0.5-1.6\%$ during the flare decay phase. These filling factors correspond to flare areas that are an order of magnitude larger than those measured for most mid-M dwarf flares.

Updated version in response to referee report. 6 pages, 3 figures, 2 tables. Submitted to ApJL. For a brief video explaining this paper, see http://youtu.be/uue8G0NnjJU

References in corpus (9)

• Constraining the Age-Activity Relation for Cool Stars: The SDSS DR5 Low-Mass Star Spectroscopic Sample
• Stellar SEDs from 0.3-2.5 Microns: Tracing the Stellar Locus and Searching for Color Outliers in SDSS and 2MASS
• Young L Dwarfs Identified in the Field: A Preliminary Low-Gravity, Optical Spectral Sequence from L0 to L5
• Low-Mass Dwarf Template Spectra from the Sloan Digital Sky Survey
• Activity and Kinematics of Ultracool Dwarfs Including An Amazing Flare Observation
• A White Light Megaflare on the dM4.5e Star YZ CMi
• M Dwarfs in SDSS Stripe 82: Photometric Light Curves and Flare Rate Analysis
• Multiwavelength observations of a giant flare on CN Leonis I. The chromosphere as seen in the optical spectra
• Twenty-three new ultra-cool subdwarfs from the Sloan Digital Sky Survey

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