Characterizing a Dramatic $ΔV\sim9$ Magnitude Flare on an Ultracool Dwarf Found in the ASAS-AN Survey [SSA]

http://arxiv.org/abs/1310.4515


We analyze a $\Delta V\sim9$ magnitude flare on the newly identified M8 dwarf SDSS J022116.84+194020.4 (hereafter {\name}) detected as part of the All-Sky Automated Survey for Supernovae (ASAS-SN). This is the first photometric detection of a dramatic flare on an ultracool dwarf near enough to the Sun (d$\sim$76 pc) for follow-up spectroscopy. Using infrared and optical spectra, we confirm that {\name} is an M8 dwarf with strong quiescent H$\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 {\name}. When modeled with a simple, classical flare light-curve, this flare is consistent with a total $U$-band flare energy $E_U\sim$ 10$^{31}$ erg, confirming that 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 10% to 34% during the flare peak and 0.5% to 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.

Read this paper on arXiv…

Date added: Fri, 18 Oct 13