X-ray and optical observations of a dMe flare star in the T Tauri field.

Abstract

The authors present observations of a newly discovered dMe flare star within 20 pc of the Sun. An EXOSAT observation of this source shows an almost complete X-ray flare light curve with rise time ≡600 s, decay time ≡1500 s, and peak luminosity L_x = 6.1×10²⁹erg s^-1, a 40-fold increase in brightness over the quiescent level (1.5×10²⁸erg s^-1). The total energy in the flare is 2.7×10³² < E_x < 3.3×10³³erg. The authors also present results of two Einstein IPC observations. They identify the source with a hitherto unstudied nearby star with magnitude V ≡ 13 and spectral type ≡dM5e, at a distance of ≡13 pc. A loop model for the quiescent corona gives physically unrealistic values for the size of the loop structure; however, considering the quiescent corona to be uniform and symmetrical gives acceptable values for the mean pressure and density. For the flare, the authors explore a variety of different physical assumptions about the cooling mechanism and derive possible values for loop lengths and electron densities.