EUVE Observations of a Rare Impulsive Flare on EV Lac

Previous abstract Next abstract

Session 5 -- Chromospheres/Coronae/Active Binaries
Display presentation, Monday, 30, 1994, 9:20-6:30

[5.19] EUVE Observations of a Rare Impulsive Flare on EV Lac

C. W. Ambruster (Villanova U.), A. Brown (JILA), B. Pettersen (Geodetic Inst., Norway), R.E. Gershberg (Crimean Astrophys. Obs.)

\def\etal{et~al.\ }

The M dwarf flare star EV Lac, known for producing extreme flares at both optical and X-ray wavelengths, was observed with EUVE during 1993 Sep 9-13. Most stellar soft X-ray flares are gradual-phase flares, and this has been true also of flares observed with EUVE from AU Mic (Cully \etal 1993, Ap.J. Lett 414, L49), and AD Leo (Hawley \etal 1993, BAAS 25, 856): both had durations $>$ 1 day. EV Lac, however, continued its atypical behavior by producing a rare \bf impulsive \rm flare lasting only about 2 minutes, but with a factor $\sim 10$ flux increase in the 70 \AA\ - 180 \AA\ passband. It was seen simultaneously in independent detectors (the spectrometers and the Deep Survey instruments), and accounted for a significant fraction of the flux from the entire 100 ksec observation. We derive a density estimate for the flare, and also the emission measure distribution of both the flare and the quiescent corona.

Author C.W. Ambruster acknowledges support from NASA grant NAG 5-2279.

Monday program listing