A CORONAL MASS EJECTION MODEL FOR THE 1992-JULY-15 FLARE ON AU-MICROSCOPII OBSERVED BY THE EXTREME-ULTRAVIOLET-EXPLORER

Citation
Sl. Cully et al., A CORONAL MASS EJECTION MODEL FOR THE 1992-JULY-15 FLARE ON AU-MICROSCOPII OBSERVED BY THE EXTREME-ULTRAVIOLET-EXPLORER, The Astrophysical journal, 435(1), 1994, pp. 449-463
Citations number
55
Categorie Soggetti
Astronomy & Astrophysics
Journal title
ISSN journal
0004637X
Volume
435
Issue
1
Year of publication
1994
Part
1
Pages
449 - 463
Database
ISI
SICI code
0004-637X(1994)435:1<449:ACMEMF>2.0.ZU;2-B
Abstract
The dM1e flare star AU Microscopii (AU Mic) was observed by the EUVE D eep Survey Instrument on 1992 July 14-18. A large flare was detected i n the Deep Survey Lexan/Boron (DS Lex/B) (65-190 Angstrom) band and th e SW (70-190 Angstrom) and MW (140-380 Angstrom) spectrometers. The fl are consisted of a sharp impulsive peak lasting approximately 2 hours followed by a decaying tail lasting about a day. We present a simple, single temperature, dynamic model for the flare decay which is consist ent with the DS Lex/B light curve and reproduces the strongest, high-t emperature spectral lines in the released EUVE spectra. In this model, we assume the long decay time is due to an ejected, magnetically conf ined, low beta plasmoid expanding self similarly in the ambient medium in a manner reminiscent of solar coronal mass ejections. We demonstra te that the long tail of the DS Lex/B light curve can be explained by rapid expansion, causing the plasma to become tenuous sufficiently qui ckly that it avoids catastrophic radiative cooling. From this model, w e estimate the mass of the plasmoid to be approximate to 10(20) g and the total energy of the event to be approximate to 10(36) ergs. These values are approximately 10(4) times as large as those seen during the largest solar coronal mass ejection (CME) events. We argue that the r esults of our model are consistent with other measurements of stellar flare parameters. We also estimate a mass-loss rate of a few times 10( -13) M. yr(-1) and discuss the role of mass loss from dMe stars in the mass balance of the interstellar medium. We estimate the rotational b raking timescale from these events to be less than 500 million years a nd suggest that CME's may be an important source of angular momentum l oss from late-type stars.