Dynamics of Flares on Late Type Dme-Stars - Part Two - Mass Motions and Prominence Oscillations during a Flare on Ad-Leonis

Details Dynamics of Flares on Late Type Dme-Stars - Part Two - Mass Motions and Prominence Oscillations during a Flare on Ad-Leonis Dynamics of Flares on Late Type Dme-Stars - Part Two - Mass Motions and Prominence Oscillations during a Flare on Ad-Leonis

Jul 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...274..245h&link_type=abstract

Astronomy and Astrophysics, Vol. 274, NO. 1/JUL(I), P. 245, 1993

Astronomy and Astrophysics

Astrophysics

22

Stars: Activity, Stars: Magnetic Fields, Stars: Flares, Stars: Individual: Ad Leo

Scientific paper

On 28 March 1984 at 3:22 UT, a 2.1 magnitude flare in the U-band was observed simultaneously in several wavelength regions, including low resolution spectrophotometry in the wavelength range 3600-4400Å. This flare displayed enhanced emission in chromospheric lines for a duration of about 50 min. By studying in detail the emission line centroid displacements and asymmetries, we discovered several new exciting phenomena. In this paper we present evidence for complex velocity fields. A deeper investigation of the plasma physical parameters and the kinetic energy associated with these mass motions is discussed by Houdebine et al. (1993).
Prior to the flare onset, weak P-Cygni profiles were observed in the Call resonance lines which we interpret as evidence for the preflare motion of a solar like "dark filament". The loop radius is estimated to be of the order of 5 1O7 m. During the impulsive phase, a high velocity mass ejection was observed (Houdebine et al. 1990, Paper I) with red-shifts in the Balmer line cores, the CaII K and HeI 4026Å. This latter event is interpreted as the downward motion of chromospheric condensations initiated by highly energetic particle beams (in the MeV range) and a subsequent chromospheric evaporation. The inferred minimum energy flux deposited by the beam in the transition region is about 9 1010 which corresponds to the energy of a large flare on the Sun. Later during the flare, a 2.68 min periodic oscillation occurred in the line centroids with a peak to peak amplitude up to ˜ 95 km s-1. We show that it is most likely the signature of periodic motions in a prominence that may have been initiated by flare-born disturbances. This prominence (whose minimum radius and apex magnetic field strength are 2 1O7m and 20G respectively) expanded slowly during the gradual phase, and finally disrupted, ejecting part of its mass higher in the corona. The loop disruption signatures are well defined reversed P-Cygni profiles that are sustained for several minutes. During the post-flare stage, we found clues for clouds of plasma spread across the stellar disc with a minimum filling factor of 17%.

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