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Issue A&A Volume 383, Number 2, February IV 2002 Page(s) 548 - 557 Section Formation, structure and evolution of stars DOI 10.1051/0004-6361:20011743

A&A 383, 548-557 (2002)
DOI: 10.1051/0004-6361:20011743

Observations and modelling of a large optical flare on AT Microscopii

D. García-Alvarez¹, D. Jevremovic^{1, 2}, J. G. Doyle¹ and C. J. Butler<sup>1

1</sup>  Armagh Observatory, College Hill, Armagh BT61 9DG N. Ireland
    e-mail: djc@star.arm.ac.uk, jgd@star.arm.ac.uk, cjb@star.arm.ac.uk
²  Astronomical Observatory, Volgina 7, 11070 Belgrade, Yugoslavia

(Received 26 September 2001 / Accepted 5 December 2001)

Abstract
Spectroscopic observations covering the wavelength range 3600-4600 Å are presented for a large flare on the late type M dwarf AT Mic (dM4.5e). A procedure to estimate the physical parameters of the flaring plasma has been used which assumes a simplified slab model of the flare based on a comparison of observed and computed Balmer decrements. With this procedure we have determined the electron density, electron temperature, optical thickness and temperature of the underlying source for the impulsive and gradual phases of the flare. The magnitude and duration of the flare allows us to trace the physical parameters of the response of the lower atmosphere. In order to check our derived values we have compared them with other methods. In addition, we have also applied our procedure to a stellar and a solar flare for which parameters have been obtained using other techniques.

Key words: stars: activity -- stars: chromospheres -- stars: flare -- stars: late-type

Offprint request: D. García-Alvarez, dga@star.arm.ac.uk

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