Summary: Astronomy & Astrophysics manuscript no.
(will be inserted by hand later)
Observations and modelling of a large optical flare on AT
Microscopii
D. Garc'ia­Alvarez 1 , D. Jevremovi'c 1;2 , J.G. Doyle 1 , and C.J. Butler 1
1 Armagh Observatory, College Hill, Armagh BT61 9DG N.Ireland
e­mail: dga@star.arm.ac.uk, djc@star.arm.ac.uk, jgd@star.arm.ac.uk, cjb@star.arm.ac.uk
2 Astronomical Observatory, Volgina 7, 11070 Belgrade, Yugoslavia
Received ....., 2001; accepted ...., .....
Abstract. Spectroscopic observations covering the wavelength range 3600--4600 š A 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: late­type
1. Introduction

Source: Armagh Observatory

Collections: Physics