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| Paper: |
Semi-Empirical Models of Stellar Flares |
| Volume: |
154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop |
| Page: |
1500 |
| Authors: |
Jevremovic, D.; Houdebine, E. R.; Butler, C. J. |
| Abstract: |
We present a small grid of model atmospheres that reproduce the spectral signatures observed during a flare in the atmosphere of a dM4.5e star. We first designed a semi-empirical model for the quiescent chromosphere using the MULTI radiative transfer code (Carlsson 1986) with an improved treatment of the Stark broadening (Holtsmark profiles). We use the photospheric model of Allard & Hauschildt (1995) on which we superimpose a chromosphere and transition region. By changing the temperature structure of the chromosphere and transition region we were able to match the fluxes in the Balmer lines. We assume that, at chromospheric heights, changes in electron temperature and hydrogen ionisation balance during flares are controlled by the bombardment of a beam of energetic electrons. In the calculation of the new temperature structure, we assume that the energy distribution of electrons produced by collisional ionisation by a beam of electrons has a sharp maximum at E = 1/4 x E_i (Janev et al. 1987; Omidvar 1965), where E_i is the ionisation potential for level i. The penetration depth of the beam is calculated following Houdebine (1992). We compare the results of these calculations with observations of three small flares on Gl 866. |
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