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Astron. Astrophys. 336, 281-289 (1998)

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Building reliable models of M dwarf chromospheres: the impact of the usual assumptions

Ambretta Falchi 1 and Pablo J.D. Mauas 2

1 Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50155 Firenze, Italy
2 Instituto de Astronomía y Física del Espacio, CC 67, Suc. 28, 1428-Buenos Aires, R. Argentina

Received 23 December 1997 / Accepted 19 May 1998


We study different approximations usually made to simplify the calculation of chromospheric models of M dwarf stars. The approximations we discuss in details are: the assumption that the minority species are in LTE, the omission of the contribution of numerous atomic and molecular lines (line blanketing ) to the opacity, and the Complete Frequency Redistribution for the [FORMULA] line.

We consider a "cold" chromospheric model corresponding to a low activity dM star and a "hot" one corresponding to a very active dMe star. We find that the assumptions under study affect more strongly the cold than the hot model. In particular the approximation of Complete Frequency Redistribution in the [FORMULA] line, through the statistical equilibrium and ionization equilibrium equation, changes the electron density in the high chromosphere and strongly affects other line profiles.

Key words: stars: atmospheres – stars: chromosphere – stars: late-type

Send offprint requests to: A. Falchi

© European Southern Observatory (ESO) 1998

Online publication: July 7, 1998