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Astron. Astrophys. 318, 835-840 (1997)

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The intrinsic Ly to H ratio in M dwarf stars

J.G. Doyle 1, M. Mathioudakis 1, 2, V. Andretta 1, 3, C.I. Short 1 and P. Jelinsky 4

1 Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland (jgd@star.arm.ac.uk, cis@star.arm.ac.uk)
2 current: Dept. of Pure and Applied Physics, Queens University of Belfast, Belfast BT7 1NN, N. Ireland (m.mathioudakis@qub.ac.uk)
3 current: NASA/GSFC, Laboratory for Astronomy and Solar Physics, Code 682, Greenbelt, MD 20771, USA (andretta@gsfc.nasa.gov)
4 Center for EUV Astrophysics, University of California, Berkeley CA 94720-5030, USA (patj@cea.berkeley.edu)

Received 24 February 1996 / Accepted 19 October 1996


Using Ly [FORMULA] line profiles generated from a grid of M dwarf model atmospheres we calculate the attenuation factor [i.e. Ly [FORMULA] (obs)/ Ly [FORMULA] (intrin)] due to the interstellar medium as a function of hydrogen column density. Then using selected model atmospheres, attenuation factors were calculated for those M dwarfs with available Ly [FORMULA] observations. The prime motivation in this work has been to look afresh at the intrinsic Ly [FORMULA] to H [FORMULA] flux ratio, an important constraint in the radiative transfer modelling of M dwarfs. For those active dMe stars where both lines were observed, the intrinsic ratio is [FORMULA] (with [FORMULA] % variation). The major uncertainty in this work has been the interstellar hydrogen column density, emphasizing the need for further work in this area and in particular an accurate model of its variation in all directions.

Key words: lines: profiles – stars: activity: chromospheres; late-type – ISM: general

Send offprint requests to: J.G. Doyle

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998