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Astron. Astrophys. 345, 618-628 (1999)

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A non-LTE inversion procedure for chromospheric cloud-like features

R. Molowny-Horas 1, P. Heinzel 2, P. Mein 1 and N. Mein 1

1 Observatoire de Paris, Section de Meudon, DASOP, F-92195 Meudon Principal Cedex, France
2 Astronomical Institute, Academy of Sciences of the Czech Republic, CZ-25165 Ondejov, Czech Republic

Received 12 November 1998 / Accepted 1 February 1999


A fast inversion procedure which provides estimates of the temperature, electronic density, microturbulence, geometrical thickness and bulk velocity of chromospheric features, so-called "clouds", has been implemented. The procedure has been divided into two steps: 1) the construction of a large grid of models by means of a multi-level non-LTE transfer code, which solves in a fast and reliable way the radiative transfer problem of the formation of the H[FORMULA] line inside an isolated, isothermal cloud laying above the photosphere, and 2) the implementation of searching, matching and interpolating algorithms which yield an inversion of the observed line profile in terms of the grid's computed profiles. The aforementioned 5 parameters, on which the profiles depend, can be reduced to 4 if one defines the so-called emission measure from the geometrical thickness and electronic density parameters. We show that this strategy yields excellent results when dealing with solar filaments. The main advantages of this approach are also discussed.

Key words: line: profiles – radiative transfer – methods: data analysis – Sun: chromosphere – Sun: filaments

Send offprint requests to: P. Mein

© European Southern Observatory (ESO) 1999

Online publication: April 19, 1999