Non-LTE inversion of chromospheric Caii cloud-like features

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

Corresponding author: K. Tziotziou, Kostas.Tziotziou@obspm.fr

Received: 22 June 2000
Accepted: 14 November 2000

Abstract

A chromospheric cloud-like feature observed in the 8542 ÅCaii line is studied by a two step inversion procedure which provides estimates of its temperature, electronic density, microturbulence, geometrical thickness and bulk velocity. The first step involves the computation of a large grid of models by a multi-level non-LTE transfer code which gives the Caii line depth-dependent mean intensity inside an isolated, isothermal cloud lying above the chromosphere. The second step involves the inversion of the observed profiles with the grid of computed synthetic Caii profiles. A searching and matching algorithm is implemented followed by an interpolation algorithm which permits a more accurate determination of the parameters on which the profiles depend. The five grid parameters are reduced to four by defining the emission measure from the geometrical thickness and electronic density. We show that this inversion procedure gives accurate results for some of our inversion parameters when dealing with solar filaments and is complementary to a previous study of the same object in the line. The main advantages, problems and future extension of the inversion approach are also discussed.