A modelling of circumstellar BAII lines for the hypergiant phi Cassiopeiae.

The spectra of a yellow hypergiant ρ Cas from years 1969-1970 document the activity in the circumstellar envelope. For its analysis there has been proposed a new version of the method of solution of the equation of radiative transfer in a spherical, expanding layer. Introduced changes allow to compute a spectral line profile formed in a shell when a star, with a given radius and a specified spectral line flux, is placed in its center. In the application to the case of circumstellar BaII lines of ρ Cas the modelling was extended to multilevel case. Performed calculations resulted in new information about the envelopes structure: the layer of BaII formation should be accelerated and cooling while expanding in order to explain the observed details of line shapes. The maximum temperature of the envelope is estimated to be 12000K and the mass loss rate is about 10^-3 M_sun yr^-1.