Instabilities in the envelope of the Be star HD 37202 xi Tau. II.

Th 1970 - 67 radial velocities, profiles, equivalent widths of the lines of the shell star Tauri and the electron density in the lower layers of hydrogen show a slow pseudo-periodic variation of about 7 years. The pulsation of the envelope is instigated by instability of the inner layers. During every active phase of these layers, fast variations in the radial velocities of the He I, Mg U and metallic lines are observed and violet satellite lines appear. Changes in the number of visible Balmer lines show that the electron density changes by about a factor 8 in the outer envelope during the 7 years period. At the same time changes in the equivalent widths and profiles of lines of H, Na I and Ca II indicate a parallel change in density of the material in the outer envelope. The variation of the emission H and H profiles is closely connected with the motion of the envelope. The emission Balmer decrement is 3.6. Key words: Tauri - unstable shell star - profiles - emission lines - Balmer decrement