A study of ultraviolet spectra of zeta Aurigae/VV Cephei systems. VII. Chromospheric density distribution and wind acceleration region.

Abstract

Chromospheric eclipse spectra have been obtained for three Zeta Aurigae binary systems using the International Ultraviolet Explorer (IUE) spacecraft. In order to fit average density models to the chromospheres, 3 samples of column densities (for 31 Cygni, 32 Cygni, and Zeta Aurigae K giants) were used. Wind velocities were derived assuming a continuous outflow of matter and a known M-dot value. It is shown that wind acceleration region of Zeta Aurigae underwent a temporary energy deficiency and mass loss at the time of the 1979 eclipse. The density gradients and wind acceleration regions of 31 Cygni and 32 Cygni, were found to be very similar in the corresponding eclipses of 1981 and 1982. The density and velocity structure of 31 and 32 Cygni are represented by power laws which correspond to the Alfven wave driven wind models of Hartmann and McGregor (1980). The location of the main power input per unit mass is also discussed. A sketch of the eclipse geometry of 31 Cygni is provided.