A Model for the Chromosphere/Wind of 31 Cygni and its Implications for Single Stars

Abstract

I develop a detailed empirical model for the chromosphere and wind of 31 Cyg based on a previously published analysis of IUE spectra from the 1993 eclipse and on the thermodynamics of how the wind must be driven. I then use this model to interpret observations of single supergiant stars and to assess the evidence that their winds are fundamentally different from those of supergiants in the binary systems. This model naturally predicts a certain level of clumping of the gas to balance the pressure that drives the wind. It also predicts that anisotropic turbulence, such as would result from transverse displacements of Alfven waves directed along radial magnetic flux lines, would not give the roughly Gaussian profiles of emission lines seen in cool giant stars. Furthermore, it implies that C II] may not tell us much at all about general conditions in chromospheres. Finally, I speculate that chaotic magnetic fields, in dynamical equilibrium with the gas of the wind, are the actual driving mechanism.Comment: Submitted to A