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

TL;DR

This paper presents an empirical model of 31 Cygni's chromosphere and wind, offering insights into stellar wind mechanisms, magnetic influences, and differences between single and binary supergiant stars.

Contribution

It introduces a detailed empirical model based on IUE spectra, exploring wind driving mechanisms, magnetic effects, and implications for single versus binary supergiant stars.

Findings

Model predicts gas clumping to balance wind pressure.

Transverse Alfven waves do not produce Gaussian emission line profiles.

C II] lines may not reliably indicate chromospheric conditions.

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.