Mechanisms of Solar (and Stellar) Mass Loss

Abstract

The fundamental theory for mass loss from late-type stars such as our Sun was developed by Gene Parker in the 1950’s (Parker 1958), and has been largely understood since then; refinements since then have largely focused on physically more realistic fluid equations (which take into account, for example, the effects of multi-component fluids and corrections to energy transport by classical thermal conduction) and additional mechanisms for driving the wind (e.g., heating and momentum deposition by magnetohydrodynamic waves). Nevertheless, if one were to ask most professional solar wind theorists what the generally accepted model for the solar wind is, the answer is most likely a shrug of the shoulders: It has not been possible to develop a detailed theory for solar wind mass loss which takes into fill account all of the observed complexities of this outflow; and the status of wind research for other late-type stars (meaning late-type giants and supergiants) is not in recognizably better shape. In tis paper, I will sttempt to focus on this embarassment, and will try to explain why it is that this problem has turned out to be so remarkably difficult. Along the way, I will provide a brief overview of the basic theory, and of the observational perspectives of few years ago as contrasted with what is now known from the most recent data provided by the Ulysses spacecraft. Based on these discussions, I will then focus on a highly selective overview of what is to be explained, and the current status of theory in these regards.