Winds of Main-Sequence Stars: Observational Limits and a Path to Theoretical Prediction

TL;DR

This paper reviews observational challenges and recent theoretical approaches to understanding and predicting the weak stellar winds of solar-type main-sequence stars, highlighting hybrid methods and models linking coronal heating to mass loss.

Contribution

It introduces new observational constraints and discusses the development of models that connect coronal heating with stellar wind properties for solar-like stars.

Findings

Traditional diagnostics are limited in detecting solar-like winds.

Hybrid observational and theoretical methods provide new constraints.

Modeling suggests sub-photospheric convection influences stellar wind properties.

Abstract

It is notoriously difficult to measure the winds of solar-type stars. Traditional spectroscopic and radio continuum techniques are sensitive to mass loss rates at least two to three orders of magnitude stronger than the Sun's relatively feeble wind. Much has been done with these methods to probe the more massive outflows of younger (T Tauri) and older (giant, AGB, supergiant) cool stars, but the main sequence remains terra incognita. This presentation reviews the limits on traditional diagnostics and outlines more recent ideas such as Lyman alpha astrospheres and charge-exchange X-ray emission. In addition, there are hybrid constraints on mass loss rates that combine existing observables and theoretical models. The Sackmann/Boothroyd conjecture of a more massive young Sun (and thus a much stronger ZAMS wind) is one such idea that needs to be tested further. Another set of ideas involves a strong proposed coupling between coronal heating and stellar mass loss rates, where the former is easier to measure in stars down to solar-like values. The combined modeling of stellar coronae and stellar winds is developing rapidly, and it seems to be approaching a level of development where the only remaining ``free parameters'' involve the sub-photospheric convection. This talk will also summarize these theoretical efforts to predict the properties of solar-type main-sequence winds.