Estimating stellar wind parameters from low-resolution magnetograms

TL;DR

This paper introduces a computationally efficient method to estimate stellar wind parameters and magnetic field geometry from low-resolution spectropolarimetric data, aiding understanding of stellar angular momentum evolution.

Contribution

The paper presents a new method to determine 3D stellar wind geometry and loss rates from low-resolution observations, with quantified accuracy based on solar magnetogram analysis.

Findings

Predicted wind speeds are within 5% of full resolution values.

Mass and angular momentum loss rates are within 5-20%.

X-ray emission measures can be significantly underestimated.

Abstract

Stellar winds govern the angular momentum evolution of solar-like stars throughout their main-sequence lifetime. The efficiency of this process depends on the geometry of the star's magnetic field. There has been a rapid increase recently in the number of stars for which this geometry can be determined through spectropolarimetry. We present a computationally efficient method to determine the 3D geometry of the stellar wind and to estimate the mass loss rate and angular momentum loss rate based on these observations. Using solar magnetograms as examples, we quantify the extent to which the values obtained are affected by the limited spatial resolution of stellar observations. We find that for a typical stellar surface resolution of 20$^{\rm o}$-30$^{\rm o}$, predicted wind speeds are within 5$\%$ of the value at full resolution. Mass loss rates and angular momentum loss rates are within 5-20$\%$. In contrast, the predicted X-ray emission measures can be under-estimated by 1-2 orders of magnitude, and their rotational modulations by 10-20$\%$.