The effect of activity on stellar temperatures and radii

TL;DR

This study demonstrates that active low-mass stars are systematically cooler and larger than inactive stars of similar luminosity, confirming that stellar activity significantly affects stellar temperature and radius predictions.

Contribution

The paper extends the understanding of activity-related stellar property differences from binary systems to single stars, providing a unified explanation for observed discrepancies.

Findings

Active stars are cooler than inactive stars at similar luminosity.

Active stars have larger radii consistent with binary star observations.

Results support the hypothesis that stellar activity influences stellar structure.

Abstract

Recent analyses of low-mass eclipsing binary stars have unveiled a significant disagreement between the observations and the predictions of stellar structure models. Results show that theoretical models underestimate the radii and overestimate the effective temperatures of low-mass stars but yield luminosities that accord with observations. A hypothesis based upon the effects of stellar activity was put forward to explain the discrepancies. In this paper we study the existence of the same trend in single active stars and provide a consistent scenario to explain systematic differences between active and inactive stars in the H-R diagram reported earlier. The analysis is done using single field stars of spectral types late-K and M and computing their bolometric magnitudes and temperatures through infrared colours and spectral indices. The properties of the stars in samples of active and inactive stars are compared statistically to reveal systematic differences. After accounting for a number of possible bias effects, active stars are shown to be cooler than inactive stars of similar luminosity therefore implying a larger radius as well, in proportions that are in excellent agreement with those found from eclipsing binaries. The present results generalise the existence of strong radius and temperature dependences on stellar activity to the entire population of low-mass stars, regardless of their membership in close binary systems.