From Starspots to Stellar Coronal Mass Ejections -- Revisiting Empirical Stellar Relations

TL;DR

This paper reevaluates empirical relations between starspot sizes and stellar activity indicators to better understand their impact on stellar energetic events, which are crucial for assessing exoplanet habitability around cool stars.

Contribution

It revisits and refines the empirical relation between starspot size and stellar temperature, analyzing its implications for stellar flare and coronal mass ejection estimates.

Findings

Revised the empirical starspot size-temperature relation.

Assessed impact on flare energy and CME estimates.

Implications for exoplanet habitability studies.

Abstract

Upcoming missions, including the James Webb Space Telescope, will soon characterize the atmospheres of terrestrial-type exoplanets in habitable zones around cool K- and M-type stars searching for atmospheric biosignatures. Recent observations suggest that the ionizing radiation and particle environment from active cool planet hosts may be detrimental for exoplanetary habitability. Since no direct information on the radiation field is available, empirical relations between signatures of stellar activity, including the sizes and magnetic fields of starspots, are often used. Here, we revisit the empirical relation between the starspot size and the effective stellar temperature and evaluate its impact on estimates of stellar flare energies, coronal mass ejections, and fluxes of the associated stellar energetic particle events.