Starspot Area Coverage: Correlation with Age and Spectral Type in FGK and M Stars

Abstract

Starspots, analogous to sunspots, are surface manifestations of stellar magnetic activity. Their study provides crucial insights into stellar dynamo processes and the evolution of magnetic phenomena. However, due to limited data on magnetic activity across stellar lifetimes, the relationship between starspot area coverage and stellar properties remains underexplored. This work investigates the correlation between starspot area coverage and stellar age, effective temperature, and rotation period in FGK and M stars using data from Kepler and CoRoT. We utilized the starspot transit mapping method to analyze 11 stars, calculating starspot area coverage by integrating spot areas on the stellar surface. The average starspot coverage ranged from 4% to 29%, consistent with theoretical models of stellar magnetic evolution. Our analysis revealed a strong anticorrelation with stellar age (Spearman ρ = −0.80), confirming a significant decline in magnetic activity over time, but a weak anticorrelation between starspot coverage and rotation period. Regarding the relationship between absolute starspot area coverage and effective temperature, we found a moderate positive correlation (Spearman ρ = 0.40), with the majority of stars with an absolute area coverage of (2–4 ± 0.6) × 1010 km2. Incorporating starspot coverage into isochrone models could significantly improve stellar age estimates, especially for young stars. Moreover, these measurements are crucial for refining stellar dynamo models and advancing our understanding of magnetic field generation.