EPIC 219511354, A Binary Pair of Active K-stars: Modeling Activity-induced Radius Inflation by Magneto-convection

Abstract Magnetically active low-mass stars are observed to have their empirical radii R “inflated” and their empirical T eff reduced relative to standard predictions. Models which have been proposed to replicate these discrepancies include magneto-convection (M-C), and/or star-spots (S-S). Here we raise the question: is there any reason to prefer a dominant role for either M-C or S-S in order to replicate the data? In the binary EPIC 219511354, the empirical M and R values have remarkably high (1%–2%) precision. To replicate these data, the S-S model requires almost the entire (88%–94%) secondary surface to be spotted. Here, we report that our M-C model fits the empirical R and T eff values for both members of the binary within 1σ error bars without needing spots. If an areal spot coverage of 94% is regarded as physically implausible, the M-C model could be considered preferable over S-S in EPIC 219511354.