A Stringent Test of Magnetic Models of Stellar Evolution

TL;DR

This study tests magnetic models of stellar evolution against precise measurements of a binary star system, showing magnetic inhibition of convection can explain observed size and temperature discrepancies in stars.

Contribution

It provides the first detailed comparison of magnetic stellar models with well-characterized binary stars in an open cluster, estimating magnetic field strengths consistent with observations.

Findings

Magnetic models reproduce observed stellar radii and temperatures within uncertainties.

Estimated magnetic field strengths are around 1600-1800 G, aligning with X-ray based estimates.

Supports magnetic inhibition of convection as a key factor in stellar evolution discrepancies.

Abstract

Main-sequence stars with convective envelopes often appear larger and cooler than predicted by standard models of stellar evolution for their measured masses. This is believed to be caused by stellar activity. In a recent study, accurate measurements have been published for the K-type components of the 1.62 day detached eclipsing binary EPIC 219511354, showing the radii and temperatures for both stars to be affected by these discrepancies. This is a rare example of a system in which the age and chemical composition are known, by virtue of being a member of the well-studied open cluster Ruprecht 147 (age $\sim$ 3 Gyr, [Fe/H] = +0.10). Here we report a detailed study of this system with non-standard models incorporating magnetic inhibition of convection. We show that these calculations are able to reproduce the observations largely within their uncertainties, providing robust estimates of the strength of the magnetic fields on both stars: $1600 \pm 130$ G and $1830 \pm 150$ G for the primary and secondary, respectively. Empirical estimates of the magnetic field strengths based on the measured X-ray luminosity of the system are roughly consistent with these predictions, supporting this mechanism as a possible explanation for the radius and temperature discrepancies.