# A Bright Short Period M-M Eclipsing Binary from the KELT Survey: Magnetic Activity and the Mass-Radius Relationship for M-dwarfs

## TL;DR

This paper reports the discovery and detailed analysis of a short-period M-dwarf eclipsing binary system, revealing that both stars are larger and cooler than standard models predict, likely due to magnetic activity.

## Contribution

The study provides precise measurements of an M-dwarf binary system and demonstrates the impact of magnetic activity on stellar radii and temperatures, advancing understanding of low-mass star properties.

## Key findings

- Both stars are 17-28% larger than predicted by standard models.
- Stars are 4-10% cooler than standard stellar models.
- Magnetic activity explains the observed radius and temperature discrepancies.

## Abstract

We report the discovery of KELT J041621-620046, a moderately bright (J$\sim$10.2) M dwarf eclipsing binary system at a distance of 39$\pm$3 pc. KELT J041621-620046 was first identified as an eclipsing binary using observations from the Kilodegree Extremely Little Telescope (KELT) survey. The system has a short orbital period of $\sim$1.11 days and consists of components with M$_1$ = $0.447^{-0.047}_{+0.052}\,M_\odot$ and M$_2$ = $0.399^{-0.042}_{+0.046}\,M_\odot$ in nearly circular orbits. The radii of the two stars are R$_1$ = $0.540^{-0.032}_{+0.034}\,R_\odot$ and R$_2$ = $0.453\pm0.017\,R_\odot$. Full system and orbital properties were determined (to $\sim$10% error) by conducting an EBOP global modeling of the high precision photometric and spectroscopic observations obtained by the KELT Follow-up Network. Each star is larger by 17-28% and cooler by 4-10% than predicted by standard (non-magnetic) stellar models. Strong H$\alpha$ emission indicates chromospheric activity in both stars. The observed radii and temperature discrepancies for both components are more consistent with those predicted by empirical relations that account for convective suppression due to magnetic activity.