A low-mass eclipsing binary within the fully convective zone from the NGTS

TL;DR

This paper reports the discovery and detailed characterization of a rare, field-age, low-mass eclipsing binary system composed of nearly equal-mass M dwarfs, providing valuable data to refine stellar models.

Contribution

It presents the first detailed measurements of a low-mass, fully convective eclipsing binary at field age, expanding the sample for testing stellar evolution models.

Findings

Component masses are approximately 0.174 M_sun.

Radii are about 0.205 and 0.217 R_sun.

Temperatures are around 3000 K, consistent with M5 dwarfs.

Abstract

We have discovered a new, near-equal mass, eclipsing M dwarf binary from the Next Generation Transit Survey. This system is only one of 3 field age ($>$ 1 Gyr), late M dwarf eclipsing binaries known, and has a period of 1.74774 days, similar to that of CM~Dra and KOI126. Modelling of the eclipses and radial velocities shows that the component masses are $M_{\rm pri}$=0.17391$^{+0.00153}_{0.00099}$ $M_{\odot}$, $M_{\rm sec}$=0.17418$^{+0.00193}_{-0.00059}$ $M_{\odot}$; radii are $R_{\rm pri}$=0.2045$^{+0.0038}_{-0.0058}$ $R_{\odot}$, $R_{\rm sec}$=0.2168$^{+0.0047}_{-0.0048}$ $R_{\odot}$. The effective temperatures are $T_{\rm pri} = 2995\,^{+85}_{-105}$ K and $T_{\rm sec} = 2997\,^{+66}_{-101}$ K, consistent with M5 dwarfs and broadly consistent with main sequence models. This pair represents a valuable addition which can be used to constrain the mass-radius relation at the low mass end of the stellar sequence.