A low-mass eclipsing binary within the fully convective zone from the Next Generation Transit Survey

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 three field-age (>1 Gyr), late M dwarf eclipsing binaries known, and has a period of 1.74774 d, similar to that of CM Dra and KOI126. Modelling of the eclipses and radial velocities shows that the component masses are Mpri =0.17391 -0.00099+0.00153 M⊙, Msec = 0.17418 -0.00059+0.00193 M⊙; and the radii are Rpri = 0.2045-0.0058+0.0038 R⊙, Rsec = 0.2168 -0.0048+0.0047 R⊙. The effective temperatures are Tpri = 2995 -105+85 K and Tsec = 2997 -101K+66, consistent with M5 dwarfs and broadly consistent with main-sequence models. This pair represents a valuable addition that can be used to constrain the mass-radius relationship at the low-mass end of the stellar sequence.