An M dwarf Companion to an F-type Star in a young main-sequence binary

TL;DR

This study characterizes a rare young binary system consisting of an F-type star and a very low-mass M dwarf, providing insights into the properties and evolution of such systems.

Contribution

It presents detailed measurements of an F+dM binary system, including the lowest-mass M dwarf known, and discusses its youth and evolutionary state.

Findings

Primary star is an early F-type main-sequence star.

Secondary star is among the lowest-mass M dwarfs known.

Binary system is young, below ~250 Myrs, with no spin-orbit synchronization.

Abstract

Only a few well characterized very low-mass M dwarfs are known today. Our understanding of M dwarfs is vital as these are the most common stars in our solar neighborhood. We aim to characterize the properties of a rare F+dM stellar system for a better understanding of the low-mass end of the Hertzsprung-Russel diagram. We used photometric light curves and radial velocity follow-up measurements to study the binary. Spectro- scopic analysis was used in combination with isochrone fitting to characterize the primary star. The primary star is an early F-type main-sequence star with a mass of (1.493 +- 0.073) Msun and a radius of (1.474 +- 0.040) Rsun. The companion is an M dwarf with a mass of (0.188 +- 0.014) Msun and a radius of (0.234 +- 0.009) Rsun. The orbital period is (1.35121 +- 0:00001)d. The secondary star is among the lowest-mass M dwarfs known to date. The binary has not reached a 1:1 spin-orbit synchronization. This indicates a young main-sequence binary with an age below ~250 Myrs. The mass-radius relation of both components are in agreement with this finding.