The masses and radii of HD186753B and TYC7096-222-1B: the discovery of two M-dwarfs that eclipse A-type stars

TL;DR

This paper reports the discovery and characterization of two new eclipsing binary systems involving Am stars and M-dwarfs, providing precise measurements of their masses and radii, and insights into stellar spin-down processes.

Contribution

It presents the first detailed measurements of M-dwarfs orbiting Am stars in eclipsing binaries, expanding understanding of such systems.

Findings

HD186753B has a mass of 0.24 M_sun and radius of 0.31 R_sun.

TCY7096-222-1B has a mass between 0.29 and 0.54 M_sun and radius of 0.263 R_sun.

Am stars show low rotational velocities matching orbital velocities, indicating spin-down by M-dwarfs.

Abstract

We present observations of two new single-lined eclipsing binaries, both consisting of an Am star and an M-dwarf, discovered by the Wide Angle Search for Planets transit photometry survey. Using WASP photometry and spectroscopic measurements we find that HD186753B has an orbital period of P=1.9194 days, a mass of M=0.24 +/- 0.02 M_sun and radius of R=0.31 +/- 0.06 R_sun; and that TCY7096-222-1B has an orbital period of P=8.9582 days, a mass between 0.29 and 0.54 M_sun depending on eccentricity and radius of R=0.263+0.02-0.07 R_sun. We find that the Am stars have relatively low rotational velocities that closely match the orbital velocities of the M-dwarfs, suggesting that they have been "spun-down" by the M-dwarfs.