The Masses and Radii of HD186753B and TYC7096-222-1B: The First M-dwarfs known to Eclipse A-type Stars (Research Note)

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 ± 0.02M⊙ and radius of R = 0.31 +0.06 −0.06R⊙; and that TCY7096-222-1B has an orbital period of P = 8.9582 days, a mass of between 0.29 and 0.54 M⊙ depending on eccentricity and radius of R = 0.263 +0.02 −0.07 R⊙. 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.