Research Note

The masses and radii of HD 186753B and TYC7096-222-1B: the discovery of two M-dwarfs that eclipse A-type stars

¹ Astrophysics Group, Keele University, Keele, Staffordshire ST5 5BG, UK e-mail: sjb@astro.keele.ac.uk
² Centre for Astrophysics & Planetary Science, School of Physical Sciences, University of Kent, Canterbury, Kent CT2 7NH, UK
³ School of Physics and Astronomy, University of St. Andrews, North Haugh, Fife KY16 9SS, UK
⁴ Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland
⁵ Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Bat. B5C, Liège 1, Belgium
⁶ Vanderbilt University, Department of Physics and Astronomy, Nashville, TN 37235, USA
⁷ Astrophysics Research Centre, School of Mathematics & Physics, Queens University, University Road, Belfast BT7 1NN, UK
⁸ Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK

Received: 20 August 2009
Accepted: 1 October 2009

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 HD 186753B has an orbital period of days, a mass of and radius of ; and that TCY7096-222-1B has an orbital period of days, a mass of between 0.29 and 0.54  depending on eccentricity and radius of . 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.