A&A 508, 391-394 (2009)
DOI: 10.1051/0004-6361/200913154

Research Note

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

S. J. Bentley¹, B. Smalley¹, P. F. L. Maxted¹, C. Hellier¹, D. M. Wilson^{1, 2}, D. R. Anderson¹, A. Collier Cameron³, M. Gillon^{4, 5}, L. Hebb^{3, 6}, D. L. Pollacco⁷, D. Queloz⁴, A. H. M. J. Triaud⁴, and R. G. West<sup>8

1</sup>  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 P=1.9194 days, a mass of and radius of ; and that TCY7096-222-1B has an orbital period of P=8.9582 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.

Key words: binaries: eclipsing -- stars: early-type -- stars: late-type -- stars: individual: HD 186753 -- stars: individual: TCY7096-222-1

© ESO 2009

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