We report the discovery of the partially eclipsing binary LP 133-373. Nearly identical eclipses along with observed photometric colors and spectroscopy indicate that it is a pair of chromospherically active dM4 stars in a circular 1.6 d orbit. Light and velocity curve modeling to our differential photometry and velocity data show that each star has a mass and radius of 0.340+/-0.014 M_sun and 0.33+/-0.02 R_sun. The binary is itself part of a common proper motion pair with LP 133-374 a cool DC or possible DA white dwarf with a mass of 0.49-0.82 M_sun, which would make the system at least 3 Gyr old.
@article{arxiv.astro-ph/0703061,
title = {LP133-373: A New Chromospherically Active Eclipsing dMe Binary with a Distant, Cool White Dwarf Companion},
author = {T. R. Vaccaro and M. Rudkin and A. Kawka and S. Vennes and T. D. Oswalt and I. Silver and M. Wood and J. A. Smith},
journal= {arXiv preprint arXiv:astro-ph/0703061},
year = {2011}
}