2MASS J05162881+2607387: A new low-mass double-lined eclipsing binary

We show that the star known as 2MASS J05162881+2607387 (hereafter J0516) is a double-lined eclipsing binary with nearly identical low-mass components. The spectroscopic elements derived from 18 spectra obtained with the High Resolution Spectrograph on the Hobby-Eberly Telescope during the fall of 2005 are K-1 = 88.45 +/- 0.48 and K-2 = 90.43 +/- 0.60 km s(-1), resulting in a mass ratio of q = K-1/K-2 0.978 +/- 0.018 and minimum masses of M-1 sin(3)i = 0.775 +/- 0.016 M-circle dot and M-2 sin(3)i = 0.759 +/- 0.012 M-circle dot, respectively. We have extensive differential photometry of J0516 obtained over several nights between 2004 January and March ( epoch 1) and between 2004 October and 2005 January plus 2006 January ( epoch 2) using the 1 m telescope at the Mount Laguna Observatory. The source was roughly 0.1 mag brighter in all three bandpasses during epoch 1 when compared to epoch 2. Also, phased light curves from epoch 1 show considerable out-of-eclipse variability, presumably due to bright spots on one or both stars. In contrast, the phased light curves from epoch 2 show little out-of-eclipse variability. The light curves from epoch 2 and the radial velocity curves were analyzed using our ELC code with updated model atmospheres for low-mass stars. We find the following: M-1 = 0.787 +/- 0.012 M-circle dot, R-1 = 0.788 +/- 0.015 R-circle dot, M-2 = 0.770 +/- 0.009 M-circle dot, and R-2 = 0.817 +/- 0.010 R-circle dot. The stars in J0516 have radii that are significantly larger than model predictions for their masses, similar to what is seen in a handful of other well-studied low-mass double-lined eclipsing binaries. We compiled all recent mass and radius determinations from low-mass binaries and determine an empirical mass-radius relation of the form R(R-circle dot) = 0.0324 + 0.9343M(M-circle dot) + 0.0374M(2)(M-circle dot).