Mon-735: a new low-mass pre-main-sequence eclipsing binary in NGC 2264

We present Mon-735, a detached double-lined eclipsing binary (EB) member of the similar to 3Myr old NGC 2264 star-forming region, detected by Spitzer. We simultaneously model the Spitzer light curves, follow-up Keck/HIRES radial velocities, and the system's spectral energy distribution to determine self-consistent masses, radii, and effective temperatures for both stars. We find that Mon-735 comprises two pre-main-sequence M dwarfs with component masses of M = 0.2918 +/- 0.0099 and 0.2661 +/- 0.0095 M-circle dot, radii of R = 0.762 +/- 0.022 and 0.748 +/- 0.023 R-circle dot, and effective temperatures of T-eff = 3260 +/- 73 and 3213 +/- 73 K. The two stars travel on circular orbits around their common centre of mass in P = 1.9751388 +/- 0.0000050 d. We compare our results for Mon-735, along with another EB in NGC 2264 (CoRoT 223992193), to the predictions of five stellar evolution models. These suggest that the lower mass EB system Mon-735 is older than CoRoT 223992193 in the mass-radius diagram (MRD) and, to a lesser extent, in the Hertzsprung-Russell diagram (HRD). The MRD ages of Mon-735 and CoRoT 223992193 are similar to 7-9 and 4-6 Myr, respectively, with the two components in each EB system possessing consistent ages.