Program: GS-2005A-C-7

The discovery and analysis of pre-main-sequence (PMS) eclipsing binary star systems is of critical importance to the study of star formation and young stellar populations. With only five PMS eclipsing binaries currently known, the evolutionary tracks which are used to infer fundamental stellar properties such as masses and ages---and from which stellar initial mass functions are derived---remain largely uncalibrated by empirical mass determinations, particularly below $1\, {\rm M}_\odot$. We have an extensive observing program underway to substantially increase the sample of low-mass PMS eclipsing binaries. In 2000B--2002A we completed our study of the first of these systems, V1174 Ori, which includes the first sub-solar-mass ($0.7\, {\rm M}_{\odot}$) PMS star yet discovered in an eclipsing binary. In 2002B/2003A we began a comprehensive spectroscopic and photometric study of a new, very low-mass, eclipsing binary in the Orion star-forming region. A preliminary orbit solution based on our {\it Gemini/Phoenix} data gives component masses of $0.06\, {\rm M}_\odot$ and $0.04\, {\rm M}_\odot$, making these the first empirical mass determinations for substellar PMS stars. We propose here to complete our study of this new PMS eclipsing binary system. Specifically, we request additional spectroscopic observations with {\it Gemini/Phoenix} with which to derive a precise double-lined orbit. These observations will be complemented by photometric monitoring with the CTIO 0.9m and 1.3m telescopes to provide multi-band light curves for detailed modeling and analysis.