The Highly Eccentric Pre-Main Sequence Spectroscopic Binary RX J0529.3+1210

The young system RX J0529.3+1210 was initially identified as a single-lined spectroscopic binary. Using high-resolution infrared spectra, acquired with NIRSPEC on Keck II, we measured radial velocities for the secondary. The method of using the infrared regime to convert single-lined spectra into double-lined spectra, and derive the mass ratio for the binary system, has been successfully used for a number of young, low-mass binaries. For RX J0529.3+1210, a long-period (462 days) and highly eccentric (0.88) binary system, we determine the mass ratio to be 0.78 +/- 0.05 using the infrared double-lined velocity data alone, and 0.73 +/- 0.23 combining visible light and infrared data in a full orbital solution. The large uncertainty in the latter is the result of the sparse sampling in the infrared and the high eccentricity: the stars do not have a large velocity separation during most of their similar to 1.3 yr orbit. A mass ratio close to unity, consistent with the high end of the 1 sigma uncertainty for this mass ratio value, is inconsistent with the lack of a visible light detection of the secondary component. We outline several scenarios for a color difference in the two stars, such as one heavily spotted component, higher-order multiplicity, or a unique evolutionary stage, favoring detection of only the primary star in visible light, even in a mass ratio similar to 1 system. However, the evidence points to a lower ratio. Although RX J0529.3+1210 exhibits no excess at near-infrared wavelengths, a small 24 mu m excess is detected, consistent with circumbinary dust. The properties of this binary and its membership in lambda Ori versus a new nearby stellar moving group at similar to 90 pc are discussed. We speculate on the origin of this unusual system and on the impact of such high eccentricity, the largest observed in a pre-main-sequence double-lined system to date, on the potential for planet formation.