THE HIGHLY ECCENTRIC PRE-MAIN-SEQUENCE SPECTROSCOPIC BINARY RX J0529.3+1210

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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 ∼1.3 yr orbit. A mass ratio close to unity, consistent with the high end of the 1σ 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 ∼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 μm excess is detected, consistent with circumbinary dust. The properties of this binary and its membership in λ Ori versus a new nearby stellar moving group at ∼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.