The peculiar periodic YSO WL 4 in ρ Ophiuchus

We present the discovery of 130.87 day periodic near-infrared flux variability for the Class II T Tauri star WL 4 (=2MASS J16271848-2429059, ISO-Oph 128). Our data are from the 2MASS Calibration Point Source Working Database and constitute 1580 observations in J, H, and K(s) of a field in rho Ophiuchus used to calibrate the 2MASS All- Sky Survey. We identify a light curve for WL 4 with eclipse amplitudes of similar to 0.4 mag lasting more than one-quarter the period and color variations in J-H and H-K(s) of similar to 0.1 mag. The long period cannot K s be explained by stellar rotation. We propose that WL 4 is a triple YSO system, with an inner binary orbital period of 130.87 days. We posulate that we are observing each component of the inner binary alternately being eclipsed by a circumbinary disk with respect to our line of sight. This system will be useful in investigating terrestrial-zone YSO disk properties and dynamics at similar to 1 Myr.