The Peculiar Periodic YSO WL 4 in Rho Ophiuchus

TL;DR

This paper reports the discovery of a 130.87-day periodic near-infrared flux variability in the YSO WL 4, likely caused by eclipses in a triple system with a circum-binary disk, offering insights into young stellar object disk dynamics.

Contribution

It introduces the first observed long-period eclipsing variability in a YSO, suggesting a triple system with a circum-binary disk as the cause.

Findings

Periodic flux variability of 130.87 days in WL 4

Eclipse amplitudes of ~0.4 mag observed

Color variations of ~0.1 mag in J-H and H-Ks

Abstract

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 Ks 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 ~0.4 mag lasting more than one-quarter the period, and color variations in J-H and H-Ks of ~0.1 mag. The long period cannot 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 circum-binary disk with respect to our line of sight. This system will be useful in investigating terrestrial zone YSO disk properties and dynamics at ~1 Myr.