ABSTRACT. We present spatially resolved near- and mid-infrared (1–25 μm) imaging of the WL 20 triple system in the nearby (d = 125 pc) ρ Ophiuchi star-forming cloud core. We find WL 20 to be a new addition to the rare class of "infrared companion systems," with WL 20 E and WL 20 W displaying Class II (T Tauri star) spectral energy distributions (SEDs) and total luminosities of 0.61 and 0.39 L, respectively, and WL 20 S, the infrared companion, having a Class I (embedded protostellar) SED and a luminosity of 1.0–1.8 L. WL 20 S is found to be highly variable over timescales of years, to be extended (40 AU diameter) at mid-IR wavelengths, and to be the source of the centimeter emission in the system. The photospheric luminosities of 0.53 L for WL 20 E and 0.35 L for WL 20 W estimated from our data, combined with existing, spatially resolved near-IR spectroscopy, allow us to compare and test current pre–main-sequence evolutionary tracks. The most plausible, nonaccreting tracks describing this system are those of D'Antona & Mazzitelli published in 1998. These tracks give an age of (2–2.5) × 10⁶ yr and masses of 0.62–0.68 M for WL 20 E and 0.51–0.55 M for WL 20 W. The age and mass of WL 20 S cannot be well determined from the currently available data. WL 20 E and W fall into the region of the H-R diagram in which sources may appear up to twice as old as they actually are using nonaccreting tracks, a fact that may reconcile the coexistence of two T Tauri stars with an embedded protostar in a triple system. The derived masses and observed projected separations of the components of the WL 20 triple system indicate that it is in an unstable dynamical configuration, and it may therefore provide an example of dynamical evolution during the pre–main-sequence phase.

Key words: binaries: close; stars: formation; stars: individual (WL 20); stars: pre-main sequence

Print publication: Issue 2 (2001 February)
Received 2000 August 11, accepted for publication 2000 November 7