A high spatial resolution infrared view of the T Tauri multiple system

We present the results of our monitoring study of the IR photometric and spectroscopic variability of the T Tau multiple system. We also present data on the apparent position of T Tau South ( T Tau S) with respect to T Tau North (T Tau N), and two new spatially resolved observations of the T Tau Sa-Sb binary. T Tau N has not varied by more than 0.2 mag in K and L' flux during the 8 years of our observations, although its Brgamma and Bralpha emission-line fluxes have varied by nearly a factor of 4 during this time. For the unresolved T Tau S system, we have derived a 20 yr light curve based on our images and on measurements available in the literature. T Tau S varies by 2-3 mag in K- and L'-band brightness in a "redder when faint'' manner, consistent with changes along the line of sight in the amount of material that follows an interstellar medium extinction law. Absorption in the 3.05 mum water ice feature is seen only in the spectra of T Tau S, and it displays variations in depth and profile. H-2 (2.12 mum) emission is also detected only at the position of T Tau S; the H-2, Brgamma, and Bralpha emission-line fluxes also vary. We have found that the apparent positions of T Tau S with respect to T Tau N and T Tau Sb with respect to Sa are consistent with gravitationally bound orbital motion. The possible orbits of the T Tau S binary imply that Sa is likely the most massive component in this young triple. A reanalysis of the motion of the radio source associated with T Tau S provides no evidence for an ejection event in the T Tau system.