Resolved near-infrared spectroscopy of the mysterious pre-main-sequence binary system T Tauri S

We obtained new near-infrared images of the prototypical pre-main-sequence triple system T Tau, as well as the first resolved medium-resolution spectra of the close pair T Tau S. At the time of our observations, the tight binary had a 13 AU projected separation and showed significant motion since its discovery 3 yr before. The orbit cannot be strongly constrained yet, but the observed motion of T Tau Sb with respect to T Tau Sa suggests that the system is at least as massive as T Tau N itself. This may indicate that T Tau N is not the most massive star in the system. The spectrum of T Tau Sa, which is totally featureless except for a strong Brgamma emission line, identifies this component with the infrared companion, whose exact nature remains obscure but may be the consequence of its being the most massive component of the system. Contrasting sharply with T Tau Sa, the spectrum of T Tau Sb shows numerous photospheric features consistent with an early-M spectral type. The presence of a strong Brgamma emission line and of a significant veiling continuum classifies this object as a deeply embedded T Tauri star. From these observations, we conclude that both components of T Tau S are embedded in their own dense circumstellar cocoons of material, which are probably fed by a much more extended structure.