The environment of FS Tau observed with HST WFPC2 in narrow-band emission line filters

We present the results of HST WFPC2 observations of FS Tau and its environment obtained in the narrow-band emission line filters H alpha and [S II] (lambda = 6716,6731 Angstrom). Based on these data the morphology of line emission within this region can be studied on a size scale of 0.1" for the first time. Despite the fact that FS Tau A has strong forbidden emission lines, there is no evidence for extended emission at these wavelengths beyond 0.5" from the components of this close T Tauri binary system. In the FS Tau B outflow interesting morphological properties can be studied at high spatial resolution. In this jet we find a structure where circular or elliptical jet knots are correlated with minima of the jet width. The overall width of this jet decreases with distance from the source. The FS Tau B jet is thus a rare example of a jet which may be recollimated far away from its source. The jet is much more prominent in H alpha than in [S II], while the counterjet shows the opposite behaviour. The line ratio H alpha/[S II] increases with lateral distance from the jet axis which is indicative of entrainment of ambient material.