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

TL;DR

This study uses HST WFPC2 narrow-band imaging to analyze the morphology of emission lines around FS Tau, revealing detailed jet structures and potential recollimation far from the source.

Contribution

First high-resolution imaging of FS Tau's emission line morphology, showing jet recollimation and detailed knot structures in the outflow.

Findings

No extended emission beyond 0.5" around FS Tau A.

Jet width decreases with distance, indicating recollimation.

H alpha emission is stronger in the jet, while [S II] dominates the counterjet.

Abstract

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.