1998AJ....115.1554E

We report on an imaging and kinematic study of the jets and outflows emanating from DG Tau, DG Tau B, FS Tau B, T Tau, and CoKu Tau 1. The kinematic data are based on proper-motion measurements and long-slit spectroscopy, and the imaging data on deep narrowband [S II] λλ6716, 6731, Hα, and continuum images. The individual objects and their peculiarities are discussed in detail. The six investigated jets and flows differ from each other in their morphology, spatial extent, and their degree of variations in velocity and in the ratio ζ between the knot pattern speed and the flow speed. Possible reasons for these large differences are briefly discussed. In DG Tau, FS Tau B, and T Tau strong velocity variations are indicated, while for DG Tau B very small velocity variations, if any, are observed (≤7% in some flow sections). The small velocity variations in DG Tau B, together with large variations in the ζ-values in this and other young stellar object (YSO) jets, pose severe difficulties for any model that explains the observed knots by internal shocks resulting from velocity variations. Our results from DG Tau B and other YSO jets strongly indicate that for a significant fraction of knots in YSO jets other mechanisms probably excite the internal shocks.

The bipolar outflow from FS Tau B apparently shows indications of a highly collimated and a poorly collimated flow in both outflow lobes. To our knowledge, L1551 IRS 5 is the only other case where such an unusual situation is also indicated. About 60" northeast of FS Tau B we have found an independent faint 150"-long jetlike outflow oriented approximately perpendicular to the FS Tau B jet, which we have designated FS Tau C (HH 276).