HST/STIS Spectroscopy of the Optical Outflow from DG Tau: Indications for Rotation in the Initial Jet Channel

We have carried out a kinematical, high angular resolution (~ 0".1) study of the jet from DG Tau within 0."5 from the source (or 110 AU along this flow). We analysed line profiles extracted from a set of seven spectra taken with STIS on board the Hubble Space Telescope, with the slits parallel to the jet axis but displaced transversely every 0".07. For the flow of moderate velocity (-70 km/s), we have found systematic differences in the radial velocities of lines emitted on alternate sides of the jet axis. The results are corrected for the effects due to uneven illumination of the slit. The relative Doppler shifts range from 5 to 20 km/s. If this is interpreted as rotation, the flow is then rotating clockwise looking from the jet towards the source and the derived toroidal velocities are in the range 6 - 15 km/s. Using recent estimates of the mass loss rate, one obtains for the considered velocity regime, an angular momentum flux of ~ 3.8x10E-5 M_sun/yr AU km/s. Our findings may constitute the first detection of rotation in the initial channel of a jet flow. The derived values appear to be consistent with the predictions of popular magneto-centrifugal jet-launching models, although we cannot exclude transverse outflow asymmetries other than rotation.Comment: aastex, 23 pages, 5 b/w figures, 3 color figures, ApJ in pres

Observations of jet diameter, density and dynamics

Collimated jets are believed to be an essential ingredient of the star formation process, and we are now able for the first time to test observationally the theories for their formation and propagation. The major advances achieved in recent years are reviewed, regarding the observed morphology, kinematics and excitation properties of jets, from the parsec-scale `giant outflows' down to the `microjets' from T Tauri stars. High angular resolution images and spectra have provided valuable estimates of jet diameter, space velocity, temperature, ionization fraction, electron and total density, both along and across the flow. We can thus calculate key physical quantites, as the shock excitation parameters, or the mass and momentum fluxes in the flow. The results obtained appear to validate the popular magneto-centrifugal models for jet launching, although some important issues are still under debate, as to the cause of knotty structures, observed wind thermal properties, and the dynamical relationship between jets and molecular outflows. Among the most interesting recent findings, we mention the observed indications for jet rotation, with inferred toroidal velocities consistent with the prescribed angular momentum balance between infall and outflow