SUB-ARCSECOND MORPHOLOGY AND KINEMATICS OF THE DG TAURI JET IN THE [O-I]LAMBDA-6300 LINE

We present the first 3D spectre-imaging observations of the [O I]lambd a 6300 line in an active T Tauri star: DG Tau. The morphological struc ture of the mass outflow is revealed with unprecedented spatial resolu tion (0.35 ''). It consists of an unresolved inner peak containing two thirds of the total line flux, followed by a collimated jet-like body extending out to similar to 1.5 '' from the star, and two resolved kn ots at distances of 2.7 '' and 4 ''. One of the outer knots possesses a curved morphology and transverse velocity gradient strongly suggesti ve of a resolved bow-shock. Time variability in the ejection velocity (with timescale Delta t similar or equal to 8.5 yr) could explain the presence of such a bowshock, the spacing of knots at distances greater than or equal to 1 '' from the star, and the strong velocity gradient s along the jet observed closer to the star. The unresolved inner peak , centered at similar to 20 AU of the star, is apparently stationary a nd possibly linked to the initial jet collimation. Our size limit and absolute photometry for this peak set new constraints on the jet mass loss rate (between 1.3 x 10(-8) and 6.5 x 10(-6) M. yr(-1)), lowering previous estimates by a factor 5 to 25. Finally, our high sensitivity combined with velocity information allows us to detect unambiguously t he counterjet of the system (v similar or equal to +230 km/s), and to establish the existence of a diffuse halo of low-velocity [O I] emissi on, which might trace a wider flow or an extended scattering nebula.