Magnetocentrifugal Launching of Jets from Accretion Disks. II. Inner Disk‐driven Winds

We follow numerically the time evolution of axisymmetric outflows drivenmagneto-centrifugally from the inner portion of accretion disks, from theirlaunching surface to large, observable distances. Special attention is paid tothe collimation of part of the outflow into a dense, narrow jet around therotation axis, after a steady state has been reached. For parameters typical ofT Tauri stars, we define a fiducial ``jet'' as outlined by the contour ofconstant density at 10^4 cm^{-3}. We find that the jet, so defined, appearsnearly cylindrical well above the disk, in agreement with previous asymptoticanalyses. Closer to the equatorial plane, the density contour can either bulgeoutwards or pinch inwards, depending on the conditions at the launchingsurface, particularly the mass flux distribution. We find that even though adense, jet-like feature is always formed around the axis, there is no guaranteethat the high-density axial jet would dominate the more tenuous, wide-anglepart of the wind. Specifically, on the 100 AU scale, resolvable by HST andground-based adaptive optics for nearby T Tauri winds, the fraction of the windmass flux enclosed by the fiducial jet can vary substantially, again dependingon the launching conditions. We show two examples in which the fraction is ~20%and ~45%. These dependences may provide a way to constrain the conditions atthe launching surface, which are poorly known at present.Comment: 11 pages, 6 figures. Accepted for publication in ApJ, scheduled for vol. 595, October 1, 200