  We present survey results which suggest rotation signatures at the base of
T-Tauri jets. Observations were conducted with the Hubble Space Telescope
Imaging Spectrograph at optical and near ultraviolet wavelengths (NUV). Results
are presented for the approaching jet from DG Tau, CW Tau, HH 30 and the
bipolar jet from TH 28. Systematic asymmetries in Doppler shift were detected
across the jet, within 100 AU from the star. At optical wavelengths, radial
velocity differences were typically 10 to 25 (+/-5) km/s, while differences in
the NUV range were consistently lower at typically 10 (+/-5) km/s. Results are
interpreted as possible rotation signatures. Importantly, there is agreement
between the optical and NUV results for DG Tau. Under the assumption of steady
magnetocentrifugal acceleration, the survey results lead to estimates for the
distance of the jet footpoint from the star, and give values consistent with
earlier studies. In the case of DG Tau, for example, we see that the higher
velocity component appears to be launched from a distance of 0.2 to 0.5 AU from
the star along the disk plane, while the lower velocity component appears to
trace a wider part of the jet launched from as far as 1.9 AU. The results for
the other targets are similar. Therefore, if indeed the detected Doppler
gradients trace rotation within the jet then, under the assumption of steady
MHD ejection, the derived footpoint radii support the existence of magnetized
disk winds. However, since we do not resolved the innermost layers of the flow,
we cannot exclude the possibility that there also exists an X-wind or stellar
wind component.
