Further Indications of Jet Rotation in New Ultraviolet and Optical<i>Hubble Space Telescope</i>STIS Spectra

Abstract

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