Time Variability and the Origin of Knots

Multi-epoch high-angular resolution imaging observations allow to probe the variability of the ejection process. Large proper motions, on the order of the jet flow velocity, have been inferred from the combination of space and ground-based AO observations for the small-scale knots in the DG Tau, RW Aur, and CW Tau jets [13, 21, 30, 38]. These properties, combined with the line ratios indicative of shock conditions and the morphology suggestive of bow-shock type structures as in the DG Tau case, suggest that knots are likely internal working surfaces produced by time variable ejection velocity and/or direction, as in the younger HH jets. Inferred variability timescales are ~1—10 yrs. This variability timescale is also observed at the base of the younger,

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