Physics
Scientific paper
Feb 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt........51e&link_type=abstract
PhD thesis, Universität Heidelberg, (1992)
Physics
11
Scientific paper
The first extended proper motion measurements in jets from young stars are presented. In five well-known jet systems (HH 34, HH 46/47, DG Tau, DG Tau B, Haro 6-5B), consisting of a total of eight optically observable jets and counterjets, as well as of six bow shocks, proper motions of the knots (condensations) have been measured. These measurements are based on deep CCD images, taken through narrow-band filters, which are centred on the Hα or the [SII]λλ6716,6731 lines. They have been taken on at least three different epochs with a total epoch difference of at least four years. For several observing runs the seeing conditions were excellent (≅ 0.''6 -- 0.''9). The proper motion measurements presented allow further principal insights into the physics of the jets and their bow shocks. Among the main results are the following: In all eight investigated jets and counterjets the knots are clearly moving. Their tangential velocities reach values from close to the detection limit (≅ 20 km s-1) up to 400 km s-1, with most of the measured values in the range from 100 to 350 km s-1. Please note that the knots are generally interpreted as the cooling regions of oblique, crossing shock waves within the jets. For the first time the ratio ζ of the pattern speed of the knots to the fluid speed in the jets is investigated. The measured ζ-values range from 0.2 to 1.0, with most values between 0.4 and 1.0. Values larger than 1.0 are not observed. The proper motion measurements put important constraints on the various hitherto proposed jet models: obviously they are in contrary with models of stationary jets, which interpret the jet knots as standing shock waves. Also non-stationary models, in which the knots arise from the interaction of jet material of different velocity, are in most cases not supported by the measured ζ-values. The measurements are, however, in agreement with jet models, which interpret the knots as running shock waves, excited by Kelvin-Helmholtz instabilities along the jet channel. In the four Herbig-Haro objects HH 34N, HH 34S, HH 47C and HH 47D, which have been interpreted as bow shocks of jets, the internal flow patterns of the condensations have been investigated. They yield important data for detailed investigations of the complex flow motions in the jet head. The measured flow patterns support the idea, that these Herbig-Haro objects are indeed the bow shocks of the jets.
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