SIMBAD references

High spatial resolution imaging observations of the L 1551 IRS 5 jet have been performed. The system has continued to evolve since it was observed by Neckel & Staude (1987). The tangential velocities of individual features within the jet suggest the presence of three different velocity systems. These velocities have all been constant over the past ten years of observation, although there is some indication that one of the components has recently been re-accelerated. The geometry suggested by the observational evidence is that of a conical volume, which is inclined towards the observer by some 30deg. The jet knots appear to run along narrower channels near the surface of the cone. The flow times of the individual knots exhibit a regular pattern, which indicates precession of the jet and/or ejection of the knots with periods of about 20 years. The force required to accelerate the observable knot material to the inferred space velocities is of the order of 10^–6 M_☉ km/s/yr, which is very much smaller than the average momentum transfer rate to the molecular material in the immediate surroundings of the jet.