A kinematical study of the jet GGD 34

Abstract

CCD images and spectra of high spectral resolution of GGD 34 are analyzed. The object is a jet consisting of three major condensations separated 0.08 pc one of each other and aligned over 0.17pc in the east-west direction. The three condensations emit strongly in [SII], [NII] and Halpha. The westernmost condensation has also significant continuum emission coming from what seems to be the bow-shaped borders of a cavity. A detailed study of the excitation conditions, densities and velocity field is presented. The excitation of the object is very low and the line ratios can be reproduced by mild radiative shocks at velocities less-than-or-equal-to 40 km s-1. The radial velocity of the gas is high, congruent-to 180 km s-1, indicating that the excitation is much lower than expected if the flow kinetic energy is fully spent into gas heating. This is generally observed in young stellar objects (YSO) jets. The exciting source of the outflow seems to be located at the western end of GGD 34, illuminating the cavity. The two easternmost condensations GGD 34/B and GGD 34/C are connected by a neatly shaped lobe emitting in [SII] and Halpha. The width of the lobe varies from 0.012pc in the condensations to 0.034 in the space in between. The lobe is not symmetric with respect to the jet axis but has a rather sinusoidal morphology. The velocity field in this region also can be well fitted by a sine curve. Morphology and velocity field are correlated; however they are not accompanied by significant changes in the excitation degree. We suggest that the properties of GGD 34 are produced by a ''kink'' plasma instability.