HST Observations of the HH 47 and HH 111 Stellar Jets

AbstractThe superb spatial resolution made possible by the WFPC2 imager on the Hubble Space Telescope has opened a new era in the study of shocks in stellar jets. This paper summarizes the results of imaging surveys of two of the brightest and best resolved stellar jets, HH 111 and HH 47. The new HST images show that the jets appear quite different in the Ha and [S II] lines; Ha concentrates in distinctive filaments while [S II] tends to be clumpier and more widespread. Filamentary Hα emission should trace the location of the shock fronts if the preshock gas is neutral, because a significant fraction of the incident H gas becomes excited collisionally before becoming ionized in moderate velocity shocks.Both HH 111 and HH 47 exhibit multiple bow shocks along the channel of the jet, and in some cases we observe the classical double shock structure of a bow shock/Mach disk expected within the working surface of a jet. The jet material is considerably denser than that of the ambient gas. Ejection angles vary a few degrees with time, giving some jets a ‘wiggling’ appearance. However, motion along the jet appears to be radial; there is no convincing evidence for azimuthal motion in the radial velocity data. Multiple bow shocks observed along the jets probably arise from unsteady accretion of a protostellar disk onto the central object.