HUBBLE-SPACE-TELESCOPE IMAGES OF THE HH-111 JET

We have observed the Herbig-Haro jet HH 111 with the Wide Field and Pl anetary Camera 2 aboard the Hubble Space Telescope (HST) through narro w-band filters isolating Her and [S II] lambda lambda 6716,6731 emissi on. The new images fully resolve the body of the jet into a series of small bow shocks, which we conclude form as fast jet material overruns slower, previously ejected jet material. Collisionally excited Ha emi ssion emits in a series of sharp arcs in the jet and along the major b ow shocks along the flow. This emission marks the locations of shock f ronts in the gas. The [S Ii] emission typically follows Ha in a coolin g zone behind the shocks. In some but not all cases, a Mach disk appea rs within the bow shocks. Some Balmer arcs in the jet form complete bo w shocks, while others are one-sided. The jet has a pronounced sinuous structure which we ascribe to variations in the velocity and angle of ejection from the embedded driving source. The faintness of the shock s that propagate outside the jet beam suggests that the surrounding me dium has a much lower density than the jet. Weak shocks along the peri phery of the jet appear to accelerate a tube of slow CO gas along the base of the HH 111 jet. High-velocity CO and H-2 emission observed alo ng the axis of the jet likely originates in jet gas that has cooled an d become molecular. We discuss the similarities and differences betwee n the three extended jets thus far observed by HST(HH 34, HH 47, and H H 111). In all cases, the jets move into the wake of previously ejecte d jet material, and form shocks where they overrun slower jet gas. All three jets show faint Balmer arcs along the periphery of the jet beam s, which may indicate a common mechanism by which their associated CO outflows are accelerated. (C) 1997 American Astronomical Society.