THE BOW SHOCK AND MACH DISK OF HH 34

We have used the Rutgers/CTIO imaging Fabry-Perot interferometer to acquire spatially resolved line profiles across the bow shock and Mach disk of the Herbig-Haro object HH 34 in [O III] lambda5007, Halpha, and [S II] lambdalambda6716, 6731. Profiles were obtained with approximately 1"5 spatial and 35 km s-1 FWHM velocity resolution. We have separated the Mach disk emission in this outflow from the bow shock emission both spatially and kinematically. Our observations provide the first detailed kinematic information about the shocked material behind the Mach disk of a stellar jet. The preshock gas to the south of HH 34 must flow outward at approximately 150 km s-1 with respect to the stellar energy source to account for the observed kinematics of the line emission in HH 34. Hence, HH 34 is probably a secondary ejection that moves into the outflowing wake of an earlier ejection, a scenario also proposed by Heathcote & Reipurth to explain proper motions in HH 34. Our new measurements of the electron density as a function of position and velocity, combined with new models of the bow shock emission, show that the magnetic field inhibits the compression of the post-bow shock gas. We estimate the ambient magnetic field to be 10-20 muG in front of HH 34. The magnetic energy density in the preshock gas is less than 10(-3) of the ram pressure, which implies that the magnetic field is not important in the flow dynamics of HH 34. By balancing the ram pressures in the bow shock and Mach disk, we estimate the jet-to-ambient density ratio eta approxiamtely 10. This is approximately 10 times higher than previous estimates for eta in this outflow.