The Bow Shock and Mach Disk of HH 34
Morse, J. (UNC), Hartigan, P. (UMass), Cecil, G. (UNC), Raymond, J. (CfA), and Heathcote, S. (CTIO)
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 HH34 in
[O III] 5007, H-alpha, and [S II] 6716, 6731. Profiles were obtained with 1.5" spatial and
35 km/s FWHM velocity resolution. We have separated the Mach disk emission in this ourflow 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 about 150 km/s
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 microGauss in front of HH 34. The magnetic energy density 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 dentsity ratio to be about 10. This is 10 times
higher than previous estimates for this outflow.
Published in Ap.J. 399, 231, 1992