THE BOW SHOCK AND MACH DISK OF HH-111V

We present spatially resolved line profiles in Halpha and [S II] lambd alambda6716, 6731 across the working surface region in the Herbig-Haro object HH 111V. Data were acquired with the Rutgers/CTIO imaging Fabr y-Perot interferometer on the CTIO 4 m telescope at approximately 1.3' ' FWHM spatial and approximately 35 km s-1 FWHM kinetic resolution. We separate Mach disk emission spatially and kinematically from the bow shock emission. We have used the Halpha flux measured at the apex of t he bow shock to estimate the preshock density of approximately 200 cm- 3. Our detailed measurements of the electron density as a function of position and velocity across the bow shock, combined with new models o f the bow shock emission, show that an ambient magnetic field of appro ximately 30 muG inhibits the compression of the postshock gas. Our mod els indicate that the magnetic field also contributes to extending the cooling distance behind the shock to resolvable scales, as observed i n the spatial separation of [S II] and Halpha in the emission-line ima ges of Reipurth et al. However, the ram pressure at the bow shock HH 1 11V exceeds the magnetic energy density by a factor of approximately 1 0(3), so the magnetic field is not large enough to change the directio n of the flow. The preshock medium must flow away from the stellar ene rgy source at approximately 300 km s-1 to account for the observed kin ematics of the line emission in HH 111V. Hence, this working surface i s a secondary ejection moving into the wake of an earlier ejection. HH 111 is the third case (HH 34 and HH 47 are other examples) of a stell ar jet where the brightest bow shock moves into the wake of a previous high-velocity ejection. Balancing the ram pressures in the bow shock and Mach disk yields an estimated jet-to-ambient density ratio approxi mately 10, similar to our previous estimate for the HH 34 jet (Morse e t al.).