High Spectral Resolution H2 Measurements of Herbig-Haro Objects 38, 46/47, and HH 120

Abstract

We report high spectral resolution (R=20,000) measurements of the H2 1-0 S(1) line in Herbig-Haro Objects 38, 46/47, and 120. The long-slit spectra reveal complex velocity structure with evidence for bow-shock structures as well as prompt entrainment and shock heating of ambient molecular gas. Individual knots within HH 38 show distinct double peaked velocity stucture, consistent with that expected from spatially unresolved bow shocks. A portion of the HH 47A bow shock is resolved in our measurements, and the kinematics of the H2 trace closely that found for H-alpha emission. The evidence indicates that the preshock medium for HH 47A that formed in the wake of a previous ejection contains molecular clumps. The HH 46CjetA feature in the HH 46/47 counterflow is suggestive of a bow shock emerging from near the base of the flow, with H2 emission arising from ambient cloud material excited in the oblique flanks of the bow shock. HH 46F is situated downstream at the boundary between an ovoid cavity and the ambient could material, and represents either entrainment by a stellar wind that fills the cavity or entrainment in the far wing of a giant bow shock. For HH 120, the H2 velocity results also corroborate those found from atomic emission, and there is substantial evidence that the preshock medium is inhomogeneous, producing clumps of H2 emission on the wings of a bow shock that has an apex at HH 120A.