Echelle spectroscopy of H2 in the HH 111 jet

Abstract

Near-Infrared echelle spectra of the Herbig-Haro knots F-P in the western lobe of the HH 111 outflow are presented. 10 adjacent, parallel slit positions were observed so that the kinematics could be mapped across the width of the flow. We find broad (FWZI ∼ 100 kms-1), two-component H2 profiles in the knots nearest the source; the profiles converge to a single, intermediate-velocity peak (VLSR ∼ 50 kms-1) at knot P. The kinematic signature of the HH 111 jet in H2 is very similar to that seen at optical wavelengths (from both radial and tangential velocity measurements). In conjunction with published proper-motion (knot/shock pattern speed) measurements, we interpret the data in terms of a simple geometrical bow shock model. The model infers a high pre-shock velocity, of the order of 200-250 kms-1, with H2 excitation in the extended bow wings in knots L, H and F, though exclusively near the bow bead in knot P, with probably C-type shock excitation throughout.