HCO+ emission in the HH7-11 region - the slowest component of the outflow

The region of the high-velocity outflow in HH7-11 has been mapped in the J = 4-3 transition of HCO+. The results are compared with published optical, CO and J = 1-0 HCO+ maps. Unlike the latter interferometric data, we see a bright compact source associated with the exciting star, plus weaker emission throughout the region. Extended emission surrounds the line of HH objects, and has a structure very similar to that of the blueshifted CO outflow. Spectra of the J = 4-3 and 3-2 lines in selected positions within the flow region indicate two physical components: (i) cool gas at a density of a few x 10(6) cm-3 at the velocity of SSV13 and the ambient cloud; and (ii) warm (35 K) gas at a few x 10(5) cm-3 blueshifted by almost-equal-to 1 km s-1. The close agreement between the HCO+ and higher velocity CO suggests that the former arises from the densest, slowest component of the molecular flow. The structure appears to favour a confined jet rather than a shocked cloudlet model.