A Giant Herbig-Haro Flow from a Massive Young Star in G192.16−3.82

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Abstract
We report the discovery of a 10 pc–long Herbig-Haro (HH) flow powered by a moderately massive young star associated with the compact H II region G192.16-3.82. At a distance of 2 kpc, the luminosity of G192.16-3.82 is about 3000 L⊙. The HH 396/397 complex consists of a network of filamentary emission-line objects tracing a pair of collimated and limb-brightened outflow lobes that emerge from an opaque cloud core. The Hα- and [S II]-bright nebulosity has a large area covering factor, extending well beyond the mapped extent of the associated high-velocity molecular outflow. The HH 396/397 complex contains some shocks with a surface brightness comparable to HH 168 in Cepheus A, placing these among the brightest known HH objects. Furthermore, a large fraction of a 1' by 18' region surrounding G192.16-3.82 is laced with lower surface brightness emission-line features, making HH 396/397 one of the most spatially extended HH complexes studied so far. The dynamical age of this outflow is in the range 104 to 105 yr. We discuss plausible evolutionary scenarios for outflows powered by high-mass protostars and argue that the G192.16-3.82 outflow complex is relatively evolved. Despite being very elongated, this HH flow is most likely powered by a moderately collimated wind, rather than a highly collimated jet.

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