It is becoming increasingly evident that Herbig-Haro (HH) flows play a crucial role in the formation process of low mass stars by regulating the delicate balance between mass accretion and angular momentum release, by driving the ubiquitous molecular outflows, and by imparting energy and momentum to their surroundings.
The HH 111 jet in Orion has been extensively studied since its discovery a decade ago (Reipurth 1989). It is very highly collimated, consists of a large number of individual knots, and moves with a velocity of several hundred km s-1 at an angle of only 10o to the plane of the sky (Reipurth, Raga, Heathcote 1992). Recently it was found that the jet is part of a giant HH complex stretching over 7.7 pc (Reipurth, Bally, Devine 1997a). Near-infrared observations have revealed a remarkable symmetry between the optical jet and a near-infrared counterjet, and also show that a second bipolar flow, HH 121, emerges from the source, suggesting that it is a binary (Gredel & Reipurth 1993,1994). The jet is co-axial with a major well collimated molecular outflow (e.g. Cernicharo & Reipurth 1996, Nagar et al. 1997). The jet is driven by IRAS 05491+0247 = VLA 1, a class I source with a luminosity of about 25 and surrounded by cold dust (e.g. Stapelfeldt & Scoville 1993, Yang et al. 1997).
© European Southern Observatory (ESO) 1999
Online publication: December 2, 1999