Astron. Astrophys. 322, L25-L28 (1997)

1. Introduction

The well known Herbig-Haro objects, HH 1 and HH 2, the first objects of their class to be discovered (Herbig 1951; Haro 1952), are situated in L1641, a dark molecular cloud located in the southern part of the Ori A complex. L1641 is at a distance of 470 pc and it is known as a region of low- and intermediate-mass star formation.

HH 1 and HH 2, separated by , are moving in opposite directions (Herbig & Jones 1981) constituting a bipolar optical outflow, emanating from the powering source VLA 1, which lies midway between them (Pravdo et al. 1985).

Chernin and Masson (1995) mapped the region around VLA 1 in CO J 2-1 with resolution and found an outflow with a red-shifted lobe which peaks at (, ) from VLA 1. The redshifted outflow lobe has a major axis with a position angle similar to the angle of for the HH 1-2 axis. They claim that this outflow is powered not by VLA 1 but by VLA 3, a radio continuum source to the north center of HH 1-2 flow, close to a H₂ O maser. They did not detect any outflow associated with VLA 1 but suggested that higher resolution observations with a beam less than would be necessary in order to separate out a possible weak HH 1-2 outflow from the strong VLA 3 outflow. They have estimated that they have only detected one-fourth of the material in the outflow that is moving at velocities significantly greater than the line width of the ambient cloud. With this correction, they derived a total mass of 0.3 for the VLA 3 outflow. Any molecular outflow associated with VLA 1 would have to be extremely weak, and they estimated an upper limit of 0.03 for its mass.

Ogura (1995) has reported the discovery of a pair of giant (linear size 1 pc) bow shock structures located symmetricaly about HH 1-2. This was interpreted as an evidence for recurrent outflow activity of the exciting source. Further evidence is provided by the discovery that HH 1-2 is moving into a medium which is itself flowing at a speed of 200 km s^-1 (Noriega-Crespo et al. 1989), suggesting a previous outflow in this region.

Recently, Choi et al. (1997) have reported observations of several molecular transitions around the HH 1-2 region. Their CO J 3-2 observations have indicated the presence of a weak molecular outflow in the VLA 1 area. The existence of the strong redshifted outflow from VLA 3 and the low resolution of their map around VLA 1 did not allow them clearly to identify VLA 1 as the powering source of the weaker outflow. The need for a larger map of CO J 3-2 around VL A 1 was pointed out by the authors.

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

helpdesk.link@springer.de