L1551 NE or L1551 IRS 5: Which Source Drives HH 28/29?

Abstract

We have obtained deep high-resolution interference filter images of the HH objects in the L1551 molecular cloud in 1990 and 1997, and we suggest that the well-known and well-studied objects HH 28 and 29 are driven by the deeply embedded class 0 source L1551 NE, not by the well-known IRS 5 source. We find a new, small bipolar HH flow, HH 454, surrounding L1551 NE. This new HH flow is aligned along the axis of a highly collimated infrared jet from this source, is blueshifted by 110 km s-1 southwest of the source, and is redshifted by 100–130 km s-1 northeast of L1551 NE. A line through the L1551 NE source and along this well-defined flow axis passes straight through HH 29 and within parts of the more distant HH 259 and HH 28. The proper motion of HH 29 exhibits a complex flow pattern with some knots appearing to move away from the nearby source IRS 5 while other parts are moving away from L1551 NE. The HH 29 object encompasses several bright, stationary knots that have faded between the two epoch images. When these stationary knots are excluded from the proper-motion analysis, the resulting overall flow vector points away from L1551 NE, not from IRS 5. Most components of HH 259 and some parts of HH 28 also appear to be moving in a direction pointing away from L1551 NE rather than from IRS 5. In the opposite, redshifted lobe, we find a new, distant HH object, HH 286, but it is unclear whether L1551 NE or IRS 5 is the driving source. Altogether, it appears that L1551 NE plays a much more prominent role than hitherto anticipated in the outflow activity of this highly complex and confused region.