2002A&A...382.1021D

To search for further evidence of H₂ line emission towards the central engines of Herbig-Haro (HH) flows we have obtained near-infrared Fabry-Perot images of eight Class I outflow sources (SVS13 [HH7-11], L1551-IRS5, HH26-IRS, HH72-IRS, SSV63E [HH24C], SSV63W [HH24J], HH34-IRS and HH111-IRS) and two Class 0 sources (HH24-MMS and HH25-MMS). Elongated H₂ emission (on scales of a few arcseconds) is detected from four of the Class I YSOs. These small-scale ``jets'' are associated with the base of more extended, parsec-scale HH outflows (and the ``Molecular Hydrogen Emission Line'' regions, or MHELs, discussed in Davis et al., 2001MNRAS.326..524D). In L1551-IRS5 we detect two jet components in H₂; these may be the molecular counterparts of the two known optical jets from this binary protostellar system, or they may represent H₂ excitation along the walls of a narrow, edge-brightened cavity. In addition to the small-scale MHEL jets, analysis of the data also suggests the presence of discrete molecular shock fronts formed along the jet axes close to the energy sources. In the most clear-cut example, SVS13, we see an H₂ knot at a distance of about 440AU from the outflow source; assuming a flow velocity of ∼200km/s, then the dynamical age of this molecular feature is only 10yrs. In these data we also see evidence for both collimated jets and wide-angled winds from the same sources. Indeed, even in one of the two Class 0 sources, HH25MMS, a poorly-collimated flow component seems to be present. A two-component wind model may therefore be appropriate for outflows from Class I (and possibly even Class 0) protostars.