Near-infrared Fabry-Perot imaging of Herbig-Haro energy sources: Collimated, small-scale H2 jets and wide-angled winds

Abstract

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 (SVS 13 [HH 7-11], L 1551-IRS5, HH 26-IRS, HH 72-IRS, SSV 63E [HH 24C], SSV 63W [HH 24J], HH 34-IRS and HH 111-IRS) and two Class 0 sources (HH 24-MMS and HH 25-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. 2001). In L 1551-IRS 5 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, SVS 13, we see an H2 knot at a distance of about 440 AU from the outflow source; assuming a flow velocity of ∼200 km s-1, then the dynamical age of this molecular feature is only 10 yrs. 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, HH 25MMS, 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.