2020A&A...642A.216S

Context. We present SOFIA/FIFI-LS observations of five prototypical, low-mass Class I outflows (HH111, SVS13, HH26, HH34, HH30) in the far-infrared [OI]_63µm and [OI]_145µm transitions.
Aims. Spectroscopic [OI]_63µm,145µm maps enable us to study the spatial extent of warm, low-excitation atomic gas within outflows driven by Class I protostars. These [OI] maps may potentially allow us to measure the mass-loss rates (M_jet) of this warm component of the atomic jet.
Methods. A fundamental tracer of warm (i.e. T∼500-1500K), low-excitation atomic gas is the [OI]_63µm emission line, which is predicted to be the main coolant of dense dissociative J-type shocks caused by decelerated wind or jet shocks associated with protostellar outflows. Under these conditions, the [OI]_63µm line can be directly connected to the instantaneous mass ejection rate. Thus, by utilising spectroscopic [OI]_63µm maps, we wish to determine the atomic mass flux rate M_jet ejected from our target outflows.
Results. Strong [OI]_63µm emission is detected at the driving sources HH111IRS, HH34IRS, SVS13, as well as at the bow shock region, HH7. The detection of the [OI]_63µm line at HH26A and HH8/HH10 can be attributed to jet deflection regions. The far-infrared counterpart of the optical jet is detected in [OI]_63µm only for HH111, but not for HH34. We interpret the [OI]_63µm emission at HH111IRS, HH34IRS, and SVS13 to be coming primarily from a decelerated wind shock, whereas multiple internal shocks within the HH111 jet may cause most of the [OI]_63µm emission seen there. At HH30, no [OI]_63µm,145µm was detected. The [OI]_145µm line detection is at noise level almost everywhere in our obtained maps. The observed outflow rates of our Class I sample are to the order of M_jet∼10^–6M_☉/yr, if proper shock conditions prevail. Independent calculations connecting the [OI]_63µm line luminosity and observable jet parameters with the mass -loss rate are consistent with the applied shock model and lead to similar mass-loss rates. We discuss applicability and caveats of both methods.
Conclusions. High-quality spectroscopic [OI]_63µm maps of protostellar outflows at the jet driving source potentially allow a clear determination of the mass ejection rate.