A multi-epoch near-infrared study of the HH 7-11 protostellar outflow

Abstract

We present near-infrared observations of the protostellar outflow HH 7–11 in the molecular hydrogen 1–0 S(1) and [Fe ii] 1.644-μm emission lines. Images at four epochs spread over 11 yr constrain the proper motions of the H2 emission knots to be less than 0.045 arcsec yr−1 , corresponding to tangential speeds of under 47 km s−1 at 220-pc distance, consistent with the proper motions derived in the optical range for the atomic component. Reanalysis of previous observations shows that variability and distortion of the SVS 13 reference star led to erroneous high H2 proper motions. The SVS 13 K-band flux is a factor of 3 higher in 1994–2000 than in 1989. Numerous H2 subknots are identified on images taken in 1998 and 2000. No significant relative variability is found in these subknots, consistent with slow outflow evolution. Compact [Fe ii] emission peaks are found at the locations of atomic emission-line features observed in the optical range. We also identify in this line an elongated feature corresponding to the proposed jet Mach disc.