Proper Motions and Shock Wave Dynamics in the HH 7-11 Stellar Jet

Abstract: We have used the Hubble Space Telescope to acquire new broad-band and narrow-band images of the optical line emission and red continuum associated with the HH 7-11 stellar jet in the NGC 1333 star formation region. Combining the new narrow-band images of H$\alpha$, [O~I] $\lambda$6300 and [S II] $\lambda$6716 allows us to measure electron densities and excitations at each point in the outflow with the spatial resolution of HST, while the I-band image traces out the boundary of the cavity evacuated by the outflow. Comparing these images with those taken $\sim$ 20 years ago yields high precision proper motions for all the HH objects in the outflow. HH 11 is a bullet-like clump, and emerges from the exciting source SVS 13A towards the Earth at 24 degrees to line of sight. In contrast, HH 8 and HH 10 consist of two rings of shocked gas that show no bulk proper motions even though the emitting gas is blueshifted. The HH 8 rings are expanding with time. These shocks mark places where ambient material located along the path of the jet redirects the outflow. HH 7 consists of multiple shells, and emits strongly in H$_2$ in what appears to be a terminal bow shock for the outflow, implying that the jet has yet to fully break out of its nascent cloud core. The jet largely fragments into clumps by the time it reaches HH 7. As in the case of HH 110, deflection from ambient material plays a key role in producing observable shock waves in the HH 7-11 outflow.