Proper Motions of the HH 47 Jet Observed with theHubble Space Telescope

Abstract

We present a proper-motion study of the shock waves within the classic stellar jet HH 47 based on Hubble Space Telescope (HST) Hα and [S II] images of the region taken over two epochs. Individual knots within the jet and in the bow shock/Mach disk working surface of HH 47A move significantly in the 5 yr that separate the images, and the excellent spatial resolution of HST makes it possible to measure the proper motions with enough precision to easily observe differential motions throughout the flow. The bright portion of the jet emerges at 375 ± 25 from the plane of the sky with an average velocity of 300 km s-1. Dynamical ages of the shock waves in the jet range from a few decades for knots recently ejected by the source to ~1300 yr for the faint extended bow shock HH 47D. The jet curves, but motions of knots in the jet are directed radially away from the exciting source, and velocity variability in the flow drives the shock waves that heat the jet internally. The jet orientation angle varies with time by about 15° and currently points to the northwestern portion of a cavity outlined by a reflection nebula, where a quasi-stationary shock deflects the jet. The major working surface HH 47A is more complex than a simple bow shock/Mach disk and contains numerous clumps that move relative to one another with velocities of ~±40 km s-1. Small clumps or instabilities affect the Mach disk, and dense clumps may move all the way through the working surface to cause the bumpy morphology seen at the bow shock. A localized area between the bow shock and Mach disk varies significantly between the two sets of images.