Hubble Space Telescope WFPC2 Imaging of XZ Tauri:Time Evolution of a Herbig-Haro Bow Shock

We report observations of dramatic morphological changes in the extremely young Herbig-Haro object ejected by the pre-main-sequence binary XZ Tauri. Hubble Space Telescope images taken in 1995 showed a filled bubble of emission nebulosity extending 4" north-northeast of the system in the direction of a previously known jet. New images obtained in 1998 show that the bubble has undergone a remarkable transition into a limb-brightened structure as it continues its motion away from the binary. The new images suggest that we may be witnessing the initial formation of the postshock cooling zone in a newly emerging Herbig-Haro bow shock system, probably accompanied by significant temporal evolution in the nebula's emission line spectrum.

Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, operated under NASA contract NAS5-26555.