Outflows in the Orion Nebula: HH 540 from the Beehive Proplyd

Abstract

We present Hubble Space Telescope Advanced Camera for Surveys images of the giant proplyd 181-826 in the southern Orion Nebula. This object exhibits a variety of known proplyd properties-an optically visible central star, a silhouette disk, a bright proplyd ionization front, and a bipolar microjet emerging along the disk axis that powers a larger Herbig-Haro flow. The proplyd ionization front is remarkable because of its large size (a radius of about 800 AU) and because of its corrugated structure consisting of a set of coaxial rings with the same orientation as the embedded silhouette disk. The rings are centered on the disk/jet axis, and we discuss possible mechanisms for their formation. The silhouette disk has an outer radius of about 160 AU, and its axis is inclined by an angle of about 60° with respect to our line of sight. A prominent reflection nebula protrudes along the disk axis toward the south, marking the base of the approaching outflow, and a faint knot on the north side of the disk indicates that the nebula is bipolar. Fabry-Pérot images reveal a high-velocity blueshifted jet with a mass-loss rate of about 10^-8 M_solar yr^-1 emerging along the disk axis. It has a velocity (corrected for the outflow inclination angle) of about 160 km s^-1 and can be traced for about 1' toward the south. A chain of three lower velocity blueshifted bow shocks, collectively known as HH 540, extend several arcminutes south of 181-826 along the same axis, tracing a large-scale outflow powered by this jet.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555.