HE II Line Emission as a Tracer of Nonradiative Preionized Shocks: Application to Winds and Circumstellar Disks in the Orion Nebula

摘要: Collisionally excited Balmer line emission from H occurs whenever neutral hydrogen enters a sufficiently strong shock. Such has many important applications for the study of Herbig-Haro objects and supernova remnants. This paper explores collisional excitation ionization H-like ion He II in shocks, process that may prove to be useful cases where no because preshock is completely ionized. Like lines H, also radiate at shock, though complexities broad narrow components present should absent emission. New narrowband images Trapezium region Orion λ4686 adjacent continuum near this wavelength fail show any signatures shocks. Upper limits on fluxes these images, combined with predictions brightness nonradiative give an upper limit mass-outflow rate Θ1 Ori C consistent mass-loss estimated UV observations. The new HH 202 represents superposition two bow shocks moving opposite directions, which explains some anomalies seen previously emission-line source taken Hubble Space Telescope (HST).