A photoionized Herbig-Haro object in the Orion nebula

Abstract

The spectra of Herbig Haro objects are usually characteristic of ionization and excitation in shock-heated gas, whether an internal shock in an unsteady outflow or a bow shock interface with the interstellar medium. We examine the eastern-most shock -- the leading optically visible shock -- of a Herbig Haro outflow (HH 529) seen projected on the face of the Orion Nebula, using deep optical echelle spectroscopy, showing that the spectrum of this gas is consistent with photoionization by ${\theta }^1$ Ori C. By modeling the emission lines, we determine a gas-phase abundance of Fe which is consistent with the depleted (relative to solar) abundance found in the Orion nebula -- evidence for the presence of dust in the nebula and therefore in the Herbig Haro outflow. The spectrum also allows for the calculation of temperature fluctuations, $t^2$, in the nebula and the shock. These fluctuations have been used to explain discrepancies between abundances obtained from recombination lines versus those obtained from collisionally-excited lines, although to date there has not been a robust theory for how such large fluctuations ($t^2>0.02$) can exist.

50 pages, 8 figures, To be published in ApJ

Cited by in corpus (8)

• Properties of the ionized gas in HH202. II: Results from echelle spectrophotometry with UVES
• Deviations from He I Case B Recombination Theory and Extinction Corrections in the Orion Nebula
• High Velocity Features in the Orion Nebula
• Large Scale Flows from Orion-South
• Photoionized Herbig-Haro objects in the Orion Nebula through deep high-spectral resolution spectroscopy I: HH529II and III
• Photoionized Herbig-Haro objects in the Orion Nebula through deep high-spectral resolution spectroscopy II: HH204
• Photoionized Herbig-Haro objects in the Orion Nebula through deep high-spectral resolution spectroscopy III: HH514
• Gas-phase Fe/O and Fe/N abundances in Star-Forming Regions. Relations between nucleosynthesis, metallicity and dust