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.

arXiv comment50 pages, 8 figures, To be published in ApJ

References in corpus (9)

• Constraints on the Stellar/Sub-stellar Mass Function in the Inner Orion Nebula Cluster
• A reappraisal of the chemical composition of the Orion nebula based on VLT echelle spectrophotometry
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• 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
• Chemical abundances in the protoplanetary disk LV2 (Orion): clues to the causes of the abundance anomaly in HII regions
• Integral field spectroscopy of selected areas of the Bright Bar and Orion-S cloud in the Orion Nebula
• The Nature and Frequency of Outflows from Stars in the Central Orion Nebula Cluster
• 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
• Small-spatial scale variations of nebular properties and the abundance discrepancy in three Galactic HII regions
• Exploring the effects of high-velocity flows in abundance determinations in H II regions. Bidimensional spectroscopy of HH 204 in the Orion Nebula
• Scaling for the intensity of radiation in spherical and aspherical planetary nebulae
• The Integral Field View of the Orion Nebula