HH 529 spectroscopy

We examine the easternmost 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 that 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 be.