  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.
