VLT Spectroscopic Analysis of HH 202. Implications on dust destruction
  and thermal inhomogeneities
  We present a long-slit spectroscopic analysis of Herbig-Haro 202 and the
surrounding gas of the Orion Nebula using data from the Very Large Telescope.
Given the characteristics of the Orion Nebula, it is the ideal object to study
the mechanisms that play a role in the evolution of H II regions, notably dust
destruction by interstellar shocks, which is a poorly understood subject. The
use of long-slit allowed us to determine the spatial variation in its physical
conditions and chemical abundances observing a broad area of the Orion Nebula;
our results are consistent with those from previous studies albeit with
improved uncertainties in some determinations. Special attention is paid to
Iron (Fe) and Oxygen (O) abundances, which show a peak at the apex of the
shock, allowing us to estimate that 57% of the dust is the destroyed at this
position; we also calculate the amount of depletion of oxygen in dust grains,
which amounts to 0.126 +/- 0.024 dex. Finally we show that O abundances
determined from collisionally excited lines and recombination lines are
irreconcilable at the center of the shock unless thermal inhomogeneities are
considered along the line of sight in the form of the t^2 parameter proposed by
Peimbert (1967).
