VLT Spectroscopic Analysis of HH 202. Implications on dust destruction and thermal inhomogeneities

TL;DR

This study uses VLT spectroscopy to analyze Herbig-Haro 202 in the Orion Nebula, revealing dust destruction mechanisms, spatial variations in physical conditions, and the importance of thermal inhomogeneities in abundance determinations.

Contribution

It provides detailed spatial analysis of dust destruction and thermal inhomogeneities in HH 202, improving understanding of H II region evolution.

Findings

57% of dust destroyed at shock apex

Oxygen depletion in dust grains quantified as 0.126 +/- 0.024 dex

Reconciliation of O abundance lines requires considering thermal inhomogeneities

Abstract

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).