Self-consistent grain depletions and abundances I: The Orion Nebula as a test case

TL;DR

This paper investigates how varying dust depletion levels in the Orion Nebula affects spectral line ratios and the physical structure of the H II region, using a modified CLOUDY model for efficient exploration.

Contribution

It introduces a streamlined method for CLOUDY users to vary dust depletion levels with a single parameter, enabling comprehensive analysis of depletion effects on nebular spectra.

Findings

Line ratios are significantly affected by dust depletions.

Adjusting dust abundances influences the temperature and structure of the H+ layer.

Depletion variations alter the physical conditions within the nebula.

Abstract

Atomic species in the interstellar medium (ISM) transition out of their gas phase mainly by depletion onto dust. In this study, we examine if there is any change to the spectral line ratio predictions from a photoionization model of the Orion H II region when the degree of dust depletions is altered according to the most recently published model. We use equations and parameters published by previous works, in order to streamline the calculation of depleted abundances within CLOUDY. Our aim is for CLOUDY users to be able to vary the level of depletion using a single parameter in the input file. This makes it possible to explore predictions for a large range of depletions more efficiently. Finally, we discuss the results obtained for a model of the Orion Nebula when the degree of depletions are manipulated in this way. We found that the intensity of line ratios are significantly affected by depletions onto dust grains. Further, we found that adjusting dust abundances along with depletion affects the structure and the overall temperature of the H$^+$ layer across the H II region.