On the O/H, Mg/H, Si/H and Fe/H Gas and Dust Abundance Ratios in Galactic and Extragalactic H II Regions

TL;DR

This paper investigates the gas and dust abundance ratios of elements like O, Mg, Si, and Fe in various H II regions, revealing how dust depletion varies with metallicity and impacts abundance comparisons.

Contribution

It provides new measurements of Mg/H, O/H, and Fe/O ratios in specific nebulae and quantifies dust depletion effects across different metallicities.

Findings

Depletion of oxygen increases with metallicity, from 0.08 to 0.12 dex.

Mg, Si, and Fe show significant dust depletion in H II regions.

Dust depletion must be considered when comparing nebular and stellar abundances.

Abstract

We derive the Mg/H ratio in the Orion nebula and in 30 Doradus. We also derive the O/H and the Fe/O ratios in the extremely metal poor galaxy SBS 0335-052. We estimate the dust depletions of Mg, Si, and Fe in Galactic and extragalactic H II regions. Based on these depletions we estimate the fraction of O atoms embedded in dust as a function of the O/H ratio. We find an increasing depletion of O with increasing O/H. The O depletion increases from about 0.08 dex, for the metal poorest H II regions known, to about 0.12 dex, for metal rich H II regions. This depletion has to be considered when comparing nebular with stellar abundances.