Refractory element depletion and the determination of abundances in H II regions

Photoionization models have been used to show that the strengths of abundance diagnostics such as [O II]λ3727 and [O III]λ5007 in low-excitation H II regions are very sensitive to the gas-phase depletion factors of refractory elements. As a result, observationally unconstrained levels of elements such as Mg, Si, and Fe employed in models to infer nebular properties may lead to uncertainties of a factor of 2 in the abundances of elements such as O, N, and S.