Ionization correction factors for sodium, potassium, and calcium in planetary nebulae

We use a large grid of photoionization models that are representative of observed planetary nebulae (PNe) to derive ionization correction factors (ICFs) for sodium, potassium, and calcium. In addition to the analytical expressions of the ICFs, we provide the range of validity where the ICFs can be safely used and an estimate of the typical uncertainties associated with the ICFs. We improved the pr...