IRON TO OXYGEN ABUNDANCE RATIO IN THE ORION NEBULA

It is shown that partly ionized zones are responsible for most of the O I and Fe II emission in H II regions, and in the Orion Nebula in particular. Given thast O0 and Fe+ are the dominant ionization states of O and Fe respectively in the partly ionized zone, the observed Fe+/O0 ratio provides a reasonable measure of the Fe/O ratio in the region. Employing appropriate conditions of temperature and electron density in the zone, we find that the Fe/O abundance ratio in Orion is much closer to the solar value than in earlier studies. Depletion of iron into grains within the ionized region of the nebula may therefore be considerably less than previously estimated or assumed.