Facing the Abundance Discrepancy in the Orion Nebula
The spectral analysis of HII regions allows one to determine the chemical composition of the ionized gas phase of the interstellar medium (ISM) from the solar neighborhood to the high-redshift galaxies. Therefore, it stands as an essential tool for our knowledge of the chemical evolution of the Universe. However, it turns out that chemical abundances of heavy-element ions determined from the bright collisionally excited lines (CELs) are systematically lower than the abundances derived from the faint recombination lines (RLs) emitted by the same ions. Today, this controversial issue is known as abundance discrepancy problem and it is far from negligible. In the analysis of Galactic and extragalactic HII regions the O2+/H+ ratio calculated from the OII RLs is between 0.10 and 0.35 dex higher than that obtained from the [OIII] CELs. In this talk, we will face this problem in the benchmark object of the solar vicinity, the Orion Nebula. Due to its high surface brightness and proximity, the Orion Nebula is an ideal lab, which allows us to study in detail the possible role of its rich and well-resolved internal structure (such as Herbig-Haro objects, protoplanetary disks or bars) on the abundance discrepancy.
About the talk
University of Hawaii, USA