On the Abundance Discrepancy Problem in H II Regions

The paper operates within the paradigm of determining chemical abundances in photoionized nebulae (H II regions). This field has long faced the "abundance discrepancy problem," an anomaly where abundances from recombination lines (ORLs) are higher than from collisionally excited lines (CELs). Two competing explanations exist: the "temperature fluctuations" paradigm and the "two-phase" (chemically inhomogeneous) model. This research tests the validity and universality of these models, which were largely developed in the context of planetary nebulae, by applying them to H II regions.

This paper is classified as Model Drift because it investigates a well-known anomaly—the abundance discrepancy—and reveals significant inconsistencies in the proposed solutions when applied to a different class of objects. By analyzing a sample of H II regions, the authors find that the abundance discrepancy factor (ADF) is constant, unlike in planetary nebulae. Their results challenge the universality of the popular two-phase model and instead show more consistency with the older temperature fluctuations paradigm. This demonstrates that the current explanatory models are "drifting" and failing to provide a unified explanation, necessitating refinement or alternative theories.