Resumen
Our main source of uncertainty in the determination of chemical abundances in H II regions and planetary nebulae arises from a discrepancy: the abundances implied by recombination lines are larger than those implied by collisionally excited lines. The discrepancy amounts to a factor of 2 in most objects, but reaches much higher values in some planetary nebulae. There are several possible explanations for this effect. Here we explore a recent proposal and determine what kind of deviations from a Maxwellian electron energy distribution are needed in order to reproduce the measured abundance discrepancies. We note the parallelisms between this explanation and other explanations that are based on the sensitivity to temperature of collisionally excited lines: the presence of metal-rich inclusions within the ionized gas or temperature fluctuations in a chemically homogeneous gas.
