Kinematical analysis of PNe with high ADF: Hf 2-2 and M 1-42

ABSTRACT We use deep Echelle spectroscopy of the planetary nebulae Hf 2-2 and M1-42 to study the characteristics of the plasma that gives rise to their high abundance discrepancy factors (70 and 20, respectively). We analyse position–velocity diagrams for forbidden and permitted lines (92 and 93 lines in Hf 2-2 and M 1-42, respectively), to compare their kinematic behaviour and to determine the physical characteristics of the emitting plasma. We confirm that there are two plasma components in both nebulae: a normal nebular plasma that emits both forbidden and permitted lines and an additional plasma component that emits the permitted lines of O i, C ii, N ii, O ii, and Ne ii. These plasma components have different spatial distributions, with the additional plasma component being the more centrally concentrated. Their physical conditions are also different, with the additional plasma component being denser and cooler. We find that, in these objects, the additional plasma component contains masses of N$^{2+}$ and O$^{2+}$ ions that are at least as large as the normal nebular plasma. In both objects, we find strong gradients in the electron temperature in small volumes near the central star. Compared to NGC 6153, we find that the larger ADFs in Hf 2-2 and M 1-42 are due to larger masses of ions that emit only in the permitted lines, and not due to the physical conditions.