The case of NGC 6302: the impact of shocks in the derivation of nitrogen abundances

Abstract

ABSTRACT High nitrogen abundance is characteristic of Type I planetary nebulae, as well as their highly filamentary structure. In the present work, we test the hypothesis of shocks as a relevant excitation mechanism for a Type I nebula, NGC 6302, using recently released diagnostic diagrams to distinguish shocks from photoexcitation. The construction of the diagrams depends on emission-line ratios and kinematical information. NGC 6302 shows the relevance of shocks in peripheral regions and their importance to the whole nebula. Using shocks, we question the usual assumption of ionization correction factor calculation, justifying a warning regarding broadly used abundance derivation methods. From kinematical analysis, we derive a new distance for NGC 6302 of $805\pm 143\,$ pc.