A MUSE view of planetary nebulae with large abundance discrepancies

Abundance determinations in planetary nebulae (PNe) are of crucial interest to understand the nebular emission of such objects and to integrate them into a description of the chemical evolution of the host galaxy. In the case of PNe where the presence of a metal-rich phase is suspected, metallic abundances have revealed to be much higher (more than a factor of 10) when computed from the faint recombination lines (RLs) than from the bright collisionally excited lines (CELs). This is a particular case of the well-known abundance discrepancy (AD) problem, and certainly deserves in-depth studies. We present state-of-the-art Integral Field Unit (IFU) observations obtained with the Multi Unit Spectroscopic Explorer (MUSE) at the VLT of four high-AD PNe. This excellent dataset allows us to explore the spatial distribution of the physical properties of the nebula, as well as variations in its chemical composition. We show that the presence of a cold region emitting mainly metal RLs implies a detailed treatment to obtain a pertinent evaluation of the enrichment of this cold gas phase. We describe how the so-called "abundance discrepancy factor" (ADF) is no longer valid for these objects as we have to consider the weight of the emission of hydrogen and helium lines, that are emitted in both components. We propose a methodology to correct chemical abundances to properly compute chemical abundances, both from CELs and RLs.