Abstract

The mixed-chemistry problem in planetary nebulae

Lizette Guzman-Ramirez (Leiden Observatory, The Netherlands)

Albert Zijlstra (JBCA, University of Manchester, UK), Eric Lagadec (Observatroy Cote d'Azur, France), Roger Wesson (University College London, UK), Jeronimo Bernard-Salas (The Open University, UK), Mikako Matsuura (Cardiff University, UK), Raghvendra Sahai (JPL, USA)

Planetary nebulae (PNe) represent the last stage of evolution of intermediate mass stars (0.8 to 8M_sun) and, hence, by their very nature are fundamental to galactic evolution. The massive envelopes ejected during their earlier evolution (AGB phase) are an important source of recycled material in the form of dust and molecular gas into the interstellar medium. A small fraction of PNe show both O- and C-rich dust features and are therefore classified as mixed-chemistry objects. The origin of their mixed-chemistry is still uncertain. Our chemical models show that the PAHs, C-rich dust, may form in irradiated dense tori, and HST images confirm the presence of such tori in some of the objects. Using the VISIR/VLT, we identified that PAHs are present at the outer edges of the tori in a sample of Galactic Bulge PNe (Guzman-Ramirez, et al., 2011, 2014, 2015). On the other hand, in the Galactic Disk, very few PNe have shown to harbour these mixed-chemistry phenomenon. There are two scenarios that we predict for the formation of PAHs in these O-rich environments: 1. If the CO photodissociation is the main producer of PAHs, then we should observe these molecules in the dense tori. 2. If the central star just became C-rich, then the PAHs must be observed in the outflows of the PNe while the silicates will be in the tori. JWST will allow us to study the spatial distribution of the PAHs and silicates in these planetary nebulae.

Talk