Planetary nebulae trace the end phase of the life of low-mass and intermediate-mass stars, at the crossroads of stellar and galactic evolution. They result from AGB mass loss, itself a poorly understood process. The bright nebulae are significant drivers of the chemical evolution of galaxies: they are the dominant source of carbon in the modern Universe, a significant source of nitrogen, and a source of half of all elements heavier than iron. The beautiful nebular shapes have led to in-depth hydrodynamics studies with applicability in many fields. The central stars contain a large population of close binaries, which connects planetary nebulae to the developing field of transients. Outreach, publicity and education have made significant use of planetary nebulae.
Planetary nebula populations have been observed at distances of tens of Mpc, where the underlying lower-mass stars themselves are undetectable. They are the only stars (other than supernovae) whose individual spectra can be measured out to the distance of the Coma cluster. They allow one to measure the velocities of stars at large distances from the centres of galaxies where the dark matter dominates, and they trace the assembly of diffuse light in cluster of galaxies.
- Planetary nebulae as tracers of stellar evolution: the giant branch-white dwarf connection; mass loss and stellar winds; binary interactions; eruptive events and transients
- Planetary nebulae as hydrodynamics events: shaping of stellar winds, dusty winds, jet launching, jet-nebula interaction; the asterosphere; outflow shaping by binary interactions
- Planetary nebulae as astrochemistry laboratories: molecular evolution; polycyclic aromatic hydrocarbons and fullerenes; dust formation and destruction; photo-dissociation regions
- Planetary nebulae as abundances decoders: atomic physics; photo-ionization and shocks; the forbidden-line vs recombination line abundance discrepancy; primary elemental production and ISM enrichment
- Planetary nebulae as unique tools to study the structure and evolution of galaxies: star formation histories, abundance gradients, structural components and dark matter, galaxy dynamics, hierarchical mass assembly