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Radiation from the CSPN permeates into the circumstellar shells, controlling the physical conditions and local structures (see, e.g., Villaver et al. The evolutionary history of the progenitor (the central star of a PN, CSPN) is imprinted in the circumstellar shells. So far, more than 2000 PNe in the Milky Way have been identified ( Frew 2008 Parker et al.
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Therefore, being relatively isolated from surrounding objects, PNe provide unique laboratories to further our understanding of the stellar evolution and the chemical evolution of galaxies, from high-temperature fully ionized plasma to low-temperature dusty molecular gas. While PNe are famous for their spectacular circumstellar structures seen via bright optical emission lines arising from the ionized gas component of the nebula, the ionized part of PNe is surrounded by the neutral gas and dust components (i.e., the PDR). Planetary nebulae (PNe) are low-mass stars that have completed mass loss during the preceding AGB phase and consist of a hot central star (≳30,000 K evolving to become a white dwarf) and an extensive circumstellar shell. Hence, understanding of stellar mass loss is important in characterizing the cosmic mass recycling and chemical evolution in galaxies. These cold components of the mass-loss ejecta will provide the seed material for the formation of the next generation of stars and planets. Besides gas, molecules and solid-state particles (i.e., dust grains) participate in the stellar mass loss and make up a significant part of the circumstellar shells as the photodissociation region (PDR). This stellar mass loss becomes significant when stars evolve into the final stage of stellar evolution, i.e., the asymptotic giant branch (AGB) stage for low-mass stars (1-8 M ⊙) and core-collapsed supernova explosions for high-mass stars (>8 M ⊙).Įither way, the mass-loss process would expel a significant fraction of mass contained in stars as the circumstellar shells, which would eventually become part of the interstellar medium (ISM). Hence, the chemical evolution of galaxies has always been made possible by stellar nucleosynthesis, convection/dredge-up, and, ultimately, stellar mass loss. The life cycle of matter in the universe is intimately connected with the stellar evolution because stars are the most fundamental building blocks of the universe. A significant fraction of the total mass (about 70%) is found to exist in the PDR, demonstrating the critical importance of the PDR in PNe that are generally recognized as the hallmark of ionized/H + regions. The estimated total gas mass (0.41 M ⊙) corresponds to the mass ejected during the last AGB thermal pulse event predicted for a 2.5 M ⊙ initial-mass star.
Nebula 3 modules code#
Through iterative fitting using the Cloudy code with empirically derived constraints, we find the best-fit dusty photoionization model of the object that would inclusively reproduce all of the adopted panchromatic observational data. Our excitation energy diagram analysis indicates high-excitation temperatures in the photodissociation region (PDR) beyond the ionized part of the nebula, suggesting extra heating by shock interactions between the slow AGB wind and the fast PN wind. We derive the best-fit distance of 0.46 kpc by fitting the stellar luminosity (as a function of the distance and effective temperature of the central star) with the adopted post-AGB evolutionary tracks. Empirical nebular elemental abundances, compared with theoretical predictions via nucleosynthesis models of asymptotic giant branch (AGB) stars, indicate that the progenitor is a solar-metallicity, 2.25–3.0 M ⊙ initial-mass star. We perform a comprehensive analysis of the planetary nebula (PN) NGC 6781 to investigate the physical conditions of each of its ionized, atomic, and molecular gas and dust components and the object’s evolution, based on panchromatic observational data ranging from UV to radio.