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A statistical view of low-ionization structures in planetary nebulae

Published online by Cambridge University Press:  06 October 2025

M. Belén Mari*
Affiliation:
Valongo Observatory, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil email: mbmari@unc.edu.ar
Stavros Akras
Affiliation:
Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, Greece
Denise R. Gonçalves
Affiliation:
Valongo Observatory, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil email: mbmari@unc.edu.ar

Abstract

More than three decades after the pioneering imaging catalog by Balick (1987), where the small-scale and low-ionization structures (LISs) in planetary nebulae (PNe) became evident, the present study conducts a comprehensive statistical analysis of LISs’ physical-chemical and excitation properties. Gathering the largest dataset to date, we compare LISs with high-ionization components (rims/shells) across a diverse sample of PNe. Key findings include lower electron densities (NeS ii) in LISs than in adjacent rims/shells and comparable electron temperatures (Te N ii and O iii) between these two nebular componets. Various optical diagnostic diagrams, while revealing a clear excitation stratification between these groups of components, are not good enough to clearly pinpoint the main excitation mechanism behind the LISs line-emission. Photoionization and shock models highlight a notable overlap between mechanisms, emphasizing the coexistence of both excitation processes. Contrary to expectations, shocks are unlikely to be the primary excitation source for most of LISs in PNe.

Information

Type
Contributed Paper
Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of International Astronomical Union

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