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Session: Stars, Planets and the Interstellar Medium

Name: Dr. Stavros Akras (IAASARS/NOA)
Coauthors: No coauthors were included.
Type: Oral
Title: Do we really comprehend Planetary Nebulae?
Abstract:

Planetary nebulae (PNe) are expanding shells of gas ejected by evolved stars. The structure of this gas can be explained by the dissociation/ionization/excitation processes of molecular and atomic gas illumated by an intense UV stellar radiation field. The overall picture of PNe depicts a highly ionized gas close to the central UV sources (central stars), and a lower ionized gas further out until it becomes neutral, atomic and even further molecular. However, this picture is broken by the presence of low-ionization structures (LISs) embedded in the nebula, and they should not be there. The recent discoveries of molecular hydrogen gas in these structures has confirmed that we still miss pieces from the puzzling nature of PNe. In this talk, I will start with a brief presentation of what we have learn about LISs over the last 30 years and then I will discuss the latest discoveries that have raised new questions. The big question in the field of PNe and more general in stellar evolution is "Are LISs mini-photodissocation regions?"