Gas Dynamics in Planetary Nebulae: From Macro-structures to FLIERs |
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Authors: | Mario Perinotto |
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Institution: | (1) Dipartimento di Astronomia, Università di Firenze, Italy |
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Abstract: | Purpose of this paper is to clarify how Planetary Nebulae (PNe) are very interesting laboratories to study cosmic gas dynamics.
I first recall the history of PNe which are generated from low and intermediate mass stars through successive mass loss processes
starting in the Reg Giant phase of evolution and continuing also after the termination of the pulsed AGB phase, where most
of the nebular mass is believed to be ejected. The correpondings tellar winds are the ingredients of the nebula. Their initial
properties and subsequent mutual interactions, under the action of the evolving stellar radiation field, are responsible for
the properties of the nebula. The observed structures of PNe are considered in detail. Larger scale macroscopic structures
(MACS) are examined separately from quite smaller scale microscopic structures (MICS). The formation of MACS, at least in
cases of round to moderately elliptical PNe, is shown to be reasonably well understood in terms of existing hydrodynamical
models. Considering the kinematical behaviour, MICS can be separated into FLIERs (Fast Low Ionization Emitting Regions) and
SLOWERs (slowly moving). Attention is focussed on FLIERs and on the proposed mechanisms to interpret them. Recent observations
with the Hubble Space Telescope have provided us with a wealth of detailed (subarcsec) information on the nebular structures.
The inner structure of FLIERs is here illustrated to consist of substructures of various shapes with an high degree of individually
from object to object, also within the same PN. These new data call for deeper thoretical efforts to solve the problems of
cosmic gas dynamics, posed by their observed properties. An ample account is given of the most relevant original works, in
an effort to allow the non specialist reader to quickly become acquainted with the status of art in the various aspects of
the subject.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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