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Título
:
Low-ionization Structures (LISs) in Planetary Nebulae: Observations versus Models
Conferencista:
Denise Rocha Goncalves, Instituto de Astrofisica de Canarias Tenerife-Spain
Data
:
Terça-feira, 14/08/01 15H30M
Local
:
Auditório L.B.F. Clauzet - Água Funda
Sumário
:
Low-ionization small-scale structures potentially contain important information
about the mass loss and radiative processes that lead to the formation and
development of a planetary nebula. Recently, we have obtained morphological and
kinematical data for 10 PNe with the aim of studying the physical properties,
origin, and evolution of the LISs therein contained. Results are both promising
and puzzling since we have found LISs with notably different properties relative
to each other, in terms of expansion velocities, shapes, sizes, and locations
relative to the main nebular components. It appears that several physical
processes have to be considered in order to account for the formation and
evolution of all the different LISs that we observed.
In particular, the following basic questions are open. Are magnetic fields,
either in single or binary stars, necessary for producing jets in PNe, as
generally believed for jets in young stellar objects and active galactic nuclei?
Which processes, even in complex systems like interacting binary stars,
can produce multiple systems of highly collimated outflows expanding in
directions almost perpendicular to each other as observed in some PNe? How do
low-velocity collimated LISs form? Are symmetric pairs of knots recent ejecta
from the central stars or fossil condensations tracing a peculiar mass-loss
geometry during the asymptotic giant branch (AGB)? Are nonsymmetrical LISs
formed by in situ instabilities? Taking advantage of our recent work and of the
information that is spread throughout the literature, we carefully address these
points analizing the 50 PNe presently known to possess this kind of structure.