Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: VISIR-VLT high resolution study of the extended emission of four
  obscured post-AGB candidates   The onset of the asymmetry of planetary nebulae (PNe) is expected to occur
during the late Asymptotic Giant Branch (AGB) and early post-AGB phases of low-
and intermediate-mass stars. Among all post-AGB objects, the most heavily
obscured ones might have escaped the selection criteria of previous studies
detecting extreme axysimmetric structures in young PNe. Since the most heavily
obscured post-AGB sources can be expected to descend from the most massive PN
progenitors, these should exhibit clear asymmetric morphologies. We have
obtained VISIR-VLT mid-IR images of four heavily obscured post-AGB objects
barely resolved in previous Spitzer IRAC observations to analyze their
morphology and physical conditions across the mid-IR. The VISIR-VLT images have
been deconvolved, flux calibrated, and used to construct RGB composite pictures
as well as color and optical depth maps that allow us to study the morphology
and physical properties of the extended emission of these sources. We have
detected extended emission from the four objects in our sample and resolved it
into several structural components that are greatly enhanced in the temperature
and optical depth maps. They reveal the presence of asymmetry in three young
PNe (IRAS 15534-5422, IRAS 17009-4154, and IRAS 18454+0001), where the
asymmetries can be associated with dusty torii and slightly bipolar outflows.
The fourth source (IRAS 18229-1127), a possible post-AGB star, is better
described as a rhomboidal detached shell. The heavily obscured sources in our
sample do not show extreme axisymmetric morphologies. This is at odds with the
expectation of highly asymmetrical morphologies in post-AGB sources descending
from massive PN progenitors. The sources presented in this paper may be
sampling critical early phases in the evolution of massive PN progenitors,
before extreme asymmetries develop.

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The categories of this paper are: math-ph
3
The categories of this paper are: physics
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The categories of this paper are: stat
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The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
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The categories of this paper are: q-fin
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The categories of this paper are: acc-phys
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The categories of this paper are: bayes-an
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The categories of this paper are: cs
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The categories of this paper are: cond-mat
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The categories of this paper are: nlin
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The categories of this paper are: atom-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: nucl-th
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The categories of this paper are: ao-sci
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The categories of this paper are: chao-dyn