Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Multipolar Planetary Nebulae: Not as Geometrically Diversified as
  Thought   Planetary nebulae (PNe) have diverse morphological shapes, including
point-symmetric and multipolar structures. Many PNe also have complicated
internal structures such as torus, lobes, knots, and ansae. A complete
accounting of all the morphological structures through physical models is
difficult. A first step toward such an understanding is to derive the true
three-dimensional structure of the nebulae. In this paper, we show that a
multipolar nebula with three pairs of lobes can explain many of such features,
if orientation and sensitivity effects are taken into account. Using only six
parameters - the inclination and position angles of each pair - we are able to
simulate the observed images of 20 PNe with complex structures. We suggest that
the multipolar structure is an intrinsic structure of PNe and the statistics of
multipolar PNe has been severely underestimated in the past.

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The categories of this paper are: chem-ph
20
The categories of this paper are: acc-phys
27
The categories of this paper are: comp-gas
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The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
26
The categories of this paper are: bayes-an
4
The categories of this paper are: cond-mat
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The categories of this paper are: cmp-lg
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The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
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The categories of this paper are: plasm-ph
3
The categories of this paper are: physics
9
The categories of this paper are: nlin
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The categories of this paper are: dg-ga
7
The categories of this paper are: hep-th
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The categories of this paper are: q-alg