Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Planetary Nebulae: Exposing the Top Polluters of the ISM   The high mass loss rates of stars in their asymptotic giant branch (AGB)
stage of evolution is one of the most important pathways for mass return from
stars to the ISM. In the planetary nebulae (PNe) phase, the ejected material is
illuminated and can be altered by the UV radiation from the central star. PNe
therefore play a significant role in the ISM recycling process and in changing
the environment around them. We show some highlights of the results of
observations that have been carried out using the Spitzer instruments to study
the gas and dust emission from PNe in the Milky Way and nearby galaxies.
Spitzer is especially sensitive to the cool dust and molecules in the PNe shell
and halos. We present new results from our program on Galactic PNe, including
IRAC and IRS observations of NGC 6720 in the ring and halo of that nebula.

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The categories of this paper are: funct-an
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
28
The categories of this paper are: alg-geom
3
The categories of this paper are: physics
7
The categories of this paper are: hep-th
12
The categories of this paper are: nucl-th
0
The categories of this paper are: hep-ph
16
The categories of this paper are: stat
14
The categories of this paper are: math-ph
20
The categories of this paper are: acc-phys
4
The categories of this paper are: cond-mat
36
The categories of this paper are: cmp-lg
2
The categories of this paper are: math
35
The categories of this paper are: mtrl-th