Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The reactivation of water maser emission in the planetary nebula IRAS
  18061--2505 through a born-again episode   Water maser emitting planetary nebulae (H$_2$O-PNe) are believed to be among
the youngest PNe. We present new optical narrow- and broad-band images,
intermediate- and high-resolution long-slit spectra, and archival optical
images of the H$_2$O-PN IRAS 18061--2505. It appears a pinched-waist bipolar PN
consisting of knotty lobes with some point-symmetric regions, a bow-shock near
the tip of each lobe, and a very compact inner nebula where five components are
identified in the spectra by their kinematic and emission properties. The water
masers most probably reside in an oxygen-rich ring tracing the equatorial
region of the bipolar lobes. These two structures probably result from common
envelope evolution plus several bipolar and non-bipolar collimated outflows
that have distorted the lobes. The bow-shocks could be related to a previous
phase to that of common envelope. The inner nebula may be attributed to a late
or very late thermal pulse that occurred before 1951.6 when it was not
detectable in the POSSI-Blue image. Chemical abundances and other properties
favour a 3--4 M$_{\odot}$ progenitor, although if the common envelope phase
accelerated the evolution of the central star, masses <1.5 M$_{\odot}$ cannot
be discarded. The age of the bipolar lobes is incompatible with the existence
of water masers in IRAS 18061--2505, which may have been lately reactivated
through shocks in the oxygen-rich ring, that are generated by the thermal
pulse, implying that this PN is not extremely young. We discuss H$_2$O-PNe and
possibly related objects in the light of our results for IRAS 18061--2505.

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The categories of this paper are: dg-ga
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: cs
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The categories of this paper are: math
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The categories of this paper are: q-alg
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The categories of this paper are: q-bio
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The categories of this paper are: patt-sol
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The categories of this paper are: adap-org
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The categories of this paper are: quant-ph
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The categories of this paper are: stat
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The categories of this paper are: alg-geom
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The categories of this paper are: ao-sci
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The categories of this paper are: cmp-lg