Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Kn 26, a New Quadrupolar Planetary Nebula   Once classified as an emission line source, the planetary nebula (PN) nature
of the source Kn 26 has been only recently recognized in digital sky surveys.
To investigate the spectral properties and spatio-kinematical structure of Kn
26, we have obtained high spatial-resolution optical and near-IR narrow-band
images, high-dispersion long-slit echelle spectra, and intermediate-resolution
spectroscopic observations. The new data reveal an hourglass morphology typical
of bipolar PNe. A detailed analysis of its morphology and kinematics discloses
the presence of a second pair of bipolar lobes, making Kn 26 a new member of
the subclass of quadrupolar PNe. The time-lap between the ejection of the two
pairs of bipolar lobes is much smaller than their dynamical ages, implying a
rapid change of the preferential direction of the central engine. The chemical
composition of Kn 26 is particularly unusual among PNe, with a low N/O ratio
(as of type II PNe) and a high helium abundance (as of type I PNe), although
not atypical among symbiotic stars. Such an anomalous chemical composition may
have resulted from the curtail of the time in the Asymptotic Giant Branch by
the evolution of the progenitor star through a common envelope phase.

15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
13
The categories of this paper are: quant-ph
24
The categories of this paper are: dg-ga
1
The categories of this paper are: cs
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
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The categories of this paper are: chao-dyn
11
The categories of this paper are: hep-lat
35
The categories of this paper are: mtrl-th
9
The categories of this paper are: nlin
23
The categories of this paper are: solv-int
26
The categories of this paper are: bayes-an