Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Kinematics of Molecular Hydrogen Emission from Pre-planetary Nebulae:
  RAFGL 2688 and RAFGL 618   We present high spectral resolution maps of near-infrared molecular hydrogen
emission from the bipolar pre-planetary nebulae RAFGL 2688 and RAFGL 618,
obtained with the NOAO Phoenix spectrometer. The measured velocity gradients
along the polar axes of both nebulae indicate that the highest velocity gas
lies closest to the central stars. These results support the suggestion that
the polar H_2 emission regions of both nebulae contain shocked gas formed as
fast (~50-150 km/s), collimated, post-asymptotic giant branch (AGB) winds
collide with slower-moving (~10-20 km/s) material previously ejected while the
central stars were still on the AGB. The kinematics of H_2 emission
perpendicular to the polar axis of RAFGL 2688 are consistent with a model
combining expansion along the equator at 5-10 km/s with rotation about the
polar axis at 5-10 km/s. The rapid onset of the common envelope phase of a
close binary system may explain both the bipolar structure of RAFGL 2688 and
the presence and complex kinematics of its shocked H_2 emission.

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The categories of this paper are: plasm-ph
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The categories of this paper are: math-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: dg-ga
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The categories of this paper are: q-fin
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The categories of this paper are: cond-mat
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The categories of this paper are: acc-phys
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The categories of this paper are: eess
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The categories of this paper are: supr-con
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The categories of this paper are: nlin
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The categories of this paper are: solv-int
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The categories of this paper are: adap-org
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The categories of this paper are: stat
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-th
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The categories of this paper are: mtrl-th