Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Evidence for cold plasma in planetary nebulae from radio observations
  with the LOw Frequency ARray (LOFAR)   We present observations of planetary nebulae with the LOw Frequency ARray
(LOFAR) between 120 and 168 MHz. The images show thermal free-free emission
from the nebular shells. We have determined the electron temperatures for
spatially resolved, optically thick nebulae. These temperatures are 20 to 60%
lower than those estimated from collisionally excited optical emission lines.
This strongly supports the existence of a cold plasma component, which
co-exists with hot plasma in planetary nebulae. This cold plasma does not
contribute to the collisionally excited lines, but does contribute to
recombination lines and radio flux. Neither of the plasma components are
spatially resolved in our images, although we infer that the cold plasma
extends to the outer radii of planetary nebulae. However, more cold plasma
appears to exist at smaller radii. The presence of cold plasma should be taken
into account in modeling of radio emission of planetary nebulae. Modelling of
radio emission usually uses electron temperatures calculated from collisionally
excited optical and/or infrared lines. This may lead to an underestimate of the
ionized mass and an overestimate of the extinction correction from planetary
nebulae when derived from the radio flux alone. The correction improves the
consistency of extinction derived from the radio fluxes when compared to
estimates from the Balmer decrement flux ratios.

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The categories of this paper are: hep-lat
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The categories of this paper are: bayes-an
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The categories of this paper are: solv-int
1
The categories of this paper are: cs
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The categories of this paper are: adap-org
16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
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The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-fin
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The categories of this paper are: atom-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: funct-an
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The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci