Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Radio Recombination Lines in Galactic HII Regions   We report radio recombination line (RRL) and continuum observations of a
sample of 106 Galactic HII regions made with the NRAO 140 Foot radio telescope
in Green Bank, WV. We believe this to be the most sensitive RRL survey ever
made for a sample this large. Most of our source integration times range
between 6 and 90 hours which yield typical r.m.s. noise levels of 1.0--3.5
milliKelvins. Our data result from two different experiments performed,
calibrated, and analyzed in similar ways. A CII survey was made at 3.5 cm
wavelength to obtain accurate measurements of carbon radio recombination lines.
When combined with atomic (CI) and molecular (CO) data, these measurements will
constrain the composition, structure, kinematics, and physical properties of
the photodissociation regions that lie on the edges of HII regions. A second
survey was made at 3.5 cm wavelength to determine the abundance of 3He in the
interstellar medium of the Milky Way. Together with measurements of the 3He+
hyperfine line we get high precision RRL parameters for H, 4He, and C. Here we
discuss significant improvements in these data, with both longer integrations
and newly observed sources.

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The categories of this paper are: hep-ph
22
The categories of this paper are: chao-dyn
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The categories of this paper are: cs
28
The categories of this paper are: alg-geom
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
18
The categories of this paper are: econ
19
The categories of this paper are: eess
12
The categories of this paper are: nucl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: math
10
The categories of this paper are: q-bio
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The categories of this paper are: q-fin
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-ex