Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The HCN/HNC abundance ratio toward different evolutionary phases of
  massive star formation   Using the HCN and HNC J=1--0 line observations, the abundance ratio of
HCN/HNC has been estimated for different evolutionary stages of massive star
formation: Infrared dark clouds (IRDCs), High-mass protostellar object (HMPOs),
and Ultra-compact HII regions (UCHIIs). IRDCs were divided into `quiescent IRDC
cores' and `active IRDC cores', depending on star formation activity. The
HCN/HNC ratio is known to be higher at active and high temperature regions
related to ongoing star formation, compared to cold and quiescent regions. Our
observations toward 8 quiescent IRDC cores, 16 active IRDC cores, 23 HMPOs, and
31 UCHIIs show consistent results; the ratio is 0.97~($\pm~0.10$),
2.65~($\pm~0.88$), 4.17~($\pm~1.03$) and 8.96~($\pm~3.32$) in these respective
evolutionary stages, increasing from quiescent IRDC cores to UCHIIs. The change
of the HCN/HNC abundance ratio, therefore, seems directly associated with the
evolutionary stages of star formation, which have different temperatures. One
suggested explanation for this trend is the conversion of HNC to HCN, which
occurs effectively at higher temperatures. To test the explanation, we
performed a simple chemical model calculation. In order to fit the observed
results, the energy barrier of the conversion must be much lower than the value
provided by theoretical calculations.

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The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
16
The categories of this paper are: stat
9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
8
The categories of this paper are: hep-ex
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
24
The categories of this paper are: dg-ga
2
The categories of this paper are: math
0
The categories of this paper are: hep-ph
34
The categories of this paper are: chem-ph