Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Mid-Infrared Emission Features in the ISM: Feature-to-Feature Flux
  Ratios   Using a limited, but representative sample of sources in the ISM of our
Galaxy with published spectra from the Infrared Space Observatory, we analyze
flux ratios between the major mid-IR emission features (EFs) centered around
6.2, 7.7, 8.6 and 11.3 microns, respectively. In a flux ratio-to-flux ratio
plot of EF(6.2)/EF(7.7) as a function of EF(11.3)/EF(7.7), the sample sources
form roughly a $\Lambda$-shaped locus which appear to trace, on an overall
basis, the hardness of a local heating radiation field. But some driving
parameters other than the radiation field may also be required for a full
interpretation of this trend. On the other hand, the flux ratio of
EF(8.6)/EF(7.7) shows little variation over the sample sources, except for two
HII regions which have much higher values for this ratio due to an ``EF(8.6\um)
anomaly,'' a phenomenon clearly associated with environments of an intense
far-UV radiation field. If further confirmed on a larger database, these trends
should provide crucial information on how the EF carriers collectively respond
to a changing environment.

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The categories of this paper are: gr-qc
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The categories of this paper are: alg-geom
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The categories of this paper are: quant-ph
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The categories of this paper are: q-bio
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The categories of this paper are: nucl-th
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The categories of this paper are: cs
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The categories of this paper are: hep-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: dg-ga
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The categories of this paper are: mtrl-th
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The categories of this paper are: comp-gas
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The categories of this paper are: physics
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The categories of this paper are: chem-ph
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The categories of this paper are: math-ph
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The categories of this paper are: math
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The categories of this paper are: cond-mat