Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Extinction due to amorphous carbon grains in red quasars from the SDSS   We construct a quasar extinction curve based on the blue and red composite
quasar spectra of Richards et al. (2003) prepared from the SDSS survey. This
extinction curve does not show any traces of the 2200 A feature characteristic
of the Interstellar Medium, and this indicates that graphite grains are likely
absent close to quasar nuclei. The extinction is best modeled by AC amorphous
carbon grains, assuming a standard distribution of grain sizes (p=3.5) but
slightly larger minimum grain size (a_{min} = 0.016 microns) and lower maximum
grain size (a_{min} = 0.12 microns) than the respective canonical values for
the interstellar medium. The dust composition is thus similar to that of the
dust in AGB stars. Since graphite grains form from amorphous carbon exposed to
strong UV irradiation the results indicate that either the dust forms
surprisingly far from the active nucleus or in a wind that leaves the nucleus
quickly enough to avoid crystallization into graphite.

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The categories of this paper are: plasm-ph
0
The categories of this paper are: hep-ph
12
The categories of this paper are: nucl-th
13
The categories of this paper are: quant-ph
31
The categories of this paper are: ao-sci
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The categories of this paper are: eess
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The categories of this paper are: nucl-ex
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The categories of this paper are: cond-mat
5
The categories of this paper are: gr-qc
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The categories of this paper are: q-alg
2
The categories of this paper are: math
36
The categories of this paper are: cmp-lg
10
The categories of this paper are: q-bio
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The categories of this paper are: patt-sol
14
The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th