Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Variability of Disk Emission in Pre-Main Sequence and Related Stars. I.
  HD 31648 and HD 163296 - Isolated Herbig Ae Stars Driving Herbig-Haro Flows   Infrared photometry and spectroscopy covering a time span of a quarter
century are presented for HD 31648 (MWC 480) and HD 163296 (MWC 275). Both are
isolated Herbig Ae stars that exhibit signs of active accretion, including
driving bipolar flows with embedded Herbig-Haro (HH) objects. HD 163296 was
found to be relatively quiescent photometrically in its inner disk region, with
the exception of a major increase in emitted flux in a broad wavelength region
centered near 3 microns in 2002. In contrast, HD 31648 has exhibited sporadic
changes in the entire 3-13 micron region throughout this span of time. In both
stars the changes in the 1-5 micron flux indicate structural changes in the
region of the disk near the dust sublimation zone, possibly causing its
distance from the star to vary with time. Repeated thermal cycling through this
region will result in the preferential survival of large grains, and an
increase in the degree of crystallinity. The variability observed in these
objects has important consequences for the interpretation of other types of
observations. For example, source variability will compromise models based on
interferometry measurements unless the interferometry observations are
accompanied by nearly-simultaneous photometric data.

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The categories of this paper are: funct-an
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The categories of this paper are: bayes-an
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The categories of this paper are: alg-geom
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The categories of this paper are: plasm-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: chao-dyn
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The categories of this paper are: supr-con
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The categories of this paper are: math-ph
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The categories of this paper are: cs
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The categories of this paper are: math
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The categories of this paper are: eess
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ph
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The categories of this paper are: solv-int
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The categories of this paper are: chem-ph
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The categories of this paper are: physics