Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cold Disks: Spitzer Spectroscopy of Disks around Young Stars with Large
  Gaps   We have identified four circumstellar disks with a deficit of dust emission
from their inner 15-50 AU. All four stars have F-G spectral type, and were
uncovered as part of the Spitzer Space Telescope ``Cores to Disks'' Legacy
Program Infrared Spectrograph (IRS) first look survey of ~100 pre-main sequence
stars. Modeling of the spectral energy distributions indicates a reduction in
dust density by factors of 100-1000 from disk radii between ~0.4 and 15-50 AU,
but with massive gas-rich disks at larger radii. This large contrast between
the inner and outer disk has led us to use the term `cold disks' to distinguish
these unusual systems. However, hot dust [0.02-0.2 Mmoon] is still present
close to the central star (R ~0.8 AU). We introduce the 30/13 micron, flux
density ratio as a new diagnostic for identifying cold disks. The mechanisms
for dust clearing over such large gaps are discussed. Though rare, cold disks
are likely in transition from an optically thick to an optically thin state,
and so offer excellent laboratories for the study of planet formation.

27
The categories of this paper are: comp-gas
4
The categories of this paper are: cond-mat
9
The categories of this paper are: nlin
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
22
The categories of this paper are: chao-dyn
24
The categories of this paper are: dg-ga
28
The categories of this paper are: alg-geom
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
20
The categories of this paper are: acc-phys
12
The categories of this paper are: nucl-th
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
15
The categories of this paper are: nucl-ex