Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Constraints on Planetesimal Collision Models in Debris Disks   Observations of debris disks offer a window into the physical and dynamical
properties of planetesimals in extrasolar systems through the size distribution
of dust grains. In particular, the millimeter spectral index of thermal dust
emission encodes information on the grain size distribution. We have made new
VLA observations of a sample of seven nearby debris disks at 9 mm, with 3"
resolution and $\sim5$ $\mu$Jy/beam rms. We combine these with archival ATCA
observations of eight additional debris disks observed at 7 mm, together with
up-to-date observations of all disks at (sub)millimeter wavelengths from the
literature to place tight constraints on the millimeter spectral indices and
thus grain size distributions. The analysis gives a weighted mean for the slope
of the power law grain size distribution, $n(a)\propto a^{-q}$, of $\langle q
\rangle = 3.36\pm0.02$, with a possible trend of decreasing $q$ for later
spectral type stars. We compare our results to a range of theoretical models of
collisional cascades, from the standard self-similar, steady-state size
distribution ($q=3.5$) to solutions that incorporate more realistic physics
such as alternative velocity distributions and material strengths, the
possibility of a cutoff at small dust sizes from radiation pressure, as well as
results from detailed dynamical calculations of specific disks. Such effects
can lead to size distributions consistent with the data, and plausibly the
observed scatter in spectral indices. For the AU Mic system, the VLA
observations show clear evidence of a highly variable stellar emission
component; this stellar activity obviates the need to invoke the presence of an
asteroid belt to explain the previously reported compact millimeter source in
this system.

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The categories of this paper are: bayes-an
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The categories of this paper are: nucl-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: solv-int
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The categories of this paper are: nlin
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The categories of this paper are: math-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-ex
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The categories of this paper are: eess
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The categories of this paper are: econ
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The categories of this paper are: supr-con
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The categories of this paper are: alg-geom
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The categories of this paper are: adap-org
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The categories of this paper are: plasm-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: math