Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Continuum and CO/HCO+ Emission from the Disk Around the T Tauri Star
  LkCa 15   We present OVRO Millimeter Array lambda = 3.4 - 1.2 mm dust continuum and
spectral line observations of the accretion disk encircling the T Tauri star
LkCa 15. The 1.2 mm dust continuum emission is resolved, and gives a minimum
diameter of 190 AU and an inclination angle of 57+/-5 degrees. There is a
noticeable, but at present poorly constrained, decrease in the continuum
spectral slope with frequency that may result from the coupled processes of
grain growth and dust settling. Imaging of the fairly intense emission from the
lowest rotational transitions of CO, 13CO and HCO+ reveals a rotating disk and
emission extends to 750 AU and the characteristic radius of the disk is
determined to be around 425 AU (HWHM) based on model fits to the CO velocity
field. The disk mass derived from the CO isotopologues with ``typical'' dense
cloud abundances is still nearly two orders of magnitude less than that
inferred from the dust emission, which is probably due to extensive molecular
depletion in the cold, dense disk midplane. N2H+ 1-0 emission has also been
detected which, along with HCO+, sets a lower limit to the fractional
ionization of 10^{-8} in the near-surface regions of protoplanetary disks. This
first detection of N2H+ in circumstellar disks has also made possible a
determination of the N2/CO ratio (~2) that is at least an order of magnitude
larger than those in the envelopes of young stellar objects and dense clouds.
The large N2/CO ratio indicates that our observations probe disk layers in
which CO is depleted but some N2 remains in the gas phase. Such differential
depletion can lead to large variations in the fractional ionization with height
in the outer reaches of circumstellar disks, and may help to explain the
relative nitrogen deficiency observed in comets.

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The categories of this paper are: hep-ex
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The categories of this paper are: econ
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The categories of this paper are: mtrl-th
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The categories of this paper are: physics
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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: patt-sol
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The categories of this paper are: nlin
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The categories of this paper are: hep-lat
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The categories of this paper are: adap-org
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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
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The categories of this paper are: solv-int
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The categories of this paper are: supr-con
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The categories of this paper are: cs
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The categories of this paper are: bayes-an