Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Deuterated molecules in DM Tau: DCO+, but no HDO   We report the detection of the J=2-1 line of DCO+ in the proto-planetary disk
of DM Tau and re-analyze the spectrum covering the 465 GHz transition of HDO in
this source, recently published by Ceccarelli et al. (2005). A modelling of the
DCO+ line profile with the source parameters derived from high resolution HCO+
observations yields a DCO+/HCO+ abundance ratio of about 0.004, an order of
magnitude smaller than that derived in the low mass cores. The re-analysis of
the 465 GHz spectrum, using the proper continuum flux (0.5 Jy) and source
systemic velocity (6.05 km/s), makes it clear that the absorption features
attributed to HDO and C6H are almost certainly unrelated to these species. We
show that the line-to-continuum ratio of an absorption line in front of a
Keplerian disk can hardly exceed the ratio of the turbulent velocity to the
projected rotation velocity at the disk edge, unless the line is optically very
thick (tau > 10 000). This ratio is typically 0.1-0.3 in proto-planetary disks
and is about 0.15 in DM Tau, much smaller than that for the alleged absorption
features. We also show that the detection of H2D+ in DM Tau, previously
reported by these authors, is only a 2-sigma detection when the proper velocity
is adopted. So far, DCO+ is thus the only deuterated molecule clearly detected
in proto-planetary disks.

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The categories of this paper are: supr-con
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-lat
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The categories of this paper are: comp-gas
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The categories of this paper are: stat
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The categories of this paper are: chem-ph
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The categories of this paper are: q-bio
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The categories of this paper are: hep-ph
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The categories of this paper are: math
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The categories of this paper are: alg-geom
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The categories of this paper are: ao-sci
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The categories of this paper are: cmp-lg
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The categories of this paper are: nucl-ex
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The categories of this paper are: bayes-an
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The categories of this paper are: dg-ga
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The categories of this paper are: q-alg