Issue |
A&A
Volume 440, Number 2, September III 2005
|
|
---|---|---|
Page(s) | 583 - 593 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20052991 | |
Published online | 01 September 2005 |
Deuterated H3^+ in proto-planetary disks
1
Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 09, France e-mail: cecilia.ceccarelli@obs.ujf-grenoble.fr
2
Sterrenkundig Instituut “Anton Pannekoek”, Kruislaan 403, 1098SJ Amsterdam, The Netherlands
Received:
4
March
2005
Accepted:
6
June
2005
Probing the gas and dust in proto-planetary disks is central
for understanding the process of planet formation. In disks
surrounding solar type protostars, the bulk of the disk mass resides
in the outer midplane, which is cold (≤20 K), dense (≥107 cm-3) and depleted of CO.
Observing the disk midplane
has proved, therefore, to be a formidable challenge. Ceccarelli et al. (2004) detected
H2D+ emission in a proto-planetary disk
and claimed that it probes the midplane gas. Indeed, since all
heavy-elements bearing molecules condense out onto the grain
mantles, the most abundant ions in the disk midplane are predicted
to be H and its isotopomers. In this article, we carry out a
theoretical study of the chemical structure of the outer midplane of
proto-planetary disks. Using a self-consistent physical model for
the flaring disk structure, we compute the abundances of H
and
its deuterated forms across the disk midplane. We also provide the
average column densities across the disk of H
, H2D+,
HD
and D
, and line intensities of the ground transitions
of the ortho and para forms of H2D+ and HD
respectively.
We discuss how the results depend on the cosmic ray
ionization rate, dust-to-gas ratio and average grain radius, and
general stellar/disk parameters. An important factor is the poorly
understood freeze-out of N2 molecules onto grains, which we
investigate in depth. We finally summarize the diagnostic values of
observations of the H
isotopomers.
Key words: ISM: abundances / ISM: molecules / stars: formation / astrochemistry / planetary systems: protoplanetary disks
© ESO, 2005
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