Untitled - Laboratoire d'Astrophysique de l'Observatoire de Grenoble

Figure 3.7: Detection of HDO in the proto-planetary disk surrounding the solar type protostar DM Tau (Ceccarelli
et al. 2005). The figure shows the HDO ground state transition at 464 GHz, which has been observed
in absorption against the continuum emitted by the cold dust in the disk midplane. The fact that the line is in
absorption implies that vapor water forms a blanket covering the entire disk of DM Tau.
surfaces irradiated by X-rays. These experiments aim to simulate the conditions in the proto-planetary disks
surrounding solar type protostars, which are known to be strong X-rays emitters (§3.2.6 and 3.2.7).
In the incoming years, we plan to increase the Astromol involvement in the studies of the proto-planetary
disks, notably their chemical and physical structure. This will also involve a more systematic use of the interferometric
instruments (today Plateau de Bure, tomorrow ALMA), in addition to the already used millimeter
and sub-millimeter single dishes (IRAM-30m, JCMT and CSO).
Meanwhile, Astromol has obtained the following important results on the study of young gas rich protoplanetary
disks:
• The discovery of a way to probe the cold gas in the disk midplane. The midplane of the young protoplanetary
disks that surround Sun-like protostars is so cold and dense that all heavy-elements molecules,
included CO, condense onto the grain mantles, disappearing from the gas phase. Since the bulk of the mass
of the disk resides in the midplane, it is of paramount importance to have a way to probe this component,
for studying how the disk evolves: the condensation of the dust, the dispersion of the gas, etc... Astromol,
using the knowledge acquired in its studies on the molecular deuteration (§3.2.2), has proposed to observed
the ground state transition of the H2D + molecular ion, and obtained the first detections in 2004 (Ceccarelli
et al. 2004). The H2D + observations not only provide the first means to probe the disk midplane, but
they also provide a means to measure its ionization degree, a key parameter in the theories of viscous
accretion of proto-planetary disks (Ceccarelli & Dominik 2005).
• The discovery of deuterated water vapor in proto-planetary disks. In general, water is a key molecule
to observe, because it is a major actor in the cooling of the gas, as well as in its chemical composition.
Deuterated water has the additional interest that the Oceans on the Earth are believed to be formed by the
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