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

particular, we calculated a 9D H2O-H2 potential energy surface of unprecedented accuracy and complexity
(Faure et al 2005a). The associated quenching rate for vibrationally excited water has been calculated
using a classical Monte Carlo canonical approach which corrects by more than one order of magnitude
the existing estimations (Faure et al 2005b). These results will lead to a thorough re-interpretation of
vibrationally excited water emission spectra from space.
iv) We have also reconsidered the role of electrons in the collisional excitation of molecules in harsh environments
(PDR’s, planetary nebulae, etc) in collab. with the group of J. Tennyson at UCL. Rotational
transitions with ∆J > 1, which are neglected in pure dipolar approximations, were found to have rate
constants similar or even larger than those with ∆J = 1. Results of astrophysical relevance have been
obtained for H + 2 , CO+ , NO + , HCO + , H + 3 , H3O + , and asymmetric-top isotopologs of water H2O, HDO
and D2O (Faure et al. 2004 and references therein).
3.2 Star Formation
3.2.1 Overview
Astromol members carry out observational and theoretical studies of the star formation process. These cover
low to high mass (§3.2.5) stars, and concern the very first stages represented by the Molecular Clouds and
Pre-Collapse phases to the last phases before the so called Pre-Main-Sequence (PMS) phase, which is a target
of the FOST team research. Specifically, Astromol studies focus on:
• Molecular Clouds, as the nurseries of newly forming stars (§3.2.2, 3.2.6);
• Pre-Stellar Cores, the condensations just before the collapse sets in ((§3.2.2);
• Class 0 sources, believed to be the youngest known protostars (§3.2.2, 3.2.3, 3.2.6, 3.2.7);
• Class I sources, believed to represent the transition between Class 0 sources and PMS objects (§3.2.2,
3.2.3, 3.2.6, 3.2.7);
• Proto-planetary disks (this part is described in §3.5)
• Molecular outflows, the result of the interaction of the material ejected during the Class 0 and Class I
phases with the surrounding Molecular Clouds (§3.2.4).
To study the formation of the stars and how this influences the surroundings, Astromol members use observational
facilities which span the X-ray (§3.2.6) to radio frequency range. In addition, although molecular
spectroscopy is the Astromol privileged tool to study star forming regions, also dust continuum emission and
features (§3.2.7) have been used by the Astromol members. Consequently, a wide range of models is developed
to interpret such a wide range of observations. The following sections give a brief summary of the Astromol
research in the mentioned fields.
3.2.2 The deuteration in the first phases of star formation
Molecular deuteration was considered sort of a solved problem in Astrophysics, until the first detections of
multiply deuterated molecules in low mass star forming regions, which showed molecular D/H ratios enhanced
by up to 8 orders of magnitude with respect to the elemental D/H ratio (Ceccarelli et al. 1998 A&A 338, L43;
2001 A&A 372, 998; 2002 A&A 381, L17; Loinard et al. 2000 A&A 359, 1169; 2001 ApJ 552, L173). The
current models were unable to fully explain those observations (e.g. Roberts & Millar 2002, A&A 361, 388).
Astromol observational work in the 2002-2005 period has helped to solve the problem, which now is much better
mastered. Specifically, the following aspects were elucidated:
• The extreme deuteration observed in low mass protostars sets on during the pre-collapse phase, when the
matter is very dense (≥ 10 6 cm −3 ) and cold (≤ 10 K). This is in the so called Pre-Stellar-Core phase. A
key factor which makes the deuteration so extreme is the CO freeze-out onto the grain mantles (Bacmann
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