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

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tens of visual magnitudes, hence probe deeply into the densest regions of molecular clouds. When correlated with the IR extinction in front of the same stars, which depends essentially on the dust grain size distribution, one has in principle (with sufficient IR data) a powerful tool to measure the metallicity of molecular clouds. This was done successfully by Vuong et al. (2003) for the nearby ρ Oph cloud (up to AV ∼ 50), resulting in a solar cloud metallicity (Z ∼ Z⊙). Other clouds were also studied, but the available data do not probe sufficiently dense regions to establish a good NH,X vs. AV correlation. 3.2.7 Dust around protostars The continuum emission (spectral and spatial distributions) from the dust in the protostellar envelopes gives important information on the structure of the envelope. The study of the dust continuum is in fact a technique used by several groups in the world. It is complementary to that exposed in §3.2.3, which uses the rotational transitions of molecules. Astromol has used both techniques wherever the opportunity presented (Maret et al. 2004). However, Astromol research on the dust continuum has been more original in the analysis of the dust features in the Far Infrared, and specifically in the range (45-200 µm) observed by the Long Wavelength Spectrometer (LWS) on board ISO. This range of wavelengths was thought to not contain any interesting dust feature. However, Astromol has revealed that an important feature is observed between 90 and 100 µm (Ceccarelli et al. 2002b). A systematic study of the LWS spectra of low to intermediate protostars has found that more than 50% of the protostars show up this feature (Chiavassa et al. 2005). The nature of the carrier of the observed feature is not totally sure. At present, the most reasonable hypothesis is that calcite is responsible for it. In support of this interpretation, very recently calcite has been revealed in the comet Temple 1 (Deep Impact mission; Lisse et al. 2005, IAU Circular 8571). This is an important observation, because it shows a clear link between the comets and the proto-stellar phase. Furthermore, and mostly important, the presence of calcite in protostars and comets rises the question of its formation. On Earth and in the Solar System objects (meteorites), calcite is formed by aqueous alteration. However, both in protostars and comets, evidently, no liquid water is present. We have proposed that the interaction of the X-rays emitted from the central object (§3.2.6) with the dusty envelope, could be at the origin of the calcite formation (Ceccarelli et al. 2002b). The interest in this discover is that, if the calcite interpretation is confirmed, this may have some far reaching consequences because the same mechanism forming calcite may be also form pre-biotic molecules. 3.3 Molecular Physics 3.3.1 Overview The near-future large scale observatories HERSCHEL and ALMA will open up the Universe to high spatial and spectral resolution studies of molecules. These new missions will make a major breakthrough in our knowledge of the key astrochemical processes involved in the origin and evolution of planets, stars, and galaxies. HERSCHEL and ALMA will lead to a multitude of molecular line data in a great variety of astrophysical environments. Identification, analysis and interpretation of this data in terms of the physical and chemical characteristics of the astronomical sources will require a concerted effort by physicists, chemists and astronomers in the areas of molecular spectroscopy, collisional excitation processes, chemical reactions, and astronomical modeling. In this ambitious context, our objective since 2002 is to focus our theoretical activity on the calculation and renewal of potential energy surfaces (PES) and collisional data for astrophysics. Several recent studies have shown that inaccuracies in the PES are indeed the largest source of error in collisional rate calculations. Furthermore, the standard quantum close-coupling method used to compute these rates is computationally efficient at low temperatures only. The development of reliable approximate quantum treatments or methods based on classical mechanics are thus highly desirable. The specific objectives of our theoretical work are therefore: • Calculations of PES at the highest level of accuracy by employing state-of-the-art ab initio methods. • Calculations of collisional rate constants by employing both full dimensional quantum calculations and practical quantum/classical approximations. 56
• Monitoring of the error propagation from the PES to the collisional rates, and subsequent monitoring of the collisional approximations, with first results for inelastic rotational rates involving CO, HC3N, (also H2O and NH3 in collab. with M.L. Dubernet and E. Roueff), and for H2O quenching.Corresponding tools will be included in the BASECOL database. Furthermore, the dependence of astronomical modeling to the accuracy of collisional rates is also a very challenging issue which our group has started to address. 3.3.2 Potential energy surfaces Within the Born-Oppenheimer approximation, inelastic cross sections and rate constants are obtained by solving for the motion of the nuclei on an “electronic” PES, which is independent of the masses of the nuclei. Recent studies have demonstrated that computational techniques employing advanced treatments for both electronic and nuclear motion problems have the ability to rival the accuracy of experimental data. These studies all employed convergent hierarchies of basis sets and correlation methods to solve the electronic structure problem. The CCSD(T)-R12 method In contrast to conventional calculations, correlated methods that include explicitly the inter-electronic coordinates into the wave function can describe properly the electron-electron correlation cusp and offer a direct way of reaching the basis set limit values within a single calculation, i.e. without extrapolation. Among various explicitly correlated methods, the R12 coupled cluster theory with singles, doubles and perturbative triples (CCSD(T)-R12) (Noga & Kutzelnigg 1994 J. Chem. Phys., 101, 7738) is computationally practical and proved highly accurate (Ramajäki et al. 2004 Mol. Phys, 102 2297), in particular using adequate R12-suited basis sets (Kedˇzuch et al. 2005 Mol. Phys., 103, 999). Generalizing the idea of Kutzelnigg (Kutzelnigg 1985 Theor. Chim. Acta, 68, 445), in CCSD(T)-R12 one takes care of the correlation cusp by inclusion of linear terms in the inter-electronic coordinates into the exponential wave function expansion. Our corresponding production code DIRCCR12 1 implements an original trick to accelerate the calculations of CCSD triples and is efficiently parallelized up to 6-8 processors. It provides auto-adaptative algorithms to handle load imbalance, heterogeneous processors and distributed scratch disks on clusters. It achieves a typical parallel performance over 500 Mflops per processor on the IBM Power4 Regatta supercomputer at IDRIS with minimal I/O bottlenecks. This code is routinely used either for conventional CCSD(T) calculations or for explicitely correlated CCSD(T)-R12 using our specifically developed R12-suited basis sets for H to Ne. H2O – H2 We have constructed a full nine-dimensional interaction potential for H2O – H2 calibrated using high-accuracy, explicitly correlated wave functions. All degrees of freedom are included using a systematic procedure transferable to other small molecules astrophysically or atmospherically relevant. CCSD(T)-R12 5D calibration calculations were run on the IDRIS and CINES national computers, while the Monte Carlo sampling of the 9D hypersurface was the first dimensioning application of the Grenoble computer grid (CiGri), developed with support from the ACI Grid. The resulting 9D hypersurface contains in particular all relevant information to describe the interaction of H2 with all H2O isotopomers in zero point or excited bending states. As a first application, we estimated rate constants for the vibrational relaxation of the ν2 bending mode of H2 O obtained from quasiclassical trajectory calculations in the temperature range of 500 – 4000 K. Our hightemperature (T > 1500 K) results are found compatible with the single experimental value at 295 K. Our rates are also significantly larger than those currently used in the astrophysical literature and will lead to a thorough reinterpretation of vibrationally excited water emission spectra from space (see Faure et al JCP 2005 122, 221102). In a second paper (Faure et al, JCP 2005 123 104309) we emphasized the role of rotation in the vibrational relaxation of water. As a further conclusion of this quasiclassical analysis, we also predict that the popular 1 see the repository http://www-laog.obs.ujf-grenoble.fr/∼valiron/ccr12/index.html for details on the code and for related bib- liography 57
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LABORATOIRE D’ASTROPHYSIQUE DE GR
Page 6 and 7: III Team ASTROMOL 41 2 Presentation
Page 8 and 9: 8.1.3 Graduate Students . . . . . .
Page 10 and 11: VI Team SHERPA 145 15 Results 147 1
Page 13: Part I Foreword: Presentation of th
Page 17: Part II Executive Summary A 18th ce
Page 20 and 21: of CNRS for technicians and enginee
Page 22 and 23: Figure 1.3: New LAOG organigram (20
Page 24 and 25: heart attack. Manuel went back to t
Page 26 and 27: Figure 1.6: PhD student repartition
Page 28 and 29: • LAOG researchers (and publishin
Page 30 and 31: and published 95 papers in four yea
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Page 34 and 35: 1.5 From dreams to reality: Human r
Page 36 and 37: and accretion disks with heavy nume
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Page 41: Part III TEAM ASTROMOL Sub-arcsecon
Page 44 and 45: • we develop quantum and classica
Page 46 and 47: Table shows not only the volume of
Page 48 and 49: • Herschel-HIFI: Astromol is invo
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Page 52 and 53: • The hot corinos. More spectacul
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Page 60 and 61: Rate constant (cm 3 s -1 ) 1e-09 1e
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Page 77: Part IV TEAM FOST The first image o
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equipments for these tasks, from de
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10.1.3 Current trend of large equip
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• Improving High Angular Resoluti
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Chapter 11 Results 11.1 Towards hig
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Figure 11.2: NAOS-CONICA image of t
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on PUEO at CFHT. The IFS experts (A
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Figure 11.5: Image of the binary st
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Figure 11.7: PICNIC low noise infra
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have taken responsibilities: A. Che
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Figure 11.10: thermal modeling of W
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Figure 12.1: All the GRIL projects
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12.2 Optical interferometry As for
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the VLTI. CHARA is equipped with an
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• ANR Alterdetect, with IMEP : si
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Mixed GRIL-other team profiles 1. A
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Name Grade Comm. Project Berger Jea
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• First fringes in the H band wit
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Table 15.1: List of the permanent S
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15.4 Transport phenomena in accreti
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Figure 15.2: Spectral energy distri
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states, combining a still powerful
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Excitation of turbulence by Cosmic
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Table 15.2: Former PhD students of
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Chapter 16 Perspectives The distinc
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Ray background. The second project
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164
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- Ceccarelli Cecilia (AT) - Delfoss
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Among the various areas of expertis
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-responsable du groupe ”logiciel
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Chef de l’ Equipe ASTROMOL du LAO
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jury de concours: 1 concours IR CNR
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Chapter 20 Appendix 4: The Jean Mar
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20.10 Formation des utilisateurs La
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