LERMA UMR8112

Laboratoire d’Études du Rayonnement et de la Matière en Astrophysique et Atmosphères



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Study of van der Waals systems for Astrophysics and for Planetology

by Mathieu Bertin - published on , updated on

Team

M.L. Dubernet (Astronomer, Observatoire de Paris), C. Boursier (50%, Lecturer, UPMC), E. Quintas-Sanchez (Post-Doc 2015-2016, Observatoire de Paris), P. Tuckey (Syrte, Astronomer, Observatoire de Paris), C. M. Zwölf* (Senior Software Engineer, Observatoire de Paris), N. Moreau* (Software Engineer, Observatoire de Paris), Y.A. Ba* (Software Engineer, Observatoire de Paris)
* on databases and VAMDC

Research

The study of the dynamics of van der Waals systems allows to calculate microscopic quantities that are of interest both for the analysis of spectra and the modelisation of the interstellar medium, of solar planetary, exo-planets and cometary atmospheres.
By van der Waals systems we mean 2-body non-reactive systems between an atom and a molecule, and/or between molecules (the 3-body systems are irrelevant for the above astrophysical applications).

Potential energy surface of HCS+ - He (M.-L. Dubernet, P. Tuckey, E. Sanchez-Quintas, submitted to JCP 2015)

Our theoretical activities include:

  • the calculation of non-reactive potential energy surfaces via ab initio quantum chemistry
  • the calculation of van der waals bound states, the comparison between experimental results and theoretical values allowing to test some range of the potential energy surface
  • the determination of collisional excitation rate coefficients of neutral/ionic molecules by atoms and/or molecules. These calculations use the above potential energy surfaces combined with either quantum or semi-classical dynamical calculations
  • the determination of pressure molecular line broadening and shitfting coefficients using quantum and/or semi-classical methodologies

Our expertise includes an experimental expertise on collisional relaxation of molecules, the collection, evaluation and diffusion of collisional data through the BASECOL database and the interoperable access to many atomic and molecular databases through the VAMDC Consortium that we lead at present. The activities related to databases and VAMDC are linked to the "Tâche de Service" SO5 of CNRS-INSU-AA.

"Rotational excitation of 45 levels of ortho/para—H2O by excited ortho/para—H2 from 5K to 1500K: state-to-state, effective and thermalized rate coefficients (F. Daniel, M.L. Dubernet, A. Grosjean, A.&A., 2011, 536 p A76+"
State-to-state cross-sections in _A2 as a function of relative kinetic energy (in cm-1) for the para-H2O transitions: from level 4(211) to 1(000) (1a), to 2(111) (1b), to 3(202) (1c); from level 7(322) to 1(000) (2a), to 2(111) (2b), to 4(211); and from level 16(440) to 2(111) (3a), to 10(331) (3b), to 14(524) (3c), with the following para-H2 transitions: j2 = 0 -> j’2 = 0 (black), j2 = 0 -> j’2 = 2 (red), j2 = 2 -> j’2 = 0 (green) and j2 = 2 -> j’2 = 2 (blue)

Research Collaborations

Our activities are carried out in collaboration with astrophysical colleagues who regularly use our results in their modelisation and/or in their interpretation of observed spectra. We have co-directed the FP6-RTN project "Molecular Universe" and we were part of a key project in HERSCHEL. At present C. Boursier is co-I of a project called « Non-LTE diagnostics of CIRS observations of Titan’s mesosphere ». This is a CDAPS project (Cassini Data Analysis and Participating Scientists from NASA whose PI is Dr. A. Kutepov (the Catholic University of America).
Some of the theoretical activities are carried out in collaboration with groups exploring either new methodologies or new dynamical effects (Dr T. Stoecklin’s group from University of Bordeaux and Prof. D. Babikov’s group from Milwaukee University, USA).

Contracts

The activities are supported via european projects (FP6-RTN "Molecular Universe", the overheads of the e-science FP7 "VAMDC project", the ASTRONET CATS project, via the national program: " Physico-Chimie du Milieu Interstellaire (PCMI)" and "Planétologie (PNP)". Calculations are carried out on the group’s cluster, on Paris Observatory clusters, on MesoPSL and on national facilities at IDRIS and CINES.
The BASECOL database and the VAMDC activities have been supported by 2 european FP7 e-science contracts (2009-2012, 2012-2014), by the ASTRONET CATS project and by some support from Paris Observatory Scientific Councel.

Past Members

• F. Daniel (PhD - 2004-2007), (calculations on N2H+ — He, H2O—H2), PhD de l’Ecole Doctorale Astronomie et Astrophysique, ED127, at present post-doc at Grenoble Observatory
• S. Marinakis (Post-Doc, 2009-10) (calculations on CS-H2 and BASECOL), ASTRONET CATS contract, presently Oxford University
• L. Nenadovic (Software Engineer, 2010-2012) (VAMDC, SPECTCOL, VAMDC contract, at present student
• M. Doronin (Software Engineer, 2010-2012) (VAMDC standards, Portal, BASECOL), VAMDC Contract, presently PhD LERMA-LCT
• S. Pilon (Communication, 2013) (VAMDC), VAMDC Overheads
• Y.A. Ba (Software Engineer, 2011-2014) (BASECOL, SPECTCOL), VAMDC Contract, VAMDC Overheads, SUP@VAMDC Contract, at present permanent staff at Paris Observatory
• F. Portier (Technology Transfer, 2014), (SUP@VAMDC), SUP@VAMDC Contract & SUP@VAMDC Overheads
• M. Ivanov (Post-Doc, 2013) (semi-classical method, H2O-He), VAMDC Overheads
• E. Quintas-Sanchez (Post-Doc, 2014) (QCT calculations, PES of H2O- HCN), VAMDC Overheads

Visitors

• A. Semenov (PhD of Prof. D. Babikov, Milwaukee University), (semi-classical method, H2O-He), 2014

Key References

• The water series of papers (M.L. Dubernet, F. Daniel, A. Grosjean)
• The BASECOL reference paper (M.L. Dubernet et al, A.&A., 2013, vol. 553, p A50)
• The VAMDC reference paper (M.L. Dubernet et al., JQSRT, 2010, vol. 210, p 2151)

Séminaires à venir

Vendredi 20 septembre 2019, 14h00
Atelier, Paris
Challenging a Newtonian prediction through Gaia wide binaries
Xavier HERNANDEZ
UNAM, Mexico
résumé :
Under Newtonian dynamics, the relative motion of the components of a binary star should follow a Keplerian scaling with separation. Once orientation effects and a distribution of ellipticities are accounted for, dynamical evolution can be modelled to include the effects of Galactic tides and stellar mass perturbers. This furnishes a prediction for the relative velocity between the components of a binary and their projected separation. After reviewing recent work evidencing the existence of a critical acceleration scale in Elliptical Galaxies and Globular Clusters, I will show new results showing such a phenomenology in Gaia wide binaries using the latest and most accurate astrometry available. The results are consistent with the Newtonian prediction for projected separations below 7000 AU, but inconsistent with it at larger separations, where accelerations are expected to be lower than the critical a0 value of MONDian gravity. This result challenges Newtonian gravity at low accelerations and shows clearly the appearance of gravitational anomalies of the type usually attributed to dark matter at galactic scales, now at much smaller stellar scales.


 
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