LERMA UMR8112

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



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Collisional Excitation and Reactivity of Interstellar Molecules

by Jean-Hugues Fillion, Mathieu Bertin - published on , updated on

Members

F. Dayou (Ass. Prof.), C. Balança (Ass. Prof.), A. Spielfiedel (researcher CNRS), L. Tchang-Brillet (Prof.), N. Feautrier (voluntary researcher), I. Oueslati (PhD student)

Context

Informations on the physical conditions and chemical abundances in astrophysical environments can be deduced from observation of the emitted light by modeling the profiles (intensities and shapes) of the atomic and molecular spectral lines. In order to retrieve a reliable diagnostic, it is mandatory to know with precision the main excitation mechanisms that drive the populations among the quantum states of atoms and molecules, namely, the radiative energy transfers and inelastic collisions with the main perturbers. In addition, the confrontation of the molecular abundances inferred from the spectra with those predicted by chemical models based on reactions networks serve to trace back the evolution of matter in the observed media. In that case, detailed informations on a wealth of chemical and photo-induced reactions taking place in the gas-phase and on dust grains are necessary to properly describe the mechanisms of molecular synthesis in astrophysical environments.

Research Activities


Science developed within our group aims at studying fundamental properties of atoms and molecules by means of methodology developments and numerical simulations. A common thread to our investigations is to characterize how atomic and molecular systems interact with their environment, being light, others isolated species or solid materials. Quantum chemistry methods are employed to determine the properties (structure, energetics, charge distributions and electric properties) of the interacting systems, being in their ground or excited electronic states. From these calculated properties, the parameters relevant to astrophysical modelings are then derived from dynamics simulations based on quasi-classical and quantum (time-dependent and time-independent) methods, thereby providing valuable informations on the microscopic mechanisms for the process under study.

Several issues are currently addressed along these lines in our group, such as the gas-phase collisional processes that drive the ro-vibrational excitation of neutral and ionic molecular species relevant to probe interstellar and circumstellar media. Similar works concern the electronic excitation of neutral and ionised atomic elements of interest for the study of stellar atmospheres. Poorly known gas-phase reactions are also studied, in particular chemical reactions involving small neutral radicals that can still be fast down to the very low temperatures of dense molecular clouds, as well as photo-induced processes for small molecular species playing an important role in photodissociation regions. Heterogeneous chemistry is considered too, using large cluster molecules as models of solid materials to describe the chemical reactions taking place at the surface of dry dust grains.

Developed themes & collaborations

  • Ro-vibrational excitation of molecules by collisions IPAG (Grenoble), LOMC (Univ. Le Havre), LSAMA (Univ. Tunis), CAB. INTA (CSIC, Madrid, Spain), IEM (CSIC, Madrid, Spain), IFF (CSIC, Madrid, Spain), CIQ (Univ. Morelos, Cuernavaca, Mexico)
  • Electronic excitation of atomic species by collisions LMSME (Univ. Marne-la-Vallée), Herzen Univ. (St Petersburg, Russia), Uppsala Univ. (Uppsala, Sweden)
  • Gas-phase chemical and photo-induced reactions PhLAM (Univ. Lille 1), ISM (Univ. Bordeaux), IPR (Univ. Rennes 1), ICB (Univ. Dijon), INSTEC (La Havana, Cuba), IFF (CSIC, Madrid, Spain), QFA (Univ. Autonoma, Madrid, Spain)
  • Formation mechanisms of small molecules on silicate dust grains LPMC (Univ. Tunis)

Fundings

National Program of CNRS "Physique et Chimie du Milieu Interstellaire" (PCMI)
National Program of CNRS "Physique Stellaire" (PNPS)
Specific Action GAIA (AS GAIA)

Séminaires à venir

Vendredi 19 juillet 2019, 14h00
Salle de l'atelier, Paris
Magnetic fields in Young Protostellar Disks and Jets, and some Astro-chemistry
Chin Fei Lee
ASIAA, Taiwan
résumé :
Magnetic fields in Young Protostellar Disks and Jets, and some Astro-chemistry
Chin Fei Lee, ASIAA Taiwan

I will present our recent ALMA observations towards 3 young protostellar
systems, reporting the possible field morphology in their disks and jets.
In particular, I will report the field morphology implied from the dust
polarizations and SiO line polarizations, and discuss the possible toroidal
and poloidal fields in the disks and jets. I will also discuss the
formation process and the growth of the protostellar disks, and the possible
magnetic braking that reduces the angular momentum in the envelope.
Interestingly, more than 10 organic molecules including prebiotic molecules
are detected in the atmosphere of one of the disks. I will compare their
abundances to those in the hot corinos around low-mass protostars and touch
on the possible formation mechanism of those molecules. Some of the
molecules seem to be formed on CO icy grains and some in the gas phase.
 
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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