LERMA UMR8112

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



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Spin, Photons and Ices

by Jean-Hugues Fillion - published on , updated on

Team Composition

Xavier Michaut (Ass. Prof. – Team leader), Jean-Hugues Fillion (Prof.), Mathieu Bertin (Ass. Prof.), Géraldine Féraud (Ass. Prof.), Laurent Philippe (Ass. Prof.), Pascal Jeseck (Engineer), Thomas Putaud (PhD student), Rémi Dupuy (PhD student)

Context

The colder parts of space presents a high variety of molecules, ranging from the simplest ones ( H2, H2O or CO), to organics of increasing complexity (alcohols, aldehydes, carboxylic acids…). The advent of new earth-based or space radiotelescopes allows for their detection with increasing precision in star or planet-forming regions, as well as the determination of their intrinsic molecular properties such as their nuclear spin state, that may be linked to the thermal history of these species.
In these regions, the extremely low temperatures (10-100 K) imply that the majority of the complex molecules forms or condenses onto dust grains, forming ice mantles that constitute the main molecular reservoir. Sublimation of those ices continuously enriches the gas phase, and therefore determines its composition and abundance ratios, and influences the intrinsic properties of the gaseous molecules. Desorption phenomenon and exchange between gas and solid phases are thus a key step that needs to be considered in order to get a better understanding of the observations in the cold regions of the interstellar medium.

The Team

The group “Spins, Photons and Ices” is an experimental physics team, whose interest lies on adsorption and desorption of astrophysics-relevant molecules, and on their role in the quantum states – in particular nuclear spin states – of desorbed molecules. The experiments performed by the team aim at simulating these processes in laboratory, with the objective to quantitatively understand them at a microscopic scale. For this purpose, spectroscopic methods are used (mass spectrometry, mid and very high resolution infrared spectroscopy, multiphoton laser spectroscopy…), together with vacuum, ultrahigh vacuum and cryogenic techniques to mimic the extreme conditions of the interstellar medium.
The team has at its disposal two complementary experimental setups. The SPICES setup is an ultrahigh vacuum setup (pressure E-10 Torr), in which molecular ices and adsorption and – thermal or photo-induced – desorption processes studies are carried-on. SPICES is designed to be adaptable to several kinds of light sources, for spectroscopy or to simulate the interstellar radiation fields: IR to VUV laser sources, available at the laboratory, or synchrotron light source (DESIRS beamline, SOLEIL synchrotron at St Aubin – France) with which part of the experiments is realized. The second setup, the CoSpiNu setup, is designed for the study of small, astrophysics-relevant molecules, in gas phase, at solid-gas interface or trapped in noble gas matrices at very low temperatures. The setup comprises an in-vacuum, very high resolution Fourier Transform InfraRed (FTIR) spectrometer, able to detect very small amounts of gaseous molecules, and to determine their nuclear spin state and its evolution.

Developed themes & collaborations

  • Adsorption and thermal desorption of atoms and molecules from astrophysics-relevant surfaces – SPICES setup, PhD of M. Doronin, collaborations with Y. Ellinger, A. Markovitz, F. Pauzat (LCT - Paris).
  • UV Photo-induced desorption: quantification and molecular mechanisms – SPICES setup, collaborations with H. Linnartz (Leiden Observatory - NL), K. Öberg (Harvard Smithsonian - USA), V. Baglin (CERN - CHE). Experiments realized partly at the SOLEIL synchrotron (France).
  • Nuclear spin conversion in noble gas matrices and at the solid-gas equilibrium –CoSpiNu setup, collaborations with C. Pardaneau, S. Coussan, C. Martin (PIIM – Marseille), P. Cacciani, M. Khelkhal et J. Cosleou (PhLAM – Lilles), P. Ayotte, P.-A. Turgeon, J. Vermette (Sherbrook University, Canada).
  • Desorption processes and its influence on quantum states of gas phase molecules – SPICES and CoSpiNu setups

Contracts and fundings : ANR Gasospin (ANR-09-BLAN-0066-01), National Program of CNRS « Physique et Chimie du Milieu Interstellaire » (PCMI), Université Pierre et Marie Curie experimental platform « Astrolab », Université Pierre et Marie Curie Labex « MiChem », Ile-de-France region funding through the program DIM-ACAV (« astrophysique et conditions d’apparition de la vie »).

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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