LERMA UMR8112

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



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Address and access to LERMA sites

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LERMA is situated on 5 sites in the Paris region :

- Observatoire de Paris (Paris and Meudon sites)
- University Pierre and Marie Curie (UPMC)
- ENS
- University of Cergy Pontoise (UCP)

Access to Observatoire de Paris (Paris site)
- Postal Address : 61, avenue de l’Observatoire - 75014 PARIS
- Pedestrian and vehicle access : 77, Avenue Denfert-Rochereau - 75014 Paris
- Telephone : +33 1 40 51 22 21 - Fax : +33 1 43 54 18 04
- Access

Access to Observatoire de Paris (Meudon site)
- Postal address and pedestrian access : Observatoire de Paris, site de Meudon - 5, place Jules Janssen - 92195 Meudon cedex
- Vehicle access and goods : 11, avenue Marcelin Berthelot, 92195 Meudon
- Standard : +33 1 45 07 75 30
- Access

Access to UPMC
- Postal address : UPMC - case courrier 76 - 4 place Jussieu - 75252 Paris cedex 05
- Pedestrian access : 4, place Jussieu - 75252 Paris cedex 05
- Access :

  • Tour 32-33 2ème et 3ème étage
  • Tour 24-34 5ème étage

Access to l’ENS
- Postal address : LERMA/L.R.A. - Département de Physique ENS - 24, rue Lhomond - 75231 PARIS Cedex 05
- Accès

Access to Cergy Pontoise
- Postal address : LERMA/LAMAP - Site de Neuville II - UFR Sciences et Techniques - Département de physique - 5, mail Gay Lussac - 95031 Cergy-Pontoise cedex
- Access

Séminaires à venir

Vendredi 22 mars 2019, 14h00
Salle de l'atelier, Paris
New Planckian quantum phase of the Universe before Inflation: Its present day and Dark Energy implications
Sanchez, Norma
LERMA
résumé :
The physical history of the Universe is completed by including the quantum planckian and super-planckian phase before Inflation in the Standard Model of the Universe in agreement with observations. In the absence of a complete quantum theory of gravity, we start from quantum physics and its foundational milestone: the universal classical-quantum (or wave-particle) duality, which we extend to gravity and the Planck domain. A new quantum precursor phase of the Universe appears beyond the Planck scale. Relevant cosmological examples as the Cosmic Microwave Background, Inflation and Dark Energy have their precursors in this era. A whole unifying picture for the Universe epochs and their quantum precursors emerges with the cosmological constant as the vacuum energy, entropy and temperature of the Universe, clarifying the so called cosmological constant problem which once more in its rich history needed to be revised. The consequences for the deep universe surveys, and missions like Euclid will be outlined.
 
Vendredi 5 avril 2019, 14h00
Salle de l'atelier, Paris
The magnetized interstellar medium in the Galaxy through Faraday tomography of the radio sky
Andrea BRACCO
ENS
résumé :
The study of the diffuse Galactic interstellar medium (ISM) is both a
waypoint to investigate the processes that turn gas into stars and to
account for foreground contaminations in modern high-precision
cosmological probes of the Universe.

New structures in the diffuse ionized and magnetized ISM have been
recently observed through Faraday tomography of polarization data at low
radio frequencies. Although the physical origin of these structures
remains uncertain, interesting correlations with tracers of neutral ISM,
such as atomic hydrogen lines and interstellar dust polarization, have
been found. This opens an observational window on the first stages of
phase transition between diffuse/warm and denser/colder gas under the
presence of magnetic fields, allowing us to constrain their role in
structure formation in the ISM.

In my talk I will present an overview of the recent findings in the
diffuse Galactic ISM with the LOFAR radio polarization data. I will
highlight the relevance of a thorough statistical description of these
data both for Galactic studies and for modeling their impact as a
foreground to the detection of the atomic hydrogen 21cm hyperfine
transition from the Epoch of Reionization, a key step with the upcoming
Square Kilometre Array (SKA).
 
Vendredi 12 avril 2019, 14h00
Salle de l'atelier, Paris
Radiation magnetohydrodynamic models and spectral signatures of plasma flows accreting onto young stellar object
Salvatore COLOMBO
LERMA
résumé :
According to the largely accepted magnetospheric accretion scenario, classical T Tauri Stars (CTTSs) are young stars that accrete material from their circumstellar disk. The objective of my PhD project is to shed light on the processes governing the physics of the accreting plasma flows, through complete radiation magnetohydrodynamic models. In this talk, I will present the results obtained during my 18 month period in Paris.

First, I will focus on the results obtained from a 3D magnetohydrodynamical (MHD) model of a star-disk system. We simulate the effects of series of flares occurring on the surface of the disk. We observe that each flare produces a hot loops that links the star to the disk; all the loops build up a hot extended corona that irradiates the disk from above. Moreover, the flares trigger overpressure waves that travel through the disk and modify its configuration. Accretion funnels may be triggered by the flaring activity and thus contribute to the mass accretion rate of the star. The accretion columns can be perturbed by the flares. As a result, the streams are highly inhomogeneous, with a complex density structure, and clumped.

Second, I will provide the first assessment of the role of radiation effects on the dynamics and the structure of the impact region of the accreting column onto the stellar surface. In particular, we proved the existence of a radiative precursor in the pre-shock part of the accreting column. To achieve such a result, we have, for the first time, developed a Non Local Thermodynamic Equilibrium (non-LTE) radiation hydrodynamics model, which we implemented in the 3D MHD PLUTO code.”

 
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