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

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Présentation détaillée du LERMA

14 janvier 2019

Présentation du LERMA

Le LERMA (Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères) est une unité mixte de recherche (UMR 8112) commune au CNRS et à 3 établissements d’enseignement (...)

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12 janvier 2019

Equipe de direction

Directeur : Benoit SEMELIN
benoit.semelin @ obspm.fr
Directeur adjoint : Martina WIEDNER
martina.wiedner @ obspm.fr
Directeur adjoint : Ludovic PETITDEMANGE
ludovic.petitdemange @ (...)

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11 janvier 2019

Equipe administrative

L’équipe administrative du LERMA est composée de 7 agents. Elle travaille en étroite relation avec les services administratifs du CNRS (délégation Ile de France-Meudon (DR5) et INSU), de l’Observatoire (...)

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Séminaires à venir

Vendredi 21 février 2020, 14h00
Salle de l'atelier, Paris
Angular momentum properties of young protostellar envelopes
Mathilde GAUDEL
résumé :
One of the main challenges to the formation of solar-like stars is the “angular momentum problem”: if the angular momentum of the pre-stellar parent core is totally transferred to the central stellar embryo during the main accretion phase, the gravitational force can not counteract the centrifugal force and the embryo fragments prematurely before reaching the main sequence. To form a star such as our Sun, the gas of the rotating envelope needs to redistribute its angular momentum by 5 to 10 orders of magnitude before reaching the central stellar embryo. Class 0 protostars are key objects to identify the mechanisms responsible for the angular momentum redistribution : they grow by accretion of the matter from the surrounded envelope (Menv>>Mstar) extending to scales 10000 au. At the end of this cornerstone phase, most of the final stellar mass has been accreted and the embryo is surrounding by a large disk (~100 au).

In order to tackle this issue, we used high angular resolution observations (0.5’’, i.e. ~50 au) from the CALYPSO (Continuum and Lines in Young Protostellar Objects, PI: Ph. André) IRAM large program for a sample of 12 Class 0 protostars with d<400 pc. We established, for the first time homogeneously in a large sample, robust constraints on the radial distributions of specific angular momentum within protostellar envelopes in a large range of scales from ~50 to 10000 au (Gaudel et al. 2020, submitted). Two distinct regimes are revealed: a constant profile at small scales (<1600 au) and an increasing of the angular momentum at larger radii (1600-10000 au).

From the constant profile, I will discuss angular momentum conservation and disk formation as possible solutions to reconnect the angular momentum measured in the inner protostellar envelopes to what is expected in T-Tauri disks. Furthemore, velocity gradients observed on large scales (>3000 au) - that are historically used to measure the rotation of the core and quantify the angular momentum problem - are not due to pure envelope rotation. I will examine the influence of the interstellar filament dynamics (turbulence, collapse, shocks) within which protostars are buried and the imprints of the initial conditions of the pre-stellar phase in the large scales of the envelope.
Vendredi 28 février 2020, 14h00
Salle de l'atelier, Paris
Filament Paradigm and Galactic Star Formation
Shu-ichiro INUTSUKA
Nagoya University
résumé :
Recent observations have emphasized the importance of the formation and evolution of magnetized filamentary molecular clouds in the process of star formation. Theoretical and observational investigations have provided convincing evidence for the formation of molecular cloud cores by the gravitational fragmentation of filamentary molecular clouds. Thus, the mass function and rotations of molecular cloud cores should be directly related to the properties of the filamentary molecular cloud, which determines the initial size and mass distribution of a protoplanetary disk around a protostar created in a core. In this talk I explain our current understanding of the star formation processes in the Galactic disk, and summarize various processes that are required in describing the filamentary molecular clouds to understand the star formation rate/efficiency, the stellar
initial mass function, and the angular momentum distribution of protoplanetary disks in their early evolutionary phase.
Vendredi 20 mars 2020, 14h00
Salle de l'atelier, Paris
The challenges of observing the Epoch of Reionization and Cosmic Dawn
Kateyn institute
résumé :
Low-frequency observations of the redshifted 21cm line promise to open a new window onto the first billion years of cosmic history, allowing us to directly study the astrophysical processes occurring during the Epoch of Reionization (EoR) and the Cosmic Dawn (CD). This exciting goal is challenged by the difficulty of extracting the feeble 21-cm signal buried under astrophysical foregrounds orders of magnitude brighter and contaminated by numerous instrumental systematics. Several experiments such as LOFAR, MWA, HERA, and NenuFAR are currently underway aiming at statistically detecting the 21-cm brightness temperature fluctuations from the EoR and CD. While no detection is yet in sight, considerable progress has been made recently. In this talk, I will review the many challenges faced by these difficult experiments and I will share the latest development of the LOFAR Epoch of Reionization and NenuFAR Cosmic Dawn key science projects.
Vendredi 17 avril 2020, 14h00
Salle de l'atelier, Paris
Patricia TISSERA
Universidad Andres Bello, Santiago, Chili
Vendredi 24 avril 2020, 14h00
Salle de l'atelier, Paris
Philippe ANDRE
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