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 24 janvier 2020, 14h00
Salle de l'atelier, Paris
Unveiling the accretion-ejection connection in nascent Sun-like stars
résumé :
Disks around nascent stars are the birthplace of planets. However, many critical aspects of planet formation are still highly uncertain, in particular the impact of winds on disk evolution. Indeed, magnetic outflows launched from the disk surface (‘MHD disk-winds’) have recently been invoked to extract angular momentum and drive accretion, regulate dust growth, and prevent inward planet migration. The unique combination of sensitivity and angular resolution offered by ALMA and the future JWST is now allowing us to conduct stringent tests on the presence of MHD disk-winds and quantify their impact on planet-forming disks.

In this seminar, I first present an ALMA study of the Sun-like protostellar system HH212 that has uncovered a SO/SO2 rotating flow wider and slower than the axial rotating SiO jet. The global kinematics and the mass-flux of the flow down to 0.04-0.02” (16-8 au) scales may be fitted by an MHD disk-wind model launched out to the outer disk radius (~40 au), with SiO tracing the dust-free streamlines from 0.05?0.3 au (Tabone+2017; Tabone+2020a). The surprising molecular richness of the dust-free part of the wind is further investigated with astrochemical models (Tabone+2020b). The extension of such tests to more evolved sources, together with tests based on the observed perturbation of the wind by bow-shocks (Tabone+2018), are also discussed. Finally, I present my current modelling effort to derive the local UV radiation field in disk atmospheres - a key parameter that controls the chemistry of the disk and the launching of the wind - from the OH lines to be observed by JWST/MIRI.
Vendredi 31 janvier 2020, 14h00
Salle de l'atelier, Paris
The role of feedback- and accretion-driven turbulence in galaxy build-up
résumé :
Cosmological models describe accurately the growth of large scale, dark matter-dominated, structures, but largely fail to reproduce the baryon content and physical properties of galaxies. Why? Essentially because the build-up of galaxies is regulated by a complex interplay between gravitational collapse, galaxy merging and feedback related to AGN and star formation, for which we still miss a robust theory. The energy released by these processes has to dissipate for gas to cool, condense, and form stars. How gas cools is thus a key to understand galaxy formation and why it such an inefficient process. In this seminar, I will discuss a few examples where turbulence driven by gas accretion, feedback, and galaxy interactions, which is largely ignored in models of galaxy formation, and captured in current simulations only over a limited range of scales, may have a major impact on galaxy and halos properties.

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 17 avril 2020, 14h00
Salle de l'atelier, Paris
Patricia TISSERA
Universidad Andres Bello, Santiago, Chili
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