Tout public Lagrange
De l’alerte à l’action sur le changement climatique, quels enjeux nouveaux pour la science et la modélisation
mardi 22 janvier 2019, 10h30, NEF - Mont Gros - CION - talk in French - retransmis à Valrose Salle O. Chesneau
Hervé Le Treut - Institut Pierre Simon Laplace (IPSL)
Les années récentes ont vu une transformation importante des enjeux climatiques : les émissions massives de gaz à effet de serre ont réduit de manière drastique les objectifs qu'il est possible
d'atteindre, et obligent à une gestion de la planète prenant en compte le caractère irrémédiable d’une part importante des évolutions futures. Quels sont les outils numériques et les connaissances qui peuvent éclairer la décision ? La nécessité d’une adaptation préventive, qui prend toute son importance à l’échelle locale, impose-t-elle des approches scientifiques nouvelles ? Des réponses à ces questions seront proposées sur la base d’exemples.
mardi 29 janvier 2019, 10h30, NEF - Mont Gros - CION - talk in english - retransmis à Valrose (Attention: Salle M. Dugué)
Jenny SORCE - CRAL, Lyon
To unveil the nature of 95% of the Universe, missions such as Euclid aim at reaching a few percent precision. In this quest for precision, tensions between the standard cosmological model
and observations already arise: local and global H0 measurements are incompatible at more than 3 sigma, anomalies emerge within the CMB, etc. These tensions suggest that we should perhaps not be so quickly inclined to disregard our observational site as a bias factor: Accuracy is not Precision. Few percent precision and local biases are of the same order of magnitude. A precise mapping of the local distribution of matter is essential to properly account for these biases. Simulations constrained to resemble the local Universe constitute the tool of choice for such a mapping. I will summarize the genesis of the initial conditions of such simulations as well as present a few results that promise to tremendously impact our understanding of the local biases that will matter in futur e analyses. I will also present prospects for significant progress (the GMO-Constrained LOcal & Nesting Environment Simulations) to reach an Accurate Precision Cosmology.
Improved line formation models for more accurate stellar chemical abundances
mardi 5 février 2019, 10h30, NEF - Mont Gros - CION - talk in english - retransmis à Valrose (Salle O. Chesneau)
Anish Amarsi, MPIA Heidelberg
Stars leave their fingerprints on the light that they emit, in the form of absorption and emission features. Decoding this information to infer stellar parameters and chemical compositions is of key
interest to astronomers. However, such measurements are heavily model dependent, and for late-type stars such as the Sun their accuracy is often limited by the use of one-dimensional (1D) hydrostatic model atmospheres and the assumption of local thermodynamic equilibrium (LTE); it is not uncommon for 1D LTE abundance errors to reach 0.4 dex. Recently however it has become feasible to relax both assumptions simultaneously, i.e. to perform 3D non-LTE spectroscopic analyses. In this talk I shall review the physics of this more accurate method, present our latest results for carbon, oxygen, and iron abundances in the Sun as well as in disk and halo stars across the Milky Way, and discuss our efforts going forw ard to improve the accuracy of large stellar surveys like Gaia, APOGEE, GALAH, WEAVE, and 4MOST.
The Bar Connection: Effects of the bar on the Milky Way bulge and disc
mardi 26 février 2019, 10h30, NEF - Mont Gros - CION - talk in english - retransmis à Valrose (Salle O. Chesneau)
Francesca FRAGKOUDI - MPA Garching, Germany
It is well established that the Milky Way contains a stellar bar, which plays a dominant role in shaping its dynamics, both in the inner regions, i.e. in the bulge, and
out in the disc, close to the Solar Neighbourhood. In this talk I will show the effects of the bar on both these regions, making use of idealised N-body simulations of isolated galaxies as well as cosmological zoom-in simulations. I will show that we can explain the chemo-morphological and chemo-kinematic relations of stellar populations in the Milky Way bulge (e.g. from large spectroscopic surveys, such as APOGEE) in terms of the thin and thick disc being mapped into the boxy/peanut bulge by the bar. In this scenario the alpha-rich, metal-poor stars in the bulge are part of the same population as the alpha-enhanced thick disc at the Solar Neighbourhood, which indicates that almost the entirety of the mass of the bulge can be explained in terms of a pure disc (i.e. in-situ) origin. I will then focus on the effects of the bar on the disc of the Milky Way, connecting the underlying orbital structure at the bar OLR in N-body simulations with the substructures seen in phase-space in Gaia DR2.
mardi 5 mars 2019, 10h30, NEF - Mont Gros - CION - talk in english - retransmis à Valrose (Salle O. Chesneau)
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mardi 12 mars 2019, 10h30, NEF - Mont Gros - CION - talk in english - retransmis à Valrose (Salle O. Chesneau)
Dominique Meyer -
Magnetic fields in nearby galaxies: a low-frequency radio continuum perspective
mardi 19 mars 2019, 10h30, NEF - Mont Gros - CION - talk in english - retransmis à Valrose (Salle O. Chesneau)
Sarrvesh SRIDHAR - ASTRON, The Netherlands
mardi 2 avril 2019, 10h30, NEF - Mont Gros - CION - talk in english - retransmis à Valrose (Salle O. Chesneau)
Faustine CANTALLOUBE - MPIA Heidelberg, Germany
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mardi 28 mai 2019, 10h30, NEF - Mont Gros - CION - talk in english - retransmis à Valrose (Salle O. Chesneau)
Maria BERGEMANN - MPIA Heidelberg, Germany
Recherche dans l'Historique