Calendar

Mai
15
mar
Céline Reylé : L’archéologie galactique à l’ère des grands relevés @ Univers
Mai 15 @ 14 h 30 min – 15 h 30 min
Séminaire

Les grands relevés spectroscopiques (Gaia-ESO, APOGEE, LAMOST, GALAH) apportent des contraintes sur les propriétés de surface des étoiles, y compris leur composition chimique. Depuis une dizaine d’années, l’astérosismologie (CoRoT, Kepler) ajoute des contraintes supplémentaires en sondant les intérieurs stellaires. D’autre part, le satellite Gaia commence à fournir des parallaxes et des données astrométriques avec une précision inégalée. 

La diversité et la variété des grands relevés actuels ouvrent donc de nouvelles perspectives pour comprendre l’histoire de notre Galaxie, reposant sur une meilleure compréhension de la physique stellaire, et ceci pour toutes les populations d’étoiles



La synthèse de populations stellaires est une méthode puissante pour exploiter au mieux la synergie de ces données. Nous avons perfectionné le modèle de la Galaxie de Besançon (BGM) en incluant des modèles d’évolution stellaire, calculés avec STAREVOL, pouvant suivre les propriétés chimiques et sismiques des étoiles au cours de leur vie. Nous montrons ici les premières comparaisons du BGM avec les abondances de surface du carbone et de l’azote d’étoiles géantes de Gaia-ESO pour illustrer l’effet des mécanismes de transport dans les étoiles géantes. En particulier nous montrons que les hypothèses de physique stellaire ont un impact très important sur la détermination des âges, l’un des paramètres piliers pour l’archéologie galactique.



Cette approche prometteuse pourra être appliquée pour tester d’autres processus physiques importants pour la physique stellaire (diffusion atomique, rotation, binarité). Ces modèles fourniront des méthodes de datation des étoiles robustes et applicables à grande échelle dans la Voie Lactée.

Mai
22
mar
Olivier Berné: Studies of the interstellar medium in the JWST era @ Univers
Mai 22 @ 11 h 00 min – 12 h 00 min
Séminaire
The James Webb Space Telescope (JWST) is the next flagship mission of NASA, and involves ESA and the Candian Space Agency (CSA). With a price cap estimated to 9 billions dollars, it is the most expensive space mission since Apollo. This is justified by the very ambitious scientific and technical objectives (observing first lights, 6.5m deployable mirror etc.), and by the promise of having an impact on the general public as large as Hubble.  
The idea of this presentation is to illustrate the capabilities of the JWST when applied to emblematic scientific case-studies of the interstellar medium (ISM) such as : the photochemistry of aromatic macromolecules in space (PAHs and fullerenes), the physics of radiative feedback from massive stars on the ISM, or the mechanisms driving mass loss by photoevaporation in protoplanetary disks. I will also discuss the Early Release Science observing project we are in charge of, which was accepted and will be conducted in the very first days of the scientific phase of the JWST mission. It is expected that this project will provide a first glimpse of what can be done scientifically, notably for the case studies mentioned above, and beyond. This project, which will target the Orion Nebula (or the Trifid in case of shift in launch date), is fully open to the community, and the data will be made public immediately after they are collected. 
Mai
31
jeu
Astro Cafe: A Practical Overview of Stellar Spectroscopy and Abundance Analysis
Mai 31 @ 14 h 00 min – 15 h 00 min
Astro Cafe

A Practical Overview of Stellar Spectroscopy and Abundance Analysis

presented by

Laia Casamiquela

 

I will present a brief and practical overview of stellar spectroscopy  and abundance analysis using high resolution spectroscopic data. First,  I will briefly explain some basic concepts and ingredients to understand  how to derive atmospheric parameters and chemical abundances from a  stellar spectrum. Then I will illustrate the process doing a real time  analysis of real spectra with the code iSpec (Blanco-Cuaresma et al. 2014).

Juin
6
mer
Niels Ligterink: Prebiotic building blocks: From interstellar observations to laboratory synthesis @ Atmosphere
Juin 6 @ 11 h 00 min – 12 h 00 min
Séminaire

Prebiotic molecules show chemical similarities with biologically relevant molecules, such as amino acids, nucleobases, sugars and peptide chains, and are thought to be involved in their formation.  The interstellar presence of prebiotic molecules has led to the idea that biotic molecules on Earth may have derived from these interstellar molecules.

In this seminar, observations of prebiotics towards the young sun-like protobinary IRAS 16293-2422 are presented, showing that prebiotic molecules likely were present at the earliest formational stages of our Solar system. Solid-state formation pathways of these molecules are investigated in the laboratory and show that much of the prebiotic inventory can derive from reactions on icy dust grains.

Juin
20
mer
Jean-Loup Baudino: Are we ready to characterise exoplanet atmospheres with the James Webb Space Telescope observations ? @ Univers 21
Juin 20 @ 11 h 00 min – 12 h 00 min
Séminaire

The James Webb Space Telescope (JWST )will open a
new area in the domain of exoplanet atmosphere
characterizations  and  will  require  accurate  
models  to  interpret the observations.  In this context,
we propose a protocol to compare various atmospheric
codes,  to identify and discuss the significant
differences in the results and to help the codes evolve
to become as consistent as possible.  We applied this
protocol on 3 forward models and one retrieval.  We updated
them to account for the major differences and we are now
able to identify the remaining differences observable with
the JWST.

Juin
27
mer
Vincent Hue — Juno at Jupiter: Juno-UVS overview and observations of the Io footprint @ Univers 21
Juin 27 @ 11 h 00 min – 12 h 00 min
Séminaire
Juno is currently on an elliptical and polar orbit around Jupiter, since July 2016, and has successfully gathered data during 12 perijoves sequences. Juno offers a fantastic opportunity to study Jupiter’s magnetosphere and its spectacular auroral emissions, which can be seen as a window screen of the entire Jovian magnetosphere. The Juno Ultraviolet Spectrograph (UVS) is a UV spectrograph with a bandpass spanning 70 to 205 nm and is designed to characterize Jupiter’s UV emissions. We present a brief overview on Juno-UVS operations. We then present observations of the Io footprints as seen by UVS. The Io footprints are a characterization of the complex magnetodynamic interaction at Io and modulated by the inner magnetosphere of Jupiter. Previous observations taken with the Hubble Space Telescope allowed the characterization of the footprints as a function of Io’s centrifugal latitude, despite observational bias that Earth-based observers are subject to. Juno’s unique vantage point in the Jovian system removes these biases allowing UVS access to the full range of Io’s varying centrifugal latitude and all possible local time geometries. 
Sep
12
mer
Marcelo Tucci Maia — Solar Twins: planet-host star chemical connection and chemical evolution of the Galaxy @ Univers 21
Sep 12 @ 11 h 00 min – 12 h 00 min
Séminaire
Solar twins are stars that have spectra very similar to the Sun, with effective temperature, surface gravity and metallicity around solar values. This similarity allow us to determine very precise stellar parameters and chemical abundances (~0.01 dex), that makes possible the investigation of effects that can imprint subtle changes in the chemical pattern of a star, for example planet engulfments. 
Also, the high precision atmospheric parameters that can be derived for these objects permit us a reliable determination of their ages using a traditional isochrone method which, in association with the abundances determination, can bring many benefits to studies of the chemical evolution of the Galaxy.
I will talk about the differential method, and discuss about past and recent works on the planet-host star chemical connection and the chemical evolution of the Galaxy.
Sep
14
ven
Jack Lissauer: Kepler’s Multiple Planet Systems @ Univers 21
Sep 14 @ 11 h 00 min – 12 h 00 min
Séminaire

More than one-third of the 4000+ planet candidates found by NASA’s Kepler spacecraft are associated with target stars that have more than one planet candidate, and such “multis” account for the vast majority of candidates that have been verified as true planets.The large number of multis tells us that flat multiplanet systems like our Solar System are common. Virtually all of the candidate planetary systems are stable, as tested by numerical integrations that assume a physically motivated mass-radius relationship. Statistical studies performed on these candidate systems reveal a great deal about the architecture of planetary systems, including the typical spacing of orbits and flatness. The characteristics of several of the most interesting confirmed Kepler & K2 multi-planet systems will also be discussed.

Sep
19
mer
Matt Clement : Planet formation in the inner solar system and the early instability model @ Salle 261
Sep 19 @ 11 h 00 min – 12 h 00 min
Séminaire

The leading evolutionary model for the outer solar system, an orbital instability between the solar system’s giant planets, has been shown to greatly disturb the orbits of the young terrestrial planets. Undesirable outcomes such as over-excited orbits, ejections and collisions can be avoided if the instability occurs before the inner planets are fully formed. Such a scenario also has the advantage of limiting the mass and formation time of Mars when it occurs within several million years (Myr) of gas disk dissipation. The dynamical effects of the instability cause many small embryos and planetesimals to scatter away from the forming Mars, and lead to heavy mass depletion in the Asteroid Belt. We present new simulations of this scenario that demonstrate its ability to accurately reproduce the eccentricity, inclination and resonant structures of the Asteroid Belt. Furthermore, we perform simulations using an integration scheme which accounts for the fragmentation of colliding bodies. The final terrestrial systems formed in these simulations provide a better match to the actual planets’ compact mass distribution and dynamically cold orbits. An early instability scenario is thus very successful at simultaneously replicating the dynamical state of both the inner and outer solar system.

Sep
26
mer
Clément Baruteau — Observational predictions of the presence of giant planets in the dust’s radio emission of protoplanetary discs @ Univers 21
Sep 26 @ 11 h 00 min – 12 h 00 min
Séminaire

The classical picture of protoplanetary discs forming smooth, continuous structures of gas and dust has been challenged by the growing number of spatially resolved observations. These observations indicate that radial discontinuities and large-scale asymmetries may be common features of the emission of protoplanetary discs, and they are often interpreted as signatures of the presence of (hidden) planets. They stress the need to better understand how disc-planets interactions generally, and planetary migration more specifically, impact the dust’s thermal emission in protoplanetary discs. In this talk, I will report our recent and ongoing efforts in predicting the dust’s radio emission in protoplanetary discs due to the presence and migration of massive gap-opening planets, via two-fluid (gas+dust) hydrodynamical simulations post-processed with radiative transfer calculations. I will show how these predictions apply to the discs around AB Aurigae and MWC 758.