Since circumstellar dust in debris disks is short-lived, dust-replenishing requires the presence of a reservoir of planetesimals which continuously supply the disk with fine dust through their mutual collisions. In this talk I will summarize selected studies related to the properties of this dust and the structure of debris disks on various scales.
Introduction to Supervised Regression and Classification with Machine Learning Methods
Observations of Galactic dust are a highlight and a lasting legacy of the Planck space mission.
Spectacular images combining the intensity of dust emission with the texture derived
from polarization data have received world-wide attention and become part of the general scientific
knowledge. Beyond this popular success, the dust maps are an immense step forward
for Galactic astrophysics, greatly superseding earlier observations. Planck has provided us with the data
needed to statistically characterize the structure of the Galactic magnetic field and its coupling with
interstellar matter and turbulence. Planck multi-frequency observations have also opened a new perspective
on interstellar dust, upsetting existing models. Futrhermore, the astrophysics of dust emission has
become inter-connected to a paramount objective of observational cosmology: the quest for curl-like
(B-mode) polarization of the cosmic microwave background expected to arise from primordial
gravitational waves produced during the inflation era in the very early Universe. I will introduce
these science topics and highlight key results and perspectives of on-going research.
Francois Boulanger
Ecole Normale Superieure, Paris, France
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.
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).
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.
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.
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.