Single stellar populations, being born from the same molecular cloud at virtually the same time, are often assumed to share the same chemical composition. While this assumption is quite accurate for the initial chemical composition of the stars, once stellar evolution sets in it does not hold any longer. Processes such as atomic diffusion, the first dredge-up and extra-mixing result in variations in the stellar surface chemical composition depending on their evolutionary stage. This has broad implications: e.g., atomic diffusion effects put a constraint to the precision achievable by chemical tagging methods, while the post-dredge-up [C/N] ratio can be used for the age-dating of field stars. Open clusters are ideal examples of single stellar populations and are therefore extremely useful for the study of stellar evolution. I will present an investigation of stellar evolutionary effects in the well-known old open cluster M67 based on high-resolution spectra from APOGEE and the Gaia-ESO Survey, including a comparison with the predictions of stellar evolutionary models.
With the wealth of ancillary data available in large domains of the
spectrum (GALEX, HST, CFHT, Spitzer, Herschel, etc), panchromatic studies of
galaxies are thus one of the keys to understand how galaxies evolved since their
formation. After describing the assets of spectral energy distributions (SED)
analysis and explaining how we can model them, I will discuss the star formation history of the
bulk of galaxies and show with a concrete case how we can identify and characterize galaxies
than underwent a rapid star formation quenching with a sample of well-known local galaxies, the Herschel
Reference Survey. This sample contains galaxies from the field but also from the
dense environment of the Virgo cluster. From this pilot study, I will go to
higher redshifts in order to blindly identify sources that have just been
quenched using CANDELS/GOODS-South data and try to identify possible causes for
this.
The key to understand our origins is in the interiors and atmospheres of the giant planets. Jupiter is the biggest planet in our system and the most influential one: its large mass shaped the architecture of the solar system and due to its fast formation it contains valuable information of the solar system formation history.
In orbit since July 2016, the first orbits of Juno mission had led to a remarkable improving of the planet gravity data, changing our knowledge of the planetary interior and leading to a much better comprehension of the giant planet and its role in the solar system.
In this seminar, I will present the new Juno results, the models we use to understand Jupiter’s interior and its differential rotation and the main challenges and questions that remained to be solved.
ALMA has already produced many impressive and scientifically compelling results. However, continuous technical upgrades and development are key for ALMA to continue to lead astronomical research through the 2020-2030 decade and beyond. The East Asia ALMA development program consists of the execution of short term projects, and the planning and initial studies for longer term developments that are essential for future upgrades. We present an overview of all these ongoing East Asia ALMA development projects and upgrade studies, which aim to maintain and even increase the outstanding scientific impact of ALMA in the near future and over the coming decades.
La nébuleuse d’Orion est l’une des régions célestes les plus observées de la Voie Lactée. Elle est le siège d’une intense formation stellaire particulièrement bien étudiée dans les domaines mm et submm qui révèlent l’intérieur des régions froides et sombres, inobservables en optique, où se forment les étoiles. La haute résolution spatiale et la sensibilité de l’interféromètre de l’IRAM au Plateau de Bure et de l’interféromètre ALMA, ainsi que la grande bande en fréquence offerte par ALMA nous ont permis de : cartographier l’émission de plusieurs molécules complexes organiques, estimer les abondances moléculaires et adresser quelques questions importantes en lien avec la complexité moléculaire dans Orion. Nos observations ne conduisent pas à un schéma unique de formation et d’excitation moléculaire, mais la chimie à l’œuvre dans les ‘fragments’ proto-stellaires au centre de la nébuleuse d’Orion peut être comparée à la chimie qui domine dans les comètes du système Solaire.
The exploration of Jupiter’s and Saturn’s system respectively by Galileo (1996-2003) and Cassini-Huygens (2004-2017), has revealed that several moons around Jupiter (Europa, Ganymede, Callisto) and around Saturn (Titan, Enceladus, Mimas) harbor a subsurface salty ocean underneath their cold icy surface. By flying through the icy-vapor plume erupting from Enceladus’ south pole, Cassini proceeded for the first time to the analysis of fresh materials coming from an extraterrestrial ocean. These analyses revealed that Enceladus possess all the ingredients for the emergence of life. Even if there is no direct evidence yet, similar ingredients might also be present within Europa, Ganymede and Titan, which will be characterized by future exploration missions currently under development at ESA (JUICE) and NASA (Europa Clipper, Dragonfly).
Even if the astrobiological potential of these ocean worlds are very promising, at the exception of Enceladus, their oceanic environments are still poorly known. In this seminar, after giving an overview of the current knowledge on these ocean moons, I will present how future exploration and laboratory works will allow us to better determine the physico-chemical conditions of their subsurface oceans. In particular, I will discuss the possible occurrence of active aqueous processes on these bodies and the implications for the habitability of their subsurface oceans. Finally, I will discuss how the numerical models and experiments developed for ocean moons can be used to characterize the physico-chemical evolution of water-rich exoplanets that we are just starting to unveil.
Gabriel Tobie, Laboratoire de Planétologie et Géodynamique, CNRS/Univ. Nantes