In a hierarchically-formed Universe, the Milky Way is a test-bed to study in details the mechanisms that shape galaxies. The synergy between the Gaia space satellite and the ground-based spectroscopic survey WEAVE gives access, for the first time, to more than thirty tracers of the past of our Galaxy for a million stars of the extended Solar neighbourhood, and to a dozen of tracers for another two million stars outside of it. Our project concerns the study of the Galactic disc, a structure that encodes both internal (e.g. stellar radial migration) and external (e.g. accretion events) mechanisms that come into play in the chemo-dynamical evolution of our Galaxy. We have built a versatile team with nodes in Nice, Paris and Strasbourg, including experts in Galaxy evolution, simulations and modelling. The team members are heavily involved in both WEAVE and Gaia in order to extract the maximum of information available in those combined catalogues. Over the course of the four-year MWDisc ANR project, and alongside to the accumulation of the WEAVE data (starting in Q1 2021), we aim to produce added-value catalogues for the WEAVE stellar targets (containing homogeneous stellar chemical abundances, ages, orbits and extinctions) and models associated to the diffusion of mono-age populations by time-varying perturbations and superposition of perturbations (associated to the spiral arms and the Galactic bar). These models and catalogues will allow us, in turn, to evaluate the star formation history in various regions of the disc, put constraints on the merger tree of the Milky Way (including the analysis of existing simulations of ours), to link the geometrical properties of the thin and thick disc with their chemical counterparts and finally to characterize the efficiency of radial migration throughout the disc.

The lowest metallicity stars are also the oldest ones and they carry the imprint of the first supernovae. Since the very first stars are likely short-lived and inaccessible to us, the lowest metallicity stars are also those that can inform us most on the first generation of stars, how they enriched their environment, and produced the first structures that, through hierarchical formation, built up the primordial constituents of the galaxies we observe today. These stars are exceedingly rare and few of them are known today. In order to efficiently improve on this situation, we have put in place the Pristine international collaboration. Focussed around a wide narrow-band photometric survey conducted at the Canada-France-Hawaii Telescope and a large dedicated spectroscopic campaign, Pristine is many times more efficient than previous attempts at finding the precious low-metallicity stars. From the detailed study of these stars, we will: hunt for the most extreme low-metallicity stars; place constraints on star formation during the earliest epoch of the universe; reliably unveil the properties of the faintest known dwarf galaxies that orbit the Milky Way and are promising cosmological probes; decompose the Milky Way into its main components to place our Galaxy in the global context of galaxy formation and evolution; deconstruct the stellar halo of the Milky Way into its constituent substructures, which will then be used to constrain the mass and shape of the Milky's Way potential. In order to reliably achieve these significant goals, we request funding to support Pristine in France and ensure the project is staffed adequately to yield high-impact scientific returns in the field of very low metallicity stars. Our team is built around experts of the field in Nice (OCA/Lagrange), Paris (GEPI), and Strasbourg (Observatoire astronomique de Strasbourg) and represents a large part of the full Pristine collaboration. To complement this team, we ask for funding for a PhD student and two postdoctoral researchers who will be spread over the three French nodes of our project, along with funds to support the team and secure the visibility and active partnership of the French team members within the full international Pristine collaboration. We wish to emphasize that the effort already invested by the current team members into preparing the survey (successful telescope time proposals, data acquisition, reduction, and calibration, start of the spectroscopic follow-up campaign) means that the Pristine project is a low risk but high return project if it were to be supported by the ANR. It builds on large facilities and surveys with a significant French involvement (CFHT, Gaia, WEAVE) and it promises numerous high impact papers to be published in the high-visibility fields of Galactic archaeology and near-field cosmology in which France is a world leader.

Being affected throughout their lifetime by a strong mass-loss due to radiative winds, fast rotation, and a high binarity rate, massive stars pose several challenges to the understanding of their observational properties and evolution. The aim of our project is to improve our knowledge of these objects by coupling state-of-the-art two-dimensional simulations of stellar interiors including rotation, pulsations, and mass-loss, with radiative transfer models of their atmospheres and environment, in order to compare the resultant predictions with observations at the highest spectral and angular resolutions. This unique combination of fundamental modelling, radiative transfer, and confrontation with observations will enable us to improve the models of massive stars, as well as our understanding of the underlying physics. Our project relies on the successes of the ESTER code (Toulouse), which models rapidly rotating early-type stars in two-dimensions, and of the TOP pulsation code (Paris-Meudon) for carrying out asteroseismic inferences. From the combination of these codes with radiative transfer models for the atmosphere and the circumstellar environment (winds and disks, which can be composed of gas and dust), we will create a complete and physically consistent modelling tool of massive stars (typically with masses between 4 and 20 solar masses). This physical model will allow us to simulate polychromatic images from which several observables can be computed, in particular those for long baseline optical/infrared spectro-interferometry. We will use this model to compute and deliver to the community, improved grids of models of typical massive stars (interiors, atmospheres, and extended environment). Tools to use these model grids for the analysis of spectro-interferometric data (innovative imaging and model fitting methods) will be developed/adapted for the project and also provided to the community. In addition to these models and dedicated analysis tools, the success of our project for a deep physical study of massive stars relies on the unique expertise in the development and exploitation of spectro-interferometric instruments in Nice, in particular MATISSE, the new mid-infrared instrument of the Very Large Telescope Interferometer (VLTI) array at ESO-Paranal, and SPICA, the upcoming visible beam-combiner for the Center for High Angular Resolution Astronomy (CHARA) array at Mount Wilson Observatory. From our physical analysis of many existing and near-to-come spectro-interferometric data, we will be able to constrain many key parameters defining the central star (mass, temperature, age, rotation rate...) and its environment (mass-loss, and wind and disk structures, i.e. density and temperature law, chemistry, dynamics) of about 200 stars from our survey list. In particular, we will obtain a detailed view (including models and reconstructed images) of about 25 primary targets, which will constitute a unique set of landmark massive stars, spanning different types (e.g. classical Be, B[e], fast rotators, beta Cephei stars, slowly rotating B stars, supergiants). The results of this unprecedented study will also provide invaluable information for a global, unified understanding of the structure and evolution of massive stars.

Owing to a high-resolution cathodoluminescence systematic study of carbonaceous chondrites and NASA OSIRIS-REx returned samples, O-Return is a 4 years ANR project aiming at gaining new information on the conditions of formation (e.g. condensation, crystallization, annealing) of refractory inclusions and chondrules, the first solids in the Solar System, and on their astrophysical setting (e.g., shock waves, impacts). Through the different tasks of O-Return that we will emplace, our approach will consist: i) to perform an unprecedented high-resolution cathodoluminescence study of olivines and pyroxenes, the most abundant phases in magnesian (type I) chondrules, and to extend the survey to Amoeboid Olivine Aggregates (AOA), the most common type of refractory inclusions in carbonaceous chondrites. This study will give us an unique inventory of their mode of crystallization and their variability, ii) to synthesize thin films of Mg-rich olivine and pyroxene doped with known CL activator concentrations (Al, Mn, Cr) at the level of a few ppm and to acquire their optical characteristic for serving as new standards, in order to upgrade high-resolution cathodoluminescence imaging to a quantitative mode of detection of trace elements and lattice defects, and iii) to model olivine and pyroxene crystallization conditions/modes in both chondrites and OSIRIS-REx returned materials to gain insights on 1) locations for chondrule/AOA formation in the disk, 2) their putative astrophysical settings, and 3) the dynamical regimes reigning in the protoplanetary disk. To achieve this work, the O-Return project will develop an original and transdisciplinary research merging expertises from both materials and planetary sciences between two renowned laboratories J-L LAGRANGE and Centre of Research on Hetero-Epitaxy and Applications (CRHEA). The originality of this project lies in the use of high-resolution cathodoluminescence, which has never been fully exploited on extraterrestrial objects, and the synthesis of unique standards, which will allow a quantified interpretation of the CL signature of chondrites and OSIRIS-REx returned samples. Owing to this innovative combination, the expectation is to provide a quantum leap improvement in our understanding of the early evolution of the Solar System and Youg Stellar Objects.

WEAVE-QSO and J-PAS are two large astrophysical surveys active from 2022 to 2029, on two major observatories, supported by two international collaborations: WEAVE-QSO (European) and J-PAS (Brazilian-Spanish). These two surveys are partners towards a common goal: cosmology and galaxy formation in the first half of the history of the universe using data of unprecedented quality and size. J-PAS does this by performing imaging in 56 colours and WEAVE-QSO follows this up with spectroscopy. The exploitation of this data presents a variety of challenges and opportunities that we seek to address through machine learning. In some cases, initial steps have been undertaken, in other cases the project is in the cradle. The leads of these surveys propose to pool the expertise of the partners and bring together innovative methods for the fullest exploitation of our large common data set.