GEPI

The scientific theme of the Stellar and Galactic Physics team is twofold. On the one hand the study of the structure and properties of our Galaxy and the galaxies of the Local Group, to constrain their formation and evolution, on the other hand the study of the fundamental properties of stars, such as their internal structure and the associated physical and chemical mechanisms.

Our team, a pioneer in space astrometry with the Hipparcos satellite, is deeply involved in the Gaia space mission. It has played a major role in the design of the instruments and in particular the Radial Velocity Spectrometer (RVS). Today, the team contributes to the Gaia-DPAC consortium in the processing of spectroscopic data (for which it is responsible) and multiple systems, as well as data validation. In particular, the team led the validation of the first two Gaia catalogues (DR1: September 2016, DR2: April 2018) and the production of the largest catalogue of stellar radial velocities containing more than 7 million measurements.

We are also deeply involved in the design of the WEAVE spectroscopic surveys at the William Herschel Telescope and MOONS at the VLT, with the French responsibility for the WEAVE survey.

In addition to the characterisation of the fundamental properties of stars and the physical properties of the Galaxy, our team also combines a strong expertise in modelling. We develop advanced chemical evolution models to describe the evolution of galactic stellar populations, as well as to reconstruct the stellar formation of our Galaxy; we develop dynamic and chemo-dynamic simulations to model the key evolutionary processes of a disk galaxy like ours (satellite accretions, formation and evolution of the stellar bar and bulge, secular evolution); we develop hydrodynamic simulations to model stellar atmospheres (effective temperature, granularity, velocity fields) and the impact their structure has on chemical abundances.

Our expertise thus allows us to cover a wide range of themes and spatial scales: from the first stars formed in the Milky Way, and mainly distributed in the stellar halo, to the most metal-rich stars in the disc and bulge; from the structure of the interstellar medium to the history of gas accretion in our Galaxy as a function of time; from globular galactic clusters to the dwarf galaxies of the Local Group.