Summary & Objectives
Understanding how galaxies form is one of the biggest questions in modern astrophysics and cosmology. The Milky Way (MW) plays a central role in this quest, with the ongoing ESA Gaia mission and its complementary high precision spectroscopic and asteroseismic surveys currently revolutionizing Galactic archaeology and stellar physics. PRIMA fully exploits this extraordinary observational windfall to provide the missing keys for Galactic archaeology and to drive the art of modelling stars at the level of precision demanded by PLATO. It optimises the return of investment of Switzerland and France in these revolutionary projects.
PRIMA focuses on the Galactic components that host the oldest stars of the Milky Way and that best probe the merger history of the Milky Way, i.e., the halo, the thick disk, and globular clusters (GC). It uses the very powerful population synthesis approach to simulate the present-day stellar content of the MW, based on state-of-the-art stellar evolution modelling developed in the project and on the Galactic formation scenarios. It compares Galactic mock catalogues with multi-wavelength survey data, including asteroseismic informations. PRIMA is strategically positioned with respect to other complementary approaches to make a substantial impact in the field: it is the only method to eliminate selection biases in data analysis and to account for internal stellar processes that modify the abundances of stars along their evolution and impact their lifetimes. The project assesses merger events as well as galactic secular evolution (e.g. radial migration) on the properties of Galactic stellar populations, including GC and their escapers. The goal is to characterize the oldest stars of the MW and to decipher in situ and ex situ origins.
To achieve its objectives, PRIMA is organized around two complementary scientific hubs. The Geneva team focuses on developing state-of-the-art stellar evolution models that account for hydrodynamical transport of chemicals and angular momentum, providing a precise understanding of stellar ages and compositions. Meanwhile, the Bordeaux team develops advanced stellar population synthesis models, generating mock catalogues that allow direct comparisons between observations and predictions from stellar and galactic evolution models. Together, these complementary approaches provide the most accurate reconstruction of the Milky Way’s merger history and a deeper understanding of the origins of its oldest stars.
