STAREVOL
We use our stellar evolution code STAREVOL that we constantly improve in terms of both micro- and macro-physics within an international network gathering some of the best specialists of stellar magneto-hydrodynamics and multi-D simulations (Dumont et al 2021b for the latest version). STAREVOL couples state-of-the-art treatment of the main hydrodynamical mechanisms which transport angular momentum and chemicals in stellar interiors, treating meridional circulation as an advective process together with shear turbulence in a 1.5D manner. It includes various prescriptions for shear turbulence induced by rotation (Mathis et al 2004, 2018; Zahn 1992, Talon & Zahn 1997), penetrative convection (Augustson & Mathis 2019), angular momentum extraction by magnetised winds (Matt et al. 2015), as well as additional (ad hoc) vertical diffusivity for angular momentum (Spada et al. 2016; Eggenberger et al. 2019). Atomic diffusion for partially ionised gas is computed according to the formalism of Thoul et al. (1994), providing an excellent agreement with the predictions of the Montréal-Montpellier code which is the reference for this mechanism.
The Besançon Galaxy Model
The Besançon Galaxy model is a stellar population synthesis model (Robin et al. 2003 ; Czekaj et al. 2014 ; Lagarde et al 2017) intended to meld the formation and evolution scenarios of the Galaxy, stellar formation and evolution theory, and models of stellar atmospheres, as well as dynamical constraints, in order to make a consistent picture of the Galaxy in comparison with available observations. We consider four stellar populations, a thin disc, a thick disc, a bar, and a halo; each stellar population has a specific density distribution. The stellar content of each population is modelled through an initial mass function (IMF) and a star formation history (SFH), and follows stellar evolutionary tracks (implemented in Lagarde et al 2017, 2019). The resulting stellar properties are used to compute the observational properties using atmosphere models and assuming a 3D extinction map. A Galactic dynamical model is used to compute radial velocities and proper motions (Robin et al. 2017). The originality of the BGM is to be able to take into account the dynamical self-consistency, a 3D extinction map, the physics of transport processes occurring in stellar interiors, as well as simulate asteroseismic and surface chemical properties of stars.
The BGM has been designated as the reference stellar population synthesis model for the preparation and exploitation of data from the Gaia and EUCLID satellites, two of today's most important space missions.
The BGM is also an online service for the community (INSU’s national observation service), generating an average of around 1,660 simulations per month in 2023, with a peak in activity in 2022 (over 90,000 simulations over the year). The BGM user community covers 32 different countries around the world, with a variety of scientific fields from the study of galaxies and stars, to the understanding of planets and the interstellar medium. The developments implemented in the BGM during this project will ultimately be integrated into the online service, enabling the entire international community to access it for a variety of scientific applications.