Calendar

Fév
11
mar
Nadège Lagarde — Red giant stars: lighthouses in the Milky Way @ 306
Fév 11 @ 11 h 00 min – 12 h 00 min
Séminaire

A broad effort is ongoing with large spectroscopic surveys such as APOGEE, Gaia-ESO, GALAH, LAMOST from which stellar parameters, radial velocities and detailed chemical abundances can be measured for CoRoT, Kepler, and K2 targets. In addition, asteroseismic data of red-giants stars observed by the space missions CoRoT and Kepler allow determination of stellar masses, radii, and can be used to determine the position and ages of stars. This association between spectroscopic and asteroseismic constraints provide a new way to understand Galactic and stellar evolutions.

To exploit all potential of this combination and the large number of observations, it would be crucial to develop our approach of synthetic stellar populations. We develop the Besançon Galactic model (BGM) for which stellar evolution predictions providing the global and asteroseismic properties, as well as the surface chemical abundances along the evolution of low- and intermediate-mass stars are included. For the first time, the BGM can explore the effects of an extra-mixing occurring in red-giant stars. These synthetic populations can be compare with the significant large surveys as APOKASC (APOGEE -Kepler) or CoRoGES (CoRoT-GES).

I will present the evolution of red-giant stars, computed with the stellar evolution code STAREVOL including the effects of different hydrodynamical processes on the surface chemical abundances as well as on the Galactic chemical evolution of helium-3.
I will also present the first comparison between synthetic populations computed with the Besançon Galaxy model and the last release of the Gaia-ESO survey, exploring the efficiency of extra mixing with the stellar metallicity, mass, and age (Lagarde et al. 2019).

We emphasize the usefulness of population synthesis tools to test stellar models and transport processes inside stars. We show that transport processes occurring in red-giant stars should be taken into account in the determination of ages for future Galactic archaeology studies.

Fév
18
mar
Fabien Louvet — Physical processes behind the formation of high-mass stars and low-mass stars @ Univers 21
Fév 18 @ 11 h 00 min – 12 h 00 min
Séminaire

Star formation is a key astrophysical process. At small scale, it governs the settling of planetary systems, and the complex chemistry allowing the emergence of life. At large scale, star formation controls the energy budget of galaxies. Our knowledge about star formation is both extensive and extremely coarse. In the one hand, we know well the different steps that lead from a molecular cloud to a single star, but in the other hand, the physical processes behind those steps are, at best, debated. Building on the empirical scenario I will review some key physical processes and show the differences/similarities between low mass, and high-mass star formation.