Double Red Giant Branch and Red Clump features of Galactic disc stellar populations with Gaia GSPspec

Abstract

To disentangle the different competing physical processes at play in Galactic evolution, a detailed chrono chemicalkinematical, and dynamical characterisation of the disc bimodality is necessary, including high number statistics. Here we make use of an extremely precise subsample of the Gaia DR3 GSP-Spec catalogue of stellar chemophysical parameters. The selected database is composed of 408 800 stars with a median uncertainty of 10 K, 0.03 and 0.01 dex in Teff , log(g) and [M/H], respectively. The stellar parameter precision allows to break the age-metallicity degeneracy of disc stars. For the first time, the disc bimodality in the Kiel diagramme of giant stars is observed, getting rid of interstellar absortion issues. This bimodality produces double Red Giant Branch sequences and Red Clump features for mono-metallicity populations. A comparison with BaSTI isochrones allows to demonstrate that an age gap is needed to explain the evolutionary sequences separation, in agreement with previous age-metallicity relations obtained using sub-giant stars. A bimodal distribution in the stellar mass-[alpha/Fe] plane is observed at constant metallicity. Finally, a selection of stars with [M/H]=0.45 \pm 0.03 dex shows that the most metal-rich population in the Milky Way disc presents an important proportion of stars with ages in the range 5-13 Gyr. This old, extremely metal-rich population is possibly a mix of migrated stars from the internal Galactic regions, and old disc stars formed before the last major merger of the Milky Way. The Gaia GSP-Spec Kiel diagrammes of disc mono-abundance stellar populations reveal a complex, non linear age-metallicity relation crafted by internal and external processes of Galactic evolution. Their detailed analysis opens new opportunities to reconstruct the puzzle of the Milky Way disc bimodality.

Accepted for publication in A&A

References in corpus (22)

• Gaia Data Release 3: Summary of the content and survey properties
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South
• Gaia Data Release 3: Analysis of RVS spectra using the General Stellar Parametriser from spectroscopy
• The Gaia-ESO Survey: the Galactic Thick to Thin Disc transition
• A time-resolved picture of our Milky Way's early formation history
• Mixed modes in red giants: a window on stellar evolution
• The updated BaSTI stellar evolution models and isochrones: II. alpha-enhanced calculations
• Automated derivation of stellar atmospheric parameters and chemical abundances: the MATISSE algorithm
• The First APOKASC Catalog of Kepler Dwarf and Subgiant Stars
• The Gaia-ESO Survey: the chemical structure of the Galactic discs from the first internal data release
• The AMBRE project: The thick thin disk and thin thick disk of the Milky Way
• On the origin of the Galactic thin and thick discs, their abundance gradients and the diagnostic potential of their abundance ratios
• Beyond the two-infall model I. Indications for a recent gas infall with Gaia DR3 chemical abundances
• The chemical signature of the Galactic spiral arms revealed by Gaia DR3
• The Ages of Galactic Bulge Stars with Realistic Uncertainties
• Deciphering the evolution of the Milky Way discs: Gaia APOGEE Kepler giant stars and the Besançon Galaxy Model
• Spiral-like features in the disc revealed by Gaia DR3 radial actions
• The AMBRE Project: Spectrum normalisation influence on Mg abundances in the metal-rich Galactic disc
• The AMBRE Project: Solar neighbourhood chemodynamical constraints on Galactic disc evolution
• The Gaia-ESO Survey: Old super-metal-rich visitors from the inner Galaxy
• Gaia/GSP-spec spectroscopic properties of gamma Doradus pulsators

Cited by in corpus (6)

• Chronology of our Galaxy from Gaia colour-magnitude diagram fitting (ChronoGal) II. Unveiling the formation and evolution of the kinematically selected Thick and Thin Discs
• The Gaia spectroscopic catalogue of exoplanets and host stars
• GaiaUnlimited: The old stellar disc of the Milky Way as traced by the Red Clump
• A comprehensive Gaia view of ellipsoidal and rotational red giant binaries
• Solar twins in Gaia DR3 GSP-Spec I. Building a large catalog of Solar twins with ages
• Characterizing the Post-Red Supergiant binary system AFGL 4106 and its complex nebula with SPHERE/VLT