Colloquium: Marica Valentini (AIP)

Unfolding the history of the Milky Way halo using asteroseismology

Metal poor stars are key to understanding the history of our Galaxy. In their element abundances pattern is encoded the chemical composition of the first stars and therefore, when the stellar age is available, hints on the chemical enrichment and evolution of the Milky Way. However, to obtain precise ages for field metal poor stars is a challenging task: at present only an handful very metal-poor stars have ages, derived by using nucleo-cosmo-chronology (via Thorium and Uranium abundances).

Asteroseismology in recent years has demonstrated to be a powerful tool to derive masses, and hence ages, of red giant stars. When this technique is applied to metal poor stars,it is possible to increase the number of metal poor stars with an precise age measurement.

For this purpose I am leading a project combining asteroseismology and high resolution spectroscopy of metal-poor halo giants ([Fe/H]<-1.5 dex). Targets are identified in RAVE and APOGEE surveys. We obtained seismic information from the light curves collected by the Kepler,K2, and TESS space missions, and detailed chemical abundances, from ESO-UVES and HARPS-N high resolution spectra.  We derived iteratively the atmospheric parameters, by taking into account the seismic surface gravity. We then derived precise abundances taking into account NLTE effects. The final atmospheric parameters and abundances, together with the seismic information and, when available, Gaia parallaxes, were used for interfere stellar masses, radii and ages, via Bayesian fitting on a set of isochrones.

We obtained a unique set of metal poor stars, for which we determined precise ages. For the first time a consistent and complete approach have been adopted, in order to quantify the impact of temperature shifts, different mass-loss approaches, alpha-enrichment and corrections on seismic scaling relations. Our project shows how it is possible to obtain precise ages for field metal poor giants, and therefore to reconstruct the history of the Galactic halo.

• Date:
  Jan. 28, 2021, 2:30 p.m. – 3:30 p.m.
  
  
• Location:

  Colloquium Zoom Room

  
  
• Contact:
  Davor Krajnović