RSAA Colloquia / Seminars / Feast-of-Facts: Tuesday, 16 August 2022, 11:00-12:00; DLT & ZOOM


Arthur Alencastro Puls

"Investigating the Relationship Between Chemical Abundance Ratios and Ages in Red Giant Stars"

Recent developments have enabled the usage of asteroseismology for measurement of stellar masses, hence ages, at a high level of precision and accuracy for red giants, thanks to the exquisite photometry from space-based observatories. Combining precise chronological information with other observables such as chemical abundances is refining our understanding of the Milky Way. In this work, we dissect in depth a sample of 23 stars, making a detailed chemical analysis from high-quality HIRES@Keck spectra. We combine the chemical information with a careful asteroseismic grid-based modelling that determines the fundamental parameters of these 23 stars, ages included, and we study their kinematics to complete their big picture. These stars were selected due to being identified as outliers in past surveys, with their previously estimated ages in disagreement with their overall chemistry: old and metal-rich, young and metal-poor, young and alpha-rich. The chemical abundances are derived with a classical 1D LTE spectroscopic method. The asteroseismic grid-based modelling uses interpolation of several observables, including asteroseismic information. The kinematic analysis relies on modelling with GalPy. Our results confirm the need for a model-based correction in the determination of stellar masses in red giants. However, such correction was not enough to make the ’young and metal-poor’ objects be old enough to have ages compatible with the expectations for the formation of the Milky Way halo. Two of these stars were identified as being likely accreted by the Milky Way, while two other stars are potential evolved blue stragglers. Our findings also suggest that the uncertainties of Gaia (E)DR3 parallaxes might be underestimated. Also, the understanding of the stars in the core He-burning phase is still hampered by uncertainties regarding mass loss in the previous evolutionary stage. Finally, we show that our method yields better precision in the determination of stellar masses of red giants when compared to recent large-scale surveys.