Asteroseismic inferences on the chemical enrichment of the Milky Way
Emma Willett (University of Birmingham)
Tuesday 06/12/2022 @ 14:00, Remote only
I will describe the two main projects I have worked on during my PhD, which both involve using asteroseismic constraints in the context of stellar ages and Galactic evolution. First, I will discuss the radial metallicity distribution of the Milky Way which provides information about the chemical enrichment of the disk and dynamical processes, particularly radial migration. We investigate the metallicity gradient with guiding radius in a sample of red giants, with global asteroseismic parameters from K2 and chemical abundances from APOGEE. We use asteroseismic ages and apply different modelling techniques to examine the evolution of the characteristics of the metallicity gradient. We find that the gradient flattens towards older ages, and we also constrain the intrinsic spread. This relationship and the scatter around it contain a signature of dynamical processes occurring on different timescales and motivate further examination of models of these effects. Second, I will talk about the helium-to-metal enrichment ratio, DY/DZ. The helium abundance of low-mass stars is usually estimated using this parameter, but it is not well constrained by current methods, which introduces significant uncertainties into stellar models. We use the luminosity of red clump (low-mass, core helium-burning) stars as a proxy for Y, and so investigate the helium enrichment history. The approach combines asteroseismic results from Kepler with spectroscopy from APOGEE and astrometry from Gaia to allow red clump stars to be used in this way for the first time.