Precision dating of old stellar populations with helium-burning stars

Alessandro Savino

ARI Heidelberg

The study of nearby resolved galaxies is a source of transformational insights into the mechanisms that regulate galaxy evolution and it provides us with a detailed view on how star formation proceeds in the medium-to-small dark matter haloes. To date, the most precise measurements of ancient star formation rely on the detection of the oldest main sequence stars. The challenging observational requirements for a such a detection impose severe limitations on the quantity and quality of old star formation histories at our disposal.

In this talk I will describe a new approach, aimed at expanding the capabilities of ancient star formation history measurements via modelling of the old horizontal branch stars. I will show that, thanks to its brightness, the horizontal branch has the potential to deliver very precise star formation histories, for a large and cosmologically representative sample of galaxies, constituting a treasure trove for the archaeological characterization of the Local Volume.

I will illustrate present and future applications of this method to different environments, ranging from the heart of the Milky Way, to nearby dwarf galaxies, to the neighbouring groups and clusters, unveiling a new and sharper view on the ancient past of present day galaxies.