Can uncertainties in the evolution of the massive stars explain EM and GW observations?  [slides]

Abstract

Recent observations of galaxies and star clusters have highlighted the need for systematic studies dedicated to exploring the impact of uncertain parameters of stellar evolution on the properties of stellar populations. While the use of fitting formulae to stellar tracks remains a popular choice for modelling stellar evolution in population synthesis codes, they are not adaptable to changes in the stellar tracks. In this talk, I will present results from an alternative approach, METISSE, which uses interpolation between sets of pre-computed stellar tracks to approximate evolution parameters for a population of stars. It can readily make use of stellar models computed with different stellar evolution codes and can compare their predictions for populations of stars. Using METISSE with the data from two different stellar evolution codes, I will show how different physical ingredients used in the evolution of massive stars, such as the treatment of their radiation dominated envelopes, can lead to differences in their evolutionary properties. These differences are important as they can help us account for observations of the stellar populations and the formation of gravitational wave progenitors.