Towards a New Generation of Massive Star Models: Improving Stellar Evolution Modelling with Hydrodynamics Simulations and Observations

Massive stars are the main drivers of the chemical evolution of galaxies. They enrich them with newly synthesised elements ejected in stellar winds or supernova explosions. Due to their extraordinary luminosities, they are visible at extragalactic distances, and thus extremely useful for the study of the distant Universe. They can also be used as standard candles, needed to evaluate the distances in the Universe (Kudritzki & Urbaneja 2012). A sound knowledge of massive star evolution is thus mandatory to achieve reliable results in various domains: stellar population, spectral synthesis, chemical evolution models, cosmology, etc.

Recent studies have highlighted severe weaknesses in the way the evolution of massive stars is currently modelled (Chieffi & Limongi 2013; Martins & Palacios 2013; Georgy et al. 2014). The major issues concern internal transport processes, such as convection and rotation-induced flows. Today, the increasing number of observations of massive stars, thanks to ground based current large spectroscopic surveys (VLT FLAMES, IACOB, MiMeS, etc. Evans et al. 2005, 2011; Simón-Díaz et al. 2015; Wade et al. 2014) and to space missions such as CoRoT, Kepler, provides strong constraints for stellar evolution models. Very soon, the GAIA satellite will deliver its first results. Their correct interpretation will rely on improved models of massive stars.

Recent advances in numerical methods and computing power have allowed us to tackle multi-dimensional simula- tions of stellar interiors (e.g. Meakin & Arnett 2007; Viallet et al. 2013), providing new insights into the turbulent processes occurring inside massive stars. Such first-principle modelling is impossible in classical stellar evolution codes. These multi-dimensional models can thus help us understand the relevant physics, and find new ways of implementing it in the classical codes, that remain necessary to simulate the whole stellar life, due to the vast range of relevant time scales.

The goal of this ISSI team is to gather specialists in stellar evolution modelling, hydrodynamics, asteroseismology, and spectroscopy to determine the actual discrepancies between the modelling and observations, and how hydrodynamics can help improve these models. The aim is to discuss how the transport processes should be included in the models in agreement with the results of the hydrodynamics simulations, and to identify the relevant observational tests to verify the stellar models.