Establishing a multi-dimensional framework to benchmark Wolf-Rayet-type outflows

• Applicant: Dr. Andreas Sander
• Subject Area: Astrophysics and Astronomy
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 496854903

The short but vibrant life of massive stars is critical for the evolution of whole galaxies, both in the early times of the Universe and now. With their high luminosity, massive stars can ionise their surroundings and expel their outermost layers in the form of a so-called stellar wind. Such radiation-driven winds affect the neighbouring interstellar matter and the evolutionary pathway of the host stars themselves.At the end of their life, massive stars collapse into exotic remnants like neutron stars and black holes - collectively referred to as compact objects (CO). Whether this collapse is accompanied by a supernova explosion and which type of remnant is formed is largely determined by the final mass of the star, stressing that the quantitative knowledge about prior mass loss is crucial. With the recent advent of gravitational wave astronomy and an ever-growing number of CO merger detections, the need to understand massive stars’ influence and evolutionary pathways has only grown further. This project is dedicated to an important piece of the evolutionary puzzle of massive stars: Classical Wolf-Rayet (WR) stars are evolved stars on the way to core-collapse with powerful winds. The mass loss in this evolutionary stage is so large that it usually determines the mass and type of the CO remnant.Despite the critical role of WR stars in modern astrophysics, the qualitative and quantitative insights into the processes participating in the launch and acceleration of WR winds are still rudimentary, thus causing major uncertainties in current evolution and population synthesis models. This uncertainty stems from the fact that the determination of WR properties (e.g., wind velocity, density structure, mass loss, and emergent spectra) requires complicated numerical radiation-hydrodynamics computations. The numerical costs of such calculations have so far prevented detailed simulations beyond one-dimensional steady-state treatments. In this project, we combine two recent advances in modelling techniques to reach beyond this limit and to create the first grid of three-dimensional, time-dependent models of WR wind outflows and their spectra. Our projects’ cornerstone is a refinement of the radiation force computation method, which opens a new perspective for the numerical treatment of WR winds within hydrodynamic codes. We will implement, test, and benchmark our new method against state-of-the-art modelling techniques. We will then create a grid of models covering a large parameter space in masses, luminosities, radii and metallicities. This grid will allow us to parametrise a new mass-loss treatment for WR stars and create an extensive spectral library, which we will use to calibrate a more detailed spectral synthesis code.

• DFG Programme: Research Grants
• International Connection: Belgium, United Kingdom, USA
• Cooperation Partners: Dr. Levin Hennicker; Nathaniel Kee, Ph.D.; Dr. Nicolas Moens; Professor Jon Sundqvist, Ph.D.; Professor Dr. Jorick Vink