The fundamental role of stellar multiplicity in stellar dynamics and evolution

31 October - 25 November 2022

Antoine Mérand, Henri M.J. Boffin, Sylvia Ekström, JJ Eldridge, Michela Mapelli

Most stars are not isolated: they are born, live and die in pairs or multiple systems. Not only stellar multiplicity is an important ingredient in the dynamic evolution of stellar clusters, but interactions play a crucial role in all the stages of stellar evolution: transfer of angular momentum, irradiation, accretion and stripping, merging, etc., leading to a wide range of most interesting phenomena such as supernovae, gamma-ray bursts, or gravitational waves. The recent decade has seen important developments on all these fronts, leading to the need in many cases to rewrite textbooks. On the one hand, advances in observation techniques are revealing an ever-growing fraction of stars being in multiple systems and the importance of binarity in many phenomena or observations. On the other hand, more modelling and theoretical works now need to include stellar multiplicity as a major ingredient.

Our meeting intends to create a dialogue between observers, modelers and theoreticians to share problems, ideas and methods around stellar multiplicity and interaction. This is only one side of the coin: even if for some research fields stellar multiplicity is a given and well embedded in methods, its importance is controversial in other fields, despite observational and/or theoretical evidence. Our meeting also aims at addressing these controversies by providing a stage for the latest arguments, and a constructive environment for dialogue and fostering scientific collaboration.

Week 1: Multiple stars in stellar populations and clusters and the role of binaries in the study of the Universe

Multiple stars play a key role in the dynamics of clusters. They also need to be taken into account when studying integrated stellar populations, including galaxies, as the most luminous stars are the product of binary evolution (Luminous Blue Variable, Supernovae, gamma-ray bursts, gravitational wave sources, …). Because of this, they can also be used to probe the most distant parts of the Universe, as is the case for Type Ia supernovae which play a key role in determining the Hubble constant and the acceleration of the expansion of the Universe.


Week 2: Multiple stars and their close environments

Binary and multiple stars impact considerably their close environment, whether on small or large scales. For example, binaries are now thought to be responsible for the morphology and possibly also the formation of a majority of planetary nebulae. Some systems resulting from binary interactions are also producers of specific chemical elements (e.g. r-process elements like gold is thought to be produced in mergers) or of dust. As such they contribute to the chemical evolution of galaxies. Another related question is how does binarity affect the formation of planets. Some planets have been found around binary system, even around post-mass transfer systems, and this is a very hot current topic of research. We will also cover here the observational tools that can be used for the study of binaries.


Week 3: Topical conference “ImBaSE 2022”

The Impact of Binary Stars on Stellar Evolution 2022, to be held at Max Planck Institute for Astrophysics.


Week 4: Products of multiple stars evolution

The final week will be devoted to the study of the final products of binary and multiple star evolution. Here we will consider questions such as:
- Is the end of life of massive stars dominated by binary interaction?
- Can we form Be stars without binary interaction?
- What is currently missing from numerical simulations of mass transfer and of the common envelope evolution?
- Is common envelope evolution a universal process or are there multiple mechanisms and pathways of the most extreme binary interaction?
- What are the multiple pathways that lead to formation of gravitational wave transients? What does the current gravitational wave transient catalogue tell us about binary evolution?
- What is the role of binary interactions in the diversity of core-collapse and thermonuclear supernovae?