Love in the sky

Human beings do not like to be alone : they prefer to live in couple. The same holds true for stars, even if many also live in multiple systems! It indeed appears that at least 2 stars out of 3 are members of a binary system, i.e. they are gravitationally bound to a companion. And as is true for humans, life in couple is not always a quiet story. Stars in binary systems will indeed sometime interact and exchange matter. Although this may in some cases lead to very dramatic situations, e.g. the receiving star exploding as a nova or a supernova, in general, the effects will be more subtles.

For example, astronomers have discovered a class of stars that present some chemical peculiarities impossible to explain by standard stellar evolution theory. Further research has shown that these peculiar stars are all member of a binary system. We therefore developped a theoretical model explaining the existence of these peculiar stars as the result of mass exchange between the two components of the system. Although this scenario appears very promising, we need to assert it more quantitatively. This is done by performing three-dimensional hydrodynamic simulations of the mass transfer process. Thus, using a numerical code, we resolve the hydrodynamic equations corresponding to an idealized view of the binary system. And hope to understand, with computers, how stars live in couple.

I have been working on binary stars for much of my career and mostly on the following topics:

• Binary central stars of planetary nebulae
• Barium stars
• Symbiotic stars
• Blue Straggler stars
• The mass ratio distribution of spectroscopic binary stars
• Brown dwarfs
• An interferometric view of binary stars
• Cataclysmic variables
• Numerical simulations of mass transfer
• Star formation