Accretion simulations of η Carinae and implications for the evolution of massive binaries

This contribution presented high-resolution numerical simulations of the colliding wind system η Carinae, showing accretion of the primary wind onto the secondary star close to periastron passage. We found that the stellar winds collide and develop instabilities, mainly the non-linear thin shell instability, and form filaments and clumps. We also found that a few days before periastron passage the dense filaments and clumps flow towards the secondary as a result of its gravitational attraction, and are then accreted onto the secondary. We ran our simulations for a conventional model of stellar masses, $M_1=120 \rm{M_\odot}$ and $M_2=30 \rm{M_\odot}$, and for the high-mass model, $M_1=170 \rm{M_\odot}$ and $M_2=80 \rm{M_\odot}$, that was proposed to fit better the history of giant eruptions in the 19$^{\rm th}$ Century, as well as radial-velocity variations of spectral lines during recent spectroscopic events. The results of the simulations show that the accretion process is more pronounced in the high-mass model, and that the amount of mass accreted, as well as the duration of the accretion, are also fitted much better. Our findings establish η Car as the most massive binary system in the Galaxy. As our simulations demonstrate, the presence of a binary companion can have a huge influence on the evolution of massive stars, especially at later stages where it may undergo giant episodes of mass loss.