MoBiDICT: new 3D static models of close, synchronized binaries in hydrostatic equilibrium

In close binary systems, tidal interactions and rotational effects can
strongly influence stellar evolution as a result of mass-transfer, common
envelope phases, ... All these aspects can only be treated following
improvements of theoretical models, taking into account the breaking of
spherical symmetry occurring in close binaries. Current models of binary stars
are relying either on the so-called "Roche model" or the perturbative approach
that in each case results on several assumptions concerning the gravitational,
tidal and centrifugal potentials.We developed a new non-perturbative method to
compute precise structural deformation of binary system in three dimensions
that is valid even in the most distorted cases. We then compared our new method
to the Roche and perturbative models for different orbital separations and
binary components. We found that in the most distorted cases both Roche and
perturbative models are significantly underestimating the deformation of
binaries. The effective gravity and the overall structural deformations are
also noticeably different in the most distorted cases leading, for the
interpretation of observations, to modifications of the usual gravity darkening
generally obtained through the Roche model. Moreover we found that the dipolar
term of the gravitational potential, usually neglected by the perturbative
theory, has the same order of magnitude than the leading tidal term in the most
distorted cases. We developed a new method that is capable of precisely
computing the deformations of binary system composed of any type of stars, even
compact objects. For all stars studied the differences in deformation with
respect to the Roche or perturbative models are significant in the most
distorted cases impacting both the interpretation of observations and the
theoretical structural depiction of these distorted bodies.