Binary Neutron Stars with Arbitrary Spins in Numerical Relativity

We present a code to construct initial data for binary neutron star systems in which the stars are rotating. Our code, based on a formalism developed by Tichy, allows for arbitrary rotation axes of the neutron stars and is able to achieve rotation rates near rotational breakup. We compute the neutron star angular momentum through quasi-local angular momentum integrals. When constructing irrotational binary neutron stars, we find a very small residual dimensionless spin of $\sim 2\times 10^{-4}$. Evolutions of rotating neutron star binaries show that the magnitude of the stars' angular momentum is conserved, and that the spin- and orbit-precession of the stars is well described by post-Newtonian approximation. We demonstrate that orbital eccentricity of the binary neutron stars can be controlled to $\sim 0.1\%$. The neutron stars show quasi-normal mode oscillations at an amplitude which increases with the rotation rate of the stars.Comment: 20 pages, 22 figure

Transport Processes in Stellar Interiors

International audienceStars are rotating and magnetic bodies. Moreover, more and more constraints are obtained on such dynamical processes using, for example, seismology and spectropolarimetry. Therefore, it is now necessary to get a complete and coherent picture of dynamical processes in stellar interiors. However, to simulate such processes in a star in full details would require treating length scales and time scales spanning many orders of magnitude. This is clearly not feasible, even with the most powerful computers available today. This is the reason why it is nowadays necessary to use and couple 1-D, 2-D, and 3-D modelings to get a global picture of macroscopic MHD transport processes in stellar interiors. In this review, we report the state of the art of the modeling of transport processes in stellar interiors (both in radiation and in convection zones) aimed to study the stars angular momentum history, the related profile of differential rotation, and their magnetism