Collisions between a white dwarf and a mainsequence star. 3: Simulations including the white dwarf surface
Abstract
We investigate the threedimensional hydrodynamic evolution of a collision between a 0.5 solar mass white dwarf (modeled as gravitating impermeable sphere) and a 0.5 solar mass mainsequence star (modeled as polytrope with index n = 1.5). Selfgravity is included by calculating the potential through fast FOURIER transforms on equidistant CARTESIAN grids (number of zones: 32^{3} and 64^{3}. The hydrodynamics is modeled by the 'Piecewise Parabolic Method' (PPM). The initial separation of the stars is two stellar radii and they approach each other on parabolic orbits. No energy sources (nuclear burning) or sinks (radiation, conduction) are included. The resolution in the vicinity of the white dwarf is increased by multiply nesting nine grids around the white dwarf, each finer grid being a factor of two smaller than the next coarser grid. The total dynamic range (size of the largest grid to size of the finest zone) is 8192 and 16384. This allows us to include a coarse model for the surface of the white dwarf (impermeable sphere) on the finest grid while at the same time evolving a mainsequence star on the coarser grids. In the highly dynamic evolution of central and noncentral collisions (impact parameters: 0, 0.25 and 0.5 mainsequence star radii) the mainsequence star is disrupted and forms a disk. Comparisons with earlier calculations shows that the white dwarf surface can have a large influence in forming the flow white at the same time not significantly changing global values (e.g. total energy). However, the amount of matter unbound and angular momentum transfered are highly dependent on the model for the white dwarf.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 December 1993
 Bibcode:
 1993A&A...280..141R
 Keywords:

 Astronomical Models;
 Binary Stars;
 Collisions;
 Computerized Simulation;
 Hydrodynamics;
 Main Sequence Stars;
 Three Dimensional Models;
 White Dwarf Stars;
 Angular Momentum;
 Fast Fourier Transformations;
 Flow Theory;
 Mass Flow;
 Mass Transfer;
 Mathematical Models;
 Shock Waves;
 Astrophysics