SIMBAD references

We investigate the hydrodynamics of three-dimensional classical Bondi-Hoyle accretion. A totally absorbing sphere of different sizes (10, 1, 0.1 and 0.02 accretion radii) moves at different Mach numbers (0.6, 1.4 and 10) relative to a homogeneous and slightly perturbed medium, which is taken to be an ideal gas (γ=5/3). To accommodate the long range gravitational forces, the extent of the computational volume is 32³ accretion radii. We examine the influence of Mach number of the flow and size of the accretor upon the physical behaviour of the flow and the accretion rates. The hydrodynamics is modeled by the "Piecewise Parabolic Method" (PPM). No energy sources (nuclear burning) or sinks (radiation, conduction) are included. The resolution in the vicinity of the accretor is increased by multiply nesting several (5-9) grids around the sphere, each finer grid being a factor of two smaller in zone dimension than the next coarser grid. This allows us to include a coarse model for the surface of the accretor (vacuum sphere) on the finest grid while at the same time evolving the gas on the coarser grids. For small Mach numbers (0.6 and 1.4) the flow patterns tend towards a steady state and in the case of supersonic flow additionally a Mach cone develops. For large flow velocities (Mach 10) and small enough accretors (radius of 0.1 and 0.02 accretion radii) the flow becomes unstable, destroying axisymmetry. Our 3D models do not show the highly dynamic flip-flop flow so prominent in 2D calculations performed by other authors. A new interpolation formula for the mass accretion rates is proposed and found to follow the collected numerical data to within approximately 20% over many orders of magnitude in accretor size and for Mach numbers from 0 to 10.