Dynamics of the flows accreting onto a magnetized neutron star

We investigate the unsteady column accretion of material at a rate 10(15) g s(-1) less than or equal to M less than or equal to 10(16) g s(-1) onto the surface of a magnetized neutron star using a modified first-order Godunov method with splitting. We study the dynamics of the formation and evolution of a shock in an accretion column near the surface of a star with a magnetic field 5 x 10(11) less than or equal to B less than or equal to 10(13) G. An effective transformation of the accretion flow energy into cyclotron radiation is shown to be possible for unsteady accretion with a collisionless shock whose front executes damped oscillations. The collisionless deceleration of the accreting material admits the conservation of a fraction of the heavy nuclei that have not been destroyed in spallation reactions. The fraction of the CNO nuclei that reach the stellar atmosphere is shown to depend on the magnetic field strength of the star. (C) 2004 MAIK "Nauka/Interperiodica".