  It is suggested that the accretion disk excites the eigen modes of Alfven
oscillations of the magnetic field tubes the ends of which are frozen to the
neutron star surface. The resonance takes place when the eigen Alfven frequency
coincides with the difference of the Keplerian disk rotation frequency and the
frequency of rotation of a neutron star. This model explains the two narrow
lines of QPO oscillations in kHz band and permits to calculate the masses and
radii of the neutron stars in X-ray binaries.
