SS 433: a freely precessing neutron star

Jets emerging from diametrically opposite points fixed on the surface of a freely precessing neutron star can explain naturally the motion of the spectral features of SS 433. If the rotation axis of the neutron star is close to the line-of-sight, the equations describing the velocity shifts reduce to a similar form to the equations that are applied to the precessing jet model. The hydrogen and helium observed in emission may originate from the surface of a companion star, about which the neutron star is in orbit. This companion induces the approximately 13-day radial velocity and photometric variations and may be responsible for the elongated shape of W 50. Studies of SS 433, and perhaps of Her X-1, may provide valuable insight into the interior structure of neutron stars. (author)