WINDS FROM NEUTRON-STARS AND STRONG TYPE-I X-RAY-BURSTS

A model for stationary, radiatively driven winds from X-ray-bursting n eutron stars is presented. General relativistic hydrodynamical and rad iative transfer equations are integrated from the neutron star surface outward, taking into account for helium nuclear burning in the inner, dense, nearly hydrostatic shells. Radiative processes include both br emsstrahlung emission-absorption and Compton scattering; only the freq uency-integrated transport is considered here. It is shown that each s olution is characterized by just one parameter: the mass-loss rate M, or, equivalently, the envelope mass M(env). We found that, owing to th e effects of Comptonization, steady, supersonic winds can exist only f or M larger than a limiting value M(min) almost-equal-to M(E). Several models, covering about two decades in mass-loss rate, have been compu ted for given neutron star parameters. We discuss how the sequence of our solutions with decreasing M(env) can be used to follow the time ev olution of a strong X-ray burst during the expansion/contraction phase near to the luminosity maximum. The comparison between our numerical results and the observational data of Haberl et al. (1987) for the bur sts in 4U/MXB 1820-30 gives an estimate for both the spectral hardenin g factor and the accretion rate in this source.