MODEL ATMOSPHERES AND X-RAY SPECTRA OF BURSTING NEUTRON STARS: HYDROGEN-HELIUM COMPTONIZED SPECTRA

摘要

Compton scattering plays a crucial role in determining the structure of the atmosphere of an X-ray burster and its theoretical spectrum. Our paper presents a description of the plane-parallel model atmosphere of a very hot neutron star and its theoretical flux spectrum of outgoing radiation. Our model equations take into account all bound-free and free-free monochromatic opacities relevant to hydrogen-helium chemical composition and take into account the effects of Compton scattering of radiation in thermal plasma with fully relativistic thermal velocities. We use Compton scattering terms in the equation of transfer, which precisely describe photon-electron energy and momentum exchange for photons with initial energies exceeding the electron rest mass of 511 keV. Model atmosphere equations are solved with the variable Eddington factors technique. The grid of H-He model atmospheres and flux spectra is computed on a dense mesh of 10~7 K ≤ T_(eff) ≤ 3 x 10~7 K and a surface gravity of log g. In many cases, the assumed log g approached the critical gravity log g_(cr), i.e., the Eddington limit. We confirm that H-He spectra of X-ray bursters deviate from blackbody spectra and discuss their shapes. The table of color to effective temperature ratios shows that theoretical values of T_c/T_(eff) do not exceed 1.9 in H-He atmospheres in hydrostatic and radiative equilibrium.