POLARIZATION MODES IN A STRONGLY MAGNETIZED HYDROGEN GAS

Propagation of high-frequency radiation in an anisotropic medium can b e described in terms of two normal modes with different polarizations and different absorption coefficients. We investigate the properties o f the normal modes in a strongly magnetized hydrogen gas for condition s expected in atmospheres of isolated neutron stars. We use the Kramer s-Kronig relations to obtain the polarizability tensor for the strongl y magnetized hydrogen. We derive and compute the polarizations and abs orption coefficients of the normal modes from the polarizability tenso r using both analytical approximations and numerical calculations. We find that the spectral features and anisotropy associated with the bou nd-bound and bound-free transitions in the magnetized hydrogen are man ifested in the polarization characteristics, which affect substantiall y the spectral and angular dependences of the absorption coefficients of the normal modes and the transfer of radiation in neutron star atmo spheres. There exist at least two critical frequencies at which, for a ny direction of propagation, either the normal mode polarizations are exactly linear or orientations of two polarization ellipses coincide w ith each other. For each of these frequencies there exists a direction of propagation for which the two normal modes are linearly polarized, and their polarizations and absorption coefficients fully coincide. T he unusual properties of the normal modes should manifest themselves i n the spectra, angular distribution, and polarization of the thermal-l ike radiation emitted from surface layers of neutron stars.