Electrostatic corrections to the equation of state for a fully ionized hydrogen atmosphere of magnetic neutron stars

Taking account of electrostatic corrections, we compute a more realistic equation of state for a fully ionized hydrogen gas in strong magnetic fields. For physical conditions relevant to neutron star photospheres, that is, a density of about 1 g/cm(3) and a temperature of about 10(6) K, our results show that the deviation from the ideal-gas law is at a 10% level. For a lower temperature, it can reach 20%. At deeper layers, where the density is larger and the optical depth for higher frequency radiation may still be small, the deviation can be a factor of 2 or so. Such a discrepancy is obviously not negligible when constructing neutron star atmosphere models.