Critical temperature of white dwarfs with strong magnetic field

We calculate the pressure force by cyclotron radiation in a plane-parallel, isothermal, pure-hydrogen photosphere of a white dwarf with the dipole mag netic field taking into account correct expressions for the collision frequ ency in plasma on these stars. The critical temperature at which radiation pressure force per proton equals gravitational force on a magnetic white dw arf is shown to increase due to substantial decrease of the collision frequ ency in a strong magnetic field. This means that formation of plasma envelo pes in magnetospheres of radiation-driven diskon candidates-the magnetic wh ite dwarfs GD 229, PG 1031+/-234, and GrW+70 degrees 8247-via ejection of p lasma from the star surface requires the existence of an upward temperature gradient in the photosphere.