Magnetobremsstrahlung and optical polarization: An understanding and a correction

Circularly polarized emission by bremsstrahlung (free-free electron transitions) in a magnetic field is explained in a very elementary way. An error in the pertinent section of Kemp's 1970 paper is rectified. For free-free magnetoemission, in the important limit ωtauvery-much-greater-than1, the correct result for the fractional circular polarization is q=4(Ω/sub L//ω), where Ω/sub L/=eB/2m (or eB/2mc) and ω are the Larmor and optical frequencies, respectively. This is half as large as the value in the earlier paper. (The formula q=Ω/sub L//ω for bound-bound transitions in the earlier paper, however, was correct.) The magnetobremsstrahlung result is also shown here to agree with the formula obtained from collision-damped absorption by free electrons in a magnetic field. The linear polarization is also discussed. The large linear polarization of some magnetic white dwarfs is not accounted for