Spectropolarimetry and IR photometry of magnetic white dwarfs: Vacuum polarization or rydberg states in their magnetic fields?

We suggest two mechanisms to explain IR photometric and spectropolarimetric observations of magnetic white dwarfs: vacuum polarization and the existence of Rydberg atomic states with large dipole moments arising due to atomic collisions in the strong magnetic field of the white dwarf (so-called magnetic collision-induced absorption, or magnetic CIA). Both mechanisms can explain the observed rotations of the polarization ellipses and the depression of the IR spectral energy distribution. We present the results of spectropolarimetric observations of several magnetic white dwarfs with the Special Astrophysical Observatory 6-m telescope, together with photometric observations in the near-IR obtained with the Russian-Italian AZT-24 Telescope at Campo Imperatore.