Quadratic Zeeman effect in the hydrogen Balmer lines from magnetic white dwarfs

Motivated by Preston's suggestion of using the quadratic Zeeman effect to detect large magnetic fields in DA white dwarfs, we use a variational method for an accurate calculation of the total Zeeman wavelength shifts of the hydrogen Balmer absorption lines (Ha-H10) for magnetic fields from 106 to 5 x 106 gauss. Interference effects between upper values of the principal quantum number n become significant in that range. The quadratic shifts are smaller than those given by perturbation theory, leading to an increase in the estimated magnetic field. Subject headings: magnetic stars - white dwarf stars - Zeeman effect