Balmer-series spectral lines for hydrogen atoms in parallel magnetic and electric fields of white dwarfs

We extended the two-dimensional B-spline approach recently developed to investigate the influence of a strong electric field on atomic structures and spectra for hydrogen atoms in magnetic fields of white dwarfs. Spectral lines for hydrogen in parallel magnetic and electric fields have been calculated. Wavelengths and oscillator strengths are presented for 14 Balmer α transitions as a function of magnetic and electric fields. The magnetic and electric field strengths involved span a scope, respectively, from around 23.5 to 2350 MG, and from 0 to 10⁸ V/m. Our calculations show that the shift of Balmer-series spectral lines induced by a strong electric field reduces as the magnetic field strength increases. The obtained energy levels, wavelengths, and oscillator strengths are compared to available results in the literature, and excellent agreement was discovered. The spectral data reported in this paper can be applied to interpret the shifts of spectral lines of hydrogen in magnetic white dwarfs due to the presence of electric fields, and to predict additional spectral lines dipole-forbidden in a pure magnetic field.