Observed Hα and Hβ profiles compared to the fitted model spectrum. The graph shows one observed spectrum for each binary and the best fitting model spectrum (blue smooth line). Here and in the following figures we display the observed spectra smoothed with a Gaussian of 0.15 Å FWHM, hardly affecting the spectral resolution. Δλ is the wavelength offset relative to the laboratory wavelengths of Hα and Hβ, respectively. Top left: HS 0002+1635, fitted with model spectra without modifications. Top right: WD 2146−433, a hot DA with a Gaussian added to better reproduce the central emission core (model spectrum without correction shown as dashed red line). Bottom left: WD 0126+101, one of the cool DAs displaying a broader and stronger central core than predicted by the models (model spectrum without correction shown as dashed red line). Bottom right: WD 1300−098, one of the magnetic white dwarfs.