Transmission spectra of the Hα line. The black circles represent spectra binned every five points (~0.15 Å) and the grey lines represent the original spectra (i.e. ~0.03 Å per point). The red lines indicate the best-fit Gaussian functions. The vertical dashed line indicates the rest wavelength line centre. The CLV and RM effects are corrected. An offset of the y-axis is applied to the spectra for clarity.