Spectral evolution of SN 2012aa. All spectra were normalized to the average continuum flux density measured in the line-free region 6700−7000 Å and additive offsets were applied for clarity. The dotted vertical line shows the position of Hα. Phases are with respect to the date of maximum V-band light. The spectra obtained on +8 d and +51 d were modelled using SYNOW (red curves) to identify the important line features.