Spectral evolution of SN 2007pk. Wavelengths are in the observer’s rest frame. The phase reported for each spectrum is relative to the explosion date (JD 2 454 412), late spectra have been multiplied by a factor 40 to emphasise the nebular lines. The ⊕ symbols mark the positions of the strongest telluric absorptions. The ordinate refers to the top spectrum; the other spectra are shifted downwards with respect to the previous one by 7 × 10^-16, except the third, which is shifted by 1 × 10^-15 erg s^-1 cm^-2 Å^-1.