Expansion velocity measured from the minimum of the broad P-Cygni for Hα, He Iλ5876, and Fe IIλ5169, together with the corresponding power-law fits (black, red, and blue lines, respectively). A similar double trend is seen for Hα before and after phase +30 days, while He I follows a power-law decline, although, it is contaminated by Na I D, especially at late phases. The Fe II line also shows a power-law decline, albeit with some scatter, possibly due to the difficult identification.