Maximum ejecta velocity. The extent of the Ca IIλ 3934 (black) absorption on the blue side can be traced to ∼ 12 500 km s⁻¹ at t_max+32.7 days. Mg IIλ 2796 (dark grey) has a comparable maximum velocity, albeit this region is affected by additional SN features. The location of the blue and red doublet components of Mg IIλλ 2796,2803 and Ca IIλλ 3934,3968 of the host galaxy ISM are indicated by brackets in a darker shade at the top of the figure. We also mark the position of the doublets of the CSM shell with brackets in a lighter shade. The CSM shell is detected through an additional Mg II absorption-line system blueshifted by 2918 km s⁻¹. The CSM shell is not detected in Ca II.