Extended Data Fig. 6: The Hα profile of SN 2018evt observed with WiFeS at day +307 fitted with two Gaussian functions.

The FWHM widths of the broad (cyan-dashed line) and intermediate (blue-dotted line) components yield 5877 ± 32 km s⁻¹ and 1643 ± 12 km s⁻¹, respectively. The red-solid curve gives the combination of these two components. The bottom gray line represents the Hα profile after subtracting the broad and intermediate components. An arbitrary offset has been applied to the residual spectrum for the purpose of presentation. The inset provides a zoom-in view of the P-Cygni profile as displayed in the residual spectrum. A double-Gaussian component fit to the residual spectrum near the Hα core is illustrated by the cyan curve. The location of the peak of the emission component suggests a redshift z =0.02561 ± 0.00019, the location of the minimum of the absorption component measures a wind velocity V_w = 91 ± 58 km s⁻¹.