Supernova P Cygni profiles

Robin Leadbeater

I normally just measure the shift of the absorption minimum, either relative to the line rest wavelength corrected for z if known or the emission maximum. I guess there must be higher velocities out to the edge of the line where it meets the continuum but my resolution is so low it would bias the result. It looks like the 13500km/s measured in the very early classification spectrum was based on where the broad H alpha emission met  the continuum.