Hi again Peter,
Once you feel you’ve mastered the processing of your spectra following Robin’s guidance, there is a nice little project you could try. In the same area of sky as Alhena there is a bright 4th magnitude Be star called nu Gem (Hα line in emission instead of absorption). Overlaying the spectra of Alhena and nu Gem clearly shows the difference in the Hα line between the two stars….
