I stumbled across Castor last night with my SA-100. I was not aware that it was a multiple star system but I could clearly see a smaller blob hanging off the main star and the spectrum was odd in that the top half was different from the bottom. I was able to tweak out 2 separate spectra by controlling the sample binning and it appears that I have a couple of pretty typical early A stars.
It turns out that Castor is actually 3 pairs. Pairs A and B are white dwarfs with red dwarfs and pair C is possibly two red dwarfs.
So it appears I have Aa and Ba. Castor Ba is also classified as an Am or a metallic line star. According to wiki "type of chemically peculiar star of spectral type A whose spectrum has strong and often variable absorption lines of metals such as zinc, strontium, zirconium, and barium, and deficiencies of others, such as calcium and scandium". Unfortunately, my spectra are not good enough to see any of that...