I'm collecting different star catalogs I've found in the Internet to make my own and I noticed some "strange" peculiarity in how those catalogs describe spectral type of a star.
- sometimes the type has got a slash like "G8/K0III". Does it mean it is a binary star system? A variable star? A measurement uncertainty?
- other types has an ellipsis: "K0...". This one is a completely mystery to me...
- you can find even "+" and ":"
- and the last but not least: plain weird names like "K1IIICN..."
May someone explain where those enigmatic descriptions come from? What in the way a spectral type is determined in observatories makes the need of such things?