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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.

Namely:

  • 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?

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Wikipedia has a pretty comprehensive list of all these peculiarities and their meaning. Spectral classification also is not always unique or unambiguous.

  • "/" denotes stars which could be classified as either
  • "..." denotes undescribed peculiarities
  • "+" denotes hypergiants. But see there also for deviating use of "f+" or "(f+)".
  • ":" denotes uncertain spectral classification
  • C,N,O, (any element symbol) denotes particularily strong lines from that element(s)

That said, any catalogue might want to explain uncommon nomenclature in its notes.

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