The first group exhibit weak C2 and CN features and Ha in absorption; the second, features attributable to a low C 12 /C 13 ratio; the third, strong C2 and CN features and only moderately strong Na 1 in absorption; the fourth, very strong Na 1 in absorption; and the fifth, Ha in emission. Exam ples are given of each group, stars not fitting well into any of these groups are discussed, and the significance of each group is mentioned in light of work by Bouigue, Gordon, Peery, and Richer.
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