[1] Cyano radical is a simple molecule of one carbon atom and one nitrogen atom, with absorption bands around wavelengths 388.9 and 421.6 nanometer.
[2] This group of stars was first noticed in certain G and K-type giants by J. J. Nassau and W. W. Morgan in 1949,[3] then a further 4,150 were identified by Nancy G. Roman in 1952.
[4] They can be distinguished from barium stars by the lack of s-process elements, and from other types of luminous stars by the general weakness of features other than the CN lines.
[3] The excess strength of the CN bands is classified by a positive index with increments of 0.5.
Hence, 42 Librae is a strong CN star with a class of K3-III CN2.