A CN star has unusually strong cyanogen bands in its spectrum compared to other stars of its stellar class. Cyanogen is a simple molecule of one carbon atom and one nitrogen atom, with absorption bands around wavelengths 388.9 and 421.6 nanometer. This group of stars was first noticed in certain G and K-type giants by J. J. Nassau and W. W. Morgan in 1949, then a further 4,150 were identified by Nancy G. Roman in 1952. 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.