CN star
{{Short description | Unusually strong cyano radical bands in star}}
A CN star has unusually strong cyano radical bands in its spectrum compared to other stars of its stellar class. Cyano radical is a simple molecule of one carbon atom and one nitrogen atom, with absorption bands around wavelengths 388.9 and {{val|421.6|ul=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.
The excess strength of the CN bands is classified by a positive index with increments of 0.5. A value of zero indicates a normal star and is not listed in the stellar class, while the peak value of 4 is essentially similar to a carbon star. Stars classified in the MK system with a CN suffix are considered "strong" CN stars. Hence, 42 Librae is a strong CN star with a class of {{nowrap|K3-III CN2}}. A value of 0.5 is also termed a marginal CN star, which corresponds to the typical giant stars in the Hyades cluster.
References
{{reflist|refs=
| title=Spectral types and their uses
| last=Keenan | first=Philip C.
| journal=Publications of the Astronomical Society of the Pacific
| volume=99 | pages=713–723 | date=August 1987
| doi=10.1086/132036 | bibcode=1987PASP...99..713K | s2cid=121556654 | doi-access=free }}
| title=Recognition and classification of strong-CN giants
| display-authors=1 | last1=Keenan | first1=Philip C.
| last2=Yorka | first2=Sandra B. | last3=Wilson | first3=Olin C.
| journal=Publications of the Astronomical Society of the Pacific
| volume=99 | pages=629–636 | date=July 1987
| doi=10.1086/132025 | bibcode=1987PASP...99..629K | doi-access=free }}
| title=Stars with Strong Cyanogen Absorption
| last1=Schmitt | first1=John L.
| journal=Astrophysical Journal
| volume=163 | page=75 | date=3 June 1970
| bibcode=1971ApJ...163...75S | doi=10.1086/150747 | doi-access=free }}
| title=The Spectra of the Bright Stars of Types F5-K5
| last1=Roman|first1=Nancy G.
| journal=Astrophysical Journal
| date=1 March 1952 | volume=116 | page=122
| bibcode=1952ApJ...116..122R | doi=10.1086/145598 | doi-access=free}}
| title=SMR stars, strong-CN stars, and R stars
| last1=Keenan | first1=P. C. | last2=Heck | first2=A.
| journal=Revista Mexicana de Astronomía y Astrofísica
| volume=29 | pages=103–110 | date=July 1994
| bibcode=1994RMxAA..29..103K }}
}}
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