Editing Stellar classification (section)

====Class S====
{{Main|S-type star}}
Class&nbsp;S stars form a continuum between class&nbsp;M stars and carbon stars. Those most similar to class&nbsp;M stars have strong [[Zirconium monoxide|ZrO]] [[spectral bands|absorption bands]] analogous to the [[Titanium monoxide|TiO]] bands of class&nbsp;M stars, whereas those most similar to carbon stars have strong [[sodium]] D lines and weak [[Diatomic carbon|C<sub>2</sub>]] bands.<ref>{{cite journal |last=Keenan |first=P. C. |year=1954 |title=Classification of the S-Type Stars |journal=Astrophysical Journal |volume=120 |page=484 |doi=10.1086/145937 |bibcode=1954ApJ...120..484K}}</ref> Class&nbsp;S stars have excess amounts of [[zirconium]] and other elements produced by the [[s-process]], and have more similar carbon and oxygen abundances to class&nbsp;M or carbon stars. Like carbon stars, nearly all known class&nbsp;S stars are [[asymptotic giant branch|asymptotic-giant-branch]] stars.

The spectral type is formed by the letter&nbsp;S and a number between zero and ten. This number corresponds to the temperature of the star and approximately follows the temperature scale used for class&nbsp;M giants. The most common types are S3 to S5. The non-standard designation S10 has only been used for the star [[Chi Cygni]] when at an extreme minimum.

The basic classification is usually followed by an abundance indication, following one of several schemes: S2,5; S2/5; S2 Zr4 Ti2; or S2*5. A number following a comma is a scale between 1 and 9 based on the ratio of ZrO and TiO. A number following a slash is a more-recent but less-common scheme designed to represent the ratio of carbon to oxygen on a scale of 1 to 10, where a 0 would be an MS star. Intensities of zirconium and [[titanium]] may be indicated explicitly. Also occasionally seen is a number following an asterisk, which represents the strength of the ZrO bands on a scale from 1 to 5.