A type of cool giant star with roughly equal amounts of carbon and oxygen in its atmosphere, intermediate between normal oxygen-rich stars and carbon stars. These stars show strong absorption bands from zirconium oxide and other s-process elements.
The 'S' classification was introduced in the 1940s by astronomer Paul Merrill, who noticed stars with spectra intermediate between normal M-type giants and carbon stars. The 'S' stands for the strong absorption bands of s-process elements, particularly zirconium oxide, that characterize these stars.
S-type stars are cosmic alchemists caught in the act of transformation! These stars are literally in the process of converting from normal oxygen-rich giants into carbon stars, and we can watch this stellar metamorphosis happening in real-time. They're also factories for heavy elements created by the slow neutron capture process, including many elements essential for rocky planets and life.
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