S-type star

An evolved cool giant star whose spectrum contains prominent zirconium oxide bands. Many S-type stars also show elements enriched by slow neutron capture.

Connect

Stellar spectral classification: A system for classifying stars by features in their spectra, especially temperature-sensitive absorption lines. S-type is a spectral class identified by characteristic molecular absorption bands.
Asymptotic giant branch: A late evolutionary phase of low- and intermediate-mass stars, characterized by a contracting core and two surrounding burning shells. Many intrinsic S-type stars are thermally pulsing stars on this evolutionary branch.
Chi Cygni: A long-period variable red giant whose changing brightness and spectrum have been studied extensively. It is a well-known Mira variable classified as an S-type star.
M-type star: A cool star whose spectrum commonly shows strong titanium oxide bands. M-type giants are oxygen-rich neighbors whose spectra emphasize titanium oxide rather than zirconium oxide.
Zirconium monoxide: A molecule whose electronic transitions produce absorption bands in the spectra of some cool stars. Its prominent bands are the defining spectral signature of S-type stars.
Third dredge-up: A mixing episode after a helium-shell flash that carries products of internal nucleosynthesis into a giant star's envelope. It can bring carbon and slow-neutron-capture products to an S-type star's surface.
R Andromedae: A long-period variable star in Andromeda classified as an S-type giant. Its changing spectrum illustrates S-star variability and molecular absorption.
Carbon star: A cool giant star whose atmosphere has more carbon than oxygen, producing prominent carbon-bearing molecules. Carbon stars occupy a later, more carbon-rich chemical state than many S-type giants.
Molecular band: A broad group of closely spaced spectral lines produced by molecules in a gas. Zirconium monoxide and other molecules mark the cool atmospheres of these stars.
Thermal pulse: A brief episode of unstable helium burning in the shell of an asymptotic giant branch star. Pulses drive mixing episodes that can alter the surface chemistry of intrinsic S-type stars.