Definition Red supergiant star

betelgeuse pulsating , showing spectral line profile changes (hst uv images)

supergiant luminosity classes easy determine , apply large numbers of stars, group number of different types of star single category. evolutionary definition restricts term supergiant massive stars start core helium fusion without developing degenerate helium core , without undergoing helium flash. universally go on burn heavier elements , undergo core collapse resulting in supernova.

less massive stars may develop supergiant spectral luminosity class @ relatively low luminosity, around 1,000 l☉, when on asymptotic giant branch (agb) undergoing helium shell burning. researchers prefer categorise these agb stars distinct supergiants because less massive, have different chemical compositions @ surface, undergo different types of pulsation , variability, , evolve in different way, producing planetary nebula , white dwarf. agb stars not become supernovae although there interest in class of super-agb stars, massive enough undergo full carbon fusion, may produce peculiar supernovae although without ever developing iron core. 1 notable group of low mass high luminosity stars rv tauri variables, agb or post-agb stars lying on instability strip , showing distinctive semi-regular variations.