Red giant the end of the thermal pulsing phase. Among the asymptotic-giant-branch stars belong the carbon stars of type C-N and late C-R, produced when carbon and other elements are convected to the surface in what is called a dredge-up. The first dredge-up occurs during hydrogen shell burning on the red-giant branch, but does not produce a large carbon abundance at the surface. The second, and sometimes third, dredge up occurs during helium shell burning on the asymptotic-giant branch and convects carbon to the surface in sufficiently massive stars. The stellar limb of a red giant is not sharply defined, contrary to
Red supergiant star than a hotter supergiant. For example, Alpha Herculis is classified as a giant star with a radius of while Epsilon Pegasi is a K2 supergiant of only . Although red supergiants are much cooler than the Sun, they are so much larger that they are highly luminous, typically . There is an upper limit to the luminosity of a red supergiant at around . Stars above this luminosity would be too unstable and simply don't form. Red supergiants have masses between about and . Main-sequence stars more massive than about do not expand and cool to become red supergiants. Red