Origin and occurrence of fluorine supernovae, atoms of neon could be hit by neutrinos during the explosion and converted to fluorine. In Wolf-Rayet stars (blue stars over 40 times heavier than the Sun), a strong solar wind could blow the fluorine out of the star before hydrogen or helium could destroy it. Finally, in asymptotic giant branch (a type of red giant) stars, fusion reactions occur in pulses and convection could lift fluorine out of the inner star. Only the red giant hypothesis has supporting evidence from observations. In space, fluorine commonly combines with hydrogen to form hydrogen fluoride. (This compound has been suggested as
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