At what point in a star's life are they classified as AGB?

Question

Lincoln Adams · Accepted Answer

Stars are classified as AGB when they become red giants.

All medium-sized stars between 0.6 and 10 solar masses enter the Asymptotic Giant Branch (AGB) of the Herzsprung-Russell diagram when they make their second transition into the red giant stage. A star expands into a red giant when its hydrogen supply runs out, causing the core to collapse and temperature to rise. The red color of the star is caused by cooling temperatures in the star's outer regions. When the temperature reaches #3*10^8K#, helium fusion starts and the star becomes brighter. When the helium is depleted the expands again into a red giant. Fusion takes place in shells of hydrogen and helium around the core. The core being mostly oxygen and carbon which don't fuse because the temperature is too low. This the the beginning of then AGB stage.

Cooper Ann · Answer

undefined AGB (asymptotic giant branch) stars are defined as intermediate- to low-mass stars, with masses typically 0.6–10 times that of the Sun, that have reached the end of their evolutionary cycle, burning helium in a shell surrounding the core after having used up all of the hydrogen fuel in their cores.