A is a late-stage, evolved star that has exhausted the hydrogen fuel in its core and has begun fusing hydrogen in a shell surrounding the core. This process causes the star’s outer layers to expand dramatically—sometimes to hundreds of times its original radius—while its surface temperature cools, shifting its color toward the red end of the spectrum.
After the helium flash, the star begins fusing helium in its core (helium to carbon) and hydrogen in a shell. This brief, stable phase is called the (for low-mass stars) or the Red Clump . Red Giant
Calculations suggest: