Using the Hertzsprung-Russell diagram the conditions that describe each star are :
Description Stars
It is fusing hydrogen at its core ------------------> Vega
It has lost its outer shell and retained only a hot core that is slowly losing its brightness. ----------------------------> Procyon B
Its temperature has decreased, but it is shining brighter than before ----------------------------------------------------------------------->Polaris
Hertzsprung-Russell diagram is scatterplot diagram that shows the various relationships between the intrinsic brightness of the stars plotted against their spectral types.
hence :
It is fusing hydrogen at its core describes Vega
It has lost its outer shell and retained only a hot core that is slowly losing its brightness describes Procyon B while
Its temperature has decreased, but it is shining brighter than before describes Polaris
