A highly evolved star in the final stages before becoming a planetary nebula, characterized by extreme luminosity variations and mass loss. These stars undergo thermal pulses as helium burns in a shell around an inert carbon-oxygen core.
Named for the asymptotic giant branch on the Hertzsprung-Russell diagram, where these stars appear to approach a limiting luminosity. The term combines 'asymptotic' from Greek meaning 'not falling together' with 'giant', describing their position on stellar evolution tracks.
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