An Etymological Dictionary of Astronomy and Astrophysics
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In evolutionary models of → low-mass and → intermediate-mass stars, the occurrence of a → helium shell flash on the → horizontal branch of the → post-AGB track, while → hydrogen shell burning is still going on.

→ late; → thermal; → pulse.

In evolutionary models of → post-asymptotic giant branch stars, the occurrence of the helium shell burning when the star has reached the → white dwarf cooling track. This leads to the possibility of a violent → helium shell flash and expansion on a time-scale of ≤ 10 years. The rapid expansion and prompt change in surface composition observed in → Sakurai's Object are thought to be due to such a very late thermal pulse.

→ very; → late; → thermal; → pulse.