helium shell burning
suzeš-e puste-ye heliom
Fr.: combustion de la coquille d'hélium
A stage in the evolution of an → asymptotic giant branch star, when all the helium in the core is fused into carbon and oxygen. No more fusion takes place in the core, and as a result the core contracts. The core contraction generates a sufficient temperature for fusing the surrounding layers of helium. Since helium shell burning is unstable, it causes → helium shell flashes.
helium shell flash
deraxš-e puste-ye heliomi
Fr.: flash de la couche d'hélium
A violent outburst of energy that occurs periodically in an → asymptotic giant branch star. It occurs when helium is being burnt in a thin shell surrounding the inner dense core of carbon and oxygen. → Helium shell burning is unstable, producing energy mainly in short intense flashes. The shell flash causes considerable expansion of the star followed by collapse, thus setting up deep convection. As a consequence, the → convective zone in the outer part of the star goes deeper and may → dredge-up carbon to the surface. See also → late thermal pulse; → very late thermal pulse; → AGB final thermal pulse.