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The injection of hydrogen into the convection shell powered by helium burningduring the core helium flash is commonly encountered during the evolution ofmetal-free and extremely metal-poor low-mass stars. With specifically designedmultidimensional hydrodynamic simulations, we aim to prove that an entropybarrier is no obstacle for the growth of the helium-burning shell convectionzone in the helium core of a metal-rich Pop I star, i.e. convection canpenetrate into the hydrogen-rich layers for these stars, too. We further studywhether this is also possible in one-dimensional stellar evolutionarycalculations. Our hydrodynamical simulations show that the helium-burning shellconvection zone in the helium core moves across the entropy barrier and reachesthe hydrogen-rich layers. This leads to mixing of protons into the hotterlayers of the core and to a rapid increase of the nuclear energy production atthe upper edge of the helium-burning convection shell - the hydrogen injectionflash. As a result a second convection zone appears in the hydrogen-richlayers. Contrary to 1D models, the entropy barrier separating the twoconvective shells from each other is largely permeable to chemical transportwhen allowing for multidimensional flow, and consequently, hydrogen iscontinuously mixed deep into the helium core. We find it difficult to achievesuch a behavior in one-dimensional stellar evolutionary calculations.

Multidimensional hydrodynamic simulations of the hydrogen injection flash