The Abundance Evolution of Oxygen, Sodium, and Magnesium in Extremely Metal Poor Intermediate-Mass Stars: Implications for the Self-Pollution Scenario in Globular Clusters

Abstract

We present full stellar evolution and parametric models of the surface abundance evolution of , , 16 22 O Ne , and the magnesium isotopes in an extremely metal poor intermediate-mass star (, where 23 Na M p 5 M ZAMS , ZAMS stands for the zero-age main sequence, and). and are injected into the envelope by 16 22 Z p 0.0001 O Ne the third dredge-up following thermal pulses on the asymptotic giant branch. These species and the initially present are depleted by hot bottom burning (HBB) during the interpulse phase. As a result, , , 24 23 25 Mg Na Mg and are enhanced. If the HBB temperatures are sufficiently high for this process to deplete oxygen efficiently, 26 Mg is first produced and then depleted during the interpulse phase. Although the simultaneous depletion of 23 Na and enhancement of is possible, the required fine-tuning of the dredge-up and HBB casts some doubt 16 23 O N a on the robustness of this process as the origin of the O-Na anticorrelation observed in globular cluster stars. However, a very robust prediction of our models are low and ratios whenever significant 24 25 24 26 Mg/ Mg Mg/ Mg depletion can be achieved. This seems to be in stark contrast to recent observations of the magnesium isotopic 16 O ratios in the globular cluster NGC 6752.