Off-centre convective zones in mass accreting stellar models

Abstract

We report the physical origin of transient off-centre convective zones (oCZs) that arise in mass accreting stellar models. Using detailed MESA simulations of binary evolution, we find that these oCZs are not numerical artefacts but emerge due to a local increase in density near the retreating edge of the convective core. The density enhancement raises the local opacity, which amplifies the radiative temperature gradient ${\nabla }_{\mathrm{rad}}$. If this gradient surpasses the Ledoux threshold ${\nabla }_{\mathrm{L}}$, defined by both thermal and compositional stratification, the region becomes convectively unstable. The resulting oCZs are detached from the convective core and transient: mixing within the oCZ erases the local gradient in mean molecular weight, leaving a sharp ${\nabla }_{\mu }$ discontinuity at the boundary, stabilizing the adjacent layers. This mechanism naturally explains the presence and evolution of oCZs, as previously reported in massive interacting stars.

Accepted for publication in A&AL

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Cited by in corpus (3)

• The evolutionary and asteroseismic imprints of mass accretion. The 10 M${}_{\odot }$ $\beta$ Cep case study
• Asteroseismic Imprints of Mass Transfer in Binary Stars: Probing the Interiors of Donors and Accretors with Gravity and Acoustic Modes
• The effect of near-core mixing on rejuvenation and the asteroseismic properties of massive accretors