Semi-convection: What is the underlying physical context?

TL;DR

This paper explores the physical conditions leading to semi-convective mixing in different stellar types, focusing on the roles of nuclear processes, radiation pressure, and opacity changes in stellar evolution.

Contribution

It provides a detailed analysis of the physical contexts and instabilities associated with semi-convection in various stellar evolutionary stages.

Findings

Semi-convection occurs in low mass MS stars due to CNO cycle dominance.

Massive MS stars experience semi-convection influenced by radiation pressure.

Core helium burning stars show semi-convection linked to increased opacity from carbon production.

Abstract

Stellar conditions leading to a possible semi-convective mixing are discussed in three relevant cases: (1) low mass MS stars in which the CNO cycle takes progressively the lead over the PP chain due to the increase in temperature as core hydrogen burning proceeds, (2) massive MS stars which experience a large contri- bution of the radiation pressure to the total pressure and (3) core helium burning stars for which the production of carbon in the core increases the opacity. A short discussion of semi-convection in terms of instability of non radial modes follows.