Numerical experiments to help understand cause and effect in massive star evolution

TL;DR

This paper introduces the SNAPSHOT modeling approach to isolate key internal abundance features influencing massive star evolution, revealing how internal profiles affect surface properties and evolutionary paths across different phases.

Contribution

The paper presents a novel method called SNAPSHOT that isolates internal abundance profile effects on massive star evolution, enhancing understanding of their structural and surface property variations.

Findings

Models with similar surface properties can have different internal abundance profiles.

Small changes in abundance profiles can significantly alter surface properties.

Lower metallicity stars tend to be more compact due to reduced CNO abundances and opacity.

Abstract

The evolution of massive stars is affected by a variety of physical processes including convection, rotation, mass loss and binary interaction. Because these processes modify the internal chemical abundance profiles in multiple ways simultaneously, it can be challenging to determine which properties of the stellar interior are primarily driving the overall evolution. Building on previous work, we develop a new modelling approach called SNAPSHOT that allows us to isolate the key features of the internal abundance profile that drive the evolution of massive stars. Using our approach, we compute numerical stellar structure models in thermal equilibrium covering key phases of stellar evolution. For the main sequence, we demonstrate that models with the same mass and very similar surface properties can have different internal distributions of hydrogen and convective core masses. We discuss why massive stars expand after the main sequence and the fundamental reasons for why they become red, blue or yellow supergiants. For the post-main sequence, we demonstrate that small changes in the abundance profile can cause very large effects on the surface properties. We also discuss the effects that produce blue supergiants and the cause of blue loops. Our models show that massive stars with lower metallicity tend to be more compact due to the combined effect of lower CNO abundances in the burning regions and lower opacity in the envelope.