# Effect of diffusion-induced element accumulation on the opacity inside B stars

## TL;DR

This study investigates how atomic diffusion and mixing processes in B stars can naturally enhance opacity in the Z-bump region, potentially explaining observed pulsations without arbitrary opacity adjustments.

## Contribution

It demonstrates that atomic diffusion combined with fingering mixing and mass-loss can produce the necessary opacity increase in stellar models, advancing understanding of B star pulsations.

## Key findings

- Atomic diffusion causes Fe and Ni accumulation in the Z-bump.
- Fingering mixing extends the overabundance zone.
- Mass-loss is essential for stellar evolution to match observations.

## Abstract

Stellar models with homogeneous abundances fail to reproduce the pulsation frequencies of early B-type stars. Their oscillations are excited by kappa-mechanism involving the Fe-peak elements where they are main contributors to the opacity (the "Z-bump") and a ad hoc increase of the opacity in these layers is necessary to match the observations. We test whether atomic diffusion can induce such an opacity increase through Fe and Ni accumulations in the Z-bump. With models computed using the Toulouse-Geneva Evolution Code, we show that atomic diffusion changes the abundance profiles inside the star, leading to an overabundance of the iron-peak elements in the upper envelope. The opacity may reach the amount required by seismic studies, provided that fingering mixing, which extends the size of the overabundance zone, is taken into account. Mass-loss is also required to evolve the model until the end of the main sequence.