# Helium settling in F stars: constraining turbulent mixing using observed helium glitch signature

## TL;DR

This study uses asteroseismology to analyze helium settling in F stars, revealing that turbulence at the convection zone base influences surface helium levels, with implications for stellar modeling and the cosmological lithium problem.

## Contribution

It introduces a method to constrain helium settling in F stars using helium glitch signatures, highlighting the role of turbulence in counteracting atomic diffusion.

## Key findings

- Helium settling is less than predicted by standard models due to turbulence.
- A mixed mass of about 5 x 10^-4 M_sun is needed to match observations.
- Helium signatures can help distinguish physical processes affecting stellar surface compositions.

## Abstract

Recent developments in asteroseismology -- thanks to space-based missions such as {\it CoRoT} and {\it Kepler} -- provide handles on those properties of stars that were either completely inaccessible in the past or only poorly measured. Among several such properties is the surface helium abundance of F and G stars. We used the oscillatory signature introduced by the ionization of helium in the observed oscillation frequencies to constrain the amount of helium settling in F stars. For this purpose, we identified three promising F stars for which the standard models of atomic diffusion predict large settling (or complete depletion) of surface helium. Assuming turbulence at the base of envelope convection zone slows down settling of the helium and heavy elements, we found an envelope mixed mass of approximately $5 \times 10^{-4}$M$_\odot$ necessary to reproduce the observed amplitude of helium signature for all the three stars. This is much larger than the mixed mass of the order of $10^{-6}$M$_\odot$ found in the previous studies performed using the measurements of the heavy element abundances. This demonstrates the potential of using the helium signature together with measurements of the heavy element abundances to identify the most important physical processes competing against atomic diffusion, allowing eventually to correctly interpret the observed surface abundances of hot stars, consistent use of atomic diffusion in modelling both hot and cool stars, and shed some light on the long-standing cosmological lithium problem.