Rayleigh scattering in the atmospheres of hot stars

TL;DR

This paper investigates the significance of Rayleigh scattering by neutral hydrogen and singly ionized helium in hot star atmospheres, revealing that helium scattering can be important in helium-rich stars, contrary to previous assumptions.

Contribution

It provides a detailed evaluation of Rayleigh scattering effects in hot star atmospheres, especially in helium overabundant stars, using new model atmosphere calculations.

Findings

Rayleigh scattering by neutral hydrogen is negligible in hot stars.

Rayleigh scattering by singly ionized helium can be significant in helium-rich stars.

Models show increased opacity due to helium scattering in certain hot star atmospheres.

Abstract

Rayleigh scattering is a result of an interaction of photons with bound electrons. Rayleigh scattering is mostly neglected in calculations of hot star model atmospheres because most of the hydrogen atoms are ionized and the heavier elements have a lower abundance than hydrogen. In atmospheres of some chemically peculiar stars, helium overabundant regions containing singly ionized helium are present and Rayleigh scattering can be a significant opacity source. We evaluate the contribution of Rayleigh scattering by neutral hydrogen and singly ionized helium in the atmospheres of hot stars with solar composition and in the atmospheres of helium overabundant stars. We computed several series of model atmospheres using the TLUSTY code and emergent fluxes using the SYNSPEC code. These models describe atmospheres of main sequence B-type stars with different helium abundance. We used an existing grid of models for atmospheres with solar chemical composition and we calculated an additional grid for helium-rich stars with $N$(He)/$N$(H)=10. Rayleigh scattering by neutral hydrogen can be neglected in atmospheres of hot stars, while Rayleigh scattering by singly ionized helium can be a non-negligible opacity source in some hot stars, especially in helium-rich stars.