Can an underestimation of opacity explain B-type pulsators in the SMC?

TL;DR

This paper investigates whether underestimating opacity in stellar models could explain the unexpected presence of B-type pulsators in the low-metallicity environment of the SMC, contrary to theoretical predictions.

Contribution

It explores the possibility that increasing the opacity in models can account for the observed pulsators in the SMC, challenging current assumptions about stellar opacities.

Findings

Opacity adjustments can potentially explain the excitation of pulsations in SMC B stars.

Current models underestimate the opacity in the iron-group element bump.

The study suggests revising opacity profiles to match observations.

Abstract

Slowly Pulsating B and $\beta$ Cephei are $\kappa$ mechanism driven pulsating B stars. That $\kappa$ mechanism works since a peak in the opacity due to a high number of atomic transitions from iron-group elements occurs in the area of $\log T \approx 5.3$. Theoretical results predict very few SPBs and no $\beta$ Cep to be encountered in low metallicity environments such as the Small Magellanic Cloud. However recent variability surveys of B stars in the SMC reported the detection of a significant number of SPB and $\beta$ Cep candidates. Though the iron content plays a major role in the excitation of $\beta$ Cep and SPB pulsations, the chemical mixture representative of the SMC B stars such as recently derived does not leave room for a significant increase of the iron abundance in these stars. Whilst abundance of iron-group elements seems reliable, is the opacity in the iron-group elements bump underestimated? We determine how the opacity profile in B-type stars should change to excite SPB and $\beta$ Cep pulsations in early-type stars of the SMC.