The blue-edge problem of the V1093 Her instability strip revisited using evolutionary models with atomic diffusion

TL;DR

This study uses advanced evolutionary models with atomic diffusion to accurately predict the instability strips of subdwarf B stars, naturally explaining the blue edge problem and aligning predictions with observations.

Contribution

It introduces evolutionary models incorporating atomic diffusion that naturally produce Fe and Ni enhancements, eliminating artificial abundance assumptions in pulsation analyses.

Findings

The models naturally produce Fe and Ni enhancements.

The predicted instability strip resolves the blue edge problem.

KIC 10139564 is confirmed within the instability strip.

Abstract

We have computed a new grid of evolutionary subdwarf B star (sdB) models from the start of central He burning, taking into account atomic diffusion due to radiative levitation, gravitational settling, concentration diffusion, and thermal diffusion. We have computed the non-adiabatic pulsation properties of the models and present the predicted p-mode and g-mode instability strips. In previous studies of the sdB instability strips, artificial abundance enhancements of Fe and Ni were introduced in the pulsation driving layers. In our models, the abundance enhancements of Fe and Ni occur naturally, eradicating the need to use artificial enhancements. We find that the abundance increases of Fe and Ni were previously underestimated and show that the instability strip predicted by our simulations solves the so-called blue edge problem of the subdwarf B star g-mode instability strip. The hottest known g-mode pulsator, KIC 10139564, now resides well within the instability strip {even when only modes with low spherical degrees (l<=2) are considered.