The impact of enhanced iron opacity on massive star pulsations: updated instability strips

Recently, Bailey et al. made a direct measurement of the iron opacity at the physical conditions of the solar tachocline. They found that the wavelength-integrated iron opacity is roughly 75 per cent higher than what the Opacity Project (OP) and OPAL models predict. Here, we compute new opacity tables with enhanced iron and nickel contributions to the Rosseland mean opacity by 75 per cent each, and compute three dense MESA grids of evolutionary models for Galactic O- and B-type stars covering from 2.5 to 25 M-circle dot from zero-age main sequence (ZAMS) until T-eff = 10 000 K after the core hydrogen exhaustion. We carry out non-adiabatic mode stability analysis with GYRE, and update the extension of the instability strips of heatdriven p- and g-mode pulsators, and the hybrid slowly pulsating B (SPB) - beta Cep stars. We compare the position of two confirmed late O- type beta Cep and eight confirmed hybrid B-type pulsators with the new instability domains, and justify that similar to 75 per cent enhancement, only in iron opacity, is sufficient to consistently reproduce the observed position of these stars on the log T-eff versus log g plane. We propose that this improvement in opacities be incorporated in the input physics of new stellar models.