The Impact of Enhanced Iron Opacity on Massive Star Pulsations: Updated Instability Strips

Recently, Bailey et al. (2015) 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% higher that what the OP and OPAL models predict. Here, we compute new opacity tables with enhanced Iron and Nickel contributions to the Rosseland mean opacity by 75% each, and compute three dense MESA grids of evolutionary models for Galactic O- and B-type stars covering from 2.5 to 25 M$_\odot$ from ZAMS until $T_{\rm eff}=10\,000$ 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 heat-driven p- and g-mode pulsators, and the hybrid pulsating SPB - $β$ Cep stars. We compare the position of two confirmed late O-type $β$ Cep and eight confirmed hybrid B-type pulsators with the new instability domains, and justify that $\sim$75% enhancement, only in Iron opacity, is sufficient to consistently reproduce the observed position of these stars on the $\log T_{\rm eff}$ versus $\log g$ plane. We propose that this improvement in opacities be incorporated in the input physics of new stellar models. To reproduce the results, all software, opacity tables and the new instability strips are freely available for download at the following URL: https://fys.kuleuven.be/ster/Projects/ASAMBA.

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