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

Ehsan Moravveji

Institute of Astronomy, KU Leuven

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 than 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_sun from 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 heat-driven p- and g-mode pulsators, and the hybrid pulsating 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 ~75% 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.

Reference: MNRAS Letters, in press
Status: Manuscript has been accepted


Comments: All software to compute new opacity tables, the pre-compiled opacity tables and the new instability strips are freely available for download through the following URL: