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

Abstract

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 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 -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 ∼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.

Sub-Inertial Gravity Modes in the B8v Star Kic 7760680 Reveal Moderate Core Overshooting and Low Vertical Diffusive Mixing

“…Recently, Moravveji (2016) showed that a 75% increase in the Iron and Nickel monochromatic opacities explains the position of two confirmed β Cep and eight confirmed hybrids on the Kiel diagram, which could not be explained before. The increase resulted from the direct laboratory Iron opacity measurement of Bailey et al (2015), which was later confirmed by the numerical simulations of Nagayama et al (2016).…”

“…The spectroscopic properties of KIC 7760680 from HERMES (Raskin et al 2011) high-resolution spectra are T eff = 11650 ± 210 K, =  g log 3.97 0.08 dex, [M/H] = 0.14 ± 0.09, and =  v i sin 62 5 km s −1 . The inferred T eff and g log place KIC 7760680 at the low-mass end of the SPB instability strip (Pamyatnykh 1999;Moravveji 2016). Pápics et al (2015) identified a series of  = 36 lowfrequency modes with periods between P 1 ± σ 1 = 0.86930 ± 0.00002 and P 36 ± σ 36 = 1.46046 ± 0.00004 days (their Table 1).…”

“…Therefore, in addition to solving the β Cep and hybrid pulsating massive stars excitation problem presented in Moravveji (2016), the success in explaining the excitation of the majority of observed modes by incorporating Fe and Ni monochromatic opacity enhancement is another manifestation that the default (OP and OPAL) opacity tables underestimate the Rosseland mean opacity in stellar interiors. Consequently, the stellar interior seems to be more opaque than was believed, and the next generation of stellar models should adopt the updated tables of Moravveji (2016) and/or Mondet et al (2015).…”

“…Non-adiabatic heat exchange around the iron opacity bump at » T log 5.2 K-known as the classical κ-mechanism-is responsible for their mode excitation (Dziembowski et al 1993;Gautschy & Saio 1993). Together with γ Dor stars, they are the richest main-sequence g-mode pulsators with numerous excited modes (e.g., Figure 2(e) in Moravveji 2016). Chemically inhomogeneous regions above the receding convective cores reside inside this propagation cavity, and allow for partial or complete g-mode trapping, providing a unique physical diagnostic of the chemical mixing and thermal stratification in the deep stellar interior (Miglio et al 2008;Cunha et al 2015).…”

Spectroscopic diagnostics of low-ionized iron-peak elements. Electron-impact excitation of Ni3+ and photoionization of Ni2+

“…They used models dependent upon opacities and the known optical depths of the interstellar clouds to determine its fractal dimension. Another example is the work of Moravveji (2016), whose opacity simulations, comparing measured to measured spectra, concluded that nickel ions produce an enhancement of the opacity.…”