Theoretical oscillation frequencies for solar-type dwarfs from stellar models with 〈3D〉-atmospheres

Abstract

We present a new method for replacing the outermost layers of stellar models with interpolated atmospheres based on results from 3D simulations, in order to correct for structural inadequacies of these layers. This replacement is known as patching. Tests, based on 3D atmospheres from three different codes and interior models with different input physics, are performed. Using solar models, we investigate how different patching criteria affect the eigenfrequencies. These criteria include the depth, at which the replacement is performed, the quantity, on which the replacement is based, and the mismatch in T eff and log g between the un-patched model and patched 3D atmosphere. We find the eigenfrequencies to be unaltered by the patching depth deep within the adiabatic region, while changing the patching quantity or the employed atmosphere grid leads to frequency shifts that may exceed 1 μHz. Likewise, the eigenfrequencies are sensitive to mismatches in T eff or log g. A thorough investigation of the accuracy of a new scheme, for interpolating mean 3D stratifications within the atmosphere grids, is furthermore performed. Throughout large parts of the atmosphere grids, our interpolation scheme yields sufficiently accurate results for the purpose of asteroseismology. We apply our procedure in asteroseismic analyses of four Kepler stars and draw the same conclusions as in the solar case: Correcting for structural deficiencies lowers the eigenfrequencies, this correction is slightly sensitive to the patching criteria, and the remaining frequency discrepancy between models and observations is less frequency dependent. Our work shows the applicability and relevance of patching in asteroseismology.

Stellar models with calibrated convection and temperature stratification from 3D hydrodynamics simulations

“…the effects of nonadiabaticity and the full interaction between convection and pulsations (e.g. Houdek et al 2017), as is also evident from the results of patched models (e.g Rosenthal et al 1999;Sonoi et al 2015;Ball et al 2016;Jørgensen et al 2017).…”

“…Thus, in order to patch, the interior model must correspond to a specific 3D simulation, making it impractical when modelling "real" stars. This part of the problem has been treated by Jørgensen et al (2017), who developed a technique for interpolating between the 3D simulations in a grid. The work utilized the interpolation scheme for producing the patched models with arbitrary physical parameters, and applied the method to several stars observed by the Kepler space mission (Borucki et al 2010).…”

The subgiant HR 7322 as an asteroseismic benchmark star

“…Advances in stellar modelling have made it possible to replace the outermost layers of the star with a patch of three-dimensional atmospheres (e.g. Jørgensen et al 2017). By changing the physics in the outer envelope of the star, the outer boundary of the star changes and the radius increases.…”

“…By changing the physics in the outer envelope of the star, the outer boundary of the star changes and the radius increases. However, even for a subgiant like HR 7322, which does have a larger outer super-adiabatic layer than the main-sequence stars studied in Jørgensen et al (2017), this effect only shifts the photosphere by 650-1400 km corresponding to at most ∼0.002 R (Jørgensen, private communication). We find no model parameter that solves the systematic offset between the models and the interferometric observations.…”

Coupling 1D stellar evolution with 3D-hydrodynamical simulations on-the-fly II: stellar evolution and asteroseismic applications

“…A major limitation of these patching procedures is that they have limited applicability: They can only be used to analyse a star with parameters exactly matching those of a computed simulation. In order to circumvent this, Jørgensen et al (2017) -hereafter J17established a new method to interpolate between 3D simulations in atmospheric parameters (effective temperature, T eff , and surface gravity, log g). The scheme was able to reliably reproduce the mean structure of 3D envelopes from two existing sets of simulations: The Stagger grid (Magic et al 2013) and the grid from Trampedach et al (2013).…”