Estimating the nonstructural component of the helioseismic surface term using hydrodynamic simulations

Abstract

Context.As the amount of asteroseismic data available continues to grow, the inability to accurately model observed oscillation frequencies is becoming a critical problem for interpreting these frequencies. A major component of this problem is the modeling of the near-surface layers.Aims.Our aim is to develop a method to estimate the effect of the near-surface layers on oscillation frequencies.Methods.In the proposed method we numerically estimate eigenfunctions in 3D hydrodynamic simulations. We match those to the eigenfunctions calculated from the classic equations applied to the horizontal averages of the structure variables. We use this procedure to calculate the frequency perturbation resulting from the dynamical part of the interaction of the oscillations with near-surface convection. As the last step we scale the numbers to the Sun. To provide a qualitative test of our method we performed a series of simulations, calculated the perturbations using our procedure, and compared them to previously reported residuals relative to solar models.Results.We find that we can largely reproduce the observed frequency residuals without resorting to poorly justified theoretical models. We find that, while the calculations of Houdek et al. (2017, MNRAS, 464, L124) produce similar frequency perturbations, the density-pressure phase differences computed here do not match those of that work.