Surface Patched Models for Internal Stellar Structure Models

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Özel N.

Turkish Journal of Astronomy and Astrophysics, cilt.3, ss.103-107, 2022 (Hakemli Dergi)

Özet

In stellar evolution calculations, a well-known problem in comparing observed and model-calculated frequencies comes from the hard-to-model near-surface layers of stars. Models usually employ simplified model atmospheres, and mixing length theory is used to describe convection which leads to errors in the structure of the superadiabatic region. Moreover, model oscillation frequencies calculated in the usual adiabatic approximation neglect the effects of turbulent pressure. Convection in the superadiabatic region is commanly treated with the mixing length theory (MLT). However, as a result of non-local non-linear nature of surface convection, MLT cannot correctly model this complex region. The upper boundary conditions near the optical surface do not agree with asteroseismic observations. This is reflected in asteroseismology as so-called near-surface effects, when stellar sturcture models are compared with p-mode oscillation frequencies. Therefore, we want also to improve how the outher boundary conditions are determined in stellar structure calculations. We study realistic 3D stellar atmosphere models. We precisely match stellar models to the effective temperature, the gravity at the photosphere, and the temperature at the temporally and horizantally averaged pressure at deepest point of the 3D simulations. We then replace the near-surface structure with that of the averaged simulation and compute the change in the oscillation mode frequencies.