Abstract
Context. The CoRoT and Kepler missions have provided high-quality measurements of the frequency spectra of solar-like pulsators, enabling us to probe stellar interiors with a very high degree of accuracy by comparing the observed and modelled frequencies. However, the frequencies computed with 1D models suffer from systematic errors related to the poor modelling of the uppermost layers of stars. These biases are what is commonly named the near-surface effect. The dominant effect is thought to be related to the turbulent pressure that modifies the hydrostatic equilibrium and thus the frequencies. This has already been investigated using grids of 3D hydrodynamical simulations, which also were used to constrain the parameters of the empirical correction models. However, the effect of metallicity has not been considered so far. Aims. We aim to study the impact of metallicity on the surface effect, investigating its influence across the Hertzsprung-Russell diagram, and providing a method for accounting for it when using the empirical correction models. Methods. We computed a grid of patched 1D stellar models with the stellar evolution code CESTAM in which poorly modelled surface layers have been replaced by averaged stratification computed with the 3D hydrodynamical code CO5BOLD. It allowed us to investigate the dependence of both the surface effect and the empirical correction functions on the metallicity. Results. We found that metallicity has a strong impact on the surface effect: keeping Teff and log g constant, the frequency residuals can vary by up to a factor of two (for instance from [Fe/H] = + 0.0 to [Fe/H] = + 0.5). Therefore, the influence of metallicity cannot be neglected. We found that the correct way of accounting for it is to consider the surface Rosseland mean opacity. It allowed us to give a physically grounded justification as well as a scaling relation for the frequency differences at νmax as a function of Teff, log g and κ. Finally, we provide prescriptions for the fitting parameters of the most commonly used correction functions. Conclusions. We show that the impact of metallicity through the Rosseland mean opacity must be taken into account when studying and correcting the surface effect.
Highlights
Thespace-bornemissionsCoRoT(Baglin et al.2006;Michel et al 2008; Auvergne et al 2009) and Kepler (Borucki et al 2010) have provided a rich harvest of high-quality seismic data for solar-like pulsators
We computed a grid of patched 1D stellar models with the stellar evolution code CESTAM in which poorly modelled surface layers have been replaced by averaged stratification computed with the 3D hydrodynamical code CO5BOLD
We show that the impact of metallicity through the Rosseland mean opacity must be taken into account when studying and correcting the surface effect
Summary
Thespace-bornemissionsCoRoT(Baglin et al.2006;Michel et al 2008; Auvergne et al 2009) and Kepler (Borucki et al 2010) have provided a rich harvest of high-quality seismic data for solar-like pulsators. Another complementary approach consists of investigating the physical nature of the surface effect. Sonoi et al (2015) presented a way to provide parameters for the empirical surface corrections by fitting them against a physically motivated scaling relation derived by Samadi et al (2013) All these works considered solar metallicity models while the distribution of metallicity for observed solar-like pulsators is quite large
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