Using non-solar-scaled opacities to derive stellar parameters. Toward high-precision parameters and abundances

We implemented non-solar-scaled opacities in a simultaneous derivation of fundamental parameters and abundances. We carried out a high-precision stellar parameters and abundance determination by applying non-solar-scaled opacities and model atmospheres. Our sample is composed by 20 stars including main-sequence and evolved objects. Opacities for an arbitrary composition and vmicro were calculated through the Opacity Sampling method. We obtained a small difference in stellar parameters derived with non-solar-scaled opacities compared to classical solar-scaled models. The differences in Teff, log g and [Fe/H] amount up to 26 K, 0.05 dex and 0.020 dex for the stars in our sample. These differences could be considered as the first estimation of the error due to the use of classical solar-scaled opacities to derive stellar parameters with solar-type and evolved stars. Some chemical species could also show an individual variation higher than those of the [Fe/H] (up to 0.03 dex) and varying from one specie to another, obtaining a chemical pattern difference between both methods. This means that condensation temperature Tc trends could also present a variation. We include an example showing that using non-solar-scaled opacities, the classical solution cannot always verify the excitation and ionization balance conditions required for a model atmosphere. We consider that the use of the non-solar-scaled opacities is not mandatory in every statistical study with large samples of stars. However, for those high-precision works whose results depend on the mutual comparison of different chemical species (such as Tc trends), we consider that it is worthwhile its application. To date, this is probably one of the more precise spectroscopic methods of stellar parameters derivation [abridged].