KOALA, a new ATLAS9 database -- I. Model atmospheres, opacities, fluxes, bolometric corrections, magnitudes and colours

TL;DR

The KOALA database provides an extensive set of LTE model atmospheres, fluxes, and photometric corrections with improved sampling and updated chemical compositions, facilitating more accurate stellar modeling and analysis.

Contribution

This work introduces a comprehensive, updated ATLAS9 model atmosphere grid with finer sampling, new chemical mixtures, and extensive photometric data for diverse stellar parameters.

Findings

Finer sampling improves interpolation accuracy for stellar colors.

Updated chemical mixtures affect atmospheric structures and colors.

51663 models cover a broad metallicity and alpha-enhancement range.

Abstract

We present the KOALA database, a new set of LTE, line-blanketed model atmospheres calculated with the code ATLAS9, together with the corresponding Opacity Distribution Functions and emergent fluxes. The latter were used also to calculated G-band bolometric corrections and theoretical magnitudes and colours for several photometric systems, i.e. UBVRI, 2MASS, Hypparcos-Tycho, SDSS, Galex, Euclid and Gaia DR3. With respect to the previous grids of ATLAS9 model atmospheres, we adopted the solar mixture by Caffau/Lodders and we extend the sampling in metallicity (from -5.0 to -2.5 dex with step of 0.5 dex, and from -2.5 dex to +0.5 dex with step of 0.25 dex) and in [alfa/Fe] (from -0.4 to +0.4 dex with a step of 0.2 dex). Also, we provide a finer sampling in Teff for Teff lower than 7000 K. This finer grid allows for more accurate interpolation of colours and in many cases it makes not necessary to compute a new model atmosphere, since one of the grid can be used directly. A total of 51663 model atmospheres and emergent fluxes have been computed. Finally, we discuss the impact of [M/H] and [alfa/Fe] on the thermal and pressure structures of the model atmospheres and on theoretical colours.