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

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.