Astronomy & Telescopes

KOALA, A New ATLAS9 Database — I. Model atmospheres, Opacities, Fluxes, Bolometric Corrections, Magnitudes And Colours

By Keith Cowing

Press Release

January 22, 2026

Filed under 2MASS, astronomy, Euclid, exoplanet, Gaia DR3, GALEX, Hypparcos-Tycho, KOALA, SDSS, UBVRI

KOALA, A New ATLAS9 Database — I. Model atmospheres, Opacities, Fluxes, Bolometric Corrections, Magnitudes And Colours — Main panel: comparison among ATLAS9 fluxes for the Sun calculated with suitable ODFs adopting different solar chemical mixtures: Caffau-Lodders (this work, grey line), Grevesse & Sauval (1998, blue line), Grevesse et al. (2007, green line), Magg et al. (2022, red line). Left panels: percentage difference in temperature (upper panel) and logarithm of the gas pressure (lower panel) as a function of the Rosseland optical depth of the model atmospheres with respect to that computed with Caffau-Lodders chemical mixture (same colour-code of the main panel). — astro-ph.SR

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 T_eff 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.

A. Mucciarelli, P. Bonifacio, C. Lardo

Comments: Accepted for Publication in Astronomy & Astrophysics, 13 pages, 8 figures, 1 table. All the data at this https URL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2511.10737 [astro-ph.SR] (or arXiv:2511.10737v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2511.10737
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Submission history
From: Alessio Mucciarelli
[v1] Thu, 13 Nov 2025 19:00:05 UTC (1,377 KB)
https://arxiv.org/abs/2511.10737
Astrobiology, Astrochemistry,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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