Abstract
Context. Stellar spectral synthesis is essential for various applications, ranging from determining stellar parameters to comprehensive stellar variability calculations. New observational resources as well as advanced stellar atmosphere modelling, taking three dimensional effects from radiative magnetohydrodynamics calculations into account, require a more efficient radiative transfer. Aims. For accurate, fast and flexible calculations of opacity distribution functions (ODFs), stellar atmospheres, and stellar spectra, we developed an efficient code building on the well-established ATLAS9 code. The new code also paves the way for easy and fast access to different elemental compositions in stellar calculations. Methods. For the generation of ODF tables, we further developed the well-established DFSYNTHE code by implementing additional functionality and a speed-up by employing a parallel computation scheme. In addition, the line lists used can be changed from Kurucz’s recent lists. In particular, we implemented the VALD3 line list. Results. A new code, the Merged Parallelised Simplified ATLAS, is presented. It combines the efficient generation of ODF, atmosphere modelling, and spectral synthesis in local thermodynamic equilibrium, therefore being an all-in-one code. This all-in-one code provides more numerical functionality and is substantially faster compared to other available codes. The fully portable MPS-ATLAS code is validated against previous ATLAS9 calculations, the PHOENIX code calculations, and high-quality observations.
Highlights
Electromagnetic radiation emitted from the stellar photosphere is one of the key sources of information about a star
For a K-type star for which line opacity is even more important than for the Sun, there is rather a moderate difference. This indicates that the main difference between the VALD3 and the Kurucz’s line lists are lines whose lower level have higher energies
We show the difference in the irradiance for the Anders composition and Asplund composition, both with convection but no overshoot
Summary
Electromagnetic radiation emitted from the stellar photosphere is one of the key sources of information about a star. The Echelle Spectrograph for Rocky Exoplanet- and Stable Spectroscopic Observations (ESPRESSO, see Pepe et al 2010) and the High Accuracy Radial Velocity Planet Searcher (HARPS, see Mayor et al 2003) made high-resolution spectral data for thousands of stars available, while the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST, see Ai et al 2016) provides low-resolution spectra for millions of stars The interpretation of these spectral measurements requires the modelling of stellar atmospheres on a fine grid of stellar fundamental parameters, such as effective temperature, surface gravity, and chemical composition. To achieve our goal of fast spectral synthesis for arbitrary abundances, we need to eliminate this bottleneck, and in addition make the ODF generation more user friendly This is achieved by merging the DFSYNTHE code, which calculates high-resolution opacities and uses them to obtain ODF, with the ATLAS9 code that can calculate both the atmospheric structures as well as the emergent spectra.
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