# Opacity distribution functions for stellar spectra synthesis

## TL;DR

This paper enhances the Opacity Distribution Functions method for stellar spectra synthesis, achieving significant speedups for radiative transfer calculations, crucial for analyzing vast data from space telescopes and characterizing planetary hosts.

## Contribution

The authors optimize and generalize the ODF approach, enabling faster stellar spectra synthesis and flux calculations across various filters, improving computational efficiency.

## Key findings

- Threefold speedup in spectral synthesis with optimized ODF configurations.
- Over two orders of magnitude speedup in flux calculations through filters.
- Enhanced capability for rapid analysis of stellar spectra for exoplanet research.

## Abstract

Contex. Stellar spectra synthesis is essential for the characterization of potential planetary hosts. In addition, comprehensive stellar variability calculations with fast radiative transfer are needed to disentangle planetary transits from stellar magnetically-driven variability. The planet-hunting space telescopes, such as CoRoT, Kepler, and TESS will bring vast quantities of data, rekindling the interest in fast calculations of the radiative transfer. Aims. We revisit the Opacity Distribution Functions (ODF) approach routinely applied to speedup stellar spectral synthesis. To achieve a considerable speedup relative to the current state-of-the-art, we further optimize the approach and search for the best ODF configuration. Furthermore, we generalize the ODF approach for fast calculations of flux in various filters often used in stellar observations. Methods. In a parameter-sweep-fashion, we generated ODF in the spectral range from UV to IR with different setups. The most accurate ODF configuration for each spectral interval was determined. For calculations of the radiative fluxes through filters we adapted the wavelength grid based on the transmission curve, whereafter the normal ODF procedure was performed. Results. Our optimum ODF configuration allows for a three fold speedup, compared to the previously used ODF configurations. The ODF generalization to calculate fluxes through filters results in a speedup of more than two orders of magnitude.