Korg: a modern 1D LTE spectral synthesis package

TL;DR

Korg is a fast, extensible spectral synthesis package for FGK stars that enables efficient analysis of large stellar datasets, with comparable accuracy to existing tools.

Contribution

Korg introduces a modern, efficient, and easily extensible spectral synthesis package for 1D LTE modeling of FGK stars, compatible with automatic differentiation.

Findings

Korg's synthetic spectra agree with other codes within the typical disagreement range.

Korg is 1-100 times faster than existing spectral synthesis codes.

Uncertainties in physical inputs significantly contribute to spectral synthesis disagreements.

Abstract

We present Korg, a new package for 1D LTE (local thermodynamic equilibrium) spectral synthesis of FGK stars, which computes theoretical spectra from the near-ultraviolet to the near-infrared, and implements both plane-parallel and spherical radiative transfer. We outline the inputs and internals of Korg, and compare synthetic spectra from Korg, MOOG, Turbospectrum, and SME. The disagreements between Korg and the other codes are no larger than those between the other codes, although disagreement between codes is substantial. We examine the case of a C$_2$ band in detail, finding that uncertainties on physical inputs to spectral synthesis account for a significant fraction of the disagreement. Korg is 1-100 times faster than other codes in typical use, compatible with automatic differentiation libraries, and easily extensible, making it ideal for statistical inference and parameter estimation applied to large data sets. Documentation and installation instructions are available at https://ajwheeler.github.io/Korg.jl/stable/.