# A study on missing lines in the synthetic solar spectrum near the Ca triplet

## TL;DR

This paper identifies missing lines in synthetic solar spectra near the Ca triplet, compares models with observations, and calibrates atomic parameters to improve spectral accuracy for astronomical applications.

## Contribution

It catalogs missing lines in line lists, compares synthetic and observed spectra, and calibrates atomic parameters to enhance spectral models.

## Key findings

- Missing lines identified near the Ca triplet region.
- Calibrated atomic parameters are publicly available.
- Improved synthetic spectra accuracy demonstrated.

## Abstract

Synthetic stellar spectra are extensively used for many different applications in astronomy, from stellar studies (such as in the determination of atmospheric parameters of observed stellar spectra), to extragalactic studies (e.g. as one of the main ingredients of stellar population models). One of the main ingredients of synthetic spectral libraries are the atomic and molecular line lists, which contain the data required to model all the absorption lines that should appear in these spectra. Although currently available line lists contain millions of lines, a relatively small fraction of these lines have accurate derived or measured transition parameters. As a consequence, many of these lines contain errors in the electronic transition parameters that can reach up to 200%. Furthermore, even for the Sun, our closest and most studied star, state-of-the-art synthetic spectra does not reproduce all the observed lines, indicating transitions that are missing in the line lists of the computed synthetic spectra. Given the importance and wide range of applications of these models, improvement of their quality is urgently necessary. In this work we catalogued missing lines in the atomic and molecular line lists used for the calculation of the synthetic spectra in the region of GAIA, comparing a solar model computed via a recent line list with a high quality solar atlas available in the literature. After that, we attempted the calibration of their atomic parameters with the code ALLiCE; the calibrated line parameters are publicly available for use.