The ChromaStar+ modelling suite and the VALD line list

TL;DR

The paper introduces an updated version of the ChromaStar+ suite that incorporates the extensive VALD line list, improving spectral modeling accuracy for late-type stars and enabling faster computations on multi-CPU systems.

Contribution

It presents the integration of the VALD line list into ChromaStar+, enhancing spectral modeling and computational efficiency, along with new fitting results and an automated observatory system.

Findings

Improved spectral fits to the solar SED and standard stars.

Reduced need for ad hoc opacity adjustments.

Identified and fixed a bug in spectrum synthesis.

Abstract

We present Version 2023-02-04 (ISO) of the Chroma+ atmospheric, spectrum, and transit light-curve modelling suite, which incorporates the VALD atomic line list. This is a major improvement as the previous versions used the much smaller NIST line list. The NIST line list is still available in Chroma+ for those projects requiring speed over completeness of line opacity. We describe a procedure for exploiting the ''Array job'' capability of the slurm workload manager on multi-cpu machines to compute broadband high resolution spectra with the VALD line list quickly using the Java version of the code (ChromaStarServer (CSS)). The inclusion of a much larger line list more completely allows for the many weaker lines that over-blanket the blue band in late-type stars and has allowed us to reduce the amount of additional ad hoc continuous opacity needed to fit the solar spectral energy distribution (SED). The additional line opacity exposed a subtle bug in the spectrum synthesis procedure that was causing residual blue line wing opacity to accumulate at shorter wavelengths. We present our latest fits to the observed solar SED and to the observed rectified high resolution visible band spectra of the Sun and the standard stars Arcturus and Vega. We also introduce the fully automated Burke-Gaffney Observatory (BGO) at Saint Mary's University (SMU) and compare our synthetic spectra to low resolution spectra obtained with our grism spectrograph that is available to students. The fully automated BGO, the spectrograph, and the BGO spectrum reduction procedure are fully described in a companion paper. All codes are available from the OpenStars www site: www.ap.smu.ca/OpenStars.