Using Molecular Lines to Determine Carbon and Nitrogen Abundances in the Atmospheres of Cool Stars

TL;DR

This paper presents a new molecular line analysis method using C_2 and CN bands to accurately determine carbon and nitrogen abundances in cool star atmospheres, validated through stellar examples.

Contribution

It introduces an improved molecular data-based method for C and N abundance determination, integrated into the VALD database, and demonstrates its consistency with atomic line analyses.

Findings

Molecular data analysis yields C and N abundances consistent with atomic lines.

The method is effective for solar-like stars and addresses challenges with N I lines.

Validated on three stellar spectra.

Abstract

Simultaneous analysis of the C_2 and CN molecular bands in the 5100-5200 and 7930-8100A spectral regions is a promising alternative for the accurate determination of the carbon (C) and nitrogen (N) abundance in the atmospheres of the solar-like stars. Practical implementation of this new method became possible after recent improvements of the molecular constants for both molecules. The new molecular data predicted the correct line strength and line positions; therefore, they were included in the Vienna Atomic Line Database (VALD), which is widely used by astronomers and spectroscopists. In this paper, we demonstrate that the molecular data analysis provides C and, in particular, N abundances consistent with those derived from the atomic lines. We illustrate this by performing the analysis for three stars. Our results provide strong arguments for using the combination of C_2 and CN molecular lines for accurate nitrogen abundance determination keeping in mind the difficulties of using the N1 lines in the observed spectra of the solar-like stars.