NLTE abundances of C, O, Ca, Ti, and Fe in the reference BAF-type stars

TL;DR

This paper develops accurate NLTE methods for determining elemental abundances in BAF-type stars, applying comprehensive models to improve consistency across ionization stages and analyzing high-quality spectra.

Contribution

It introduces a complete Fe I-II model atom for NLTE abundance analysis in BAF stars, enhancing the accuracy of stellar chemical composition measurements.

Findings

NLTE abundances are consistent across ionization stages for C, Ca, Ti, and Fe.

Detection and modeling of emission lines in the IR spectrum of HD 160762.

Application of NLTE methods improves spectral line fitting in stellar atmospheres.

Abstract

We present accurate methods of abundance determination based on the non-local thermodynamic equilibrium (NLTE) line formation for carbon, oxygen, calcium, titanium, and iron in the atmospheres of BAF-type stars. For C I-II, O I, Ca I-II, and Ti I-II, their comprehensive model atoms were described in our previous papers. A fairly complete model atom of Fe I-II is first applied in this study. We determine the NLTE abundances of the nine BAF-type stars with well-determined atmospheric parameters, using high-resolution and high signal-to-noise ratio spectral observations in the broad wavelength range, from the UV to the IR. For C, Ca, Ti, and Fe, NLTE leads to consistent abundances from the lines of the two ionisation stages. The C I, Ca II, and Fe II emission lines were detected in the near IR spectrum of the late B-type subgiant star HD 160762. They are well reproduced in the classical model atmosphere, when applying our NLTE methods.