Neon Abundances of B-stars in the Solar Neighborhood

TL;DR

This study models neon line formation in B-type stars using NLTE calculations, revealing significant line strengthening effects and providing a refined average neon abundance that informs solar composition estimates.

Contribution

It presents a comprehensive NLTE model for NeI and NeII lines in B-star atmospheres, improving abundance determinations with updated atomic data and experimental oscillator strengths.

Findings

NLTE effects cause strong line strengthening in NeI due to small photoionization cross-sections.

Most NeII lines show small deviations from LTE, not exceeding 0.11 dex.

Average neon abundance in B-stars is 8.02±0.05, constraining solar neon abundance.

Abstract

We constructed a comprehensive model atom for NeI -- NeII using the most up-to-date atomic data available and evaluated the non-local thermodynamic equilibrium (NLTE) line formation for NeI and NeII in classical 1D models representing the atmospheres of B-type stars. We find that the large NLTE strengthening of the NeI lines corresponding to the 2p$^5$3p $-$ 2p$^5$3s transitions array occurs due to extremely small photoionization cross-sections of 2p$^5$3s levels that leads to strong overpopulation of these levels relative to their LTE populations. The deviations from LTE for the most NeII lines are small and do not exceed 0.11~dex in the absolute value. We analysed 20 lines of NeI and 13 lines of NeII for twenty-four B-type stars in the temperature range of 10\,400 $\le$ \Teff\ $\le$ 33\,400~K. For five stars, the NLTE leads to consistent abundances of NeI and NeII, while the difference in LTE abundance can reach up to 0.50~dex. The using of the experimental oscillator strengths recently measured by Piracha et al. (2015) leads to smaller line-by-line scatter for the most investigated stars. The averaged neon abundance in twenty-four B-type stars in solar neighborhood is 8.02$\pm$0.05. This value may provide indirect constraints on solar photospheric neon abundance.