Non-LTE Abundances Of Nitrogen In The Sun And Reference A-F Type Stars

By Keith Cowing
Status Report
June 20, 2024
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Non-LTE Abundances Of Nitrogen In The Sun And Reference A-F Type Stars
Nitrogen NLTE (filled circles) and LTE (open circles) abundances log εN of the sample stars. The dotted line corresponds to the solar abundance recommended by Lodders (2021). — astro-ph.SR

A new model atom of nitrogen was developed using the energy levels of N I from laboratory measurements and also predicted in atomic structure calculations and the most up-to-date atomic data for computing radiative and collisional rates of the transitions.

Solar abundance logε,N(1D NLTE) = 7.92±0.03 was determined from lines of N I by applying the synthetic spectrum method with the plane-parallel (1D) MARCS model atmosphere and taking into account the departures from local thermodynamic equilibrium (non-LTE = NLTE effects). Having implemented the 3D-corrections of Amarsi et al. (2020), we obtained logε,N(NLTE+3D) = 7.88±0.03 for the Sun. Based on high spectral resolution spectra, the NLTE abundances of nitrogen were derived for 11 unevolved A-F type stars with reliable atmospheric parameters.

Non-LTE leads to strengthened N I lines, and the non-LTE effects grow with increasing effective temperature. For each star, non-LTE leads to smaller abundance error compared to the LTE case. For superficially normal A stars, non-LTE removes the enhancements relative to the solar nitrogen abundance obtained in the LTE case. A λ Boo-type star HD 172167 (Vega) also has close-to-solar N abundance.

The four Am stars reveal a scatter of the N abundances, from [N/H] = -0.44 to [N/H] = 0.39. The N abundances of the Sun and superficially normal A stars are consistent within 0.09 dex with the nitrogen abundance of the interstellar gas and the early B-type stars.

L. I. Mashonkina, T. A. Ryabchikova

Comments: 29 pages, 5 tables, 8 figures, accepted for publication in Astronomy Letters
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2406.11367 [astro-ph.SR] (or arXiv:2406.11367v1 [astro-ph.SR] for this version)
Submission history
From: Lyudmila Mashonkina
[v1] Mon, 17 Jun 2024 09:46:31 UTC (355 KB)

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