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arXiv 2406.11367astro-ph.SR
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太阳与参考 A-F 型恒星中氮的非 LTE 丰度

Non-LTE abundances of nitrogen in the Sun and reference A-F type stars

L. I. Mashonkina, T. A. Ryabchikova

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29 pages, 5 tables, 8 figures, accepted for publication in Astronomy Letters
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AI总结：

本文构建新氮模型原子并结合 NLTE 与 3D 校正测定太阳及 11 颗 A-F 型参考星的氮丰度，发现其与星际气体和早期 B 型星在 0.09 dex 内一致。

摘要：

本研究利用实验室测量以及原子结构计算所预测的 N I 能级，并采用用于计算跃迁辐射速率和碰撞速率的最新原子数据，开发了一个新的氮模型原子。通过应用合成光谱法、使用平面平行（1D）MARCS 模型大气，并考虑偏离局部热力学平衡（non-LTE，即 NLTE 效应），由 N I 谱线测定了太阳丰度 log ε⊙,N(1D NLTE)=7.92±0.03。在采用 Amarsi 等人（2020）的 3D 校正后，我们得到太阳的 log ε⊙,N(NLTE+3D)=7.88±0.03。基于高光谱分辨率光谱，我们为 11 颗具有可靠大气参数的未演化 A-F 型恒星推导了氮的 NLTE 丰度。非 LTE 会使 N I 谱线增强，且非 LTE 效应随有效温度升高而增大。对于每颗恒星，与 LTE 情形相比，非 LTE 都使丰度误差更小。对于表面正常的 A 型星，非 LTE 消除了 LTE 情形下所得氮丰度相对于太阳氮丰度的增强。一颗 λ Boo 型星 HD 172167（织女星，Vega）也具有接近太阳的 N 丰度。四颗 Am 星的 N 丰度呈现分散，范围从 [N/H]=-0.44 到 [N/H]=0.39。太阳和表面正常 A 型星的 N 丰度与星际气体及早期 B 型星的氮丰度在 0.09 dex 内一致。

英文摘要：

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 $\log\varepsilon_{\odot,N}$(1D NLTE) = 7.92$\pm$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 $\log\varepsilon_{\odot,N}$(NLTE+3D) = 7.88$\pm$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.

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