arXiv 2301.094622023-01-23astro-ph.SR

O型主序星晚期光谱的混合非LTE方法定量研究

Quantitative spectroscopy of late O-type main-sequence stars with a hybrid non-LTE method

Patrick Aschenbrenner, Norbert Przybilla, Keith Butler

备注：: 31 pages, 23 figures, Accepted for publication in Astronomy & Astrophysics
发表信息：: A&A 671, A36 (2023)
DOI：: 10.1051/0004-6361/202244906

摘要：

上下文光度为$\log L/L_\odot \lesssim 5.2$的晚O型星显示出弱风，质量损失率低于10 $^{-8} M_\odot$ yr $^{-1}$。这意味着它们的光球层不会受到恒星风的强烈影响。目的。一个混合的非局部热力学平衡（非LTE）的方法进行测试，分析晚O型星。本文研究了20颗光谱类型为O 8至O9.7、光度等级为V和IV的银河系O型星的样本，这些O型星以前曾在文献中使用完整的非LTE模型大气进行过研究。方法.流体静力学平面平行的大气结构和合成光谱计算与Kurucz的EQUIPAS 12代码连同非LTE线形成代码的细节和表面，占湍流压力对大气的影响，被采用。对高分辨率光谱进行了分析，以得出大气参数和元素丰度。通过考虑恒星演化轨迹和Gaia EDR 3的弛豫时间，得到了基本的恒星参数。星际红化的特点是拟合光谱能量分布从紫外到中红外。对16颗样本星的所有参数都取得了很高的精度和准确度。结果表明，湍流压力效应具有显著的影响。有效温度的不确定度为1-3%，表面重力为0.05 - 0.10 dex，质量优于8%，半径优于10%，光度优于20%。C、N、O、Ne、Mg、Al、Si的丰度一般以0.05至0.10 dex的不确定度导出，氦的不确定度一般在0.03至0.05 dex（1 $σ$标准偏差）内。到Lac OB 1b星协和疏散星团NGC 2244、IC 1805、NGC 457和IC 1396的距离被确定为副产品。

英文摘要：

Context. Late O-type stars at luminosities $\log L/L_\odot \lesssim 5.2$ show weak winds with mass-loss rates lower than 10$^{-8} M_\odot$ yr$^{-1}$. This implies that their photospheric layers are not strongly affected by the stellar wind. Aims. A hybrid non-local thermodynamic equilibrium (non-LTE) approach is tested for analyses of late O-type stars. A sample of 20 mostly sharp-lined Galactic O stars of spectral types O8 to O9.7 and luminosity classes V and IV, previously studied in the literature using full non-LTE model atmospheres, is investigated. Methods. Hydrostatic plane-parallel atmospheric structures and synthetic spectra computed with Kurucz's Atlas12 code together with non-LTE line-formation codes Detail and Surface, which account for the effects of turbulent pressure on the atmosphere, were employed. High-resolution spectra were analysed to derive atmospheric parameters and elemental abundances. Fundamental stellar parameters were derived by considering stellar evolution tracks and Gaia EDR3 parallaxes. Interstellar reddening was characterised by fitting spectral energy distributions from the UV to the mid-IR. Results. A high precision and accuracy is achieved for all derived parameters for 16 sample stars. Turbulent pressure effects turn out have significant effects. Effective temperatures are determined to 1-3% uncertainty levels, surface gravities to 0.05 to 0.10 dex, masses to better than 8%, radii to better than 10%, and luminosities to better than 20% uncertainty typically. Abundances for C, N, O, Ne, Mg, Al, Si are derived with uncertainties of 0.05 to 0.10 dex and for helium within 0.03 to 0.05 dex (1$σ$ standard deviations) in general. Distances to the Lac OB1b association and to the open clusters NGC 2244, IC 1805, NGC 457, and IC 1396 are determined as a byproduct.

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