AI 中文总结
研究热晕星HD 177566，分析其FUV和光学光谱，通过模型拟合研究元素丰度、谱线等情况，发现碳元素丰度低等特征，确定其处于特定演化轨迹，为恒星演化研究提供了相关观测数据和结论。
AI 中文摘要
我们分析了热晕星HD 177566的存档远紫外（FUV）和光学光谱。该恒星有效温度\(T_{\rm eff}=33000\pm1000\)K，表面重力\(\log g = 3.79\pm0.11\)，氦丰度\(\log N({\rm He})/N({\rm H}) = -0.86\pm0.05\)。除碳元素比其他晕星低约1个量级外，13种其他元素的丰度与其他晕星一致。我们的模型不能很好地再现低阶氢巴尔末线。氦I的漫射谱线通常比预测的更宽，但使用更新的线展宽参数可显著改善拟合。将最佳拟合模型缩放到该恒星的光学和近红外星等，得出消光\(E(B - V)=0.095\pm0.005\)，与文献值一致，但所得模型对该恒星的FUV通量预测低了两倍。该恒星的有效温度和光度\((\log L / L_{\odot}=3.50\pm0.08)\)使其处于从红水平分支演化而来的恒星的后渐近巨星分支（post - AGB）演化轨迹上。其低碳丰度\(\log N({\rm C})/N({\rm O}) = -2.18\pm0.21\)表明它在上升到渐近巨星分支时未经历显著的第三次 dredge - up。
英文摘要
We have analyzed archival FUV and optical spectra of the hot halo star HD 177566. The star has an effective temperature $T_{\rm eff} = 33{,}000 \pm 1000$ K, surface gravity $\log g = 3.79 \pm 0.11$, and helium abundance $\log N({\rm He})/N({\rm H}) = -0.86 \pm 0.05$. Abundances of 13 additional elements are consistent with those of other halo stars, save for carbon, which is underabundant by about 1 dex. The low-order hydrogen Balmer lines are not well reproduced by our models. The diffuse lines of He I are often broader than predicted, but the use of more recent line-broadening parameters significantly improves the fit. Scaling our best-fit model to the star's optical and near-IR magnitudes yields an extinction $E(B-V) = 0.095 \pm 0.005$, consistent with literature values, but the resulting model underpredicts the star's FUV flux by a factor of two. The star's effective temperature and luminosity ($\log L / L_{\odot} = 3.50 \pm 0.08$) place it on the post-AGB evolutionary tracks of a star that evolved from the red horizontal branch. Its low carbon abundance, $\log N({\rm C})/N({\rm O}) = -2.18 \pm 0.21$, indicates that it did not experience significant third dredge-up while ascending the AGB.
Comments17 pages, 8 figures, to be published in the Astrophysical Journal
