标题： HD 49798的光谱分析，一个在吸积X射线双星中的明亮、缺乏氢的sdO型供体恒星 显示英文标题

标题： Spectral analysis of HD 49798, a bright, hydrogen-deficient sdO-type donor star in an accreting X-ray binary

摘要： 上下文：HD 49798是一个明亮的（$m_{\rm V} = 8.287$），温度较高（有效温度$T_{\rm eff} = 45000$K）的光谱类型为O（sdO）的次矮星。它是唯一一个被确认的X射线双星中的sdO型质量供体星，其主星是高质量（1.28$M_\odot$）的白矮星或中子星，自转周期仅为13.2秒。目的：由于在轨道和可回收远紫外及极端紫外光谱仪（ORFEUS）数据库中存在一份高质的HD 49798光谱数据，该光谱由图宾根紫外阶梯光谱仪（TUES）获得且此前从未被分析过，因此我们基于从远紫外（FUV）到光学波长范围的观测进行了光谱分析。方法：我们使用了图宾根模型大气包（TMAP）的先进非局部热平衡（NLTE）模型大气来确定有效温度、表面重力（$\log g$）以及那些在可用观测光谱中出现谱线的元素的丰度。结果：我们确定了$T_{\rm eff} = 45000 \pm 1000$K，log(g / cm/s$^2$) =$4.46 \pm 0.10$，并重新分析了之前确定的光球H、He、N、O、Mg、Al、Si、Fe和Ni的丰度。首次测量了C、Ne、P、S、Cr和Mn的丰度。结论：我们对HD 49798进行的全波段光谱分析——从远紫外到光学——使得光球参数的误差限得以减少，并精确测定了金属丰度。 HD 49798 是一个剥离的中等质量（零龄主序质量约为 7.15 $M_\odot$）氦星，质量为 1.14(+0.30/-0.24) $M_\odot$。 在其表面显示出由于 CNO 循环和 3 alpha 燃烧核合成以及增强的 Cr、Mn、Fe 和 Ni 含量的结果。 显示英文摘要

摘要： Context: HD 49798 is a bright ($m_{\rm V} = 8.287$), hot (effective temperature $T_{\rm eff} = 45000$ K) subdwarf star of the spectral type O (sdO). It is the only confirmed sdO-type mass-donor star of an X-ray binary that has a high-mass (1.28 $M_\odot$) white-dwarf or neutron-star primary with a spin period of only 13.2 s. Aims: Since a high-quality spectrum of HD 49798, obtained with the T\"ubingen Ultraviolet Echelle Spectrometer (TUES), that has never been analyzed before is available in the database of the Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer (ORFEUS), we performed a spectral analysis based on observations from the far ultraviolet (FUV) to the optical wavelength range. Methods: We used advanced non-local thermodynamic equilibrium (NLTE) model atmospheres of the Tuebingen Model-Atmosphere Package (TMAP) to determine the effective temperature, the surface gravity ($\log g$), and the abundances of those elements that exhibit lines in the available observed spectra. Results: We determined $T_{\rm eff} = 45000 \pm 1000$ K, log (g / cm/s$^2$) = $4.46 \pm 0.10$, and re-analyzed the previously determined photospheric abundances of H, He, N, O, Mg, Al, Si, Fe, and Ni. For the first time, we measured the abundances of C, Ne, P, S, Cr, and Mn. Conclusons: Our panchromatic spectral analysis of HD 49798 -- from the FUV to the optical -- allowed to reduce the error limits of the photospheric parameters and to precisely measure the metal abundances. HD 49798 is a stripped, intermediate-mass (zero-age main sequence mass of about 7.15 $M_\odot$) He star with a mass of 1.14(+0.30/-0.24) $M_\odot$. At its surface it exhibits abundances that are the result of CNO-cycle and 3 alpha burning nucleosynthesis as well as enhanced Cr, Mn, Fe, and Ni abundances.