VLT/UVES spectroscopy of Wray 977, the hypergiant companion to the X-ray pulsar GX301-2
VLT/UVES spectroscopy of Wray 977, the hypergiant companion to the X-ray pulsar GX301-2
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DOI：
10.1051/0004-6361:20065393
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发表时间：
2006-07
影响因子：
6.5
通讯作者：
L. Kaper;A. V. D. Meer;F. L. U. O. Amsterdam;I. D. E. D. L. M. Csic-I.-D.-E.-D.-L.-M.-Csic-102493558;Madrid
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文献类型：
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作者：
L. Kaper;A. V. D. Meer;F. L. U. O. Amsterdam;I. D. E. D. L. M. Csic-I.-D.-E.-D.-L.-M.-Csic-102493558;Madrid
模型大气符合 Wray 977 的高分辨率光谱，证实了 X 射线脉冲星 GX301−2 的大质量伴星的 B 超巨星分类。该模型给出的半径为 62 R�，有效温度为 18 100 K，光度为 5 × 10 5 L�。与之前测量的 Wray 977 的恒星参数相比，这些值有所减少。推导出的恒星风质量损失率和终端速度分别为10 -5 Myr -1 和305 km s -1 。星际 Nai D 吸收表明，Wray 977 位于与人马座-船底座旋臂（1-2.5 kpc）的第一个交点后面，可能属于距离 3−4 kpc 的 Norma 旋臂的恒星群。从模型大气得出的光度与该距离（3 kpc）一致。风馈X射线脉冲星(LX ∼ 10 37 erg s -1 )的光度与邦迪-霍伊尔质量吸积率非常一致。在甚大望远镜（VLT）上使用 UVES 获得的光谱覆盖了系统的整个轨道，包括近星体通道，从中我们得出了 B 超巨星的径向速度曲线。测量的径向速度幅度为 10 ± 3k m s -1，产生质量比 q = MX/Mopt = 0.046 ± 0.014。由于没有 X 射线日食，Wray 977 的质量下限为 39 M�。采用最大中子星质量 3.2 或 2.5 M� 得出的 Wray 977 质量上限分别为 68 或 53 M�。相应的系统倾角下限是 i > 44 ° ，支持了 X 射线光曲线的下降是由于 Wray 977 的稠密星风吸收造成的观点（Leahy 2002）。 Wray 977 的“光谱”质量为 43 ± 10 M�，与二元约束得出的质量范围一致。中子星的质量为 1.85 ± 0.6 M� 。密集星风中形成的谱线时间序列（例如Hei 5876 A和Hα）表明存在尾随中子星轨道的气流。 Hα 等效宽度的长期行为表现出风力强度的强烈变化；数据采样不足以得出风质量损失率与脉冲星自转周期之间是否存在关系的结论。
Model atmosphere fits to high-resolution optical spectra of Wray 977 confirm the B hypergiant classification of the massive companion to the X-ray pulsar GX301−2. The models give a radius of 62 R� ,a n effective temperature of 18 100 K and a luminosity of 5 × 10 5 L� . These values are somewhat reduced compared to the stellar parameters of Wray 977 measured previously. The deduced mass-loss rate and terminal velocity of the stellar wind are 10 −5 Myr −1 and 305 km s −1 , respectively. The interstellar Nai D absorption indicates that Wray 977 is located behind the first intersection with the Sagittarius-Carina spiral arm (1-2.5 kpc) and probably belongs to the stellar population of the Norma spiral arm at a distance of 3−4 kpc. The luminosity derived from the model atmosphere is consistent with this distance (3 kpc). The luminosity of the wind-fed X-ray pulsar (LX ∼ 10 37 erg s −1 ) is in good accordance with the Bondi-Hoyle mass accretion rate. The spectra obtained with UVES on the Very Large Telescope (VLT) cover a full orbit of the system, including periastron passage, from which we derive the radial-velocity curve of the B hypergiant. The measured radial-velocity amplitude is 10 ± 3k m s −1 yielding a mass ratio q = MX/Mopt = 0.046 ± 0.014. The absence of an X-ray eclipse results in a lower limit to the mass of Wray 977 of 39 M� . An upper limit of 68 or 53 Mis derived for the mass of Wray 977 adopting a maximum neutron star mass of 3.2 or 2.5 M� , respectively. The corresponding lower limit to the system inclination is i > 44 ◦ , supporting the view that the dip in the X-ray lightcurve is due to absorption by the dense stellar wind of Wray 977 (Leahy 2002). The "spectroscopic" mass of Wray 977 is 43 ± 10 M� , consistent with the range in mass derived from the binarity constraints. The mass of the neutron star is 1.85 ± 0.6 M� . Time series of spectral lines formed in the dense stellar wind (e.g. Hei 5876 A and Hα) indicate the presence of a gas stream trailing the neutron star in its orbit. The long-term behaviour of the Hα equivalent width exhibits strong variations in wind strength; the sampling of the data is insufficient to conclude whether a relation exists between wind mass-loss rate and pulsar spin period.