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arXiv 1302.5201astro-ph.SR
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大质量双星系统的谱模拟

Spectral modelling of massive binary systems

Matthieu Palate, Gregor Rauw, Gloria Koenigsberger, Edmundo Moreno

摘要:

目的:我们模拟了大质量双星在轨道周期的不同阶段的光谱,占伴星的引力对恒星表面的形状和物理性质的影响。研究方法:我们使用修正的Roche势来计算封闭圆系统的恒星表面,我们使用TIDES程序来计算偏心系统的表面。在这两种情况下,我们占重力暗化和相互加热产生的辐射计算表面温度。然后,我们内插NLTE平面平行大气模式光谱在一个网格中,以获得在每个表面点的本地光谱。最后,我们总结了所有的贡献,占多普勒频移,边缘暗化,和能见度,以获得总的合成频谱。我们计算了不同的轨道相位和一组物理和轨道参数。结果:我们的模型预测线强度的变化,通过轨道周期,但未能完全再现Struve-Sahade效应。包括辐射压力,使我们能够重现表面温度分布,这是一致的观测半分离的双星系统。结论:辐射压对恒星表面的影响在(过)接触双星和分离良好的系统中很弱,但在半分离系统中可能变得非常重要。经典的vonZeipel定理对于谱计算是充分的。光谱计算得到的宽波段光变曲线不同于用瞬时轨道间距标度的Roche势等势模型计算得到的光变曲线。在许多情况下,两个高斯/洛伦兹分布的拟合无法正确测量线的等效宽度,并导致明显的变化,可以解释文献中报道的一些效应。

英文摘要:

Aims: We simulate the spectra of massive binaries at different phases of the orbital cycle, accounting for the gravitational influence of the companion star on the shape and physical properties of the stellar surface. Methods: We used the Roche potential modified to account for radiation pressure to compute the stellar surface of close circular systems and we used the TIDES code for surface computation of eccentric systems. In both cases, we accounted for gravity darkening and mutual heating generated by irradiation to compute the surface temperature. We then interpolated NLTE plane-parallel atmosphere model spectra in a grid to obtain the local spectrum at each surface point. We finally summed all contributions, accounting for the Doppler shift, limb-darkening, and visibility to obtain the total synthetic spectrum. We computed different orbital phases and sets of physical and orbital parameters. Results: Our models predict line strength variations through the orbital cycle, but fail to completely reproduce the Struve-Sahade effect. Including radiation pressure allows us to reproduce a surface temperature distribution that is consistent with observations of semi-detached binary systems. Conclusions: Radiation pressure effects on the stellar surface are weak in (over)contact binaries and well-detached systems but can become very significant in semi-detached systems. The classical von Zeipel theorem is sufficient for the spectral computation. Broad-band light curves derived from the spectral computation are different from those computed with a model in which the stellar surfaces are equipotentials of the Roche potential scaled by the instantaneous orbital separation. In many cases, the fit of two Gaussian/Lorentzian profiles fails to properly measure the equivalent width of the lines and leads to apparent variations that could explain some of the effects reported in the literature.

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