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arXiv 1003.2553astro-ph.SR
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红色变星长二次周期脉动二元模式的检验

Testing a pulsating binary model for long secondary periods in red variables

J. D. Nie, X. B. Zhang, B. W. Jiang

摘要:

红变星长次级周期的成因至今仍是一个谜,尽管已有多种模型。一些LSP星的光变曲线模仿了一个有脉动红巨星成分的食双星。为了验证这一假设,收集和分析了LMC的ESTO项目发现的两颗LSP变星77.7795.29和77.8031.42的观测数据。用Wilson-Devinney(W-D)方法模拟了光变曲线可能的食变特征。模拟结果分别为两个系统产生接触和半接触的几何形状。此外,还导出了各二元系中主要脉动分量的脉动常数。结合二元模型和脉动分量的结果,我们研究了脉动二元模型的可行性。结果表明,二元模型的径向速度曲线具有比观测值大得多的振幅和两倍于观测值的周期。此外,根据双星轨道解导出的密度得到的组分质量太低,与演化阶段和高光度都不相容。虽然从二元模型的脉动常数,这是依赖于密度的脉动模式是一致的第一或第二泛音径向脉动,我们得出的结论是脉动二元模型是一个有缺陷的模型的LSP。

英文摘要:

The origin of the long secondary periods (LSPs) in red variables remains a mystery up to now, although there exist many models. The light curves of some LSPs stars mimic an eclipsing binary with a pulsating red giant component. To test this hypothesis, the observational data of two LSP variable red giants, 77.7795.29 and 77.8031.42, discovered by the MACHO project from the LMC, are collected and analyzed. The probable eclipsing features of the light curves are simulated by the Wilson-Devinney (W-D) method. The simulation yields a contact and a semidetached geometry for the two systems, respectively. In addition, the pulsation constant of the main pulsating component in each binary system is derived. By combining the results of the binary model and the pulsation component, we investigate the feasibility of the pulsating binary model. It is found that the radial velocity curve expected from the binary model has a much larger amplitude than the observed one and a period double the observed one. Furthermore, the masses of the components based on the density derived from the binary orbit solution are too low to be compatible with both the evolutionary stage and the high luminosity. Although the pulsation mode identified by the pulsation constant which is dependent on the density from the binary-model is consistent with the first or second overtone radial pulsation, we conclude that the pulsating binary model is a defective model for the LSP.

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