arXiv 1606.048152016-06-15astro-ph.SR

仙王座EM的B态和Be态

The B and Be States of the Star EM Cepheus

Diana Kjurkchieva, Dragomir Marchev, T. A. A. Sigut, Dinko Dimitrov

备注：: 15 pages, 14 figures
DOI：: 10.3847/0004-6256/152/3/56

摘要：

我们提出了11年的高分辨率，光谱观测的恒星EM~Cep。从H $α$的发射能级可以看出，EM~Cep在B和Be星态之间转换，但大部分时间处于B~星态. EM~Cep被认为是一颗由质量几乎相等的B星组成的食近接触双星，以重现规则的光度变化;然而，这个模型是有问题的，因为在光谱中没有任何观测到的多普勒频移。我们的观测结果证实，在B星和Be星的宽谱线H $α$和HeI~6678中没有明显的多普勒频移，HeI~6678的谱线轮廓通常呈现出填充的吸收核，但在最高Be态时，我们在这条谱线上检测到微弱的发射。由于缺乏观测到的多普勒频移，我们模型EM~Cep作为一个孤立的Be星与可变的拱星盘。我们可以相当好地再现在11年期间观测到的H $α$发射轮廓，在Be状态下，盘质量为$3$到$10\times\,10^{-11}\;M_*$的数量级，周星盘与视线的倾角为$78^{\circ}$。根据2014年的一次椎间盘弹射事件，我们估计质量损失率为$\approx\,3\times 10^{-9}\;\rm M_{\odot}\,yr^{-1}$。导出的磁盘密度参数是典型的经典Be星。因此，我们认为EM~Cep是一颗经典Be星，它的光度变化是$β\;$ Cep或非径向脉动的结果。

英文摘要：

We present eleven years of high-resolution, spectroscopic observations for the star EM~Cep. EM~Cep switches between B and Be star states, as revealed by the level of H$α$ emission, but spends most of its time in the B~star state. EM~Cep has been considered to be an eclipsing, near contact binary of nearly equal-massed B stars in order to reproduce regular photometric variations; however, this model is problematic due to the lack of any observed Doppler shift in the spectrum. Our observations confirm that there are no apparent Doppler shifts in the wide spectral lines H$α$ and HeI~6678 in either the B or Be star states.The profiles of HeI~6678 typically exhibited a filled-in absorption core, but we detected weak emission in this line during the highest Be state. Given the lack of observed Doppler shifts, we model EM~Cep as an isolated Be star with a variable circumstellar disk. We can reproduce the observed H$α$ emission profiles over the eleven year period reasonably well with disk masses on the order of $3$ to $10\times\,10^{-11}\;M_*$ in the Be state with the circumstellar disk seen at an inclination of $78^{\circ}$ to the line of sight. From a disk ejection episode in 2014, we estimate a mass loss rate of $\approx\,3\times 10^{-9}\;\rm M_{\odot}\,yr^{-1}$. The derived disk density parameters are typical of those found for the classical Be stars. We therefore suggest that the EM~Cep is a classical Be star and that its photometric variations are the result of $β\;$Cep or non-radial pulsations.

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