Period and light variations for the cool, overcontact binary BX Pegasi
Period and light variations for the cool, overcontact binary BX Pegasi
复制标题
DOI：
10.1111/j.1365-2966.2004.07996.x
复制
发表时间：
2004-08
影响因子：
4.8
通讯作者：
Jae Woo Lee;Chun-Hwey Kim;W. Han;Ho‐Il Kim;R. Koch
中科院分区：
文献类型：
--
作者：
Jae Woo Lee;Chun-Hwey Kim;W. Han;Ho‐Il Kim;R. Koch
从1999年10月到2000年9月的四个晚上，我们用电荷耦合装置对WUMa型双星BX Pegasi（BX Peg）进行了新的测光观测。光变曲线在每个季节都被完全覆盖。确定了七个新的最小光照时间。发现该系统的轨道周期最近以正弦方式变化，叠加在向下的抛物线变化上。长期周期减小率为dP/dt = -8.62或9.59 × 10 - 8dyr-1，这既可以解释为质量较大的冷星星向质量较小的热组分的质量转移，也可以解释为质量转移和磁星风引起的角动量损失的组合。正弦周期变化的周期和振幅分别约为35.3年和0.015天。BX Peg的光变曲线是不对称的，并显示出逐年的光变。一个斑点模型已被应用到分析这些光变曲线。以1999年的光变曲线为参考，仅调整光斑参数，即可求解2000年的光变曲线。一个冷点模型的冷二次满足1999年和2000年观测到的光变曲线相当不错，并显示了良好的代表性的BX钉系统的光球和现场的描述。BX Peg的亮度变化与周期变化不一致，因此不符合Applegate机制的预测。我们认为周期性变化最可能的原因是由于第三个身体的光-时间效应，尽管在光曲线分析中没有检测到第三个光。如果它存在的话，这个假想的天体可能是一颗非常红的主序星星星或者是一颗白色矮星。我们已经重新解决了历史上公布的光变曲线只有斑点参数，这些非常类似于我们的斑点参数。我们推测这一结果与系统中冷星星的日冕饱和度小有关。
New charge-coupled device photometric observations of the W UMa-type binary BX Pegasi (BX Peg) were collected on four nights from 1999 October to 2000 September. The light curve was covered completely in each season. Seven new times of minimum light were determined. It was found that the orbital period of the system has varied recently in a sinusoidal way, superimposed on a downward parabolic variation. The long-term period decrease rate is deduced as dP/dt = -8.62 or 9.59 × 10 -8 d yr -1 , which can be interpreted as either mass transfer from the more massive cool star to the less massive hot component, or as the combination of mass transfer and angular momentum loss due to a magnetic stellar wind. The period and amplitude of the sinusoidal period variation were calculated to be about 35.3 yr and 0.015 d, respectively. The light curves of BX Peg are asymmetric and show year-to-year light variability. A spot model has been applied to analyse these light curves. After using the light curves of 1999 as reference ones, we solve those of 2000 by adjusting only the spot parameters. One cool-spot model on the cool secondary satisfies the observed light curves of both 1999 and 2000 quite well and shows a good representation of the BX Peg system for both the photospheric and spot descriptions. The brightness variations of BX Peg are not coincident with the period variations and so do not conform to a prediction of the Applegate mechanism. We think the most likely cause of the cyclical variation is the light-time effect due to a third body, although no third light was detected in the light-curve analysis. If it exists, the hypothetical object could be a very red main-sequence star or a white dwarf. We have solved anew the historical published light curve for only the spot parameters and these closely resemble our spot parameters. We speculate that this result is associated with the small coronal saturation of the cool star of the system.