BL andromedae and GW Tauri : close binary stars in a key evolutionary stage
BL andromedae and GW Tauri : close binary stars in a key evolutionary stage
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DOI：
10.1111/j.1365-2966.2005.09963.x
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发表时间：
2006-03
影响因子：
4.8
通讯作者：
Li-ying Zhu;S. Qian
中科院分区：
文献类型：
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作者：
Li-ying Zhu;S. Qian
给出了BL And的光电光变曲线以及GW Tau的首条CCD光变曲线。这两个天体均为短周期食双星，观测时间为2003年或2004年。利用最新版本的威尔逊 - 范哈梅（Wilson - Van Hamme）程序计算了测光要素。结果显示，BL And是一个半相接系统，主星充满其洛希瓣，次星几乎充满但仍未相接；而GW Tau是一个临界相接双星系统，相接程度较小（f = 10.9%），温度差较大，约为3100 K。对每个系统的所有可用食甚时刻（包括新的食甚时刻）都进行了分析。发现BL And的轨道周期以dP/dt = -2.36×10⁻⁸（±0.09）d yr⁻¹的速率减小，而GW Tau的轨道周期可能在减小或振荡，我们认为周期减小的可能性更大。BL And的推导结构和长期周期减小，再结合光变曲线的不对称性表明，该系统可能从当前的半相接阶段演化为相接阶段，通过L₁点从主星向次星进行物质转移，或者它可能刚刚经历热弛豫振荡理论所预测的分离阶段。相比之下，GW Tau是一个热接触不良的临界相接双星，可能处于相接阶段的初期。
A photoelectric light curve of BL And is presented along with the first CCD light curve of GW Tau. Both objects are short-period eclipsing binaries and were observed in 2003 or 2004. Photometric elements were computed using the latest version of the Wilson-Van Hamme code. The results reveal that BL And is a semidetached system with the primary component filling its Roche lobe and the secondary one almost filling but still detached, while GW Tau is a marginal-contact binary system with a small degree of contact (f= 10.9 per cent) and a large temperature difference of about 3100 K. All available eclipse times, including new ones, were analysed for each system. It was found that the orbital period of BL And is decreasing at the rate of dP/dt=-2.36 x 10(-8) (+/- 0.09) d yr(-1) while that of GW Tau may be decreasing or oscillating. We think period decrease is more probable. The derived configuration and secular period decrease for BL And combined with the asymmetry of the light curve indicate that this system may evolve from the present semidetached phase into a contact stage, with mass transfer from the primary component to the secondary one through the L-1 point, or that it might just undergo the broken stage predicted by the theory of thermal relaxation oscillations. In contrast, GW Tau is a marginal-contact binary in poor thermal contact and may be at the beginning of the contact phase.