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arXiv 1107.3586astro-ph.SR
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在分离的后公共包络二进制LTT 560中的吸积

Accretion in the detached post-common-envelope binary LTT 560

C. Tappert, B. T. Gänsicke, L. Schmidtobreick, T. Ribeiro

摘要:

在以前的研究中,我们发现,分离后的共同包络二进制LTT 560显示由两个反相组件组成的H α发射线。虽然其中一个明显是由次级晚型主序星的恒星活动造成的,但我们的分析表明,白矮星主星可能是第二个组成部分的起源。然而,数据的低分辨率意味着我们的解释仍然模糊不清。在这里,我们使用时间序列UVES数据比较的径向速度的Halpha发射组件的金属吸收线从主星和次星。我们发现,较弱的成分最肯定起源于白矮星,可能是由吸积造成的。对白矮星光谱的丰度分析得出的吸积率与恒星风引起的次级质量损失一致。第二个也是更强的H α分量是由次级恒星上的恒星活动引起的。由于在我们的时间分辨光谱学中出现了耀斑,所以很可能存在一个活跃的次级。此外,罗氏层析成像表明,在第二颗恒星的前侧和靠近第一个拉格朗日点的重要区域被星点覆盖。最后,我们推导出系统的参数,并将其置于进化的背景下。我们发现,白矮星是一个非常缓慢的旋转,这表明它有一个角动量的演变类似于场白矮星。我们预测,LTT 560将开始质量转移通过罗氏瓣溢出在约3.5 Gyrs,并得出结论,该系统是目前人口的灾变变量的祖先的代表。它很可能会演化成SU Uma型的矮新星。

英文摘要:

In a previous study, we found that the detached post-common-envelope binary LTT 560 displays an Halpha emission line consisting of two anti-phased components. While one of them was clearly caused by stellar activity from the secondary late-type main-sequence star, our analysis indicated that the white dwarf primary star is potentially the origin of the second component. However, the low resolution of the data means that our interpretation remains ambiguous. We here use time-series UVES data to compare the radial velocities of the Halpha emission components to those of metal absorption lines from the primary and secondary stars. We find that the weaker component most certainly originates in the white dwarf and is probably caused by accretion. An abundance analysis of the white dwarf spectrum yields accretion rates that are consistent with mass loss from the secondary due to a stellar wind. The second and stronger Halpha component is attributed to stellar activity on the secondary star. An active secondary is likely to be present because of the occurrence of a flare in our time-resolved spectroscopy. Furthermore, Roche tomography indicates that a significant area of the secondary star on its leading side and close to the first Lagrange point is covered by star spots. Finally, we derive the parameters for the system and place it in an evolutionary context. We find that the white dwarf is a very slow rotator, suggesting that it has had an angular-momentum evolution similar to that of field white dwarfs. We predict that LTT 560 will begin mass transfer via Roche-lobe overflow in about 3.5 Gyrs, and conclude that the system is representative of the progenitors of the current population of cataclysmic variables. It will most likely evolve to become an SU UMa type dwarf nova.

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