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arXiv 1602.06314astro-ph.SR
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激变变星中负超峰的出现：光滑粒子流体动力学模拟

The Emergence of Negative Superhumps in Cataclysmic Variables: Smoothed Particle Hydrodynamics Simulations

David M. Thomas, Matt A. Wood

发表信息：
Published in Astrophysical Journal 805:55 (15pp), 2015 April 20
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摘要：

当吸积盘相对于轨道平面倾斜时，激变变星系统中就会出现负的超级驼峰。节点线的缓慢逆行进动产生一个信号-负超级峰-其周期略小于轨道周期。以前的研究表明，倾斜的磁盘显示出负的超级驼峰，但磁盘最初如何倾斜尚未达成共识。赖的分析工作表明，当偶极距偏离主自旋轴的角度时，以及当主自旋轴本身不与双星轨道的角动量轴对齐时，主轨道上的磁场会导致磁盘中的倾斜不稳定性。然而，赖并没有将他的工作应用于负超级峰的形成。在本文中，我们添加赖的模型，现有的光滑粒子流体动力学代码。使用这个代码，我们证明了出现的负超级峰的“光变曲线”的磁偶极矩的范围。我们发现，从这些负的超级驼峰计算的周期赤字匹配那些在模拟中使用手动倾斜磁盘。当出现正的超级峰（$q \lesssim 0.33$），我们表明，从这些信号计算的周期过剩也与以前的结果是一致的。通过例子，我们表明圆盘是倾斜的，尽管倾斜度周期性变化，并且它们在逆行方向上旋进。发现导致负超级峰出现的磁场位于千高斯区。

英文摘要：

Negative superhumps are believed to arise in cataclysmic variable systems when the accretion disk is tilted with respect to the orbital plane. Slow retrograde precession of the line-of-nodes results in a signal---the negative superhump---with a period slightly less than the orbital period. Previous studies have shown that tilted disks exhibit negative superhumps, but a consensus on how a disk initially tilts has not been reached. Analytical work by Lai suggests that a magnetic field on the primary can lead to a tilt instability in a disk when the dipole moment is offset in angle from the spin axis of the primary and when the primary's spin axis is, itself, not aligned with the angular momentum axis of the binary orbit. However, Lai did not apply his work to the formation of negative superhumps. In this paper, we add Lai's model to an existing smoothed particle hydrodynamics code. Using this code, we demonstrate the emergence of negative superhumps in the "light curve" for a range of magnetic dipole moments. We show that the period deficits calculated from these negative superhumps match those in simulations using manually tilted disks. When positive superhumps appear ($q \lesssim 0.33$), we show that the period excesses calculated from these signals are also consistent with previous results. Using examples, we show that the disks are tilted, though the tilt varies periodically, and that they precess in the retrograde direction. The magnetic fields found to lead to the emergence of negative superhumps lie in the kilogauss regime.

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