The Accretion Flows and Evolution of Magnetic Cataclysmic Variables

The Accretion Flows and Evolution of Magnetic Cataclysmic Variables
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吸积流和磁灾变变量的演化

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发表时间：
2007
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通讯作者：
L. University
L. University
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文献类型：
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作者：
A. Norton;O. Butters;T. L. Parker;G. University;L. University

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我们用磁吸积模型研究了磁激变变数(MCV)的吸积流。数值模拟表明，四种流动是可能的：圆盘、水流、环流和螺旋桨。对于给定的质量比，决定吸积流的基本观察量是系统的自旋与轨道周期之比。如果中间极(IP)以其平衡自旋速率聚集，则当质量比为0.5时，PSpin/Porb≲为0.1时为盘状，PSpin/Porb≲为0.1时为流状，而PSpin/Porb∼为0.6时为环状。当恒星组分的质量比减小时，系统在这些流类型之间转换的自旋与轨道周期之比会增加。我们首次提出了MCV的演化轨迹，这使得研究它们的吸积流如何随时间变化成为可能。随着系统向更短的轨道周期和更小的质量比演化，为了保持自旋平衡，它们的自旋与轨道周期的比率通常会增加。因此，在较短的轨道周期内，环状流的相对发生率将增加，而盘状流的发生率将减少。在轨道周期低于2小时的高自转/轨道周期比下观察到的越来越多的系统，以及ex Hya环状吸积的观测证据与这一图景完全一致。
We have used a model of magnetic accretion to investigate the accretion flows of magnetic cataclysmic variables (mCVs). Numerical simulations demonstrate that four types of flow are possible: disks, streams, rings, and propellers. The fundamental observable determining the accretion flow, for a given mass ratio, is the spin-to-orbital-period ratio of the system. If intermediate polars (IPs) are accreting at their equilibrium spin rates, then for a mass ratio of 0.5, those with Pspin/Porb≲ 0.1 will be disklike, those with 0.1≲ Pspin/Porb≲ 0.6 will be streamlike, and those with Pspin/Porb ∼ 0.6 will be ringlike. The spin-to-orbital-period ratio at which the systems transition between these flow types increases as the mass ratio of the stellar components decreases. For the first time we present evolutionary tracks of mCVs, which make it possible to investigate how their accretion flow changes with time. As systems evolve to shorter orbital periods and smaller mass ratios, in order to maintain spin equilibrium their spin-to-orbital-period ratio will generally increase. As a result, the relative occurrence of ringlike flows will increase, and the occurrence of disklike flows will decrease, at short orbital periods. The growing number of systems observed at high spin-to-orbital-period ratios with orbital periods below 2 hr and the observational evidence for ringlike accretion in EX Hya are fully consistent with this picture.