The effect of rotation on the stability of nuclear burning in accreting neutron stars
The effect of rotation on the stability of nuclear burning in accreting neutron stars
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DOI：
10.1051/0004-6361/200911619
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发表时间：
2009-05
影响因子：
6.5
通讯作者：
L. Keek;N. Langer;J. Zand
中科院分区：
文献类型：
--
作者：
L. Keek;N. Langer;J. Zand
中子星星从双星伴星吸积的氢和/或氦可能会发生热核聚变。在不同的质量吸积速率下，可以分辨出不同的燃烧状态。理论模型预测氦聚变在爱丁顿极限以下的吸积率下以热核逃逸的方式进行，而在此极限以上则以稳定燃烧的方式进行。然而，观测结果表明，边界接近爱丁顿极限的10%。研究了旋转诱导输运过程对氦燃烧稳定性的影响。第一次，详细计算薄壳氦燃烧的中子星使用流体动力学恒星演化代码，包括旋转和旋转诱导磁场。我们发现，在大多数情况下，从磁场的不稳定性提供了占主导地位的贡献的化学混合，而爱丁顿-斯威特环流成为重要的高转速。随着氦扩散到更大的深度，燃烧的稳定性增加，使得稳定氦燃烧的临界吸积率被发现是较低的。最近的研究表明，湍流混合与地壳的较高热通量相结合，可以解释观测到的临界吸积率。此外，接近这个边界，我们发现振荡燃烧，以前的研究已经链接到兆赫QPO。在我们不断降低来自地壳的热通量的模型中，振荡的周期增加了几十个倍频程，类似于观察到的频率漂移，这表明这种漂移可能是由更深层的冷却引起的。
Hydrogen and/or helium accreted by a neutron star from a binary companion may undergo thermonuclear fusion. Different burning regimes are discerned at different mass accretion rates. Theoretical models predict helium fusion to proceed as a thermonuclear runaway for accretion rates below the Eddington limit and as stable burning above this limit. Observations, however, place the boundary close to 10% of the Eddington limit. We study the effect of rotationally induced transport processes on the stability of helium burning. For the first time, detailed calculations of thin-shell helium burning on neutron stars are performed using a hydrodynamic stellar evolution code including rotation and rotationally induced magnetic fields. We find that in most cases the instabilities from the magnetic field provide the dominant contribution to the chemical mixing, while Eddington-Sweet circulations become important at high rotation rates. As helium is diffused to greater depths, the stability of the burning is increased, such that the critical accretion rate for stable helium burning is found to be lower. Combined with a higher heat flux from the crust, as suggested by recent studies, turbulent mixing could explain the observed critical accretion rate. Furthermore, close to this boundary we find oscillatory burning, which previous studies have linked to mHz QPOs. In models where we continuously lower the heat flux from the crust, the period of the oscillations increases by up to several tens of percents, similar to the observed frequency drift, suggesting that this drift could be caused by the cooling of deeper layers.