Carbon-Oxygen White Dwarf Accreting CO-Rich Matter. II. Self-Regulating Accretion Process up to the Explosive Stage
Carbon-Oxygen White Dwarf Accreting CO-Rich Matter. II. Self-Regulating Accretion Process up to the Explosive Stage
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DOI：
10.1086/378952
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发表时间：
2003-12
期刊：
影响因子：
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通讯作者：
L. Piersanti;S. Gagliardi;Icko Iben, Jr.,;A. Tornambe'
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文献类型：
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作者：
L. Piersanti;S. Gagliardi;Icko Iben, Jr.,;A. Tornambe'
我们研究了旋转对双简并白色矮星系统演化的影响，这些系统可能是Ia型超新星的祖先。我们假设在合并之前，两颗白色矮星以轨道频率同步旋转，并且在合并过程中，较轻的白色矮星转变为较厚的圆盘，较重的白色矮星最初以非常高的速率（~10-5 M yr-1）吸积。由于旋转的提升效应，吸积的白色矮星膨胀，直到在表面结合所需的引力加速度和向心加速度变得相等，从而引发罗氏不稳定性。白色矮星继续吸积盘中的物质，但其吸积速度取决于外层两个相互竞争的过程之间的平衡：（1）由于吸积而产生的加热、膨胀和自旋加速;（2）由于热扩散而产生的冷却和收缩。这种平衡产生了一个吸积率，使得白色矮星的角速度ωWD和分裂角速度ωcr保持相等。由于吸积物质的角动量沉积和吸积星星的收缩，ωWD不断增加，直到转动能达到引力结合能的14%左右，然后，另一个不稳定性开始出现：结构被迫采取椭圆形并发射引力波。此后，吸积物质的角动量沉积速率和引力波的角动量损失速率之间的平衡产生了一个几乎恒定的或“平台”的吸积速率，约为4 × 10-7 M/年。在碳点火发生之前，吸积的白色矮星的质量可以增加到并超过非旋转白色矮星的质量极限。独立的初始值的吸积率，碳点火的物理条件适合实现在吸积的白色矮星的中心，由于高电子简并，最终的结果是一个事件的超新星Ia的比例。我们的研究结果适用于合并的二元白色矮星系统，在爆发性碳点火的发病，有一个总质量在1.4-1.5 M的范围内。
We investigate the effect of rotation on the evolution of double-degenerate white dwarf systems, which are possible progenitors of Type Ia supernovae. We assume that prior to merging, the two white dwarfs rotate synchronously at the orbital frequency and that in the merger process, the lighter white dwarf is transformed into a thick disk from which the more massive white dwarf initially accretes at a very high rate (~10-5 M☉ yr-1). Because of the lifting effect of rotation, the accreting white dwarf expands until the gravitational acceleration and centripetal acceleration required for binding at the surface become equal, initiating a Roche instability. The white dwarf continues to accrete matter from the disk, but at a rate that is determined by the balance between two competing processes operating in outer layers: (1) heating, expansion, and spin-up due to accretion and (2) cooling and contraction due to thermal diffusion. The balance produces an accretion rate such that the angular velocity of the white dwarf ωWD and the break-up angular velocity ωcr remain equal. Because of the deposition of angular momentum by accreted matter and the contraction of the accreting star, ωWD increases continuously until the rotational energy reaches about 14% of the gravitational binding energy; then, another instability sets in: the structure is forced to adopt an elliptical shape and emit gravitational waves. Thereafter, a balance between the rate of deposition of angular momentum by accreted matter and the rate of loss of angular momentum by gravitational waves produces a nearly constant or "plateau" accretion rate of ~4 × 10-7 M☉ yr-1. The mass of the accreting white dwarf can increase up to and beyond the Chandresekhar mass limit for nonrotating white dwarfs before carbon ignition occurs. Independent of the initial value of the accretion rate, the physical conditions suitable for carbon ignition are achieved at the center of the accreting white dwarf and, because of the high electron degeneracy, the final outcome is an event of SN Ia proportions. Our results apply to merged binary white dwarf systems which, at the onset of explosive carbon ignition, have a total mass in the range 1.4-1.5 M☉.