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arXiv 0809.1890astro-ph
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LISA幅频域中致密白矮星双星的布居边界

Population boundaries for compact white-dwarf binaries in LISA's amplitude-frequency domain

Ravi kumar Kopparapu

摘要:

在早期的调查中,我们提出了人口边界的吸入和质量转移的双白矮星(DWD)系统的距离无关的“绝对”幅度-频率域的建议天基引力波(GW)探测器,{ \it LISA}。我们假设单个白矮星的简并零温质量-半径(M-R)关系,结合罗氏几何的约束,使我们能够确定DWD系统在不同演化阶段的五个关键种群边界。本文利用\cite{DB2003}的非零熵施主M-R关系对DWD和中子星-白矮星(NSWD)双星系统的边界进行了修正。我们发现,质量转移系统占据了更大的比例的空间在“绝对”的幅频域相比,简单的T=0捐助者模型。我们还讨论了如何修改这些边界与新的进化阶段发现的\cite{Deloyeetal2007}。在初始接触阶段,我们发现,接触边界,这是结束的inspiral演化的结果,将有一定的宽度,而不是在我们早期的T=0模型中描述的突然切断。这将导致DWDs $&$ NSWDs进化轨迹之间的重叠,使得它们在该区域内仅用LISA观测无法区分。在施主绝热演化后的冷却阶段,施主半径收缩,质量传递速率下降,轨道周期演化减慢。根据供体的熵,这些系统可能位于完全退化的T=0边界内,但LISA可能无法检测到这些系统,因为它们可能低于灵敏度限值或在未分辨的DWD背景噪声内。

英文摘要:

In an earlier investigation, we proposed population boundaries for both inspiralling and mass-transferring double white dwarf (DWD) systems in the distance independent "absolute" amplitude-frequency domain of the proposed space-based gravitational-wave (GW) detector, {\it LISA}. The degenerate zero temperature mass-radius (M-R) relationship of individual white dwarf stars that we assumed, in combination with the constraints imposed by Roche geometries, permits us to identify five key population boundaries for DWD systems in various phases of evolution. Here we use the non-zero entropy donor M-R relations of \cite{DB2003} to modify these boundaries for both DWD and neutron star-white dwarf (NSWD) binary systems. We find that the mass-transferring systems occupy a larger fraction of space in ``absolute'' amplitude-frequency domain compared to the simpler T=0 donor model. We also discuss how these boundaries are modified with the new evolutionary phases found by \cite{Deloyeetal2007}. In the initial contact phase, we find that the contact boundaries, which are the result of end of inspiral evolution, would have some width, as opposed to an abrupt cut-off described in our earlier T=0 model. This will cause an overlap between a DWDs $&$ NSWDs evolutionary trajectories, making them indistinguishable with only LISA observations within this region. In the cooling phase of the donor, which follows after the adiabatic donor evolution, the radius contracts, mass-transfer rate drops and slows down the orbital period evolution. Depending upon the entropy of the donor, these systems may then lie inside the fully degenerate T=0 boundaries, but LISA may be unable to detect these systems as they might be below the sensitivity limit or within the unresolved DWD background noise.

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