Population boundaries for compact white-dwarf binaries in LISA's amplitude-frequency domain
arXiv:0809.1890 · doi:10.1088/0004-637X/697/2/2089
Abstract
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.
16 pages, 3 figures, 1 table, accepted to Astrophysical Journal; manuscript has been significantly improved from previous version as per referees comments, to include the effects of non-zero entropy WD donors on population boundaries
References in corpus (10)
- Formation and evolution of compact binaries in globular clusters: II. Binaries with neutron stars
- Six new candidate ultracompact X-ray binaries
- Optical spectroscopy of (candidate) ultra-compact X-ray binaries: constraints on the composition of the donor stars
- HST/FGS Parallaxes of AM CVn Stars and Astrophysical Consequences
- The Thermal Evolution of the Donors in AM CVn Binaries
- Measuring the spin up of the Accreting Millisecond Pulsar XTE J1751-305
- High-resolution X-ray spectroscopy of the ultracompact LMXB pulsar 4U 1626-67
- INTEGRAL spectral variability study of the atoll 4U 1820-30: first detection of hard X-ray emission
- Population Boundaries for Galactic White Dwarf Binaries in LISA's Amplitude-Frequency Domain
- The ultra-compact binary 4U1850-087 observed with INTEGRAL: hard X-ray emission from an X-ray burster