The Evolution of Compact Binary Star Systems

We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and BHs are thought to be the primary astrophysical sources of gravitational waves (GWs) within the frequency band of ground-based detectors, while compact binaries of WDs are important sources of GWs at lower frequencies to be covered by space interferometers (LISA). Major uncertainties in the current understanding of properties of NSs and BHs most relevant to the GW studies are discussed, including the treatment of the natal kicks which compact stellar remnants acquire during the core collapse of massive stars and the common envelope phase of binary evolution. We discuss the coalescence rates of binary NSs and BHs and prospects for their detections, the formation and evolution of binary WDs and their observational manifestations. Special attention is given to AM CVn-stars -- compact binaries in which the Roche lobe is filled by another WD or a low-mass partially degenerate helium-star, as these stars are thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure

Design of a side-band-separating heterodyne mixer for band 9 of ALMA

A side-band-separating (SBS) heterodyne mixer has been designed for the Atacama Large Millimeter Array (ALMA) 602-720 GHz band, as it will present a great improvement over the current double-side-band configuration under development at the moment. Here we present design details and the results of extensive computer simulations of its performance. The designed SBS mixer exploits waveguide technology. At its core it consists of a quadrature hybrid, two LO injectors, and three dumping loads. The entire structure has been analyzed in a linear circuit simulator with custom code written to accurately (verified by HFSS finite element simulations) model the hybrid structures. This technique permitted an optimization of the dimensions and the study of the consequences of deviations from the ideal situation. It is estimated that the tolerances in several of the components should be kept at less than 3 mu m

Electromagnetic performance comparisons of 0.85 THz integrated bias-tee SIS mixers with twin-junction and end-loaded tuning schemes

We compare the design of two 0.85 THz SIS mixers fed with a radial probe antenna aligned to the E-Plane of the input full-height rectangular waveguide connected to a drilled smooth-walled horn. Both designs employ the same 0.5 µm2 hybrid Nb/AlN/NbN tunnel junction technology, sandwiched between a NbTiN ground and aluminium wiring layer fabricated on top of a 40 µm quartz substrate. The two designs is differed by how we tune out the unwanted junction capacitance for broadband performance. The first design uses the commonly-used twin-junction tuning scheme; whilst the second design utilises an end-loaded scheme. We successfully achieve close to 2× the double sideband quantum noise performance for both schemes, but the twin-junction design is less sensitive to fabrication accuracy of planar circuit components utilised. However, the end-loaded design offers a much better IF bandwidth performance, almost twice wider than the twin-junction design. The need for an ultra-wide IF bandwidth mixer is becoming more pressing and important for the future and up-coming upgrades of various millimetre (mm) and sub-mm astronomical instruments, hence we conclude that the end-loaded design is a better solution for the THz heterodyne mixing applications

Superconducting chip receivers for imaging application

Experimental details of a unique superconducting imaging array receiver are discussed. Each pixel contains an internally pumped receiver chip mounted on the back of the elliptical microwave lens. Each chip comprises a quasi-optical SIS mixer integrated with a superconducting flux-flow oscillator (FFO) both fabricated from the same Nb/AlOx/Nb trilayer on a silicon substrate. Properties of the integrated lens antenna were studied using an externally pumped reference SIS mixer which showed antenna sidelobes below -17 dB and a receiver double side band noise temperature, T-RX(DSB), below 100 K within the frequency range 460 - 500 GHz that is close to the quantum noise. For the imaging array T-RX(DSB) = 150 K has been measured at 500 GHz using the internal flux-flow oscillator as a local oscillator (LO). A balanced SIS mixer was tested showing T-RX(DSB) <100 K within the range of 480 - 510 GHz using the internal LO. A computer system was developed to control simultaneously the de bias of the SIS mixer and the frequency and power provided by FFO. The system also performs automatic optimization of the receiver noise temperature

Design and fabrication of Cherenkov flux-flow oscillator

The Josephson Flux-Flow Oscillator (FFO) has been used as an on chip local oscillator at frequencies up to 650 GHz. The FFO linewidth of about 1 MHz was measured in the resonant regime at V <915 mu V for niobium - aluminum oxide - niobium tunnel junctions, while considerably larger values were reported at higher voltages. To overcome this fundamental linewidth broadening we propose a novel on chip Cherenkov radiation flux-flow oscillator (CRFFO). It consists of a long Josephson junction and a superconducting slow wave transmission line that modifies essentially the junction dispersion relation. Two SIS detectors are connected both to the long Josephson junction and the transmission line to evaluate available microwave power. The output power coming both from the long junction and the transmission line is estimated at different bias conditions

An integrated 500 GHz receiver with superconducting local oscillator

An integrated quasioptical receiver consisting of a planar double - dipole antenna, SIS mixer and superconducting Flux-Flow Oscillator (FFO) with matching circuits has been designed, fabricated and tested in the frequency range 420-530 GHz. The integrated receiver is very suitable for space applications because of its low size, mass and power consumption. All components of the receiver are integrated on a 4 mmx4 mmx0.2 mm crystalline quartz substrate using a single Nb-AlOx-Nb trilayer. The successful operation of the integrated receiver comprising a number of new crucial elements has been demonstrated. A DSB noise temperature as low as 140 K at 500 GHz and a tuning range of more than 100 GHz have been obtained. A comparison of the FFO with conventional external LO has been performed