A comprehensive population synthesis study of post-common envelope binaries

We apply population synthesis techniques to calculate the present day population of post-common envelope binaries (PCEBs) for a range of theoretical models describing the common envelope (CE) phase. Adopting the canonical energy budget approach we consider models where the ejection efficiency, \alpha_{\rmn{CE}} is either a constant, or a function of the secondary mass. We obtain the envelope binding energy from detailed stellar models of the progenitor primary, with and without the thermal and ionization energy, but we also test a commonly used analytical scaling. We also employ the alternative angular momentum budget approach, known as the $\gamma$-algorithm. We find that a constant, global value of \alpha_{\rmn{CE}} \ga 0.1 can adequately account for the observed population of PCEBs with late spectral-type secondaries. However, this prescription fails to reproduce IK Pegasi, which has a secondary with spectral type A8. We can account for IK Pegasi if we include thermal and ionization energy of the giant's envelope, or if we use the $\gamma$-algorithm. However, the $\gamma$-algorithm predicts local space densities that are 1 to 2 orders of magnitude greater than estimates from observations. In contrast, the canonical energy budget prescription with an initial mass ratio distribution that favours unequal initial mass ratios gives a local space density which is in good agreement with observations, and best reproduces the observed distribution of PCEBs. Finally, all models fail to reproduce the sharp decline for orbital periods, P_{\rmn{orb}} \ga 1 d in the orbital period distribution of observed PCEBs, even if we take into account selection effects against systems with long orbital periods and early spectral-type secondaries.Comment: Accepted for publication in the Monthly Notices of the Royal Astronomical Society. 18 pages, 10 figures. Work concerning the reconstruction of the common envelope phase presented in the previous version will now be submitted in a separate paper in the near futur

On the detection of pre-low-mass X-ray binaries

We explore the population of candidate pre-low-mass X-ray binaries in which a neutron star accretes mass from the wind of a low-mass companion (mass < 2Msun) in the framework of a binary population synthesis study. The simulated accretion-luminosity distribution shows a primary peak close to 1e31 erg/s and a secondary peak near 1e28 erg/s. The relative contribution of the two peaks depends primarily on the magnitude of the kick velocity imparted to the neutron star at birth. The secondary peak is negligible for average kick velocities larger than 200 km/s, but becomes dominant for average kick velocities smaller than 50 km/s. Regardless of the relative contributions of the two peaks, our calculations suggest that pre-low-mass X-ray binaries may provide a non-negligible contribution to the population of discrete low-luminosity X-ray sources in the Galaxy.Comment: Accepted for publication in MNRA

Angular momentum losses and the orbital period distribution of cataclysmic variables below the period gap: effects of circumbinary disks

The population synthesis of cataclysmic variables below the period is investigated. A grid of detailed binary evolutionary sequences has been calculated and included in the simulations to take account of additional angular momentum losses beyond that associated with gravitational radiation and mass loss, due to nova outbursts, from the system. As a specific example, we consider the effect of a circumbinary disk to gain insight into the ingredients necessary to reproduce the observed orbital period distribution. The resulting distributions show that the period minimum lies at about 80 minutes with the number of systems monotonically increasing with increasing orbital period to a maximum near 90 minutes. There is no evidence for an accumulation of systems at the period minimum which is a common feature of simulations in which only gravitational radiation losses are considered. The period distribution is found to be fairly flat for orbital periods ranging from about 85 to 120 minutes. The steepness of the lower edge of the period gap can be reproduced, for example, by an input of systems at periods near 2.25 hrs due to a flow of cataclysmic variable binary systems from orbital periods longer than 2.75 hrs. The good agreement with the cumulated distribution function of observed systems within the framework of our model indicates that the angular momentum loss by a circumbinary disk or a mechanism which mimics its features coupled with a weighting factor to account for selection effects in the discovery of such systems and a flow of systems from above the period gap to below the period gap are important ingredients for understanding the overall period distribution of cataclysmic variable binary systems.Comment: Accepted for publication in Ap

Eclipsing binaries in extrasolar planet transit surveys: the case of SuperWASP

Using a comprehensive binary population synthesis scheme, we investigate the statistical properties of a sample of eclipsing binaries that is detectable by an idealised extrasolar planet transit survey with specifications broadly similar to those of the SuperWASP (Wide Angle Search for Planets) project. In this idealised survey the total number of detectable single stars in the Galactic disc is of the order of 10^6-10^7, while, for a flat initial mass ratio distribution, the total number of detectable eclipsing binaries is of the order of 10^4-10^5. The majority of the population of detectable single stars is made up of main-sequence stars (60%), horizontal-branch stars (20%), and giant-branch stars (10%). The largest contributions to the population of detectable eclipsing binaries stem from detached double main-sequence star binaries (60%), detached giant-branch main-sequence star binaries (20%), and detached horizontal-branch main-sequence star binaries (10%). The ratio of the number of eclipsing binaries to the number of single stars detectable by the idealised SuperWASP survey varies by less than a factor of 2.5 across the sky, and decreases with increasing Galactic latitude. It is found to be largest in the direction of the Galactic longitude l=-7.5deg and the Galactic latitude b=-22.5deg. We also show that the fractions of systems in different subgroups of eclipsing binaries are sensitive to the adopted initial mass ratio distribution, which is one of the poorest constrained input parameters in present-day binary population synthesis calculations. This suggests that once statistically meaningful results from transit surveys are available, they will be able to significantly improve the predictive power of population synthesis studies of interacting binaries and related objects. (abridged)Comment: Accepted for publication in MNRA

Catheter Based Simultaneous Mapping of Cardiac Activation and Motion: A Review

Heart failure as a result of a variety of cardiac diseases is an ever growing, challenging condition that demands profound insight in the electrical and mechanical state of the myocardium. Assessment of cardiac function has largely relied on evaluation of cardiac motion by multiple imaging techniques. In recent years electrical properties have gained attention as heart failure could be improved by biventricular resynchronization therapy. In contrast to early belief, QRS widening as a result of left bundle branch block could not be identified as a surrogate for asynchronous contraction

Using a quantum dot as a high-frequency shot noise detector

We present the experimental realization of a Quantum Dot (QD) operating as a high-frequency noise detector. Current fluctuations produced in a nearby Quantum Point Contact (QPC) ionize the QD and induce transport through excited states. The resulting transient current through the QD represents our detector signal. We investigate its dependence on the QPC transmission and voltage bias. We observe and explain a quantum threshold feature and a saturation in the detector signal. This experimental and theoretical study is relevant in understanding the backaction of a QPC used as a charge detector.Comment: 4 pages, 4 figures, accepted for publication in Physical Review Letter

A comprehensive molecular phylogeny of Dalytyphloplanida (Platyhelminthes: Rhabdocoela) reveals multiple escapes from the marine environment and origins of symbiotic relationships

In this study we elaborate the phylogeny of Dalytyphloplanida based on complete 18S rDNA (156 sequences) and partial 28S rDNA (125 sequences), using a Maximum Likelihood and a Bayesian Inference approach, in order to investigate the origin of a limnic or limnoterrestrial and of a symbiotic lifestyle in this large group of rhabditophoran flatworms. The results of our phylogenetic analyses and ancestral state reconstructions indicate that dalytyphloplanids have their origin in the marine environment and that there was one highly successful invasion of the freshwater environment, leading to a large radiation of limnic and limnoterrestrial dalytyphloplanids. This monophyletic freshwater clade, Limnotyphloplanida, comprises the taxa Dalyelliidae, Temnocephalida, and most Typhloplanidae. Temnocephalida can be considered ectosymbiotic Dalyelliidae as they are embedded within this group. Secondary returns to brackish water and marine environments occurred relatively frequently in several dalyeliid and typhloplanid taxa. Our phylogenies also show that, apart from the Limnotyphloplanida, there have been only few independent invasions of the limnic environment, and apparently these were not followed by spectacular speciation events. The distinct phylogenetic positions of the symbiotic taxa also suggest multiple origins of commensal and parasitic life strategies within Dalytyphloplanida. The previously established higher-level dalytyphloplanid clades are confirmed in our topologies, but many of the traditional families are not monophyletic. Alternative hypothesis testing constraining the monophyly of these families in the topologies and using the approximately unbiased test, also statistically rejects their monophyly