Relativistic precession around rotating neutron stars: Effects due to frame-dragging and stellar oblateness

General relativity predicts that a rotating body produces a frame-dragging (or Lense-Thirring) effect: the orbital plane of a test particle in a non-equatorial orbit precesses about the body's symmetry axis. In this paper we compute the precession frequencies of circular orbits around rapidly rotating neutron stars for a variety of masses and equations of state. The precession frequencies computed are expressed as numerical functions of the orbital frequency observed at infinity. The post-Newtonian expansion of the exact precession formula is examined to identify the relative magnitudes of the precession caused by the Lense-Thirring effect, the usual Newtonian quadrupole effect and relativistic corrections. The first post-Newtonian correction to the Newtonian quadrupole precession is derived in the limit of slow rotation. We show that the post-Newtonian precession formula is a good approximation to the exact precession close to the neutron star in the slow rotation limit (up to \sim 400 Hz in the present context). The results are applied to recent RXTE observations of neutron star low-mass X-ray binaries, which display kHz quasi-periodic oscillations and, within the framework of beat frequency models, allow the measurement of both the neutron star spin frequency and the Keplerian frequency of the innermost ring of matter in the accretion disk around it. For a wide range of realistic equations of state, we find that the predicted precession frequency of this ring is close to one half of the low-frequency (\sim 20 - 35 Hz) quasi-periodic oscillations seen in several Atoll sources.Comment: 35 pages including 10 figures and 6 tables. To appear in the Astrophysical Journa

Hydrostatic Expansion and Spin Changes During Type I X-Ray Bursts

We present calculations of the spin-down of a neutron star atmosphere due to hydrostatic expansion during a Type I X-ray burst. We show that (i) Cumming and Bildsten overestimated the spin-down of rigidly-rotating atmospheres by a factor of two, and (ii) general relativity has a small (5-10%) effect on the angular momentum conservation law. We rescale our results to different neutron star masses, rotation rates and equations of state, and present some detailed rotational profiles. Comparing with recent observations of large frequency shifts in MXB 1658-298 and 4U 1916-053, we find that the spin-down expected if the atmosphere rotates rigidly is a factor of two to three less than the observed values. If differential rotation is allowed to persist, we find that the upper layers of the atmosphere spin down by an amount comparable to the observed values; however, there is no compelling reason to expect the observed spin frequency to be that of only the outermost layers. We conclude that hydrostatic expansion and angular momentum conservation alone cannot account for the largest frequency shifts observed during Type I bursts.Comment: Submitted to the Astrophysical Journal (13 pages, including 4 figures

Gravitational Radiation Instability in Hot Young Neutron Stars

We show that gravitational radiation drives an instability in hot young rapidly rotating neutron stars. This instability occurs primarily in the l=2 r-mode and will carry away most of the angular momentum of a rapidly rotating star by gravitational radiation. On the timescale needed to cool a young neutron star to about T=10^9 K (about one year) this instability can reduce the rotation rate of a rapidly rotating star to about 0.076\Omega_K, where \Omega_K is the Keplerian angular velocity where mass shedding occurs. In older colder neutron stars this instability is suppressed by viscous effects, allowing older stars to be spun up by accretion to larger angular velocities.Comment: 4 Pages, 2 Figure

The Effect of Neutron Star Binding Energy on Gravitational-Radiation-Driven Mass-Transfer Binaries

In a relativistic model of a neutron star, the star's mass is less than the mass of the individual component baryons. This is due to the fact that the star's negative binding energy makes a contribution to the star's total energy and its mass. A consequence of this relativistic mass deficit is that a neutron star that is accreting matter increases its mass at a rate which is slower than the mass of a baryon times the rate that baryons are accreted. This difference in the rate of change of the masses has a simple relation with the star's gravitational redshift. We show that this effect has the potential to be observed in binaries where the mass transfer is driven by angular momentum losses from the gravitational radiation emitted by the binary motion.Comment: 9 pages, 3 figures, accepted by Ap

Overview of BIM integration into the Construction Sector in European Member States and European Union Acquis

The amount of information involved in any construction project and the necessity of control of time, cost and waste, has established Building Information Modelling (BIM) as an integral part of construction sector towards achieving adequate communication of information among various parties involved in construction projects. Moreover, it can be considered as a valuable tool for the optimum selection of materials, systems and design decisions, regarding not only the improve of a structure’s performance, but also in terms of reducing its carbon footprint during its life cycle. The study attempts to present the integration of BIM into the national legislation of European Member States, with a special focus on the energy related aspects of BIM analysis. This study performs an overview of the introduction of BIM into different aspects and requirements of the EU Member States building practices, through a comprehensive literature and legislation review of relative legislative documents of the construction sector. According to the findings of this overview study, the concept of BIM has already been incorporated in many aspects of the Acquis of EU Member States, which is recognized as a valuable tool to be exploited by the construction sector, however there is still room for development in this area. The study has revealed that especially in the energy assessment of the built environment, BIM applications are still lacking from the European Legislation. Examples and good practices of employing BIM for the implementation of the European Energy targets in the building sector are also presented and discussed. The findings of this study aim to shed light on the needs and requirements in the field of BIM development for the construction sector, as well as to indicate gaps and weaknesses of the European Member States Acquis towards harmonizing with BIM practices

Conservation Laws and 2D Black Holes in Dilaton Gravity

A very general class of Lagrangians which couple scalar fields to gravitation and matter in two spacetime dimensions is investigated. It is shown that a vector field exists along whose flow lines the stress-energy tensor is conserved, regardless of whether or not the equations of motion are satisfied or if any Killing vectors exist. Conditions necessary for the existence of Killing vectors are derived. A new set of 2D black hole solutions is obtained for one particular member within this class of Lagrangians. One such solution bears an interesting resemblance to the 2D string-theoretic black hole, yet contains markedly different thermodynamic properties.Comment: 11 pgs. WATPHYS-TH92/0

Cosmological Models in Two Spacetime Dimensions

Various physical properties of cosmological models in (1+1) dimensions are investigated. We demonstrate how a hot big bang and a hot big crunch can arise in some models. In particular, we examine why particle horizons do not occur in matter and radiation models. We also discuss under what circumstances exponential inflation and matter/radiation decoupling can happen. Finally, without assuming any particular equation of state, we show that physical singularities can occur in both untilted and tilted universe models if certain assumptions are satisfied, similar to the (3+1)-dimensional cases.Comment: 22 pgs., 2 figs. (available on request) (revised version contains `paper.tex' macro file which was omitted in earlier version