Abstract: Of the many sources which gravitational wave observatories might see, merging neutron star binaries are the most predictable. Their waveforms at the observable frequencies are easy to calculate. And three systems which will merge in less than a Hubble time have already been observed as binary pulsars: two in the disk of the Galaxy, and one in a globular cluster. From the lifetimes and positions of these, a lower limit to the merger rate in the Galaxy and globular cluster system are inferred with confidence. Taking the merger rate in other galaxies to scale with the star formation rate, the merger rate expected in the local universe is computed. An ultraconservative lower limit to the rate gives three per year within 1 Gpc. The best estimate, still conservative in that it considers only systems like those already observed, gives three per year within 200 Mpc. An upper limit of three mergers per year within 23/h Mpc is set by the rate of Type Ib supernovae. The rates of black hole binary mergers and black hole-neutron star binary mergers are model-dependent, but could be comparable to the given rate of neutron-star binary mergers.

Abstract: Crust lattices in spinning-up or spinning-down neutron stars have growing shear stresses caused by neutron superfluid vortex lines pinned to lattice nuclei. For the most rapidly spinning stars, this stress will break and move the crust before vortex unpinning occurs. In spinning-down neutron stars, crustal plates will move an equatorial subduction zone in which the plates are forced into the stellar core below the crust. The opposite plate motion occurs in spinning-up stars. Magnetic fields which pass through the crust or have sources in it move with the crust. Spun-up neutron stars in accreting low-mass X-ray binaries LMXBs should then have almost axially symmetric magnetic fields. Spun-down ones with very weak magnetic fields should have external magnetic fields which enter and leave the neutron star surface only near its equator. The lowest field millisecond radiopulsars seem to be orthogonal rotators implying that they have not previously been spun-up in LMXBs but are neutron stars initially formed with periods near 0.001 s that subsequently spin down to their present periods. Accretion-induced white dwarf collapse is then the most plausible genesis for them. 29 refs.

Abstract: After presenting a general account of the observed global properties of single stars of low, intermediate, and high mass, together with their theoretical Hertzsprung-Russell diagram evolution, attention is given to the observed properties of various evolved close binaries and to an assessment of the value of comparisons between observation and crude theory in characterizing the physics of mass transfer within interacting binary systems Detailed consideration is then undertaken of such topics as stellar evolution in globular clusters, interior star changes due to nucleosynthesis and mixing, asymptotic giant branch stars of intermediate mass, the response of white dwarfs in binary systems to mass accretion, and scenarios for binary star evolution tending toward close white dwarf pairs

Abstract: CONVENTIONAL optical techniques for detecting companions to stars have been unable to confirm the existence of other planetary systems. This is because of the small angular separation (less than an arcsecond) and relative luminosity (˜10–10 of any planet with respect to its parent star. As the velocity of the star due to the motion of a planet is likely to be only about one metre per second, detection through the Doppler shift of spectral lines in the stellar atmosphere is also impractical. Here we report observations which imply the existence of a planet-sized companion orbiting a neutron star, the pulsar PSR 1829–10, whose motion can be seen by Doppler effects on the observed arrival times of the pulses from the rotating neutron star. The planet is about 10 times the mass of the Earth, and is in an almost circular six-month orbit. It is not clear whether it formed in the aftermath of the supernova that created the neutron star, or was pre-existing and somehow survived through the late phases of stellar evolution and neutron-star formation. In either case, the existence of the planet challenges conventional theories of the formation of neutron stars from supernovae and has important implications for the existence of planetary systems around other stars.

Abstract: Over 800,000 encounters of binaries with black holes having masses that range from 10 to 10,000 times that of the binary components were simulated. The calculations at many collision velocities and impact parameters were made, which made it possible to find the velocity-dependent cross sections for exchange collisions, for binary dissociation, and for changing the orbital energy and eccentricity. The distribution of closest approaches of the stars to the black hole was also found. The probability of the black hole tidally disrupting a star in the close encounters that produce exchange collisions was determined. Exchange collisions dominate over tidal dissociation if the sum of the radii of the stars is less than the binary semimajor axis. Even encounters of black holes with soft binaries can lead to exchange collisions in which the black hole captures one binary component and ejects the other at high speed. 12 refs.

Abstract: The work of Stevens and Kallman (1990) on the effect of accretion-powered X-rays from the neutron star on the dynamics of the line-driven stellar wind of the early-type primary is extended. Radiative force multipliers that now depend on the column of attenuating material, as well as the ionization parameter, are calculated. Optical depth effects are found to suppress the effects of X-ray ionization on the force multipliers. A number of dynamical models for the winds of massive X-ray binary systems (MXRBs) are calculated with these force multipliers. Unlike the optically thin models, self-consistent dynamical solutions are found for reasonable values of the X-ray luminosity. These solutions also reveal the presence of nonlinear mechanisms that affect wind dynamics, whereby relatively small changes in the force multipliers can lead to significant changes in the wind structure. The models find the existence of a self-consistent region of solution at an X-ray luminosity of about 10 to the 36th ergs/s and suggest the possible existence of high-luminosity states.

Abstract: Using the eclipses as fiducial markers, an updated ephemeris for EXO 0748 - 676 is derived and evidence is found that between February 1985 and March 1989 the 3.82-h orbital period of EXO 0748 - 676 decreased with a time scale of -5 x 10 to the 6th yr. The sense of this change is the same as that predicted by simple models for the evolution of low-mass X-ray binaries containing main-sequence companions, but is a factor about 100 faster than expected. This rapid change in orbital period could result from the expansion of the companion due to the effects of X-ray heating. The eclipse transition durations are variable, with the shortest observed taking 1.5 s and the longest 40 s. This latter figure is about an order of magnitude too large to be due to absorption effects in the atmosphere of the secondary assuming a Roche geometry and likely stellar temperature. Either flaring activity or the presence of an X-ray heated evaporative wind or a corona may enhance the scale height of the companion's atmosphere producing the extended eclipse transitions.

Abstract: It is shown, that drag force from the shock wave generated by a rotating star with nonsymmetrical magnetosphere during stellar wind accretion determines long equilibrium periods P = 10 2 -10 4 seconds of the neutron stars X-ray pulsars in massive wide binaries

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Abstract: Time-dependent, three-dimensional particle simulations of an accretion disk interacting with an incoming stream were performed as a model for disks in close binary systems. First, the results of two-dimensional simulations are confirmed; when the mass ratio, q = M 2 /M 1 , is unity, the disk is stable for the tidal instability and thus settles into a steady-state structure. If, in the other hand, q is small, say 0.15, the tidal instability is initiated when the radius of the disk exceeds a certain critical value, leading to the formation of a processing, eccentric accretion disk

Abstract: The Keplerian velocity as well as those frequencies at which instability against gravitational radiation-reaction sets in are calculated for rotating neutron star models of gravitational mass 1.5M ⊙. The investigation is based on four different, realistic neutron star matter equations of state. Our results indicate that the gravitational radiation instability sets in wellbelow (i.e., 63–71% of) the Keplerian frequency, and thatyoung neutron stars are limited to rotational periods greater than about 1 ms. In young and therefore hot (T≈1010 K) neutron stars them=5(±1) modes and in old stars after being spun up and reheated by mass accretion, them=4 and/orm=3 modes may set the limit on stable rotation.

Abstract: This talk reviews current understanding of the states of matter in the liquid interior of neutron stars — including nuclear matter, pion and kaon condensation, and normal and strange quark matter — and their effect on neutron star structure and dynamics. Learning about high density matter in the laboratory by means of ultrarelativistic heavy-ion collisions is also discussed.

Abstract: All the major viable acceleration mechanisms suggested so far in order to explain the energy of the gamma-rays observed from Cygnus X-3 are critically reviewed. It is argued that Cyg X-3 must be an accretion-fed strong X-ray binary with negligible orbital eccentricity and cannot contain a young active pulsar. It is shown that, for reasonable assumptions, the accretion disk unipolar inductor model can be ruled out as the gamma-ray source in Cyg X-3. It is confirmed that, within the framework of standard magnetospheric theories, there is little scope for extremely efficient diffusive acceleration at the accretion shock. It is concluded that the basic beam-dumping model cannot be applicable to Cyg X-3, and that the proton luminosity requirements of the source can be met if the TeV-PeV gamma-ray flux is generated by photomeson reaction on its strong X-ray field. 55 refs.

Abstract: Hard X-ray observations of Cyg X-3, obtained with the large area proportional counter telescope flown on a balloon on 18 March 1986, are presented. The source was observed for a duration about 2 h spanning the 4.8 h binary cycle. The integral intensity of the source in the 20-100 keV range shows a strong 4.8 h modulation with a broad maximum between the binary phases 0.3 and 0.7. The observed spectrum flux during the maximum intensity is well fitted with a power law spectrum of index of 2.8 ± 0.5. Fourier analysis of the data during the maximum intensity shows a periodicity at 121 s, which is attributed to transient oscillations of the type seen at the lower energies.

Abstract: A model of pulsed VHE and UHE γ-radiation from X-ray binaries is proposed. The model implies that the γ-rays are due to the bombardment of a cloud ejected from the companion normal star by the relativistic proton beam stationarily accelerated by the pulsar. In the framework of this model, all the peculiarities of the γ-radiation observed Hercules X-1/HZ Herculis are naturally explained. Namely, a) the γ-ray pulsation frequency shift with the respect to the X-ray frequency; b) episodic nature of γ-ray events with typical burst duration Δt ≲ 1 hour; c) the absence of any correlation between the γ-ray events and the orbital phase of the binary; d) the observation of γ-ray events in the phase of the deep eclipse of the pulsar. The expected γ-ray spectra in a wide range of energy, 100 MeV < E < 1 PeV, as well as the possibilities of experimental verification of the model are discussed.

Abstract: Possible evolutionary scenarios for the formation of neutron stars in interacting binaries are summarized. (1) Firstly conditions for the occurrence of accretion-induced collapse of white dwarfs are examined in relation to the origin of low mass X-ray binaries and binary millisecond pulsars. The outcome of the evolution of accreting white dwarfs is summarized as functions of accretion rate and the initial mass of the white dwarf. (2) Secondly discussed are the neutron star formation in Type Ib/Ic supernovae (SNe Ib/Ic), which are likely to be the core collapse of helium stars in binary systems. The light curves of SNe Ib/Ic (maximum brightness and decline rate) are used to infer the progenitors’ masses and the neutron star masses. (3) Thirdly the evolutionary origin of double neutron stars are discussed in relation to SNe Ib/Ic.

Abstract: The X-ray producing, inner region of the accretion disk in Active Galactic Nuclei (AGN) is likely to be non-stationary and non-axisymmetric. This non-stationarity and non-axisymmetry in disk surface brightness may be modeled by considering the presence of many hot spots on a steady, axisymmetric disk. As long as a spot can survive for a few orbital periods, its orbital frequency can be introduced into the light curve either by relativistic orbital motion or by eclipsing of the spot by the disk. These rotational effects vary with the local properties of the spot population

Abstract: Using certain simplifying assumptions, the general structure of a quasi-spherical thermal pair-balanced cloud surrounding an accreting black hole is derived from first principles. Pair-dominated hot solutions exist only for a restricted range of the viscosity parameter. These results are applied as examples to the 1979 HEAO 3 gamma-ray data of Cygnus X-1 and the Galactic center. Values are obtained for the viscosity parameter lying in the range of about 0.1-0.01. Since the lack of synchrotron soft photons requires the magnetic field to be typically less than 1 percent of the equipartition value, a magnetic field cannot be the main contributor to the viscous stress of the inner accretion flow, at least during the high gamma-ray states.

Abstract: An estimation of the lifetime of low-mass X-ray binaries (LMXB), based on a theorical formation rate in globular clusters together with the observed current abondance, is presented. It is argued that the formation rate may be more efficient than previously estimated, by an order of magnitude or more. It is conclued that LMXBs may have a typical lifetime of 10 8 yr or less. Such a short lifetime could explain the large number of millisecond radio pulsars, both in the Galaxy as well as in globular clusters, and would not contradict the standard scenario of LMXBs producing millisecond pulsars.

Abstract: Exosat observations are presented for 3 gamma-ray-burst error boxes, one of which may be associated with an optical flash. No point sources were detected at the 3-sigma level. A comparison with Einstein data (Pizzichini et al., 1986) is made for the March 5b, 1979 source. The data are interpreted in the framework of neutron star models and derive upper limits for the neutron star surface temperatures, accretion rates, and surface densities of an accretion disk. Apart from the March 5b, 1979 source, consistency is found with each model.

Abstract: Analysis and classification of the mechanisms of particle accleration in close binary systems with compact object have been carried out. The region of UHE particles generation is shown to be situated in the accretion column of a neutron star. The mechanism of particle accleration in the accretion column by the electric field of nonlinear magneto-acoustic vortices generated in the accreting plasma with unstable distribution of ‘hollow beam’-type is proposed. It is argued that the beam of relativistic particles proves to be essentially collimated. The radius of UHE particle generation is estimated.

Abstract: Contemporary Physics, 1991, Vol. 32, no. 2, 103- 119 Neutron stars and black holes in binary systems VIRGINIA TRIMBLE Neutron stars and black holes can find themselves with close stellar companions through birth or later accident (section 1 ). The systems give rise to intense variable X-ray sources and born again pulsars ( section 2) and perhaps to still odder things (section 6). They provide the best measurements of neutron star masses and the most persuasive evidence for the existence of black holes in the real world (section 3). Most of the basic evolutionary (section 1) and radiation mechanisms (section 4) required to model the observations have been in place for a decade or more and have survived discovery of new phenomena every couple of years. Many of these involve disks of gas accreting onto the stars (section 5 ) . These disks are perhaps prototypes for those in the cores of quasars. Some problems remain with (a ) relative numbers of objects in various evolutionary phases and ( b) a few extreme individual systems such as SS 433 and 1957+20 (section 6) . I. Introduction: Formation, detectability, and fate of binaries with neutron star and black hole components the primary (Roche geometry) and so encourages both transfer of material to itself from the primary and loss of gas from the system as a whole (figure 1). This means that the dividing line to produce compact remnants referred to above rises to 10-15 M 0 ; but it also means that the eventual death of the primary in a supernova explosion does not normally unbind the system [1]. Thus a third or so of the neutron stars and black holes that form will do so in close binaries. This supply can be augmented, first, through collapse of a white dwarf in an existing binary system to a neutron star when accreted material drives it above the Chandrasekhar limit (2], and, second, through incorporation of a previously existing neutron star into a binary system by tidal capture when stars are crowded close together in a cluster (3]. The signature of the firs t process should be a young neutron star (high magnetic field) in an old system (orbit circularized and perhaps with rotation and orbit periods synchronized by tidal forces) and that of the second process should be an old neutron star (low magnetic field) in a younger system (eccentric or unsynchronized o rbit; short life expectancy). Because neutron stars can both gain and lose angular momentum over their lives, rotation period is not a good age indicator [ 4], though the ratio of period to its first derivative ('slowing down time') can be.· Binary neutron stars or black holes are detectable and recognizable as such under two circumstances. First, the neutron star can act as a pulsar, radiating away its rotational kinetic energy as magnetic dipole radiation at One percent or so of all stars start life massive enough that, evolving in splendid isolation, they would leave neutron star or black hole remnants (rather than a white dwarf). The white dwarf(WD)/ neutron star (NS) dividing line falls in the range 5-9 times the mass of our sun, and the lower limit to make a black hole is even less well known, but probably at least 50 solar masses. One solar mass (M 0 ) is 2 x 10 33 g, the astronomical community being the last refuge of unregenerate cgs-ers. The boundary lines are much higher than the 1 ·4 M 0 maximum mass that can be supported by degenerate pressure (Chandrasekhar limit). This happens because stars shed all their lives, and more toward the end (like aging poodles). At least half the dots of light in the sky are really pairs of stars, with the stars close enough together to affect each others ' evolution. The more massive star at the beginning we will call the primary component of the system forever after, no matter what happens to the masses later. The presence of the secondary distorts the shapes of the gravitational equipotential surfaces a round Author's address: Astronomy Department, University of Maryland, College Park, MD 20742, U.S.A. and Department of Physics, University of California, Irvine, CA 92717, U.S.A. Taylor and Francis Ltd

Abstract: The formation of the high-energy gamma-ray and neutrino spectrum produced by the injection of a power-law proton distribution extending up to Ep = 10 exp 16 eV in the magnetosphere of accreting neutron stars is discussed. The resulting proton spectrum is calculated in the presence of advection and cooling by interactions with the X-ray spectrum of the neutron star, leading to several components of a secondary photon spectrum extending from the MeV to the PeV range, and neutrino spectrum extending from about 0.1 TeV to 0.1 PeV. The shapes of the resulting high-energy secondary spectra depend sensitively on the accreting source's X-ray spectrum and energy density as well as the magnetic field strength involved. Detailed spectra are calculated for the specific examples of Her X-1 and Cyg X-3.

Abstract: An evaluation is made of possible reasons for the persistent inability to identify white dwarf stars in the Be binary systems. It is noted that many Be stars exhibiting large optical enhancements may be Be + WD and Be + He systems, and that observations of pulsations in the H-alpha emission, as well as observation of time delays between enhancements of optical line and continuum, can identify such systems.

Abstract: Star-formation theories can be tested in light of observational evidence of star formation scenarios on the scales of galaxies, Galactic molecular clouds, and individual star-formation regions. Attention is presently given to the relative importance of atomic and molecular gas in star formation, the role of stimulated star formation, the existence of disks around stars undergoing formation, and the effect of spiral density waves. Attention is given to the processes of cloud cores and core collapse. The development of a theory of binary star formation will require the resolution of the issue as to the presence of a disk in the formation scenario, as indicated by the observation of spectral lines at higher resolutions.

Abstract: The two component neutron star model and the response of the neutron star under the influence of external white torque noise are reviewed. A new simulation technique is developed for estimating the crust core coupling time and the moment of inertia of the superfluid in the neutron star from the irregularly sampled data. The model is applied to Vela X-1, since this source has a long period P=283 s and theoretical estimates of crust-core coupling time which are proportional to P lie in the observable region, τ=1−30 d for Vela X-1.