Abstract: THE binary system Cygnus X-1 is thought to contain a black hole that accretes matter from an O-type supergiant companion. Gravitational energy of the matter in the accretion disk is transformed to thermal energy, resulting in the emission of X-rays. These are emitted in successive bursts ('shots')1. Here we demonstrate the existence of a time delay between X-rays in different energy ranges; this is manifest as a double-peaked structure in the phase lag between two X-ray energy ranges for Fourier periods between 0.2 and 20 s. Taken together with our analysis of the power density spectrum, this indicates that shots tend to occur with two preferred durations and that the X-ray energy spectrum becomes harder as the shot progresses. This is consistent with an accretion model in which clumps of matter in the disk have two preferred sizes, and are heated by the release of gravitational energy as they drift from the outer to the inner region of the disk before disappearing into the black hole.

Abstract: The vertical dynamics of a gas stream as it flows over a disk in a semidetached binary are studied. For plausible parameters, the gas stream at several scale heights above the binary orbit plane is able to flow over the disk once it passes the disk edge. Relatively high, free-flowing gas collides with the disk near the stream's closest approach with the compact object. The resulting emission is identified with a feature found in the Doppler tomography of dwarf nova Z Cha. These results can also explain the origin of asymmetric emission lines in other dwarf novae and dips in low-mass X-ray sources. 23 refs.

Abstract: Many X-ray stars that exhibit periodic and quasi-periodic oscillations in intensity are thought to be magnetic neutron stars accreting matter from a close binary companion. These lectures provide an introduction to some of the concepts needed to understand this process. The capture of material from the wind or from the atmosphere or envelope of a binary companion star is described and the resulting types of accretion flows discusssed. The reasons for the formation of a magnetosphere around the neutron star are explained. The qualitative features of the magnetospheres of accreting neutron stars are then described and compared with the qualitative features of the geomagnetosphere. The conditions for stable flow and for angular and linear momentum conservation are explained in the context of neutron star accretion and applied to obtain rough estimates of the scale of the magnetosphere. Accretion from disk flows is then considered in some detail, including the structure of geometrically-thin Keplerian flows, the interaction of the disk with the magnetosphere, and models of steady disk flows. Accretion torques and the resulting changes in the pulse frequencies of accretion-powered pulsars are considered and the predicted behavior compared with observation. Finally, the beat-frequency magnetospheric model of quasi-periodic intensity oscillations (QPOs) is described and compared with observation.

Abstract: The results of an X-ray timing and spectral study of the Be star X-ray binary system X Per are reported, based on two series of Exosat observations. The timing measurements indicate that the neutron star in the X Per system was in a net spin-down mode during the 1984-1986 period and that this trend may have been in progress since 1978. The phase-averaged X-ray spectrum is consistent with a power law of photon spectral index 1.2 with a high-energy cutoff which becomes pronounced above 5 keV. The spectral form remains fairly constant with pulse phase, except for a brief episode of spectral hardening near pulse minimum. The results are discussed in terms of current models for wide-orbit binaries containing a Be star primary and an accreting neutron star. 33 refs.

Abstract: A non-negligible (~ 15–20%) fraction of planetary nebulae is expected to be formed in close binaries in which one component fills its Roche lobe after the exhaustion of hydrogen or helium at its center. The nebula is ejected as a consequence of a frictional interaction between the stellar cores and a common envelope; the ionizing component of the central binary star may be a relatively high luminosity contracting star with a degenerate CO core, burning hydrogen or helium in a shell, or it may be a lower luminosity shell hydrogen-burning star with a degenerate helium core or a core helium-burning star. Even more exotic ionizing central stars are possible. Once the initial primary has become a white dwarf or neutron star, the secondary, after exhausting central hydrogen, will also fill its Roche lobe and eject a nebular shell in a common envelope event. The secondary becomes the ionizing star in a tight orbit with its compact companion. In all, there are roughly twenty different possibilities for the make-up of binary central stars, with the ionizing component being a post asymptotic giant branch star with a hydrogen- or heliumburning shell, a CO dwarf, a core helium-burning star, a shell helium-burning star with a degenerate CO core, a shell hydrogenburning star with a degenerate helium core, or a helium degenerate dwarf, while its companion is a main sequence star, a CO degenerate dwarf, a helium star, a helium degenerate dwarf, or a neutron star. We estimate the occurrence frequency of several of these types and comment on the prior evolutionary history of 4 observed binary central stars.

Abstract: We discuss the common envelope phase in the evolution of binary systems. The problem of the efficiency of energy deposition into envelope ejection is treated in some detail. We describe the implications of common envelope evolution for the shaping of planetary nebulae with close binary nuclei and for double white dwarf systems, considered to be the progenitors of Type I supernovae.

Abstract: The first photometric observations capable of resolving the 4.8-hr period at near-infrared wavelengths of the extraordinary X-ray source Cygnus X-3 have been obtained using a CCD at the Perkins 1.8-m telescope. The data show that the 4.8-hr light curve at I band exhibits a variety of forms ranging from being relatively quiescent within the photometric errors to showing fluctuations exceeding 1 mag on time scales of tens of minutes to several hours. There is a suggestion that the variations may be correlated with phase of the 4.8-hr infrared and X-ray period, but the pulsed fraction of the I band fluctuations is about 90 percent compared to 10-25 percent for the infrared and X-ray variations. If confirmed, these vairations may represent important new information concerning the origin of the 4.8-hr cycle and of the nature of the binary system. The mean I-magnitude of Cygnus X-3 is found to be 20.0 + or - 0.2. 23 refs.

Abstract: The analysis of the simultaneous X-ray and gamma-ray observations of Cygnus X-3 by the ESA satellite COS B indicates that there exists a negative correlation between intensities of 2-12 keV X-rays and 150-5000 MeV gamma rays of Cygnus X-3. A clear image of a gamma-ray source at the position of Cygnus X-3 is obtained from the spatial distribution of gamma-ray photons incident when Cygnus X-3 was in a low X-ray state between June 1977 and June 1980, and the correspondent gamma-ray flux of Cygnus X-3 is derived as F(E greater than 100 MeV) = (1.3 + or - 0.6) x 10 to the -6th per sq cm s. 23 refs.

Abstract: The recent discovery of a binary sub-millisecond pulsar in SN1987A strongly suggests that the rotation was important in the core collapse of the progenitor of SN1987A. The observed period of the pulsar 0.5079680 ms is close to the maximum rotation of the neutron star. The periodic modulation of the pulse period with 8 hours suggests the existence of the companion with an almost circular orbit. The mass of the companion is either ~ 1.4 Me (face-on) or ~ 10Me (edge-on) with the semi-major axis of ~2 x lOll cm. In either case, if the companion has existed before the supernova explosion, it is hard to understand why the companion has a circular orbit. The formation of the companion after the bounce of the core is proposed. If the angular momentum of the pre-supernova core is greater than ~ 6 x 10 cgs, the core fragments and a binary proto neutron star is formed. As the separation of two neutron stars decreases in several seconds, the larger mass neutron star begins to accrete the matter of the smaller mass neutron star. The sub-millisecond period of the pulsar is· the consequence of the accretion of matter with the angular momentum ~ 10 cgs. Due to the fidal disruption at the end of the accretion, the system consists of a central neutron star and a rotating thin disk. Similar to the formation of planets in the solar nebula, a Jupiter-like secondary of mass ~ 10Me with a circular orbit ·may be formed within a year at separation of ~ lOll cm. A possible detection of the gravitational radiation from the sub-millisecond pulsar and a possible origin of gamma ray bursters are also demonstrated.

Abstract: The structural response of a low-mass (0.75 solar mass) main-sequence star to mass accretion is examined, assuming that matter is added onto the star with the same entropy as at the photosphere. Calculations show that the accreting star passes through a brief phase of underluminosity and subradius after the onset of accretion. This phase is followed by a sudden increase in luminosity rates and radius. These phases are characterized by a surface convective zone which first absorbs most of the heat liberated during accretion and then retreats and dies away. During the underluminosity and subradius phase, the star grows in mass without expanding very much and returns to the main-sequence state. If accretion is terminated while surface convection persists, the star flares, convection recedes and the star cools down. 14 refs.

Abstract: Evidence has been found for the observation of ultra-high-energy gamma rays from the X-ray binary system 2A 1822-37.1. This source exhibits emission over a broad range of binary phase which appears to change over a period of years. These characteristics are similar to those observed from the UHE source Cygnus X-3. 18 refs.

Abstract: 3Me companion object, it seems hard to account for such an object in the scenario of the supernova explosion. We estim;tte the magnetic field, ellipticity and the mass of the neutron star and also the period of glitches.

Abstract: The Crosa and Boynton (1980) empirical model for discrete mass transfer in Her X-1 is further developed. The photometric features of the light curve (peaks of an hour duration and 0.3–0.7m amplitude, steps near orbital phase ϕ=0); and the linear polarization bursts are assumed to be due to the formation and eclipses of the plasma blobs produced by discrete transfer of matter from optical star surface and its interaction with the accretion disc rim. The long lifetime (∼20h) of the cold (3×104 K) blob extending up to ≈1011 cm above the disc plane, as well as the deep X-ray flickerings (τ∼300 s) during the X-ray absorption dips are assumed to arise from a dispersal of accreting matter by the Rayleigh-Taylor instability in a blob moving through a hot corona of the disk atTc=3×106 K andnc=3×1011 cm−3. Thermal equilibrium in the corona and in the blobs are supported by X-ray flux. Within the first few hours after its formation a blob disintegrates into drops withr=5×109 cm,T=3×104 K, andn=3×1013 cm−3 which move then along Keplerian orbits. Frictional interactions of the drops with the corona destroy them on a 20h time-scale. The proposed model makes it possible to interpret the diverse observational facts and to predict numerous observational displays in the optical, UV, and X-ray bands. The first results of our optical-spectrum observations of blobs are briefly described.

Abstract: The origin and growth of molecular clouds is described and mechanisms for molecular cloud support are reviewed Cloud disruption is discussed with emphasis on star formation efficiency Issues pertaining to massive star enhanced star formation are summarized, and a mechanism for bimodal star formation is presented Applications are made to the global star formation rate and to starburst galaxies

Abstract: It is argued that the measured mass of the binary millisecond pulsar PSR 0021-72A provides a strong evidence that a rapidly spinning neutron star may drastically curtail the X-ray lifetime of a binary system.

Abstract: Massive X ray binaries consist of an early type primary lossing mass via a strong stellar wind driven by the stars radiation field, and an accreting neutron star companion. The X rays from the neutron star affect the wind dynamics by changing the temperature and ionization structure. The effect of the accretion powered X rays on the radiative line force that drives the stellar wind is calculated. The consequences of these calculations for the wind dynamics in massive X ray binaries is discussed.

Abstract: Photographic observations of the large proper motion binary, Stein 2051, extended over the period 1966–87, do not support that it is a triple system as previously reported (Strand, 1977). The orbital motion is nearly linear over this interval; however, when results of plates from the Vatican Astrographic Zone from 1908–11 are included, a mass ratio is obtained,leading to a mass of 0.50 0 for the white dwarf component, given the calculated mass of 0.24 for the red dwarf component.

Abstract: Un modele du progeniteur de SN 1987 A, considerant une etoile de la sequence principale massive et un compagnon a faible masse, est presente. Ce modele explique les pulsations optiques observees dans SN 1987 A

Abstract: This paper considers the possibility of identifying a black hole on the basis of the detection of some unique effect occurring during the transit of a black hole across the stellar disk of a companion star in a binary system. The results of Monte-Carlo calculations show that the amplitude of the photometric and polarimetric light curves in a typical X-ray binary is too small to be observed with present instrumentation, but that a black hole transit might be detectable in a binary having a large separation of the components. No binary system suggested as containing a stellar-mass-sized black hole is a like candidate to exhibit an observable transit signature, with the possible exception of X Persei/4U0352+30 described by White et al. (1976).

Abstract: The basic ingredients of a model for galactic star formation are reviewed and incorporated into a simple scheme for galactic evolution. A unified model in which the star formation rate is proportional to the ratio of gas surface density to local dynamical time-scale describes star formation in starburst galaxies, protogalactic disks, and protogalactic spheroids. The possible role of active galactic nuclei in triggering early star formation provides an alternative evolutionary scheme.

Abstract: CYGNUS X-3, one of the brightest X-ray sources in the Galaxy and perhaps also a source of very-high-energy (TeV) photons or particles, is thought to be a close binary system (orbital separation ∼1011 cm and period 4.8 h) whose emission is powered by accretion of mass from a main-sequence star like the Sun onto a neutron star, or possibly a black hole. The X-ray luminosity, Lx∼ 1038 erg s-1, implies a radiation rate near the Eddington limit. Recent radio observations of CygX-3 (ref. 1) have revealed extended radio lobes on a scale of ∼0.3 pc, elongated in the same direction in which clouds of relativistic plasma, discovered by very-long-baseline interferometry observations2–4 during radio outbursts, are ejected from the binary system. I argue here that the extended radio lobes can be understood as bubbles blown into a dense interstellar medium by the cumulative energy of the bursts from the central object. If this is correct, the extended lobes of Cyg X-3 would have to be ∼2,000 years old.

Abstract: Recent work on a unified model of accretion flows and X-ray emission in low mass X-ray binaries is summarized. In this model, a weakly magnetic neutron star accretes gas simultaneously from a Keplerian disk and a corona above the inner part of the disk. Photons are produced and escape through an approximately radial inflow of gas captured from the inner disk corona. Changes in the optical depths of the central corona and the radial flow may explain the Z-shaped hardness-intensity and color-color tracks observed in the most luminous sources. Numerical simulations show that the radial flow oscillates when the luminosity rises to within a few percent of the Eddington critical luminosity L sub E, and that the oscillation frequency is approximately 5 to 10 Hz if the radial flow develops approximately 300 km from the neutron star. The 10 to 20 Hz oscillations observed in Sco X-1 when it is on the flaring branch are discussed.