Abstract: This paper presents two-dimensional numerical simulations of the gas flow in the orbital plane of a massive X-ray binary system, in which the mass accretion is fueled by a radiation-driven wind from an early-type companion star. These simulations are used to examine the role of the compact object (either a neutron star or a black hole) in disturbing the radiatively accelerating wind of the OB companion, with an emphasis on understanding the origin of the observed soft X-ray photoelectric absorption seen at late orbital phases in these systems. On the basis of these simulations, it is suggested that the phase-dependent photoelectric absorption seen in several of these systems can be explained by dense filaments of compressend gas formed in the nonsteady accreation bow shock and wake of the compact object.

Abstract: This paper presents calculations of the effect of changing X-ray ionization conditions on the radiative force experienced by the stellar wind material in a massive X-ray binary system. The radiative line force from the radiation field of the primary is parameterized in terms of the Castor et al. (1975) force multiplier. The results show that the line force decreases sharply, but in a nonlinear way, with increasing X-ray ionization. The dynamic consequences of this effect are discussed.

Abstract: Evidence for a 12.59 ms pulsar in Cygnus X-3 is presented on the basis of TeV gamma-ray observations. Evidence for pulsed emission at a phase in the 4.8 hr cycle and with a pulsar period and secular period derivative are compatible with earlier measurements (Chadwick et al., 1985). The conservative overall Rayleigh probability of uniformity of phase for this new result is 1.7 x 10 to the -6th. Data from observations of Cygnus X-3 from 1981 to 1985 are analyzed using a new X-ray ephemeris of the 4.8 hr X-ray cycle. This suggests that Cygnus X-3 is producing sporadic very high energy gamma rays at a fixed time in the 4.8 hr X-ray cycle. 28 refs.

Abstract: This paper gives an introduction to the theory of the formation and evolution of X-ray binaries and binary or low-magnetic-field radio pulsars. It deals with massive X-ray binaries, low-mass X-ray binaries, and X-ray binaries in globular clusters, as well as the transformation of some of these into millisecond radio pulsars. The paper is tutorial, the emphasis is on simple semi-analytical description.

Abstract: Un modele d'interaction entre le disque d'accretion et la magnetosphere d'une etoile a neutrons, assumant l'existence de boucles magnetiques ancrees dans le disque et s'etendant dans la couronne des deux cotes du disque, est developpe. Le transfert de moment cinetique entre le disque et l'etoile est analyse. Une interpretation des oscillations quasi-periodiques est realisee

Abstract: Irradiation models for soft X-ray transients (SXTs) are considered. These require the presence of hard X-rays for the outburst to be triggered. If the accreting object is a neutron star this flux is likely to arise in a boundary layer. For black-hole transients recent work by White and Lightman (1989) shows that two-temperature behavior is likely in the inner disk at accretion rates higher than a critical value M(dot)TT, thus providing the required hard X-rays. M(dot)TT is a function of the disk viscosity parameter alpha and the mass of the accreting object. The quiescent accretion rate of the black-hole candidate SXT A0620 - 00 is probably slightly lower than M(dot)TT and its disk is in a one-temperature state. The slow expansion of the secondary increases the mass transfer rate and when a two-temperature structure arises the system goes into outburst. This model requires alpha at about 0.1. Compared with neutron-star SXTs having similar binary parameters, black hole SXTs are likely to be brighter both in quiescence and in outburst. Their outbursts are likely to be shorter, but the quiescent intervals are expected to be similar to those in the neutron-star case. 18 refs.

Abstract: Neutron viscosity is investigated as a possible mechanism for the dissipation of kinetic energy into luminosity in the innermost parts of accretion disks around compact objects. Simplified models are presented of the self-consistent, steady-state accretion flows in which viscosity is provided by neutron collisions with accreting ions. Ion temperatures are determined by balancing the heating of ions by viscous dissipation to their cooling by Coulomb collisions with the electrons, providing a self-consistent solution between neutron production and their impact on energy dissipation. The results indicate that neutrons can indeed provide the necessary dissipation to sustain the steady-state accretion of matter at rates of about 10 to the -8th solar mass/yr or less, and electron temperatures of about 100 keV-1 MeV. Neutrons thus present a promising way of modeling bright Galactic X-ray sources.

Abstract: HD153919, an extreme Of star (spectral type O6.5Iaf+; ref. 1) has been identified as the optical counterpart of the 3.411-day eclipsing massive X-ray binary 4U1700 – 37 (ref. 2) by spectroscopic3–5 and photometric6 studies which revealed periodic optical variations in phase with the X-ray period. Here we report that the ultraviolet spectra taken with the International Ultraviolet Explorer satellite also vary in phase with the X-ray emission. In an interval of ∼200 A centred on the subordinate He II line at 1,640 A, emission lines 2–3 A wide appear and disappear, with maximum flux at binary phase 0.5 (when the neutron star is in front of the O supergiant) and minimum at phase 0.8. We suggest that these variable lines are due to Raman scattering of extreme ultraviolet photons from the X-ray source by He II ions. These Raman lines can thus be used to reconstruct a part of the unobserved extreme ultraviolet spectrum in the He II scattering zone.

Abstract: The spectral evolution of accretion disks in X-ray binaries containing black holes is studied, based on the disk instability model. The thermal transition of the outer portions of the disk controls the mass flow rate into the inner portions of the disk, thus modulating the soft X-ray flux which is thought to arise from the inner disk. Calculated soft X-ray spectra are consistent with the observations of the X-ray transient A0620 - 00 and especially ASM 2000 + 25, the soft X-ray spectra of which are well fitted by blackbody radiation with a fixed inner edge of the disk, Rin, and with monotonically decreasing temperature at Rin with time. Since the gas pressure is always dominant over the radiation pressure during the decay in these models, a two-temperature region is difficult to create. Instead, it is suggested that hard X-rays are generated in a hot (kT greater than 10 keV) accretion disk corona above the cool (kT less than 1 keV) disk.

Abstract: This thesis investigates the conditions for rapid mass transfer in binary stars. Previous theoretical calculations and observations of binaries imply the existence of several different time scales for mass transfer: nuclear, thermal, or dynamical. Since the mass transfer rates differ by several orders of magnitude, it is important to know which time scales are relevant to different systems. Dynamical time-scale mass transfer is thought to cause substantial decreases in the orbital period through mass and angular momentum losses. Thermal time-scale mass transfer is thought to transform the appearance ofthe binary as mass exchange occurs in a short time. Binaries currently transferring mass are doing so on the longest, nuclear time scale. The characteristics of binaries which divide the three time scales are estimated by calculating the response of potential mass donors in two idealized limits: an adiabatic response, where the entropy profile does not change with mass loss, and a thermal response, where thermal relaxation is allowed but nuclear burning is not. A comparison ofthe changing surface radius, £ = d'nR/d'n3)l to the Roche-lobe radius implies the critical mass ratios for dynamically and thermally unstable mass transfer. These calculations are performed here for donors between 0.25 and 20 TtQ which would fill their Roche lobes before helium burning. The adiabatic mass-loss calculations have provided a clear relation between £ad and the donor's convective envelope mass fraction (fce), with a smaller dependence on the state of the interior. Low-mass ZAMS donors and models near the base ofthe giant branch have £ad ^> 1 change to £ad ~

Abstract: Le flux pulse episodiquement, detecte par trois groupes, de la binaire RX a faible masse Her X-1, ne correspondant a aucune periode connue, est analyse. La periode de cette pulsation est determinee

Abstract: In 1939, seven years after the discovery of the neutron, nuclear physicists constructed the first models of a "neutron star." Stable results were found with masses comparable to the Sun's radii of about 10 km. Binary pulsars, pulsars with millisecond periods and pulsars in globular clusters are distinguished by their evolutionary histories, and are providing tools for fundamental tests of physics.

Abstract: Exploding stars were suggested by Baade and Zwicky (1934) as the source of bright optical displays (1049 ergs emitted in light energy, 1051 ergs in kinetic energy of particle motion) abruptly appearing inside galaxies and then fading away on time-scales of hundreds of days. Most astrophysicists today agree that this conjecture is correct, but most would not agree on the detailed physical scenario that leads to the destruction of a star.

Abstract: The X-ray flux emitted from a geometrically thin, relativistic accretion disk in the steady state approximation is investigated in order to place limits on the quiescent state mass flow rate in the soft X-ray transient black hole candidate source A0620-00. Specific attention is focused on the effects associated with gravitational redshifts, Doppler shifts, and on the enhancement of the apparent accretion disk area due to gravitational light bending on the continuum spectrum. It is found that the upper limit to the mass flow rate within the inner regions of the disk, constrained by the lack of soft X-rays in the quiescent state, is about 2.8 x 10 to the -11th solar mass/yr for black hole masses greater than about 5.4 solar mass. The optical data are consistent with these upper limits provided that the inclination angle of the binary system is less than about 65 deg. The upper limits and the lack of a hard X-ray flux, together, suggest that the soft X-ray transient model based upon a mass transfer instability situated in the stellar envelope of the companion is inapplicable to A0620-00.

Abstract: Les observations RX, realisees par le satellite Ginga, du pulsar RX, X 1722-36, sont presentees. Le spectre RX et les courbes de lumiere RX sont analyses. X 1722-36 apparait comme systeme binaire massif avec une periode orbitale en exces d'environ 9 jours.

Abstract: A set of forty high-dispersion IUE spectra of HD 153919, the Of-type primary in the 4U 1700-37 X-ray binary system, have been examined for evidence of orbital profile variability associated with the Hatchett-McCray effect. Although the effect is negligible in the resonance lines of C IV, Si IV, and N V, some subordinate lines show clear orbital changes. The variability in the absorption profile of N IV 1718, in particular, is shown to be in agreement with model calculations. The interstellar spectrum is studied, showing that highly ionized species can be maintained by the primary's radiation field alone.

Abstract: The effects of radiation shear stresses acting in accretion disks and boundary layers are considered. It is demonstrated that these stresses are dynamically unimportant for nonrelativistic flows. For accretion onto a black hole or nonmagnetic neutron star, where the system is relativistic, radiation shear stresses can contribute substantially to the total luminosity of the system. The spectral and temporal signatures of this form of heating are discussed, and those features which are unique to radiative dissipation are emphasized. The results are in broad agreement with the spectra of the nonmagnetic X-ray binary systems, including Cyg X-1.

Abstract: A review of the literature is given to summarize the present evidence for masses of neutron stars in radio pulsars as well as in X-ray binaries The material is arranged in the following sections: Introduction Methods of analysis Binary and millisecond pulsars Relativistic systems The nature of the secondaries X-ray pulsars: the better determined cases Black hole candidates A few indeterminate cases Conclusion

Abstract: A detailed analysis is presented of the importance of Comptonization in burst and persistent spectra of the low-mass X-ray binary 4U/MXB 1636-53, and from this analysis it is inferred that the inner accretion flow is geometrically thin. It is found that burst spectra of 1636-53 are very nearly Planckian in shape; from an upper limit to a high-energy excess in these spectra it is inferred that the Thomson scattering optical depth of a possible intervening hot cloud must be less than 1 during bursts, and that the Compton y parameter of that cloud must be less than 0.5. During persistent emission, Thomson optical depth of 4-8, an electron temperature of 2-5 keV, and a value of 0.8-1.1 for y are inferred.

Abstract: We study the evolution of solid, CO white dwarfs after explosive carbon ignition at central densities around 1010 g cm−3 triggered by steady accretion in a close binary system, in order to elucidate whether these stars can collapse to form a neutron star. We show that as long as the velocity of the burning front remains below a critical value of 0.006cs (∼60 km s−1), gravitational collapse is the final fate. These calculations support the accretion-induced collapse (AIC) scenario for the origin of a fraction of low-mass X-ray binaries.

Abstract: An initial mass function of main sequence stars in the solar neighbourhood is derived from the recent input data on luminosity function, and lifetime of main sequence stars The luminosity function is corrected for the possible multiplicity of the stellar systems which are counted as single stars in a photographic plate The mass function shows several humps indicating possibly the multimodality of star formation, and resolves the missing mass problem in a satisfactory manner

Abstract: BVRI photometry of the low-mass, X-ray binary 1556-605, obtained during five nights in June 1988, failed to identify an underlying orbital period. Nightly variations of 0.3 magnitude in V were present, but the colors of the system remained constant.

Abstract: A new model is proposed for the spectrum of a type II burst from the 'rapid burster'. The spectrum of a type II burst has been considered to be well fitted with a blackbody spectrum with temperature T about 1.5 keV. Recent observations with Tenma and Exosat, however, have found an excess from the blackbody spectrum in the high-energy range (E greater than 10 keV). The high-energy component is approximated to be a power-law spectrum of f(E) proportional to E exp -4, where E and f(E) are the X-ray energy and observed counts per unit energy, respectively. The model explains this high-energy component gives a method to evaluate the velocity and the optical depth of the accretion flow from observations of the high-energy component. It is shown that the spectrum observed with Tenma can be fitted with the model. 33 refs.

Abstract: Eclipsing Binary Stars, Neutron Stars, Stellar Spectrophototmetry, Ubv Spectra, X RAY Binaries, Accretion Disks, Light Curve, Main sequence stars, quantum effiency, Stellar Orbits

Abstract: The basic picture of an X-ray pulsar is that of a strongly magnetized neutron star which accretes matter from its companion. The reason for mass transfer can be a strong wind of the companion or a Roche-lobe overflow from the companion through the inner Lagrangian point. In the latter case the matter forms an accretion disk around the neutron star, in which it spirals inwards and heats up due to viscous interaction. If the neutron star is strongly magnetized, the disk does not reach to the surface of the neutron star, because at the Alfven radius the matter is dominated by the magnetic forces. The physics of this region, where the matter couples to the magnetic field lines, is not yet fully understood. The ionized matter which is on the field lines is accelerated by the strong gravitational field and falls along the magnetic field lines towards the magnetic poles of the neutron star, where it reaches velocities of about c/2 (c = is the velocity of light). The fully ionized matter is stopped in the atmosphere of the neutron star and its kinetic energy is converted into radiation energy. This region, where the radiation is produced, is called the “hot spot”.