Abstract: THE transient X-ray sources Ariel 1118–61 and Ariel 0535 + 26 have periods of 405 s (ref. 1) and 114 s (ref. 2) respectively. Rappaport and McClintock3 reported the discovery of a 283-s period in the X-ray binary 3U0900–40 (a ‘continuous’ source) which is known to have an orbital period Porb = 8.95 d. This raises the possibility that the periodic transients may be a particular stage of evolution of the more familiar class of X-ray binary of the 3U0900–40 variety. We propose that the transient phenomenon occurs during the ‘sleeping phase’4 of the binary system when the early type star is still essentially on the main sequence, significantly underfilling its Roche lobe.

Abstract: When X-ray sources in the galaxy were discovered in 1962 (Giacconi et al., 1962) it was only possible to speculate on their nature, which centered on supernova and cosmic- ray phenomena since these were the only very energetic events known. In particular, the discovery of an X-ray source associated with the Crab Nebula led to the idea that the emission might be the thermal radiation from the surface of a hot, neutron star, However, it was soon demonstrated (Bowyer et al., 1964) that a neutron star could not be responsible for the bulk of the X-radiation from the Crab, and it was not possible to exclude highly pathological conditions in otherwise ordinary stellar systems as being responsible for the X-ray sources (c.f., Hayakawa and Matsuoka, 1964).

Abstract: The very young star cluster IC 5146 is studied using star counts, with a view to determining the distribution of interstellar matter in a region where star formation recently occurred.

Abstract: CURRENT models of X-ray sources in binary systems generally assume accretion on to a neutron star, a black hole or a white dwarf as the mechanism of X-ray production. The accretion takes place from either a stellar wind or the inner Lagrangian point1–5. Here we explore the possible existence of a compact X-ray source in a binary system, where the companion star ejects its envelope to become a planetary nebula.

Abstract: The possibility of finding a relativistic star in a binary system is considered. On the basis of data on pulsars, supernovae, the distribution of A-B stars in pairs, close binary systems, and white dwarfs, it is concluded that relativistic stars should be found extremely seldom in binary systems: not more than 1 percent of relativistic stars should be in pairs, and these should be basically neutron stars and not black holes. Irrespective of whether a star is isolated or in a pair, it loses about 70 percent of its mass during evolution. In binary systems, even close ones, almost all the mass lost by the components leaves the system. An evolution scheme for stars is proposed. It is asserted that the supernova remnants in the galaxy, which are taken as type II, are situated in a dense medium and have considerably augmented their mass at the expense of interstellar matter. The mass ejected during the explosion of a supernova seldom exceeds the mass of the sun.

Abstract: The emission mechanism from X-ray soturces in close binary stars is studied.It is suggested that pair production may play an important role in the X-ray emission region which is formed by the accretion of a compact object(a neutron star or a black hole).The present model accounts qualitatively for the following observed general properties in X-ray binaries: 1.The X-ray luminosity lies within the range 10~(36)—10~(38)erg/sec. 2.The X-ray energy spectrum can in the majority of cases be represented either the power-law or the thermal bremsstrahlung form. 3.The temperature of the thermal bremsstrahlung spectrum is the order of 10~8K. 4.The form of the energy spectrum does not change appreciably when the luminosity fluctuates.

Abstract: The most direct observational evidence for the existence of neutron stars is, of course, the discovery of radio pulsars. A black hole, however, neither radiates electromagnetic energy nor energy in the form of gravitational radiation (Zel’dovich and Novikov, 1967, 1971). Thus, detection of such an object is limited to the influence of its static gravitational field, or to the electromagnetic radiation of gas undergoing accretion or acceleration in its vicinity. Spherically symmetrical accretion by a black hole lying in interstellar matter of typical density leads to a luminosity too small to be of much interest (Zel’dovich and Novikov, 1967, 1971; Schwarzman, 1970). But a black hole member of a binary system presents a more fruitful possibility: the companion star whose electromagnetic radiation is detectable, becomes the object of the black hole’s gravitational influence and is in turn a possible rich source of accretable matter. And, of course, the same possibilities present themselves if one component of the binary is a less-exotic collapsed object — a neutron star or white dwarf. Binary systems containing a white dwarf are ubiquitous; it is a curious fact, however, that not a single radio pulsar seems to be a member of a binary system (Gott et al., 1970).

Abstract: Changes of the orbit of a star passing through a homogeneous spherical cluster have been estimated. Before entering the cluster the star is supposed to move in a Keplerian parabolic orbit. When passing through the cluster the star is subject both to the attraction of the smoothed-out distribution of matter in the cluster and to dynamical friction. Due to dynamical friction the energy of the star becomes negative which leads to the elliptic-type motion of the star after leaving the cluster and to capturing the star by the cluster. The formulae for the changes of the star orbit in the cluster are given. Numerical estimation shows that open clusters transform star orbits more noticeably than do globular clusters.

Abstract: Nova-like binary systems are similar to W UMa-systems in their basic physical characteristics. Outwardly such systems are different — nova-like systems contain a white dwarf as a component, while both components of a W UMa-system are near the Main Sequence. A hypothesis is proposed, seeking the origin of contact W UMa-type systems in a fission of rapidly-rotating helium isothermal core of an evolved giant star. The contraction of the more massive component leads to the formation of a white dwarf and, consequently, to a transformation of a W UMa-type system into a nova-like system.

Abstract: The specific angular momentum of the gas captured by a black hole in a detached binary system would be quite small. An accretion disk emitting x rays cannot form around such a black hole, but fluctuations in the stellar-wind velocity and density might produce transient disks and a high degree of x-ray variability.

Abstract: Calculations for the maximum mass of a nonrotating neutron star are given. Results are compared with other neutron star masses. 13 references. (BJG)

Abstract: RADIO pulsar PSR1913+16, which has a period of about 59 ms, has been identified as a member of a binary system1. The X-ray ‘oscillars’ HerX-1 and CenX-3, which are also members of binary systems, are not radio pulsars. (I use the word ‘oscillars’ to distinguish these objects from pulsars, which maintain their periodicity much more accurately). These facts, together with the 34-d periodicity2,3 of HerX-1 and the lack of this periodicity in CenX-3, can be explained by using the rotating neutron star hypothesis for the compact object in all of these systems. As is common in pulsar theories, I assume that rotating neutron stars are oblique rotators, that they have magnetic fields and that the magnetic axes are not along the axes of rotation.

Abstract: From optical and X-ray data available for the binary X-ray sources, the masses of the components were determined univocally in three systems. A discussion about the masses in other three systems is also presented. Besides Cyg X-1, SMC X-1 is another black-hole candidate.

Abstract: The photometric elements of the eclipsing binary WX Cep are determined from 3120 photoelectrically measured observations in each of the B and V regions which were obtained in the summer of 1973 at the Pine Mountain Observatory of the University of Oregon. The analysis shows that primary minimum is produced by the occultation of the smaller, fainter type A2 star by the larger brighter star of about type A5, and that during the 10.9-hour duration of the primary eclipse it is total for about 40 minutes. The existing spectroscopic data (of uncertain quality) for this double-line binary are used to estimate the mass and radius of each component. Both components have about one solar mass which is somewhat smaller than expected for these spectral classes even if the luminosity class of each star is V.

Abstract: This note discusses the properties of the Crab pulsar assuming that it is moving in the gravitational field of the second component.

Abstract: A study of the atmospheres of OB supergiants in x-ray binary systems indicates that when the stellar surface is close enough to the saddle in the gravitational potential to provide a mass transfer rate adequate to power a compact x-ray source, large-amplitude variations in the rate of mass flow occur. 9 references. (auth)