Elliptical motions of stars in close binary systems

The motion of stars in close binary systems with conservative mass transfer is considered. It is shown that the Paczynski-Huang model that is currently used to determine the variations of the semimajor axis of the relative orbit of the stars is not correct, and leads to large errors in the derived semi-major axis. A new model is proposed, suitable for elliptical stellar orbits. The reaction forces and gravitational forces between the stars and the stream of overflowing matter are taken into account. The possibility of mass transfer in the presence of an accretion disk is considered.     

The evolution of close binary stars

A review of our current understanding of the physics and evolution of close binary stars with various masses under the influence of the nuclear evolution of their components and their magnetic stellar winds is presented. The role of gravitational-wave radiation by close binaries on their evolution and the loss of their orbital angular momentum is also considered. The final stages in the evolution of close binary systems are described. The review also notes the main remaining tasks related to studies of the physics and evolution of various classes of close binaries, including analyses of collisions of close binaries and supermassive black holes in galactic nuclei. Such a collision could lead to the capture of one of the components by the black hole and the acceleration of the remaining component to relativistic speeds.     

Massive close binary stars and gamma-ray bursts

We analyze the observed parameters of massive extremely close binaries containing Wolf-Rayet stars and black holes, and identify those systems whose supernova outbursts lead to the formation of rapidly rotating Kerr black holes. It is proposed that the formation of such a black hole is accompanied by a strong gamma-ray burst. Several types of observed systems satisfy the conditions necessary for the formation of a Kerr black hole: BH+WR, BH+OB, WR+O, and BH+K,M.     

Photoelectric lunar-occultation observations of several close binary stars

The results of photoelectric lunar-occultation observations for several stars are presented. Some of these are obvious close binary systems, while others are suspected close binaries or multiple systems, or show evidence for the presence of complex structure of some other kind. It is expected that new, efficient interferometric systems will enable detailed studies of the structure of many “ordinary” stars with an angular resolutions of 10^?4–10^?5 arcsec.     

Formation of planets during the evolution of single and binary stars

Current views of the origin and evolution of single and binary stars suggest that the planets can form aroundmain-sequence single and binary stars, degenerate dwarfs, neutron stars, and stellarmass black holes according to several scenarios. Planets can arise during the formation of a star mainly due to excess angular momentum leading to the formation of an accretion-decretion disk of gas and dust around a single star or the components of a binary. It is the evolution of such disks that gives rise to planetary systems. A disk can arise around a star during its evolution due to the accretion of matter from dense interstellar clouds of gas and dust onto the star, the accretion of mass froma companion in a binary system, and the loss of matter during the contraction of a rapidly rotating star, in particular, if the star rotates as a rigid body and the rotation accelerates with its evolution along the main sequence. The fraction of stars with planetary systems is theoretically estimated as 30–40%, which is close to the current observational estimate of ∼34%.     

High-velocity stars as a result of encounters between stars and massive binary black holes in galactic nuclei

Numerical simulations of the motions of stars in the gravitational fields of binary black holes with various component mass ratios have been carried out. Two models are considered: (1) the two-body problem with two fixed centers; (2) the general three-body problem. The first model is applicable only over short times Δt ? T, where T is the period of the binary system. The second model is applicable at all times except for during close encounters of stars with one of the binary components, r ≤ 0.00002 pc, where r is the distance from the star to the nearer black hole. In very close passages, relativistic corrections must be taken into account. Estimates of the probability of formation of high-velocity stars as a result of such interactions are obtained. It is shown that this mechanism is not suitable for the nucleus of our Galaxy due to the probable absence of a second massive black hole in the central region of the Galaxy.     

Evolution of the masses of neutron stars in binary systems

We study the growth of the masses of neutron stars in binary systems due to the accumulation of mass from the optical donors accreted onto the neutron-star surface. Possible scenarios for this accretion are considered. The masses and magnetic-field strengths of radio pulsars derived using population-synthesis methods are compared to the observational data. The population-synthesis analysis indicates that a neutron star can increase its mass from the standard value of m _x ? 1.35M_⊙ to the Oppenheimer-Volkoff limit, m _x ? 2.5M_⊙, via accretion from a companion.     

Proper motions of stars in the region of the Great Nebula in Orion

Six Tautenburg astrograph plates have been used to derive proper motions for 12 740 stars in the region of the Great Nebula in Orion. The Oricat catalog of proper motions and B and R photometry has been compiled, incorporating as well data from other published catalogs. The proper motions presented in different catalogs are compared. The Oricat catalog is useful for studies of features of the structure and kinematics of star clusters and groups.     

Criteria and methods of quantitative assessment of petroleum prospects in poorly studied large territories

The main anticlinal folds in the Donets basin arose in zones of deep-seated faults separating large, slightly disturbed basement blocks to which the synclines are confined. These blocks, in their descending and ascending movements, alternately passed each other, thus bending the sedimentary beds first on one then on the other side of the deep-seated faults. It was this, and not tangential pressure, that led to the formation of the steep anticlinal folds. In the initial stage (C₁, C₂, and the first half of C₃), very large brachyform anticlinal structures arose above the deep-seated faults. This is indicated by the reduced thickness of the Carboniferous rocks toward the crests of these structures. Later (In the second half of C₃and P₁), linear folds arose on the sites of the brachyform structures. The present inclination of the isometamorphic surfaces (surfaces of equal degrees of metamorphism) in the synclines and anticlines reflects the magnitude of the tectonic deformations that occurred in the course of the Inversion (P₂ - T). —Authors.     

A model for the population of binary stars in the Galaxy

A comparative investigation of the population of Galactic binary stars is performed for two modes of star formation: star formation at a constant rate over 10¹⁰ yrs, and a burst of star formation that reprocesses the same mass of gas into stars over 10⁹ yrs. Estimates are presented for the star-formation rates and populations of about 100 types of binaries and the products of their evolution. For most close binary systems, the models depend only weakly on the common-envelope parameter α_ce.     

Acceleration of spatial motions of stars by close-binary supermassive black holes in galactic nuclei

The conditions for the acceleration of the spatial motions of stars by close-binary supermassive black holes (SMBHs) in galactic nuclei are analyzed in order to derive the velocity distribution for stars ejected from galaxies by such black holes. A close binary system consisting of two SMBHs in circular orbits was subject to a spherically symmetrical “barrage” of solar-mass stars with various initial velocities. The SMBHs were treated as point objects with Newtonian gravitational fields. Models with binary component-mass ratios of 1, 0.1, 0.01, and 0.001 were studied. The results demonstrate the possibility of accelerating neutron stars, stellar-mass black holes, and degenerate dwarfs to velocities comparable to the relative orbital velocities of the binary-SMBH components. In the stage when the binary components are merging due to the action of gravitational-wave radiation, this velocity can approach the speed of light. The most massive binary black-holes (M ? 10⁹M_⊙) can also accelerate main-sequence stars with solar or subsolar masses to such velocities.     

Magnetorotational supernova explosions and the formation of neutron stars in close binary systems

The formation of neutron stars in the closest binary systems (P _orb<12 h) gives the young neutron star/pulsar a high rotational velocity and energy. The presence of a magnetic field of 3×10¹¹–3×10¹³ G, as is observed for radio pulsars, enables the neutron star to transfer ～10⁵¹ erg of its rotational energy to the envelope over a time scale of less than an hour, leading to a magnetorotational supernova explosion. Estimates indicate that about 30% of all type-Ib,c supernovae may be the products of magnetorotational explosions. Young pulsars produced by such supernovae should exhibit comparatively slow rotation (P _rot>0.01 s), since a large fraction of their rotational angular momentum is lost during the explosion. The magnetorotational mechanism for the ejection of the envelope is also reflected by the shape of the envelope. It is possible that the Crab radio pulsar is an example of a product of a magnetorotational supernova. A possible scenario for the formation of the close binary radio pulsar discovered recently by Lyne et al. is considered.     

Excitation of turbulence in accretion disks of binary stars by non-linear perturbations

Accretion disks in binary systems can experience hydrodynamical influences at both their inner and outer edges. The former is typical for protoplanetary disks around young T Tauri stars, while the latter is typical for circumstellar disks in close binaries. This influence excites perturbations with various scales and amplitudes in the disk. The nonlinear evolution of perturbations with a finite, but small amplitude against the background of a sub-Keplerian flow is investigated. Nonlinear effects at the fronts of perturbation waves lead to the formation of discontinuities in the density and radial velocity; i.e., to formation of shocks. The tangential flow in the neighborhood of the shock becomes equivalent to a flow in a boundary layer. Due to an instability of the tangential flow, the disk becomes turbulent. The characteristics of the turbulence depend on the parameters of the perturbations, but the Shakura–Syunyaev α parameter does not exceed ~0.1.     

Streaming motions of molecular clouds, ionized hydrogen, and OB stars in the Cygnus arm

The radial velocity fields of molecular clouds, OB stars, and ionized hydrogen in the Cygnus arm (l ～ 72°–8°) are analyzed. A gradientΔV _LSR/Δlin the mean line-of-sight velocities of molecular clouds and ionized hydrogen due to differential Galactic rotation is detected, and two groups of physically and genetically associated objects moving with different line-of-sight velocities are identified. One of the two molecular-cloud complexes (l～77.3°–80°) is located within 1 kpc of the Sun, closer to the inner edge of the arm, whereas the other complex (l～78.5°–85°) lies 1–1.5 kpc from the Sun and is farther from the inner edge of the arm. The residual azimuthal velocities of the objects in both groups are analyzed. The residual azimuthal velocities of the first molecular-cloud complex are directed opposite to the Galactic rotation (V _Θ ～ ?7 km/s), while those of the second complex are near zero or in the direction of Galactic rotation, independent of the distance to the complex (V _Θ ≥ 1 km/s). Like the molecular clouds, stars of the Cygnus arm form two kinematic groups with similar azimuthal velocities. On the whole, the mean azimuthal velocities V _Θ for the ionized hydrogen averaged over large areas agree with the velocities of either the first or second molecular-cloud complex. In terms of density-wave theory, the observed differences between the magnitudes and directions of the azimuthal velocities of the kinematic groups considered could be due to their different locations within the arm.     

Structure of the circumbinary envelopes of young binary stars with elliptical orbits

The results of two-dimensional gas-dynamical numerical simulations of the structure of matter flows in the envelopes of a number of T Tauri binary systems with elliptical orbits are considered. The main flow elements in inner regions of protoplanetary disks of these stars are described. The influence of shocks on the size of the gap—a rarified region in the inner parts of the protoplanetary disk—is analyzed. A method is proposed for estimating the size of this gap from the numerical simulations, and the gap sizes for the studied stars are determined and compared with observational results. The flow dynamics in the gap is considered, and the periodic variations of the gap size on time scales of several orbital periods are analyzed. Possible observational manifestations of the studied flows are discussed.     

Gravitational darkening coefficients of the stars in the semidetached binary V Puppis

We have analyzed high-precision vby light curvesfor the semi-detached binary V Pup in a Roche model. They are consistent with the standard gravitational darkening coefficient for hot stars, β = 0.25, rather than the value β = 1.36 ± 0.04 derived by Kitamura and Nakamura [1] using a simpler model. We rigorously estimate the confidence intervals for the allowed gravitational darkening coefficients for a star filling its Roche lobe to be β = (?0.24, +1.29) for the 99% confidence level and β = (?0.21, +1.26) for the 67% confidence level.     

Influence of binary stars on the chemical evolution of damped Lyα systems

The impact of variations in the fraction of binary stars producing type Ia supernovae, β, on the chemical evolution of spiral galaxies is analyzed numerically. Even modest variations in β appreciably affect the evolution of the relative abundances of iron-group and alpha-process elements. If a substantial number of the damped Lα systems manifest in the spectra of quasars are due to spiral galaxies, the large scatter of the abundances of various elements displayed by these systems can be accounted for by variations in β.     

Evolution of Wolf-Rayet stars in binary systems: An analysis of the mass and orbital-eccentricity distributions

We have undertaken a statistical study of the component mass ratios and the orbital eccentricities of WR + O close binary, detached main-sequence (DMS), contact early-type (CE), and semidetached (SD) systems. A comparison of the characteristics of WR + O systems and of DMS, CE, and SD systems has enabled us to draw certain conclusions about the evolutionary paths of WR + O binaries and to demonstrate that up to 90% of all known WR + O binaries formed as a result of mass transfer in massive close O + O binary systems. Since there is a clear correlation between the component masses in SD systems with subgiants, the absence of an anticorrelation between the masses of the WR stars and O stars in WR + O binaries cannot be considered evidence against the formation of WR + O binaries via mass transfer. The spectroscopic transitional orbital period P _tr ^sp corresponding to the transition from nearly circular orbits (e _sp<0.1) to elliptical orbits (e _sp≥0.1) is ～14^d for WR + O systems and ～2^d–3^d for OB + OB systems. The period range in which all WR + O orbits are circular \((1\mathop d\limits_. 6 \leqslant P \leqslant 14^d )\) is close to the range for SD systems with subgiants, \(0\mathop d\limits_. 7 \leqslant P \leqslant 15^d \). The large difference between the P _tr ^sp values for WR + O and OB + OB systems suggests that a mechanism of orbit circularization additional to that for OB + OB systems at the DMS stage (tidal dissipation of the orbital energy due to radiative damping of the dynamical tides) acts in WR + O binaries. It is natural to suggest mass transfer in the parent O + O binaries as this supplementary orbit-circularization mechanism. Since the transitional period between circular and elliptical orbits for close binaries with convective envelopes and ages of 5×10⁹ years is \(P_{tr} = 12\mathop d\limits_. 4\), the orbits of most known SD systems with subgiants had enough time to circularize during the DMS stage, prior to the mass transfer. Thus, for most SD systems, mass transfer plays a secondary role in circularization of their orbits.In many cases, the initial orbital eccentricities of the O + O binary progenitors of WR + O systems are preserved, due to the low viscosity of the O-star envelopes and the short timescale for their nuclear evolution until the primary O star fills its Roche lobe and the mass transfer begins. The mass transfer in the parent O + O systems is short-lived, and the number of orbital cycles during the early mass-transfer stage is relatively low (lower than for the progenitors of SD systems by three or four orders of magnitude). The continued transfer of mass from the less massive to the more massive star after the component masses have become equal leads to the formation of a WR + O system, and the orbit's residual eccentricity increases to the observed value. The increase of the orbital eccentricity is also facilitated by variable radial mass loss via the wind from the WR star in the WR + O system during its motion in the elliptical orbit. The result is that WR + O binaries can have considerable orbital eccentricities, despite their intense mass transfer. For this reason, the presence of appreciable eccentricities among WR + O binaries with large orbital periods cannot be considered firm evidence against mass transfer in the parent O + O binary systems. Only for the WR + O binaries with the longest orbital periods (4 of 35 known systems, or 11 %) can the evolution of the parent O + O binaries occur without filling of the Roche lobe by the primary O star, being governed by radial outflow in the form of the stellar wind and possibly by the LBV phenomenon, as in the case of HD 5980.     

Envelope structure in T Tauri binary stars with subsonic orbital motion of one component

Results of numerical modeling of the gas dynamics ofmaterial in the envelopes of T Tauri binary stars with a small component mass ratios (q = 0.08) are reported. In such systems, the less massive component is moving at a supersonic velocity, and the more massive component can move with either a subsonic or supersonic velocity. The modeling results show that the morphology of the flow changes substantially in the transition from supersonic to subsonic motion of the massive component. In particular, one of the two bow shocks vanishes, flows ofmaterial in the system are redistributed, and the characteristics of the accretion disks change. In addition, the effect of the change in the accretion mode on the evolution of the binary system and the possibility of recovering some parameters of the system from observational manifestations of shocks in the circumstellar envelope are considered.     

Wolf-Rayet stars and relativistic objects: Distinctions between the mass distributions in close binary systems

The observed properties of Wolf-Rayet stars and relativistic objects in close binary systems are analyzed. The final masses M _CO ^f for the carbon-oxygen cores of WR stars in WR + O binaries are calculated taking into account the radial loss of matter via stellar wind, which depends on the mass of the star. The analysis includes new data on the clumpy structure of WR winds, which appreciably decreases the required mass-loss rates $\dot M_{WR}$ for the WR stars. The masses M _CO ^f lie in the range (1–2)M _⊙–(20–44)M _⊙ and have a continuous distribution. The masses of the relativistic objects M _x are 1–20M _⊙ and have a bimodal distribution: the mean masses for neutron stars and black holes are 1.35 ± 0.15M _⊙ and 8–10M _⊙, respectively, with a gap from 2–4M _⊙ in which no neutron stars or black holes are observed in close binaries. The mean final CO-core mass is $\overline M _{CO}^f = 7.4 - 10.3M_ \odot$ , close to the mean mass for the black holes. This suggests that it is not only the mass of the progenitor that determines the nature of the relativistic object, but other parameters as well-rotation, magnetic field, etc. One SB1R Wolf-Rayet binary and 11 suspected WR + C binaries that may have low-mass companions (main-sequence or subgiant M-A stars) are identified; these could be the progenitors of low-mass X-ray binaries with neutron stars and black holes.