Two-dimensional hydrodynamical modeling of mass transfer in semidetached binaries with asynchronously rotating components

We have modeled the mass transfer in the three semidetached binaries U Cep, RZ Sct, and V373 Cas taking into account radiative cooling both implicitly and explicitly. The systems have asynchronously rotating components and high mass-transfer rates of the order of 10^?6M_⊙/yr; they are undergoing various stages of their evolution. An accreting star rotates asynchronously if added angular momentum is redistributed over the entire star over a time that exceeds the synchronization time. Calculations have indicated that, in the model considered, mass transfer through the point L₁ is unable to desynchronize the donor star. The formation of an accretion disk and outer envelope depends on the component-mass ratio of the binary. If this ratio is of the order of unity, the flow makes a direct impact with the atmosphere of the accreting star, resulting in the formation of a small accretion disk and a relatively dense outer envelope. This is true of the disks in U Cep and V373 Cas. When the component-mass ratio substantially exceeds unity (the case in RZ Sct), the flow forms a large, dense accretion disk and less dense outer envelope. Taking into account radiative cooling both implicitly and explicitly, we show that a series of shocks forms in the envelopes of these systems.     

Superhumps in binary systems and their connection to precessional spiral density waves

We consider a mechanism for the formation of superhumps in the TV Col system, based on the possible existence of a precessional spiral wave in the accretion disk of the system. This mechanism can act in binaries with arbitrary component-mass ratios, and our precessional spiral wave model can be applied to explain observed superhumps of all types.     

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.     

Observational Manifestations of the Precessional Wave in the Accretion Disk of a Cataclysmic Variable Star

Effects due to the interaction of the steam from the inner Lagrangian point with the accretion disk in a cataclysmic variable star are considered. The results of three-dimensional gas-dynamical numerical simulations confirm that the disk thickness in the vicinity of the interaction with the stream is minimum when the component-mass ratio is 0.6. As a consequence, some of the matter from the stream does not collide with the outer edge of the accretion disk, and continues its motion unperturbed toward the accretor. This part of the stream subsequent interacts (collides) with a thickening of the accretion disk due to the presence of a precessional wave in the disk, leading to the appearance of an additional zone of heating at the disk surface. This additional zone of enhanced luminosity (hot spot) is a direct observational manifestation of the precessional wave in the accretion disk.     

Formation of a radiative wind and accretion disk in microquasars. Generation of flare activity in the disk due to an increase in the supply of material to the Lagrange point L<Subscript>1</Subscript>. The system LMC X-3

Three-dimensional numerical hydrodynamical modeling of a radiative wind and accretion disk in a close binary system with a compact object is carried out, using the massive X-ray binary LMC X-3 as an example. This system contains a precessing disk, and may have relativistic jets. These computations show that an accretion disk with a radius of about 0.20 (in units of the component separation) forms from the radiative wind from the donor when the action of the wind on the central source is taken into account, when the accretion rate is equal to the observed value (about 3.0 × 10^?8 M _⊙/year, which corresponds to the case when the donor overflows its Roche lobe by nearly 1%). It is assumed that the speed of the donor wind at infinity is about 2200 km/s. The disk that forms is geometrically thick and nearly cylindrical in shape, with a low-density tunnel at its center extending from the accretor through the disk along the rotational axis. We have also modeled a flare in the disk due to short-term variations in the supply of material through the Lagrange point L₁, whose brightnesses and durations are able to explain flares in cataclysmic variables and X-ray binaries. The accretion disk is not formed when the donor underfills its Roche lobe by 0.5%, which corresponds to an accretion rate onto the compact object of 2.0 × 10^?9 M _⊙/year. In place of a disk, an accretion envelope with a radius of about 0.03 forms, within which gas moves along very steep spiral trajectories before falling onto the compact object. As in the accretion-disk case, a tunnel forms along the rotational axis of the accretion envelope; a shock forms behind the accretor, where flares occur in a compact region a small distance from the accretor at a rate of about six flares per orbital period, with amplitudes of about 10 ^m or more. The flare durations are two to four minutes, and the energies of individual particles at the flare maximum are about 100–150 keV. These flares appear to be analogous to the flares observed in gamma-ray and X-ray burst sources. We accordingly propose a model in which these phenomena are associated with massive, close X-ray binary systems with component-mass ratios exceeding unity, in which the donor does not fill its Roche lobe. Although no accretion disk forms around the compact object, an accretion region develops near the accretor, where the gamma-ray and X-ray flares occur.     

The formation of millisecond radio pulsars in close binary systems

An analysis of the basic parameters of a sample of radio and X-ray pulsars that are members of close binary systems is used to separate them into several families according to the nature of the pulsar companions and the previous evolution of the systems. To quantitatively describe the main parameters of close binaries containing neutron stars, we have performed numerical modeling of their evolution. The main driving forces of the evolution of these systems are the nuclear evolution of the donor, the magnetically coupled and radiation-induced stellar winds of the donor, and gravitational-wave radiation. We have considered donors that are low-mass stars in various stages of their evolution, nondegenerate helium stars, and degenerate stars. The systems studied are either the products of the normal evolution of close binaries with large initial component-mass ratios or result from inelastic collisions of old neutron stars with single and binary low-mass, main-sequence stars in the dense cores of globular clusters. The formation of single millisecond pulsars requires either the dynamical disruption of a low-mass (?0.1M_⊙) donor or its complete evaporation under the action of the X-ray radiation of the millisecond pulsar. The observed properties of binary radio pulsars with eccentric orbits combined with the bimodal spatial-velocity distribution of single radio pulsars suggest that it may be possible to explain the observed rotational and spatial motions of all radio pulsars as a result of their formation in close binaries. In this case, neutron stars formed from massive single stars or the components of massive wide binaries probably cannot acquire the high spatial velocities or rapid rotation rates that are required for the birth of a radio pulsar.     

Comparison of Dimensionless Parameters in Astrophysical MHD Systems and in Laboratory Experiments

Estimates of typical parameters of accretion flows in the representative intermediate polar EX Hydrae, the polar AM Herculis, and the “hot Jupiter” WASP-12b are presented. Dimensionless parameters of astrophysical systems are compared with those of laboratory experiments on laser ablation in magnetic fields. It is shown that laboratory simulations of astrophysical flows is possible in principle, provided that some adjustment to the magnetic field, plasma density, and plasma velocity are made.     

Impact of the magnetic field on the structure of accretion disks in semi-detached binaries

We discuss characteristic features of the magnetic gas-dynamical structure of the flows in a semi-detached binary system obtained from three-dimensional simulations, assuming that the intrinsic magnetic field of the accreting star is dipolar. The turbulent diffusion of the magnetic field is taken into account. The SS Cyg system is considered as an example. Including the magnetic field can alter the basic parameters of the accretion disk, such as the accretion rate and the characteristic density. The magnetic field in the disk is primarily toroidal.     

Formation of accretion disks in close-binary systems with magnetic fields

We have developed a three-dimensional numerical model and applied it to simulate plasma flows in semi-detached binary systems whose accretor possesses a strong intrinsic magnetic field. The model is based on the assumption that the plasma dynamics are determined by the slow mean flow, which forms a backdrop for the rapid propagation of MHD waves. The equations describing the slow motion of matter were obtained by averaging over rapidly propagating pulsations. The numerical model includes the diffusion of magnetic field by current dissipation in turbulent vortices, magnetic buoyancy, and wave MHD turbulence. A modified three-dimensional, parallel, numerical code was used to simulate the flow structure in close binary systems with various accretor magnetic fields, from 10⁵ to 10⁸ G. The conditions for the formation of the accretion disk and the criteria distinguishing the two types of flow corresponding to intermediate polars and polars are discussed.     

The effect of viscosity on the flow morphology in semidetached binary systems. Results of 3D simulations. II

We present the results of three-dimensional simulations of matter flows in semidetached binary systems with various viscosities. In low-viscosity systems, the flow structure displays the same qualitative features as in high-viscosity computations. A self-consistent solution shows the absence of a shock interaction between the stream flowing from the inner Lagrange point and the forming accretion disk (or hot spot) for any viscosity.     

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.     

Features of the Flow Structure in the Vicinity of the Inner Lagrangian Point in Polars

The structures of plasma flows in close binary systems whose accretors have strong intrinsic magnetic fields are studied. A close binary system with the parameters of a typical polar is considered. The results of three-dimensional numerical simulations of the matter flow from the donor into the accretor Roche lobe are presented. Special attention is given to the flow structure in the vicinity of the inner Lagrangian point, where the accretion flow is formed. The interaction of the accretion-flow material from the donor’s envelope with the magnetic field of the accretor results in the formation of a hierarchical structure of the magnetosphere, because less dense areas of the accretion flow are stopped by the magnetic field of the white dwarf earlier than more dense regions. Taking into account this kind of magnetosphere structure can affect analysis results and interpretation of the observations.     

Ring structures in Orion KL

We present the results of studies of the superfine structure of H₂O maser sources in the Orion Nebula. Powerful, low-velocity, compact maser sources are distributed in eight active zones. Highly organized structures in the form of chains of compact components were revealed in two of these, in the molecular cloud OMC-1. The component sizes are ～0.1 AU and their brightness temperatures are T _b =10¹²?10¹⁶ K. The structures correspond to tangential sections of concentric rings viewed edge-on. The ring emission is concentrated in the azimuthal plane, decreasing the probability of their discovery. The formation of protostars is accompanied by the development of accretion disks and bipolar flows, with associated H₂O maser emission. The accretion disks are in the stage of fragmentation into protoplanetary rings. In a Keplerian approximation, the protostars have low masses, possibly evidence for instability of the systems. Supermaser emission of the rings is probably triggered by precession of the accretion disk. The molecular cloud’s radial velocity is V _LSR=7.74 km/s and its optical depth is τ≈5. The emission from components with velocities within the maser window is additionally amplified. The components’ emission is linearly polarized via anisotropic pumping.     

Analysis of reflection effects in HS 2333+3927

The results of photometric and spectroscopic observations of the pre-cataclysmic variable HS 2333+3927, which is a HW Vir binary system, are analyzed. The parameters of the sdB subdwarf companion (T _eff = 37 500 ± 500 K, log g = 5.7 ± 0.05) and the chemical composition of its atmosphere are refined using a spectrum of the binary system obtained at minimum brightness. Reflection effects can fully explain the observed brightness variations of HS 2333+3927, changes in the HI and HeI line profiles, and distortions of the radial-velocity curve of the primary star. A new method for determining the component-mass ratios in HW Vir binaries, based on their radial-velocity curves and models of irradiated atmospheres, is proposed. The set of parameters obtained for the binary components corresponds to models of horizontal-branch sdB subdwarfs and main-sequence stars.     

Interaction of the stream from <Emphasis Type="Italic">L</Emphasis><Subscript>1</Subscript> with the outer edge of the accretion disk in a cataclysmic variable

Vertical oscillations of the gas at the outer edge of the accretion disk in a semi-detached binary due to interaction with the stream of matter from the inner Lagrangian point L ₁ are considered. Mixing of the matter from the stream from L ₁ with matter of the disk halo results in the formation of a system of two diverging shocks and a contact discontinuity, or so-called “hot line”. The passage of matter through the region of the hot line leads to an increase in its vertical velocity and a thickening of the disk at phases 0.7?0.8. Subsequently, the matter moving along the outer edge of the disk also experiences vertical oscillations, forming secondary maxima at phases 0.2?0.4. It is shown that, for systems with component mass ratios of 0.6, these oscillations will be amplified with each passage of the matter through the hotline zone, while the observations will be quenched in systems with component mass ratios ~0.07 and ~7. The most favorable conditions for the flow of matter from the stream through the edge of the disk arise for component mass ratios ~0.62. A theoretical relation between the phases of disk thickenings and the component mass ratio of the system is derived.     

Controls on salt marsh accretion: A test in salt marshes of Eastern Canada

We used¹³⁷Cs-dating to determine vertical accretion rates of 15 salt marshes on the Bay of Fundy, the Gulf of St. Lawrence, and the Atlantic coast of Nova Scotia. Accretion rates are compared to a number of factors assumed to influence vertical marsh accretion: rates of relative sea-level rise, climatic parameters (average daily temperatures and degree days) and latitude (related to insolation and day length), sediment characteristics (organic matter inventory, bulk, mineral, and organic matter density), distance of the core site from the nearest source of tidal waters, and the tidal range. Uniques to our study is a consideration of climatic parameters and latitude, which should influence organic matter production, and thus vertical accretion rates. Significant predictors of accretion rates (in order of importance) were found to be organic matter inventory, distance from a creek, and range of mean tides. Contrary to conclusions from previous studies, we found that accretion rates decreased with increasing tidal range, probably because we considered a wider span of tidal ranges, from micro- to macrotidal. Although four marshes with low organic matter inventories also show a deficit in accretion with respect to relative sea-level rise, organic matter is not limiting in two-thirds of the marshes studied, despite shorter growing seasons.     

Use of geothermal methods in outlining deep groundwater flow systems in Paleozoic interior basins of Brazil

Results of regional-scale geothermal studies are presented, providing new insights into the characteristics of deep groundwater flow systems in the Paleozoic sedimentary basins in the Amazon, Paraná and Parnaíba regions of Brazil. The study makes use mainly of bottom-hole temperature data sets for oil wells, the depths of which vary from 1,000 to 4,000 m. The techniques employed in data analysis have allowed identification of non-linear features in vertical distributions of temperature, produced by deep groundwater flows in the study area. According to the results obtained, vertical velocities of subsurface flows are found to fall in the range 10^?10 to 10^?9 m/s, while the horizontal velocities are significantly higher, of the order 10^?8 m/s. Identification of large-scale down flows has allowed inferences as to the existence of lateral movements of groundwater. The basins in the Amazon region are found to be characterized by widespread down flow of groundwater, implying the existence of distributed recharge systems operating on regional scales. There is a systematic decrease in horizontal velocities along the direction from west to east. This feature is considered indicative of gravity driven flows induced by episodes of uplift, since Miocene times, in the Andean region.     

Elliptical motion of a star in a close binary system

The motion of a rotating star in a close binary system with conservative mass exchange is considered. In contrast to the Paczyński-Huang model, the new model applied examines the relative motion of a star along an elliptical orbit in a close binary system, taking into account the mutual gravitation between the stars, reactive forces, the gravitation exered on the stars by the mass-transfer stream, and perturbations due to the rotation of the accreting star. The variations of the semi-major axis and eccentricity of the orbit and the orbital angular velocity of the accreting star as a function of the component-mass ratio q are determined. The results are applied to the BF Aurigae system.     

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.     

碎屑岩沉积从源到汇的“物-坡”耦合效应*

碎屑岩沉积体系的三维展布特征及其成因机制是建立沉积模式与预测其砂体分布的关键,更是沉积学研究的关键性科学问题。国内外绝大多数学者认为其平面形态和剖面充填型式均与其沉积的地形坡度、粒度粗细有密切的联系,但其定量关系并不清楚。建立不同类型沉积体中粒度和坡度之间的定量关系,对于预测沉积体中不同颗粒的运动方式及其分布至关重要。应用“源-汇”系统研究的思路,分析了供源区、搬运(输送)区及汇积区各自的地质特点,从单向水流对不同质量颗粒在静止/运动中的受力分析与沉积前总体地形斜坡设定2个角度,系统分析、推导并模拟了不同碎屑颗粒在纵向剖面上的运动轨迹,其表现为随着设定的坡型呈抛物线变化,反映出沉积物输送营力的变换及其随坡度变化的响应特征。建立了陆相碎屑岩沉积体系纵向剖面的流速与坡度的计算方程,明确指出沉积物的流速或流态决定其沉积方式,阐述了汇积区碎屑颗粒的加积型式与沉积物分布上的总体规律,由此提出碎屑岩沉积体系的“物-坡”耦合效应及其主要内涵,并从多个维度与源-汇的各区段,阐述了“物-坡”耦合效应在各种沉积体系的沉积物类型及其空间形态特征上的地质响应。