Formation and evolution of inclined accretion disks in intermediate polars

The results of 3D modeling of the formation of the accretion disks of intermediate polars are presented. A model with misaligned rotation axes of accretor and the orbit is onsidered, in which it is assumed that the white dwarf has a dipolar magnetic field with its symmetry axis inclined to the whitedwarf rotation and orbital axes. The computations show that, in the early stages of formation of the disk, the action of magnetic field is able to create the initial (seed) inclination of the disk. This inclination is then supported mainly by the dynamical pressure of the flow from the inner Lagrangian point L₁. As themass of the disk increases, the inclination disappears. Under certain conditions, the disk inclination does not arise in systems with misaligned white-dwarf rotation and orbital axes. The influence of the magnetic field and asynchronous rotation of the accretor may result in the formation of spiral waves in the disk with amplitudes sufficient to be detected observationally.     

Morphology of the interaction between the stream and cool accretion disk in a semidetached binary system

We analyze heating and cooling processes in accretion disks in binaries. For realistic parameters of the accretion disks in close binaries (\(\dot M \simeq 10^{ - 12} - 10^7 M_ \odot /yr\) and α?10^?1–10^?2), the gas temperature in the outer parts of the disk is from ～10⁴ to ～10⁶ K. Our previous gas-dynamical studies of mass transfer in close binaries indicate that, for hot disks (with temperatures for the outer parts of the disk of several hundred thousand K), the interaction between the stream from the inner Lagrange point and the disk is shockless. To study the morphology of the interaction between the stream and a cool accretion disk, we carried out three-dimensional modeling of the flow structure in a binary for the case when the gas temperature in the outer parts of the forming disk does not exceed 13 600 K. The flow pattern indicates that the interaction is again shockless. The computations provide evidence that, as is the case for hot disks, the zone of enhanced energy release (the “hot line”) is located beyond the disk and originates due to the interaction between the circumdisk halo and the stream.     

The mechanism of circumbinary envelope formation in close binaries

We consider the structure and formation of the circumbinary envelopes in semi-detached binary systems. Three-dimensional numerical simulations of the gas dynamics are used to study the flow pattern in a binary system after it has reached the steady-state accretion regime. The outer parts of the circumbinary envelope are replenished by periodic ejections from the accretion disk and circum-disk halo through the vicinity of the Lagrange point L₃. In this mechanism, the shape and position of a substantial part of the disk is specified by a precessional density wave. On timescales comparable to the orbital period, the precessional wave (and hence an appreciable fraction of the disk) will be virtually stationary in the observer’s frame, whereas the positions of other elements of the flow will vary due to the orbital rotation. The periodic variations of the positions of the disk and the bow shock formed when the inner parts of the circumbinary envelope flow around the disk result in variations in both the rate of angular-momentum transfer to the disk and the flow structure near L₃. All these factors lead to a periodic increase of the matter flow into the outer layers of the circumbinary envelope through the vicinity of L₃. The total duration of the ejection is approximately half the orbital period.     

Hydrodynamical modeling of mass transfer in the close binary system <Emphasis Type="Italic">β</Emphasis> Lyr

We present results of two-dimensional hydrodynamical simulations of mass transfer in the close binary system β Lyr for various radii of the accreting star and coefficients describing the interaction of the gaseous flow and the main component (primary). We take the stellar wind of the donor star into account and consider various assumptions about the radiative cooling of the gaseous flow. Our calculations show that the initial radius of the flow corresponding to our adopted mass-transfer rate through the inner Lagrange point (L₁) of (1–4) × 10^?5M_⊙/yr is large: 0.22–0.29 (in units of the orbital separation). In all the models, the secondary loses mass through both the inner and outer (L₁ and L₂) Lagrange points, which makes the mass transfer in the system nonconservative. Calculations for various values of the primary radius show a strong dependence on the coefficient fv that models the flow-primary interaction. When the radius of the primary is 0.5, there is a strong interaction between the gas flow from L1 and the flow reflected from the primary surface. For other values of the primary radius (0.1 and 0.2), the flow does not interact directly with the primary. The flow passes close to the primary and forms an accretion disk whose size is comparable to that of the Roche lobe and a dense circum-binary envelope surrounding both the disk and the binary components. The density in the disk varies from 10¹² to 10¹⁴ cm^?3, and is 10¹⁰–10¹² cm^?3 in the circum-binary envelope. The temperature in the accretion disk ranges from 30000 to 120000 K, while that in the circum-binary envelope is 4000–18000 K. When radiative cooling is taken into account explicitly, the calculations reveal the presence of a spiral shock in the accretion disk. The stellar wind blowing from the secondary strongly interacts with the accretion disk, circum-binary envelope, and flow from L₂. When radiative cooling is taken into account explicitly, this wind disrupts the accretion disk.     

Full 3D MHD calculations of accretion flow structure in magnetic cataclysmic variables with strong,complex magnetic fields

We have performed three-dimensional magnetohydrodynamical calculations of stream accretion in cataclysmic variable stars for which the white dwarf primary possesses a strong, complex magnetic field. These calculations were motivated by observations of polars: cataclysmic variables containing white dwarfs with magnetic fields sufficiently strong to prevent the formation of an accretion disk. In this case, an accretion stream flows from the L1 point and impacts directly onto one or more spots on the surface of the white dwarf. Observations indicate that the white dwarfs in some binaries possess complex (non-dipolar) magnetic fields. We performed simulations of ten polars, with the only variable being the azimuthal angle of the secondary with respect to the white dwarf. These calculations are also applicable to asynchronous polars, where the spin period of the white dwarf differs by a few percent from the orbital period. Our results are equivalent to calculating the structure of one asynchronous polar at ten different spin-orbit beat phases. Our models have an aligned dipolar plus quadrupolar magnetic field centered on the whitedwarf primary. We find that, with a sufficiently strong quadrupolar component, an accretion spot arises near the magnetic equator for slightly less than half our simulations, while a polar accretion zone is active for most of the remaining simulations. For two configurations, accretion at a dominant polar region and in an equatorial zone occurs simultaneously. Most polar studies assume that the magnetic field is dipolar, especially for single-pole accretors. We demonstrate that, with the orbital parameters and magnetic-field strengths typical of polars, the accretion flow patterns can vary widely in the case of a complex magnetic field. This may make it difficult formany polars to determine observationally whether the field is pure dipolar or is more complex, but there shoulid be indications for some systems. In particular, a complex magnetic field should be suspected if there is an accretion zone near the white dwarf’s equator (assumed to be in the orbital plane) or if there are two or more accretion regions that cannot be fitted by dipolar magnetic field. Magnetic-field constraints are expected to be substantially stronger for asynchronous polars, with clearer signs of complex field geometry due to changes in the accretion flow structure as a function of azimuthal angle. These indications become clearer in asynchronous polars because each azimuthal angle corresponds to a different spin-orbit beat phase.     

The structure of the common envelope in a close binary system

As a result of the interaction between an elliptical accretion disk and gas flowing into it from the circumbinary envelope in a close binary in the course of its orbital motion, the matter of the disk and the circum-disk halo is periodically ejected from the vicinity of the Lagrange point L₃, and a common envelope is formed in the system. Three-dimensional numerical gas-dynamical modeling is used to study the structure and dynamics of the envelope and determine its basic parameters. The evolution of the envelope is followed on timescales of the order of several orbital periods. The matter flow ejected through the vicinity of L₃ displays a spiral shape. The maximum size of the forming spiral structure is restricted by the self-intersection point, and is of the order of four to five times the component separation. We consider the dynamics of the regions directly adjacent to the spiral structure: an inner, rarified and outer, fragmented region, which further makes a transition to an expanding diffuse ring.     

Three-dimensional hydrodynamical modeling of mass transfer in the close binary system β Lyr with an accretor wind

We present three-dimensional hydrodynamical modeling of mass transfer in the close binary system β Lyr taking into account explicitly radiative cooling and the stellar wind of the accretor. Our computations show that flow forces wind out from the orbital plane, where an accretion disk with a radius of 0.4–0.5 and a height of about 0.15–0.17 (in units of orbital separation) is formed. Gas motions directed upward from the orbital plane are initiated in the region of interaction of the flow from L₁ and the accretor wind (x = 0.91, y = ?0.17); i.e., a jetlike structure forms. This structure has the shape of a gas pillar above the orbital plane, where gas moves with the velocity of stellar wind. The number density of the gas in this structure is about 10¹⁴ cm^?3, and its temperature is 20 000–45 000 K. At heights of about 0.15–0.20 above the orbital plane, in the region between the jetlike structure and the disk, two spiral shocks form. It is possible that the emission lines observed in the spectrum of β Lyr binary originate in this region.     

Interpretation of light curves of the cataclysmic variable OY Car in a model with shockless interaction between a gaseous stream and the disk

To determine the parameters of the accretion disk and shock-wave region responsible for the formation of the orbital peak in the light curve of the binary system OY Car (an SU UMa-type variable), we have analyzed its U BV R and JK light curves using two gas-dynamical models with different regions of shock interaction: one with a hot line along the stream from the Lagrange point L1 and one with a hot spot on the accretion disk. The hot-line model can better describe the quiescent state of the system: the maximum X² for the optical light curves does not exceed 207, whereas the minimum residual for the hot-spot model is X²>290. The shape of the eclipse is almost identical in both models; the main differences are in interpreting out-of-eclipse portions of the light curves, whose shape can varyin the transition from one orbital cycle to another. The hot-spot model is not able to describe variations of the system’s brightness at orbital phases ?～0.1–0.6. The rather complex behavior of the observed flux in this phase interval can be explained in the hot-line model as being due to variations of the temperature and size of the system. Based on the analysis of a sequence of 20 B curves of OY Car, we conclude that the flux variations in the primary minimum are due to variations of the luminosity of the accretion disk, whereas the flux variability in the vicinity of the orbital peak is due to the combined effect of the radiation of the disk and hot line. The JK light curves of OY Car in the quiescent state and during a small flare also indicate preference for the hot-line model, since the primaryminimum and the flux near quadratures calculated using the hot-spot model are not consistent with the observations.     

Light-curve syntheses for close binary systems: Modeling spiral waves in an elliptical disk around a white dwarf

We present an algorithm for synthesizing the light curve of a close binary consisting of a normal star (a red dwarf that fills its Roche lobe) and a spherical star (a white dwarf). The spherical component is surrounded by an elliptical accretion disk with a complex shape: it is geometrically thin near the spherical star and geometrically thick at the edge of the disk. An additional complication is presented by the presence of a one-or two-armed spiral pattern at the inner surface of the disk. The maximum height of the spiral arm above the disk surface is located at ～9 R _d , and the height decreases exponentially as the arm approaches the inner regions of the disk. Shielding of the inner hot parts of the disk by the crests of the spirals results in the formation of “steps” in out-of-eclipse parts of the orbital light curves. The algorithm takes into account the presence of a “hot line” by the lateral surface of the disk, making it possible to model binary systems in both quiescence and outburst. In the latter case, the hot line degenerates into a small bulge at the outer lateral surface of the disk, which can be considered an analog of a hot spot. The algorithm was applied to the orbital light curve of the cataclysmic binary IP Peg during its October 30, 2000, outburst. To explain the variations of the out-of-eclipse brightness of the system during the outburst, it is necessary to include the presence of a one-armed spiral wave at the inner surface of the disk, close to the periastron of the elliptical disk. We have obtained the parameters of IP Peg during the outburst for various models of the system.     

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.     

A photometric study of the eclipsing dwarf nova GY Cnc in quiescence and during an outburst

The results of photometric observations of the dwarf nova GY Cnc in the Rc filter acquired in 2013–2015 (~3900 orbital cycles, 19 nights in total) are presented, including observations during its outburst in April 2014. The binary’s orbital elements have been refined. The orbital period has changed only insignificantly during the ~30 000P_orb since the earlier observations; no systematic O–C variations were detected, only fluctuations within 0.004^d on time scales of 1500–2000P_orb. A “combined” model is used to solve for the parameters of GY Cnc during two states of the system. The flux from the white dwarf is negligible due to the star’s small size. The temperature of the donor star, T₂ ~ 3667 K (Sp M0.2 V), varies between 3440 and 3900 K (Sp K8.8–M1.7 V). The semi-major axis of the disk is a ~ 0.22a₀, on average. In quiescence, a varies within ~40%. The disk has a considerable eccentricity (e ~ 0.2?0.3) for a < 0.2a₀. The disk shape becomes more circular (e < 0.1) with increasing a. The outburst of GY Cnc was associated with increased luminosity of the disk due to the parameter α_g (related to the viscosity of the disk material) decreasing to 0.1–0.2 and the temperature in the inner parts of the disk increasing twofold, to T_in ~ 95 000 K. These changes were apparently due to the infall of matter onto the surface of the white dwarf as the outburst developed. All parameters of the accretion disk in quiescence display considerable variations about their mean values.     

富钙长石-橄榄石包体与其他部分典型包体W-L边的成因

球粒陨石中的富Ca、Al包体(简称CAI)形成于星云演化的最初始阶段,保存了大量星云形成和演化的各种信息。研究认为,包体的成因主要包括星云直接凝聚和熔融结晶,少部分甚至经历过高温蒸发过程。部分CAI最外层具有由一种或几种矿物组成的Warking-Lovering边(简称为W-L边),CAI和其W-L边对于认识早期星云环境和界定CAI的形成时间等均具有重要意义。目前,对于W-L边的形成过程研究并不深入,且一直存在争议。本文主要介绍了三个典型包体:C#1(富钙长石-橄榄石包体)、GRV 022459-2RI5(A型包体)和GRV 021579-3RI5(富尖晶石球粒状包体)及其W-L边的矿物岩石学和氧同位素组成特征。C#1包体明显经历过熔融结晶过程,W-L边氧同位素组成具有与包体内部矿物相似的富~(16)O同位素特征,表明W-L边的成因与包体的形成过程密切相关,形成于同一富~(16)O同位素组成区域,且W-L边属于包体熔融结晶过程后期的产物。矿物岩石学特征表明,GRV 022459-2RI5属于星云直接凝聚形成,其W-L边为包体形成过程最晚期星云凝聚产物。GRV021579-3RI5经历过熔融结晶过程,其W-L边为包体结晶最后阶段的产物。     

BVRI surface photometry of the galaxy NGC 3726

We present BVRI surface photometry of the late-type spiral galaxy NGC 3627. The distributions of the color indices and extinction-independent Q indices show that the observed photometric asymmetry in the inner part of the galaxy, including the bar, is due to an asymmetric distribution of absorbing material. The bluest regions of star formation are located in a ring surrounding the bar. The background-subtracted color indices of individual blue knots are used to estimate the ages of young stellar aggregates. In combination with previously published photometric data, our measurements indicate that the R-band profile of the disk is rather flat in its inner part (r<50″) and becomes steeper further from its center. We estimate the mass of the disk and dark halo by decomposing the rotation curve. The mass-to-light ratio M/L _B for the stellar disk is ≈1.4. The galaxy possesses a massive dark halo; however, the mass of the disk exceeds that of the halo in the inner part of the galaxy, which displays a regular spiral structure.     

Three-dimensional hydrodynamical modeling of the formation of the accretion disk in the SS 433 binary system

Three-dimensional hydrodynamical modeling of the formation of the accretion disk in the SS 433 binary system is carried out with various types of cooling and numerical grids. These computations show that a thick accretion disk with a height of 0.25–0.30 (in units of the component separation) is formed around the compact object, from a flow with a large radius (0.2–0.3 in the same units) that forms in the vicinity of the inner Lagrangian point. This disk has the form of a flattened torus. The number of orbits of a particle of gas in the disk is 100–150, testifying to a minimal influence of numerical viscosity in these computations. The computations also show that the stream flowing from L₁ is nearly conservative, and spirals in the disk are not formed due to the influence of the donor gravitation.     

The magnetic-field structure in a stationary accretion disk

The magnetic-field structure in regions of stationary, planar accretion disks around active galactic nuclei where general-relativistic effects can be neglected (from 10 to 200 gravitational radii) is considered. It is assumed that the magnetic field in the outer edges of the disk, which forms in the magnetosphere of the central black hole during the creation of the relativisitic jets, corresponds to the field of a magnetic dipole perpendicular to the plane of the disk. In this case, the azimuthal field component B_φ in the disk arises due to the presence of the radial field B_ρ and the azimuthal velocity component U_φ. The value of the magnetic field at the inner radius of the disk is taken to correspond to the solution of the induction equation in a diffusion approximation. Numerical solutions of the induction equation are given for a number of cases.     

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.     

Spectroscopy and doppler mapping of the binary SS Cyg during outburst

We carried out spectroscopy of the binary SSCyg in the Hα, Hβ, and Hγ lines in its active state in August and December 2006. We have estimated the parameters of the main flow elements contributing to the spectra. Profile variations during the orbital period are analyzed, and a Doppler tomogram computed for the Hα line. We consider the evolution of the line profiles with the development of the outburst. A phenomenological model explaining the observed outburst features is suggested. In this model, the main elements of the flow determining the shape of the spectral lines are the accretion disk, a toroidal shell formed in the inner parts of the disk, an expanding spherical shell around the accreting star, a region in front of the bow shock that forms due to the orbital motion of the disk in the circumbinary envelope, and the surface of the donor star near the inner Lagrange point, L1, which is heated by radiation from the accretor.     

The Fragmentation in a Protoplanetary Disk and the Properties of the Resultant Self-Gravitating Clumps

We study the fragmentation properties in the protoplanetary disk and properties of the resultant self-gravitating clumps using our newly constructed disk model. Our disk model includes the mass inflall term from a molecular cloud core and the photoevaporation winds effect. We adopt the conventional fragmentation criterion to judge whether a protoplanetary disk can fragment. In this work, we follow our previous work to investigate the properties of the resultant self-gravitating clumps. In our calculation, the initial masses of the resultant self-gravitating clumps lie in the range of tens of M_J to more than one hundred of M_J, where M_J is the Jupiter mass. These initial masses can seemingly account for the masses of extrasolar planets in magnitude. We also calculate the subsequent gas accretion of clumps in 1.27 × 10⁴ yr after the formation of self-gravitating clumps. We find that the subsequent gas accretion of self-gravitating clumps is very efficient, and the clump masses grow to hundreds of M_J and the physical radii R_c of clumps increase to about 10 AU. Additionally, we also calculate the orbital migration of clumps. We find that most clumps have short migration timescale to be accreted onto the protostar, and only a small fraction of clumps have long migration timescale (>10⁶ yr) to successfully become gas giant planets. These results are consistent with previous studies.     

The matter-flow structure in the SS Cyg system in its quiescent state from comparisons of observational and synthetic Doppler tomograms

Doppler tomograms are constructed for the quiescent state of the SS Cyg system based on Hβ and Hγ spectral-line observations carried out in August 2006 with the 2-m telescope at Terskol Peak. Gasdynamical simulations combined with the Doppler tomograms enable identification of the main features of the flow. Comparisons of synthetic tomograms with observations indicate that an accretion disk is present in the quiescent system. In the tomograms, the luminosity is maximum at the arms of the spiral tidal shock at the shock front due to the interaction between the gas of the circum-binary envelope and material in the stream issuing from the Lagrangian point L₁ (the “hot line”), and in the region behind the bow shock due to the motion of the accretor and disk in the gas of the envelope. The contribution of this last element results in appreciable asymmetry of the tomograms.     

Types of gaseous envelopes of “hot Jupiter” exoplanets

As a rule, the orbital velocities of “hot Jupiters,” i.e., exoplanets with masses comparable to the mass of Jupiter and orbital semi-major axes less than 0.1 AU, are supersonic relative to the stellar wind, resulting in the formation of a bow shock. Gas-dynamical modeling shows that the gaseous envelopes around hot Jupiters can belong to two classes, depending on the position of the collision point. if the collision point is inside the Roche lobe of the planet, the envelopes have the almost spherical shapes of classical atmospheres, slightly distorted by the influence of the star and interactions with the stellar-wind gas; if the collision point is located outside the Roche lobe, outflows from the vicinity of the Lagrangian points L₁ and L₂ arise, and the envelope becomes substantially asymmetrical. The latter class of objects can also be divided into two types. If the dynamical pressure of the stellar-wind gas is high enough to stop the most powerful outflow from the vicinity of the inner Lagrangian point L₁, a closed quasi-spherical envelope with a complex shape forms in the system. If the wind is unable to stop the outflow from L₁, an open aspherical envelope forms. The possible existence of atmospheres of these three types is confirmed by 3D numerical modeling. Using the typical hot Jupiter HD 209458b as an example, it is shown that all three types of atmospheres could exist within the range of estimated parameters of this planet. Since different types of envelopes have different observational manifestations, determining the type of envelope in HD 209458b could apply additional constrains on the parameters of this exoplanet.