A model for disk accretion by a rotating magnetic neutron star is proposed which includes a detailed
NASA Technical Reports Server (NTRS)
Jan 29, 2010 ... KY Relativistic Accretion Disk models. A set of models from Dovciak et al. (2004 ) for accretion disk spectra in the strong gravity regime. ...
NASA Website
A possible accretion model associated with the ionization instability of quasar disks is proposed to
A disk model with gas pressure viscosity. The spectrum from an accretion disk ... viscosity scales as the gas pressure. From Stella and Rosner 1984, ApJ, ...
High Energy Astrophysics: Accretion Disks II 1/59 Accretion Disks II 1 The dynamical equations Astrophysics: Accretion Disks II 2/59 The simplest accretion disc model to construct is that of the thin disc on the azimuthal angle z ...
E-print Network
Equations for the structure and appearance of supercritical accretion disks and the radiation-driven
A scenario for the central engine of AGN has been developed, consisting of a massive black hole (MBH) onto which gas accretes through an accretion disk. The accretion disk radiates the observed optical and ultraviolet continua. Surrounding the MBH is a no...
National Technical Information Service (NTIS)
The astrophysical importance of the new class of theoretical models for accretion disks concentrating mainly on the applications to active galactic nuclei are discussed. The slim accretion disks model describes several important astrophysical processes wh...
The standard model for accretion disks (e.g., Pringle, 1981; Lin and Papaloizou, 1985) parameterizes
The main physical phenomena which occur on accretion disks, are discussed. A numerical simulation of a three dimensional accretion disk model around a white dwarf in a binary system composed of two equal mass stars is developed. The smoothed particle hydr...
We examine the role of the accretion disk in the steady-burning white dwarf model for supersoft sources. The accretion luminosity of the disk is quite small compared to the nuclear burning luminosity of the central source. Thus, in contrast to standard ac...
The standard model of an accretion disk is considered. The temperature in the inner region is computed. It is assumed that the radiated power derives from comptonized photons, produced in a homogeneous single temperature plasma, supported by radiation pre...
Jan 31, 2005 ... KERRBB is a multi-temperature blackbody model for a thin, steady state, general relativistic accretion disk around a Kerr black hole. ...
Accretion Disk Coronae were first suggested to explain the incomplete eclipses and shallow profiles observed from some Low Mass X-ray Binaries (White and ...
Based on previous works on black hole accretion disks, I continue to explore the disk dynamics using the finite difference method to solve the highly nonlinear problem of time-dependent alpha disk equations. Here a radially zoned model is used to develop ...
Accretion disks around supermassive black holes are expected to be the power sources in all AGNS, including blazars. To date, though, little direct evidence for such disks exists in AGN observations. In blazars, the intense relativistic beaming would mask...
We show that most of hot, optically thin accretion disk models that ignore advective cooling are not self-consistent. We have found new types of optically thin disk solutions where cooling is dominated by radial advection of heat. These new solutions are thermally and viscously stable.
NASA Astrophysics Data System (ADS)
We consider the structure and emission spectra of nonthermal accretion disks around both strongly and weakly magnetized neutron stars. Such disks may be dissipating their gravitational binding energy and transferring their angular momentum via semicontinu...
Spectra of accretion disks hypothesized to produce the strong optical and ultraviolet flux in quasars and active galactic nuclei were calculated. The spectrum of radiation leaving the disk surface is described by non-LTE stellar atmospheres with high effe...
A new branch of equilibrium solutions for stationary accretion disks around black holes is found. These solutions correspond to moderately super-Eddington accretion rates. The existence of the new branch is a consequence of an additional cooling due to general relativistic Roche lobe overflow and horizontal advection of heat. On an ...
Energy Citations Database
Alpha models of astrophysical accretion disks assume an ad hoc viscous stress which scales locally as the total pressure. It is shown here that, if turbulent magnetic Maxwell stresses are the source of this viscosity in quasi-stellar object accretion disk models, then the ...
We propose a generalized model for stellar spin-down, disk accretion, and truncation, and the origin
Although the powering mechanism for quasars is now widely recognized to be the accretion of matter in a geometrically thin disk, the transport of matter to the inner region of the disk where luminosity is emitted remains an unsolved question. Miralda-Escud� & Kollmeier (2005) proposed a model whereby quasars ...
The nature of linear perturbations to a thin, shearing accretion disk composed of compressible material is reexamined. Modes that can carry angular momentum throughout the disk are identified, and it is shown how the subsequent dissipation of these waves through nonlinear processes can form the basis of a viscosity mechanism for ...
have been. : size and distribution of such flux tubes. We then apply the model to identified using numerical, nonlinear hydrodynamic techniques, accretion ...
Formation and Evolution of Planetary Systems Beichman et al. 3. A. How do Planets Form: Core accretion vs. Disk Fragmentation? The core accretion model of ...
A simplified model of the vertical structure of accretion disks is derived. Analytical expressions for the temperature and density structure, which represent a generalization of the gray model long known in the theory of classical stellar atmospheres, are presented. The formalism naturally explains similarities and ...
The extent to which the continuum spectral energy distributions of T Tauri stars from 0.2 to 10 microns can be explained by a simple model consisting of an active PMS star and active accretion disk is considered. The disk contributes both an IR excess due to accretion energy dissipation and ...
Using an accretion-disk model, accretion disk luminosities are calculated for a grid of black hole masses and accretion rates. It is shown that, as the black-hole mass increases with time, the monochromatic luminosity at a given frequency first increases and then decreases rapidly as this ...
We have constructed numerically global solutions of advective accretion disks around black holes that describe a continuous transition between the effectively optically thick outer and optically thin inner disk regions. We have concentrated on models of accretion flows with large mass ...
accretion disks in the western Gulf region (Texas and Louisiana). Accretion ... protostellar disks are believed to be accretion disks associated with young, ...
The response of a circular accretion disk to rapid modulation of the mass-transfer rate into the disk is explored in order to model superhumps in SU UMa stars. It is proposed that periodically enhanced flow may disrupt or heat up the outer disk and produce the dips noted just before the ...
THE X-RAY SPECTRA OF AGN ACCRETION DISK CORONAE: FIRST RESULTS A. Orr 1;2 , G. Torricelli of the present paper. The model In our model (described in detail by Torricelli et al., in preparation) we
Oct 3, 2006 ... This is an X-ray spectral model from optically-thick Advection Dominant Accretion Flow, often called "slim disk", which is expected when the ...
The solution for the radial drift velocity of thin disk accretion onto black holes must be transonic, and is analogous to the critical solution in spherical Bondi accretion, except for the presence of angular momentum. The transonic requirement yields a correct treatment of the inner region of the disk not found in ...
A model is worked out for the inner zone of an accretion disk, allowing for the existence of a vertical velocity component for the gas. The temperature in the central plane of the disk is found to be higher than in the standard theory, and it depends on the accretion rate. Some of the gas in ...
Absolute spectrophotometric observations of the dwarf nova SS Cygni have been obtained at maximum light, during the subsequent decline, and at minimum light. In order to provide a critical test of accretion disk theory, a model for a steady-state ..cap alpha..-model accretion ...
... If the mass transfer rate is below a certain limit, the accretion disk is unstable and undergoes brightness cycles (outbursts), and if above the limit, the ...
DTIC Science & Technology
A key quantity needed to model the physics of accretion disks is the turbulent viscosity nuT. Most disks calculations have thus far used an expression for nuT that ...
An effort is made to observationally constrain accretion disks on the basis of light curves from the eclipsing cataclysmic variable UX Ursae Majoris, reconstructing the spectral energy distribution across the face of an accretion disk. The spectral resolution obtained suffices to reveal not only the radial ...
The photoionization of extended narrow-line regions in Seyfert galaxies by the radiation produced in a thick accretion disk is studied. The emission-line spectrum is calculated for a range of black hole masses, varying the values of the ionization parameter and the disk size. It is found that models with a million ...
X-ray illuminated accretion disks. We show how the most relevant atomic features in the spectra depend on the assumed properties of the irradiated gas. ...
The thermal emission of accretion disks in Active Galactic Nuclei (AGN) is examined. Medium broadband AGN spectra are shown in order to explain the emission mechanism proposed. Basic behaviors from radiation theory and from hydrodynamics of importance for...
A baseline model of the composition and abundances of grains and gases in molecular cloud cores and accretion disks around young stars is defined by employing: a wide range of astronomical data and theory; the composition of primitive bodies in the solar ...
We review the empirical constraints on accretion disk models of stellar-mass black holes based on recent multiwavelength observational results. In addition to time-averaged emission spectra, the time evolutions of the intensity and spectrum provide critic...
The behavior of accretion disks can largely be understood in terms of the basic physical processes of mass, energy, and momentum conservation. Despite this, detailed modeling of these systems using modern computational techniques is challenging and contro...
The polytropic relation between pressure and density of wind gases is used to obtain solutions for optically thin hot accretion disks with winds. It is assumed that the cooling mechanisms in the disks are bremsstrahlung and Compton scattering. This extends the previous work of Takahara et al. (1989) which did not analyze winds within a ...
The results of self-consistent, azimuthally symmetric, radiation-hydrodynamic calculations of subcritical accretion disks about a Newtonian pseudo-black hole are reported. Energy generation is described by a kinematic viscosity law and a modified alpha-disk model. A disk with constant kinematic ...
Observations of T Tauri stars and young brown dwarfs suggest that the accretion rates of their disks
We calculate the structure of an effectively optically thin and geometrically thin accretion disk in
accretion? " What is the structure of the inner disk? " How do accretion disks drive jets? ... IXO will reveal the physics of disk accretion, and low L_X ...
An approximation theory of the acceleration of particles in low-density shear flows is developed and is applied to a number of astrophysical flows including accretion disks, radial accretion, and convective turbulence. In the disk application, the theory suggests a mechanism by which the bulk of the ...
We formulate a detailed, self-consistent model of magnetic viscosity in an accretion disk around a rotating, Kerr black hole, in order to help clarify the nature of viscosity in the theory of accretion disks. The magnetic field is amplified by shear and dissipated by reconnection; in ...
We discuss the effect of the Poynting flux on a magnetically dominated thin accretion disk, which is simplified to a two-dimensional disk on the equatorial plane. It is shown in the relativistic formulation that the Poynting flux caused by a rotating magnetic field with Keplerian angular velocity can balance the energy and angular ...
The results of a grid of non-Local thermodynamic equilibrium (LTE) accretion disk models are presented. These models were computed by a program which calculates the radiative transfer at positions in an accretion disk characterized by a local temperature and midplane ...
We describe a Newtonian version of the theory of thick accretion disks orbiting black holes. In view of the present inadequate knowledge of microscopic viscosity process, this theory adopts a macroscopic approach. All the uncertainties are absorbed in currently arbitrary functions lambda(xi) and f(xi) which describe the (non-Keplerian) angular momentum ...
The viscous model for accretion disks encounters difficulties both in providing a source of viscosity and in removing angular momentum from the disk outer edges where it is transported by the viscous stress. This paper investigates radiative tides as an alternative mechanism for accretion in ...
A model of a thin polytropic disk accretion onto a polytropic star through a polytropic boundary layer is analyzed and a one-parameter series of models is calculated with the stellar angular velocity varying from small to somewhat supercritical values along the series. It is demonstrated that there is no limit to ...
High resolution infrared spectroscopy is a very valuable tool for the study of the formation of low mass and very low mass stars. At the stage in which these objects are already visible, they still undergo strong mass accretion and mass loss processes. Many of the features observed on these stars can be explained by the magnetospheric accretion ...
The stability of magnetic fields within the accretion disks is examined, including the effects of magnetic buoyancy. Rayleigh-Taylor, and Kelvin-Helmholtz instabilities. The purpose of the study is to examine the efficacy of turbulent accretion (..cap alpha..-) disk models which depend upon ...
Context. We study the precession of accretion disks in the context of gamma-ray burst inner engines. Aims: Our aim is to quantitatively estimate the characteristics of gravitational waves produced by the precession of the transient accretion disk in gamma-ray bursts. Methods: We evaluate the possible periods of ...
We have constructed models for the vertical structure of disks around a black hole of 10/sup 6/ M/sub sun/ at distances from it smaller than the tidal breakup radius. These disks are massive enough that nuclear burning occurs in their central layers.
Recent work on a unified model of accretion flows and X-ray emission in low mass X-ray binaries is summarized. In this model, a weakly magnetic neutron star accretes gas simultaneously from a Keplerian disk and a corona above the inner part of the disk. P...
Slim-disk models describe advective accretion flows at high luminosities, while reducing to the standard thin disk form in the low luminosity limit. We have developed a new spectral model, slimbb, within the framework of XSPEC, which describes fully relativistic slim-disk ...
We construct a model of a geometrically thick accretion disk orbiting a 10 M/sub sun/ black hole in which most of the interior is in convective equilibrium, and in which the accretion flow and heat generation are confined mostly to the layers due to the equatorial plane. Surfaces of constant angular momentum and ...
The polarization of X radiation from an accretion disk in a binary X-ray source is investigated. Calculations are discussed which indicate that radiation from an accretion disk is linearly polarized as a result of Thomson scattering, that the hard X-ray electric vector lies in the orbital plane in the standard ...
The authors examine the possibility of neutron viscosity as the mechanism responsible for the dissipation of kinetic energy into luminosity in the innermost parts (r < 100 R sub s) of accretion disks surrounding compact objects. They present simplified models of such self-consistent, steady state accretion flows ...
The line profiles and relative fluxes of the emission lines in the quiescent spectra of cataclysmic variables contain information about the physical state of the material in the accretion disks around the white dwarfs. Several physical and phenomenological models for the emission line regions are discussed, and the resulting emission ...
Ultra-luminous Compact X-ray Sources (ULXs) in nearby spiral galaxies and Galactic superluminal jet sources share the common spectral characteristic that they have unusually high disk temperatures which cannot be explained in the framework of the standard optically thick accretion disk in the Schwarzschild metric. On the other hand, ...
Understanding boundary layer heating is crucial in determining the thermal structure of the accreted envelope of a prenova white dwarf. The matched asymptotic expansion method was used to solve consistently for the structure of accretion disks transferring matter onto rotating white dwarfs. The fraction of ...
Context. Models of the formation, evolution and photoevaporation of circumstellar disks are an essential ingredient in many theories of the formation of planetary systems. The ratio of disk mass over stellar mass in the circumstellar phase of a disk is for a large part determined by the angular momentum of the ...
In this paper we extend our previous works on spherically symmetric accretion onto black holes and superspinars to the case in which the fluid has a finite angular momentum initially. We run 2.5D and 3D general relativistic hydrodynamic simulations of the accretion of a fat disk. We study how the accretion process ...
the disk --- either entering the jet directly (the #12; BLR Accretion Disk ECC RSy ECD SSC e e + Sy FIGURE 1. Illustration of the model geometry and the relevant fl radiation mechanisms for leptonic jet models. ECD is the height of the blob above the accretion ...
Jun 28, 2007 ... Hydrodynamic Models of Line-driven Accretion Disk Winds. III. ... Hydrodynamic Modeling of Cataclysmic Variable Winds ...
Theory and Modelling Research in the LHEA - Research Topics. Low Mass X-ray Binaries -- Accretion Disk Corona Radiative Transfer � Synthetic X-ray Spectra ...
data yield the accretion disk thickness, diameter, electron density, and magnetic field. Introduction. The structure of AGN accretion disks on sub-parsec ...
The structure of AGN accretion disks on sub-parsec scales can be probed t,hrough ... GHz to map absorption caused by an inner accretion disk. ...
Nov 19, 2004 ... In an accretion disk, material near the outside moves slower than ... Depending on the angle at which we observe the accretion disk, ...
do not have accretion disks. Optical spectra are the only way that we can .... inner accretion disks) confirms the asymmetrical distribution of such stars ...
Sep 27, 2002 ... Accretion Disk Simulation ... Instead, the graphic shows spiral shock waves in a three dimensional simulation of an accretion disk -- material ...
A model is proposed for nonsteady disk accretion in the Galaxy due to dynamical friction, and it is applied to analyze how dynamical friction will affect the galactic motion of giant molecular clouds. Comparison with the observed gas distribution in the galactic disk imposes stringent constraints on the physical ...
Young stellar systems orbiting in the potential of their birth cluster can accrete from the dense molecular interstellar medium during the period between the star's birth and the dispersal of the cluster's gas. Over this time, which may span several Myr, the amount of material accreted can rival the amount in the initial protoplanetary ...
We review current models for the accumulation of the Moon from an impact-generated debris disk. Such a disk is dynamically distinguished by its substantial mass relative to the Earth and a very centrally condensed radial profile, with a mean orbital radius near the classical Roche limit. In the inner protolunar ...
Stellar black-hole candidates and active galactic nuclei are believed to contain accretion disks around black holes. Their X-ray variability is characterized by power spectra with a power law dependence on the variability frequency. The power slope beta is in the range between 1 and 2 and its most typical value is around 1.5. Mineshige et al. (1994) have ...
We investigate the model of disk/coronal accretion into a black hole. We show that the inner regions of an accretion disk in X-ray binaries can transform from a cool standard disk to an advection-dominated flow through the known properties of Coulomb interaction in a ...
We discuss the dynamics of the accretion flow onto a black hole driven by Poynting flux in a simplified model of a two-dimensional accretion disk. In this simplified model, the condition of the stationary accretion flow is found to impose a nontrivial constraint on the ...
Steady state models of magnetized accretion disks that power centrifugally driven outflows are presented. Self-similar solutions for Keplerian disks that are dominated by ambipolar diffusion are constructed and the analogous solutions for resistive disks are presented. In each case, it is shown ...
The most massive stars can form via standard disk accretion�despite the radiation pressure generated�due to the fact that the massive accretion disk yields a strong anisotropy in the radiation field, releasing most of the radiation pressure perpendicular to the disk ...
Gas giant planets have been detected in orbit around an increasing number of nearby stars. Two theories have been advanced for the formation of such planets: core accretion and disk instability. Core accretion, the generally accepted mechanism, requires several million years or more to form a gas giant planet in a protoplanetary ...
PubMed
High Energy Astrophysics: Accretion Disks I 1/60 Accretion Disks I References: Accretion Power in Astrophysics, J. Frank, A. King and D. Raine. High Energy Astrophysics, Vol. 2, M.S. Longair, Cambridge Astrophysics: Accretion Disks I 2/60 1 Overview ...
A simple model of dwarf nova accretion disks is constructed. The usual alpha-disk formalism is replaced by the assumptions that the surface density of the disk is a power function of radius and that matter falling in during quiescence accumulates in a torus at the outer edge of the ...
The evolution and stability of pair-supercritical accretion disks are examined. The microphysics of electron-positron pair processes are incorporated into a self-consistent accretion disk model, using the full set of time-dependent equations for a two-temperature disk ...
We apply the disk-corona evaporation model (Meyer & Meyer-Hofmeister) originally derived for dwarf novae to black hole systems. This model describes the transition of a thin cool outer disk to a hot coronal flow. The mass accretion rate determines the location of this transition. For a ...
The spectra of dwarf novae show broad absorption lines in outburst and strong emission lines during the quiescent state. Simplified calculations are presented for idealized disk models that demonstrate that these features can be attributed to radiative properties of accretion disks. Using these ...
The investigations of advection-dominated accretion flows (ADAFs), with emphasis on applications to X-ray binaries containing black holes and neutron stars is presented. This work is now being recognized as the standard paradigm for understanding the vari...
Sep 10, 2008 ... Intro/Motivation. Ray-Tracing. Disk/Corona Model. Results. Applications. X-Ray Polarization from Accreting Black Holes. Jeremy Schnittman ...
The evolution of thick accretion tori around black holes was investigated. Using three-dimensional computer models, it is shown that isentropic, pressure supported tori with constant specific angular momentum (Omega = r sup - 2) are unstable. Nonaxisymmet...
To study the outflows from accretion disks, we solve the set of hydrodynamic equations for accretion disks in spherical coordinates (r?phi) to obtain the explicit structure along the ?-direction. Using self-similar assumptions in the radial direction, we change the equations to a set of ordinary differential ...
Mar 1, 2011 ... Sagittae are discussed with reference to the similarity between WZ Sge and dwarf novae and the applicability of accretion disk models. ...
The inverse problem of interpreting the SS 433 optical light curves is solved for a geometrically thick model accretion disk around the compact relativistic object: most likely a black hole.
Jul 8, 2010 ... These table models provide the reflection spectrum from a constant density disk illuminated by a blackbody, as in the case of an accreting ...
A model of the object SS 433 is considered, in which the observed properties would result from supercritical disk accretion onto a neutron star possessing a strong magnetic field.
Within the framework of unsaturated Compton disk accretion onto a supermassive black hole as a model
We perform computations using a time-dependent model for the accretion disk limit-cycle mechanism to
In this paper we report 2007-2009 multicolour observations of the dwarf nova AH Her aiming to test the steady-state model for accretion disk emission.
Measured profiles of the iron K lines provide important dynamical information about emitting matrial
Apr 20, 2009... ADVECTION-DOMINATED ACCRETION, ENERGY EXTRACTION, GRO J1655-40, BINARIES, PRECESSION, DISCOVERY, MODELS, PLASMA, FLOWS, DISK ...
Mar 1, 2011 ... Author: Knight, J. W., III. Abstract: An idealized steady state model .... uniform, vertical magnetic field. The accretion flow in the disk ...
We herein present an observational and theoretical review of the winds of compact binaries. After a brief consideration of the accretion disk coronae and winds of X-ray binaries, the review concentrates on the winds of cataclysmic variables (CVs). Specifically, we consider the related problems of the geometry and mass-loss rate of the winds of CVs, their ...
Measurements of the polarization of X-rays from Cyg X-1 can yield significant information about the structure of the accretion disk which produces the observed spectrum. In particular, both the physical geometry (sensitive to large changes in the viscosity) and also the soft X-ray cutoff of the inner region of the disk have ...
The black-hole/accretion-disk model proposed to explain the high observed luminosities of AGN is discussed, reviewing the results of recent observational and theoretical investigations. The derivation of the governing equations for black holes and thick or thin disks is outlined; numerical predictions are presented in tables and ...
Disks, Accretion. USE. ACCRETION DISKS. Disks, Optical. USE. VIDEO DISKS. Disposal (In Space), Hazardous Material. USE. HAZARDOUS MATERIAL DISPOSAL (IN ...
CONSTRAINTS ON ACCRETION AND MAGNETAR MODELS D. L. KAPLAN,1 S. R. KULKARNI,1 M. H. VAN KERKWIJK,2 R. E strong new constraints on both accretion disk and magnetar models and suggest that the spectral energy, and a magnetar would require a D1015�1016 G �eld. Subject headings : ...
This is the first of two papers that investigate models of radiation-driven winds from super-critical accretion disks. The main assumptions in the models are that the mass and luminosity in the wind emanate from the radius in the disk where accretion becomes supercritical ...
Hydrodynamical winds from hot accretion disks around compact objects are investigated using a simplified model. The flow pattern above the disk is solved assuming that specific angular momentum is conserved along a stream line and that the radial component of the gravitational force balances the centrifugal force ...
A study of both the physical and the thermodynamical characteristics of a satellitary accretion disk around Saturn has been performed in order to investigate the primordial stages of the formation of the Saturn satellites. In particular, the evolution of a satellitary disk during the infall of material from the surrounding cloud is ...
The authors present a model for the high-low state transition of the X-ray Nova GS 1124-68 (Nova Muscae 1991) observed by Ginga. The model consists of an advection-dominated accretion flow (ADAF) near the central black hole surrounded by a thin accretion disk. During the rise phase of the ...
The observational appearance of a protostellar accretion disk has been calculated analytically by assuming a thin, thermally emitting disk with an unspecified power-law temperature gradient. The disk is assumed to have both a maximum and a minimum radius. The analytical spectrum is compared with data from the Rho ...
The effect of rapid accretion on a moderate-mass stellar model is studied. The surface boundary condition is examined for two modes of accretion - disk and direct impact. It is found that the effective temperature must be increased for disk accretion but not for ...
A scenario for the central engine of AGN has been developed consisting of a massive black hole (MBH) onto which gas accretes through an accretion disk. The accretion disk radiates the observed optical and ultraviolet continua. Surrounding the MBH is a nonthermal source which produces the ...
DOE Information Bridge
Based on a new estimation of their thickness, the global properties of relativistic slim accretion disks are investigated in this work. The resulting emergent spectra are calculated using the relativistic ray-tracing method, in which we neglect the self-irradiation of the accretion disk. The angular dependence of ...
The linear equations that describe the thermal stability of the convective and radiative vertical structure of an alpha model accretion disk are derived. For a specific model chosen to be representative of a dwarf nova disk, it is found that the eigenfunction for the temperature shows large ...
The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was
An effort is made to observationally constrain accretion disks on the basis of light curves from the
This thesis presents quantitative models of the magnetosphere of a magnetic star surrounded by a thin plasma disk. The model is motivated by the currently accepted picture of many accretion-powered pulsars as strongly magnetic neutron stars accreting from disks. It may also ...
One possible mechanism for giant planet formation is disk instability in which the planet is formed as a result of gravitational instability in the protoplanetary disk surrounding the young star. The final composition and core mass of the planet will depend on the planet's mass, environment, and the planetesimal accretion efficiency. ...
Five-color photometric observations of RZ Oph have been obtained from 1981 through 1986, in an effort to deduce the properties of the accretion disk in this long-period Algol. The partial eclipse of the disk by the cool star, and the partial occultation of the cool star by the disk, have both been observed in some ...
Using data from the Rossi X-Ray Timing Explorer, we investigate the spectral evolution along a "Z" track and a "?" track on the hardness-intensity diagrams of the first transient Z source XTE J1701�462. The spectral analyses suggest that the inner disk radius depends on the mass accretion rate, in agreement with the model prediction, ...
We show that a moderately massive disk (10/sup -5/--10/sup -2/ M/sub sun/) can cause the Lense-Thirring precession of the compact object (neutron star or black hole) at its center. The inner regions of the disk (r< or approx. =10/sup 8/ cm) align with the equator of an will precess at the same rate as the compact object. We propose that this ...
The wind accretor LMC X-1, along with LMC X-3 and Cygnus X-1, is one of only three known persistently bright black hole binary systems. Our long-term RXTE monitoring campaign of LMC X-1 has revealed a surprising departure from the typical accretion disk temperature-luminosity relation. This behavior is consistent with the presence of a stable ...
Accreting neutron stars provide the bulk of high luminosity X-ray sources. Decade long studies of low-mass X-ray binaries have provided a wealth of information about the various nature of X-ray emissions and proposed emission sites include the neutron star surface, an immediate boundary layer, the inner disk region, a possible compact corona, atmospheric ...
The dwarf nova SS Cygni was observed by IUE. The UV low resolution spectra show clear differences in the behavior of the accretion disk in quiescence and in outburst. A steady-state disk model can almost fit the continuum of the outburst spectra, while it...
Current models of planet and satellite formation aremarred by our lack of understanding regarding the turbulent state of accretion disks. According to the Rayleigh criterion, Keplerian disks are hydrodynamically stable. Indeed, it has been argued that a c...
Several types of cataclysmic events involving stellar-mass compact objects could result in the extreme, transient accretion onto a black hole widely believed to power gamma-ray bursts. We calculate the vertical structure of such thick accretion disks with a semi-analytical model which includes the effects of ...
The exchange of angular momentum between accreting matter and the magnetosphere of a neutron star is studied as a possible explanation for the soft X-ray emission of X-ray pulsars. The flux of soft X-radiation from Her X-1 may be related to dissipation of rotational energy of accreting matter into a layer of the disk at the radial ...
We apply our self-consistent accretion disk corona (ADC) model, with two different geometries, to the broadband X-ray spectrum of the black hole candidate Cygnus X-1. As shown in a companion paper, models in which the Comptonizing medium is a slab surroun...
Radiative winds and jets from luminous accretion disks/tori are reviewed. Among various models of astrophysical jets, plasma outflows emanating from accretion disks/tori and accelerated by the radiation pressure is the most promising one. Here explained are the roles of radiation pressure force ...
We investigate the structure of accretion disks around massive protostar applying steady state models of thin disks. The thin disk equations are solved with proper opacities for dust and gas taking into account the huge temperature variation along the disk. We explore a ...
The observed iron K{alpha} fluorescence lines in Seyfert I galaxies provide strong evidence for an accretion disk near a supermassive black hole as a source of the line emission. These lines serve as powerful probes for examining the structure of inner regions of accretion disks. Previous studies of line emission ...
We study the power spectra of the variability of seven intermediate polars containing magnetized asynchronous accreting white dwarfs, XSS J00564+4548, IGR J00234+6141, DO Dra, V1223 Sgr, IGR J15094-6649, IGR J16500-3307 and IGR J17195-4100, in the optical band and demonstrate that their variability can be well described by a model based on fluctuations ...
We present binary galaxy merger simulations of gas-rich disks (Sp-Sp), of early-type galaxies and disks (E-Sp, mixed mergers), and mergers of early-type galaxies (E-E, dry mergers) including radiative cooling, star formation, black hole (BH) accretion, and the associated feedback processes. The numerical simulations include cooling, ...
We propose a new evolutionary model of a supermassive black hole (SMBH) and a circumnuclear disk (CND), taking into account the mass-supply from a host galaxy and the physical states of CND. In the model, two distinct accretion modes depending on gravitational stability of the CND play a key role on ...
Nov 6, 2000 ... "accretion" means collecting of additional material. Two major places where astronomers see accretion disks are in binary star systems (two ...
Sep 4, 1998 ... 3. Formation of an Accretion Disk. Bonnet-Bidaud and van der Klis (1979) showed that even if the accretion is from the stellar wind, ...
We compute the properties of a geometrically thin, steady accretion disk surrounding a central rotating, magnetized star. The magnetosphere is assumed to entrain the disk over a wide range of radii. The model is simplified in that we adopt two (alternate) ad hoc, but plausible, expressions for the azimuthal ...
Using Spitzer Space Telescope photometric observations of the eclipsing, interacting binary WZ Sge, we have discovered that the accretion disk is far more complex than previously believed. Our 4.5 and 8 ?m time series observations reveal that the well-known gaseous accretion disk is surrounded by an asymmetric ...
Although disk accretion onto compact objects-white dwarfs, neutron stars and black holes-is central to much of high-energy astrophysics, the mechanisms that enable this process have remained observationally difficult to determine. Accretion disks must transfer angular momentum in order for matter to travel radially ...
The IUE data base is used to analyze the UV line shapes of cataclysmic variables RW Sex, RW Tri, and V Sge. Observed lines are compared to synthetic line profiles computed using a model of rotating bi-conical winds from accretion disks. The wind model cal...
We present the properties of accretion disk corona (ADC) models in which the radiation field, the temperature, and the total opacity of the corona are determined self-consistently. We use a nonlinear Monte Carlo code to perform the calculations. As an exa...
Active galactic nuclei (AGN) accretion disk spectra were calculated using non-LTE stellar atmosphere models for Kerr and Schwarzschild geometries. It is found that the Lyman limit absorption edge, probably the most conclusive observational evidence for th...
A cascade model for driven quasi-steady fluid turbulence is applied to calculation of the dissipation parameter, alpha, for a convection-accretion disk. The mode analysis is nonlocal in the vertical direction and allows arbitrary rotation curves. Nonaxisymmetric modes, nonlinear mode structure, and turbulent cascade dynamics are all ...
I present H- and K-band light curves of the dwarf nova cataclysmic variable (CV), IP Peg, and the novalike CV, RW Tri, and an H-band light curve of the novalike CV, SW Sex. All three systems showed contributions from the late-type secondary star and the accretion disk, including a primary eclipse of the accretion ...
The standard spectral model for analyzing the soft component of thermal emission from a thin accretion disk around a black hole is the multi-temperature blackbody (MTB) model. The widely used implementation of this model, which is known as ``diskbb,'' assumes nonzero torque at the inner edge of ...
The observed contraction of the accretion disks in the dwarf novae U Gem and Z Cha during quiescence is interpreted with simple dynamical models. The standard {alpha}-parameter viscosity prescription is replaced by macroscopic constraints that are both computationally convenient and appropriate for the study of an extensive ...
The formation and evolution of an accretion disk formed during the collapse of a rotating cloud core
Photoelectric U, B, V photometry of eclipses in the close binary system IP Peg, obtained mainly with the 6-m telescope, yields brightness profiles along the edgewise accretion disk. The radiation is dominated by a hot spot whose brightness and location in the disk depend on the state of activity in the binary. In the quiescent phase ...
Models predict that magnetic fields play a crucial role in the physics of astrophysical accretion disks and their associated winds and jets. For example, the rotation of the disk twists around the rotation axis the initially vertical magnetic field, which responds by slowing down the plasma in the ...
at relativistic bulk velocity. #12; BLR Accretion Disk ECC RSy ECD SSC e e + Sy FIGURE 1. Illustration of the model the disk --- either entering the jet directly (the ECD [External Comptonization of Direct disk radiation is the height of the blob above the accre� tion ...
The UBVR light curves of the massive eclipsing binary RY Sct, obtained at the Maidanak Observatory from 1979 to 1992, have been re-analyzed in order to prove the hypothesis of the presence of an accretion disk in the system. This hypothesis is supported by a new spectroscopic study of Grundstrom et al., and by a specific light-curve shape exhibiting a ...
We present our code for the calculation of the 1D structure and synthetic spectra of accretion disks. The code is an extension of the well-tested stellar atmosphere code PHOENIX and is therefore capable of including large lists of atomic and molecular lines as well as a large set of dust species. We assume the standard accretion ...
We calculate the temperature profiles of (thin) accretion disks around rapidly rotating neutron stars (with low surface magnetic fields), taking into account the full effects of general relativity. We then consider a model for the spectrum of the X-ray emission from the disk that is parameterized by the mass ...
We calculate upper bounds on the inner radii of geometrically thin accretion disks in galactic black hole systems by relating their rapid variability properties to those of neutron stars. We infer that the inner disk radii do not exhibit large excursions between different spectral states, in contrast with the concept that the ...
We consider hot accretion disk outflows from black hole-neutron star mergers in the context of the nucleosynthesis they produce. We begin with a three-dimensional numerical model of a black hole-neutron star merger and calculate the neutrino and antineutrino fluxes emitted from the resulting accretion ...
We obtained steady solutions of magnetized black hole accretion disks taking into account the gas pressure, magnetic pressure, and radiation pressure. We assumed the bremsstrahlung cooling in the optically thin limit and the black body cooling in the optically thick limit. W assumed that magnetic fields inside the disk are turbulent ...
``Corrugated'' plasma disks can form in the dominant gravity of a central object when the peak plasma pressure in the disk is of the same order as that of the pressure of the ``external'' magnetic field, while the magnetic field resulting from internal plasma currents is of the same order as the external field. The corrugation refers to a periodic ...
Following a suggestion by Paczynski we have constructed models for the vertical structure of disks around stars in their late stages of evolution in which the viscosity that allows the angular momentum of the disk to be transported outward is due solely to turbulence produced by convection in the outer layers of the ...
We describe an analytic model for the evolution of a protoplanetary disk heated by viscous accretion and radiation from the central star. The disk is assumed to be flared and viscosity is assumed to follow an 'alpha' model, where viscosity is proportional to the local sound ...
We present near-infrared, H-band (1.45 - 1.85 m) observations of the eclipsing dwarf nova, IP Peg, in quiescence. The light curves are composed of ellipsoidal variations from the late-type secondary star and emission from the accretion disk and the bright spot. The light curves have two eclipses: a primary eclipse of the accretion ...
