Nov 6, 2000 ... "accretion" means collecting of additional material. Two major places where astronomers see accretion disks are in binary star systems (two ...

Accretion disks are invoked to explain a host of astrophysical phenomena, from protostellar objects to AGN. And yet the mechanism allowing accretion disks to operate are completely unknown. This proposal seeks to observe the ``smoking gun'' signature of magnetically-driven viscosity in ...

Material falling (accreting) onto a black hole in a binary system, or at the center of a galaxy, forms an accretion disk about the event horizon, with the inner ...

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...

Dec 19, 1999 ... Here gas from a blue giant star is shown being stripped away into an accretion disk around its compact binary companion. ...

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 ...

accretion disks in the western Gulf region (Texas and Louisiana). Accretion ... protostellar disks are believed to be accretion disks associated with young, ...

Recent observational data has shown that the Algol-type binary system RS Vul possesses an accretion disk tilted out of the orbital plane. Magnetic effects in the surface of the donor star could produce a nontrivial effect in the flow of the accretion stream as it travels through the L1 Lagrange point. Such a ...

Accretion disks are invoked to explain a host of astrophysical phenomena, from protostellar objects to AGN. And yet the mechanism allowing accretion disks to operate are completely unknown. This proposal seeks to observe the smoking gun signature of magnetically--driven viscosity in accretion ...

The short-period Algol system TZ Eri was observed spectroscopically during 10 eclipses in order to study the accretion disk surrounding the primary star. It is shown that this disk belongs to the class of transient accretion disks which are produced by a collision of the ...

The self-sustained turbulence that develops in magnetized accretion disks is suppressed in the weakly ionized, quiescent disks of close binary stars. Because accretion still proceeds during quiescence, another viscosity mechanism operates in these systems. An anticorrelation of the recurrence ...

A method is proposed for restoring the structure of the accretion disk in a binary system from analysis of eclipse curves. Application of the method to the x-ray binary HZ Herculis yields the distribution of brightness and color temperatures over the optical accretion disk associated with the ...

The importance of simultaneous IUE and Voyager observations of luminous accretion disk systems is shown. The composite spectra of SS Cyg, VW Hyi, CPD-48 1577, and V3895 Sgr show the changes which occur in the continuum flux distributions from 3200 A down ...

... For nova-like systems, whose luminosity is dominated by the accretion disk and affected by interstellar extinction and reddening, accurate distances ...

... For nova-like systems, whose luminosity is dominated by the accretion disk and affected by interstellar extinction and reddening, accurate distances ...

Apr 12, 2011 ... The characteristics of a particular planetary system depend upon the ... planets are formed from dynamic instabilities in accretion disks. ...

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

A model for disk accretion by a rotating magnetic neutron star is proposed which includes a detailed

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...

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 disk has been constructed which ...

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 ...

This presentation describes the behavior of matter in environments with extreme magnetic and gravitational fields, explains the instability/stability of accretion disks in certain systems, and discusses how emergent radiation affects accretion flow. Magne...

The collapse of massive molecular clumps can produce high mass stars, but the evolution is not simply a scaled-up version of low mass star formation. Outflows and radiative effects strongly hinder the formation of massive stars via accretion. A necessary condition for accretion growth of a hydrostatic object up to high masses M > 20 MSun (rather than ...

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 ...

The nonaxisymmetric stability of self-gravitating, geometrically thick accretion disks has been studied for protostellar systems having a wide range of disk-to-central object mass ratios. Global eigenmodes with four distinctly different characters were id...

The notion that planetary systems are formed within dusty disks is certainly not a new one; the modern planet formation paradigm is based on suggestions made by Laplace more than 200 years ago. More recently, the foundations of accretion disk theory where...

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 #12;High Energy ...

Most Galaxy-sized systems (M host sime 1012 M sun) in the ?CDM cosmology are expected to have interacted with at least one satellite with a total mass M sat sime 1011 M sun sime 3M disk in the past 8 Gyr. Analytic and numerical investigations suggest that this is the most precarious type of accretion for the survival of thin galactic ...

Formation and Evolution of Planetary Systems: Placing Our Habitable Solar System in Context ... early evolution of accretion disks (tau < 10 Myr) and the ...

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 ...

The existence of accretion disks around young stellar objects has recently become widely accepted. The luminosity of some young stellar objects is highly variable and is generally attributed to the release of gravitational energy from matter funneled onto them by accretion disks. The inward transport of matter ...

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, ...

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. ...

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 ...

Theoretical calculations of linear polarization of thermal radiation from accretion disks in nova-like variables and dwarf novae in eruption are presented. The primary source of polarization is due to electron scattering in the disk's photosphere. It is shown that the degree of polarization can be used as a powerful probe of ...

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, ...

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 two-temperature plasma, ...

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 ...

Feb 10, 1997 ... A useful theory of planetary system formation would therefore relate ... Dissipative forces within the disk promote the accretion of most of ...

Dec 27, 1995 ... Dubbed Nova Cygni 1992, this event most probably occurred in an accretion disk binary system. Astronomers hypothesize that this system's ...

A Search for Terrestrial Planets. A Fundamental NASA Mission Goal: ... To place our Solar System in context with other planetary systems ..... Interacting binaries, accretion disks and streams, cataclysmic variables and novae ...

Apr 13, 2011 ... OBJECTIVE 2: Develop simulations that predict, in a probabilistic sense, the diversity of planetary systems that emerge during accretion of ...

APOD: 1999 December 19 Accretion Disk Binary System Explanation: Our Sun is unusual in that it is alone - most stars occur in multiple or binary systems. ...

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...

Disks, Accretion. USE. ACCRETION DISKS. Disks, Optical. USE. VIDEO DISKS. Disposal (In Space), Hazardous Material. USE. HAZARDOUS MATERIAL DISPOSAL (IN ...

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, ...

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 line profiles and ...

Net tidal torque by the secondary on a misaligned accretion disk, like the net tidal torque by the Moon and the Sun on the equatorial bulge of the spinning and tilted Earth, is suggested by others to be a source to retrograde precession in non-magnetic, accreting cataclysmic variable (CV) dwarf novae (DN) systems ...

Net tidal torque by the secondary on a misaligned accretion disk, like the net tidal torque by the Moon and the Sun on the equatorial bulge of the spinning and tilted Earth, is suggested by others to be a source to retrograde precession in non-magnetic, accreting cataclysmic variable (CV) dwarf novae (DN) systems ...

Context. The Galactic microquasar SS 433 is very luminous and ejects opposite jets at approximately one quarter the speed of light. It is regarded as a super-Eddington accretor but until recently there were no observations of accretion. Aims: We present an analysis of spectroscopic optical data obtained before and during a major flare, which yield in H? unambiguous evidence ...

The dynamics and structure of accretion disks, which accumulate a vertical magnetic field in their centers, are investigated using two- and three-dimensional MHD simulations. The central field can be built up to the equipartition level, where it disrupts a nearly axisymmetric outer accretion disk inside a ...

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 ...

The IUE was used to study processes connected with accretion disk structure and stability, wind accretion and wind-wind collisions, contact systems, and stellar activity in close binary stars. Time dependent phenomena already known from optical studies ap...

During the earliest period of solar system formation, water played an important role in the evolution of primitive dust, both after accretion of planetesimals and possible before accretion within the protoplanetary disk. Many chondrites show evidence of v...

The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was

Equations for the structure and appearance of supercritical accretion disks and the radiation-driven

An effort is made to observationally constrain accretion disks on the basis of light curves from the

Accretion events involving the infall of a massive satellite galaxy (Msat � 1011 Msun) onto a stellar disk in a Galactic-scale host halo (Mhost � 1012 Msun) are both cosmologically common and capable of inducing significant morphological and dynamical changes in the primary system. We review the work of Purcell et al. (2009) in ...

Disk accretion onto a magnetized spinning neutron star or a white dwarf will not be possible if the radius of the magnetosphere exceeds the corotation radius. A dead disk serving as a reservoir of material will then form around the star. Such a disk could retard the spin of the star; it might produce a transient ...

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 direct-impact ...

the accretion disk of the binary system and inconsistent with narrow beaming. ... luminosities are time-averaged estimates, which is critical for variable ...

Dec 10, 2009 ... "Suzaku's sensitivity to iron emission lines and its ability to measure the ... confirms the presence of low-density accretion flow in these systems. ...

Oct 29, 2010 ... Stars formed, planetary systems around stars formed from within these ... Kepler is observing accretion disks with a combined photometric ...

Planetary Systems Laboratory (693) � Laser Remote Sensing Laboratory (694) ... and normal galaxies, signatures of accretion disks in active galaxies. ...

Nov 10, 2003 ... Some stars are members of close binary systems where material from one star swirls around the other in an accretion disk. ...

evolution, and architecture of planetary systems generally. .... they are accreting gas depleted of dust from a circumbinary disk. ...

A possible accretion model associated with the ionization instability of quasar disks is proposed to

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 number of well-studied ...

The heating and radiative cooling of steady-state viscous accretion disks in close binary systems are studied. It is shown that the temperatures of the outer regions of disks do not fall below approx.6000 K over a wide range of conditions. Depending upon the mass accretion rate, the outer parts ...

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 ...

We have obtained millimeter-wavelength photometry, high-resolution optical spectroscopy, and adaptive optics near-infrared imaging for a sample of 26 Spitzer-selected transition circumstellar disks. All of our targets are located in the Ophiuchus molecular cloud (d {approx} 125 pc) and have spectral energy distributions (SEDs) suggesting the presence of inner opacity holes. We ...

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 disk. ...

Data from 30 nights of V 1357 Cyg observations in July, August, and September of 1977 are presented. The contribution of the disk to the optic brightness of the system is computed with regard for the heating of its surface by ultraviolet radiation from V ...

Spectroscopic, time-resolved observations of the accretion disk in the long-period Algol system RY Gem during eclipse are presented. It is shown that the disk is non-Keplerian and has asymmetries between the leading and trailing sides of the accretion disk similar to those ...

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...

We study rapidly accreting, gravitationally unstable disks with a series of idealized global, numerical experiments using the code ORION. Our numerical parameter study focuses on protostellar disks, showing that one can predict disk behavior and the multiplicity of the accreting star ...

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 ...

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 (the critical radius) and that the wind is ...

We have found that two members of the TW Hydrae association, TW Hydrae and Hen 3-600A, are still actively accreting, based on the ballistic infall signature of their broad Halpha emission profiles. We present the first quantitative analysis of accretion in these objects and conclude that the same accretion mechanisms which operate in ...

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, ...

Classical T Tauri stars offer a unique window into star+disk systems that are still in the accretion/outflow phase yet are no longer surrounded by an opaque circumstellar envelope. These objects hold the key to understanding how magnetospheric accretion occurs, how accretion powers outflows, ...

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 ...

The formation and evolution of an accretion disk formed during the collapse of a rotating cloud core

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 ...

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 be relevant to the luminous galactic ...

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...

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 ...

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 component of the magnetic ...

290 Stepinski:On Maonetic Dynamos in Thin Accretion Disks Around Stars pressure is smaller than gas pressure, otherwise the assumption of a thin disk ...

They could see details as fine as the neutron star's accretion disk, a ring of gas swirling around and flowing onto the neutron star, as the disk buckled ...

accretion disk where the viscosity is dominated by radiation pressure. ... viscosity norm. 2. 2cos /i d where i is the inclination of the disk and d is the ...

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 ...

Derivations are made for the mass and the mass-turnover time scale of an accretion disk as a function of the accretion rate, the observed disk radius, the non-viscous disk radius, and two parameters. These parameters depend on the effectiveness of viscosity and tidal angular momentum loss. ...

Derivations are made for the mass and the mass-turnover time scale of an accretion disk as a function of the accretion rate, the observed disk radius, the non-viscous disk radius, and two parameters. These parameters depend on the effectiveness of viscosi...

Too hot accretion disks in ULX and superluminal jet sources ... Standard accretion disk around Kerr black hole can explain the hard disk spectra? ...

A class of oscillations observed during eruption of dwarf novae has been interpreted as oscillations of the accretion disks in these systems.These oscillations are quasi-periodic with coherence times typically between three and 15 cycles. It is shown that magnetic field reconnection at high magnetic Reynolds number can drive ...

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 ...

Three-dimensional numerical simulations of gas dynamics are used to study the flow pattern in a close binary system after it has reached the steady-state accretion regime. The special attention is paid to physics of accretion disks in binary systems and, particularly, the waves in ...

I calculate the specific angular momentum of mass accreted by a binary system embedded in the dense wind of a mass losing asymptotic giant branch star. The accretion flow is of the Bondi-Hoyle-Lyttleton type. For most of the relevant parameters space the flow is basically an isothermal high Mach number accretion ...

About half of the binary systems are close enough to each other for mass to be exchanged between them at some point in their evolution, yet the accretion mechanism in wind accreting binaries is not well understood. We study the dynamical effects of gravitational focusing by a binary companion on winds from late-type stars. In ...

A model is developed for the exchange of angular momentum (torque) exerted by a satellite on a disk at a Lindblad resonance. The situation arises in galaxies affected by a central bar, in accretion disks in a close binary system, in the disturbance of the asteroid belt by Jupiter, etc. The disk ...

Observations of X-ray binaries indicate substantial half-thicknesses for the accretion disks in these systems (up to h/R ? 0.25, where h is the disk half-thickness and R its radius), while standard ? accretion disks predict appreciably smaller half-thicknesses. We study the ...

Studies of classical T Tauri stars have indicated that the accretion footprint lies in middle to polar latitudes on the star, consistent with theoretical expectations of the funnelled-accretion model. Herbig Ae stars are higher mass analogs of classical T Tauri stars. Their circumstellar disks, disk lifetimes and ...

In the last two years a hand-full of white dwarfs (WDs) with circumstellar debris disks have been discovered. The debris disks are either left over from the late stages of stellar evolution or are the result of tidally disrupted asteroids or comets, and are thus signposts of planetary systems. Our team has been investigating the ...

Accretion disk-driven magneto-centrigugal winds are one of the leading mechanism for producing bipolar outflows in many astrophysical systems. Previous studies of this mechanism have concentrated either on the disk or on the wind. We show that the structures of the disk and the wind are ...

The most energetic phenomena in the universe are systems powered by gravity through accretion. For compact stars such as white dwarfs, neutron stars, and especially black holes, the energy released per unit mass accreted can significantly exceed that released by nuclear reactions. Over the last half century a growing body of ...

Context. Even though turbulent motions are found everywhere in astrophysical systems, the origin of this turbulence is poorly understood. When cosmic structures form, they grow in mass via accretion from their surrounding environment. Aims: We propose that accretion is able to drive internal turbulent motions in a wide range of ...

The polarization parameters of the radiation from a tidally distorted star in a close binary system and the radiation of the star scattered by the accretion disk are calculated in the approximation of pure Thomson scattering. The two effects are of the same order of magnitude, and the amplitude is comparable with the percentage optical ...

Recent observations of partial X-ray eclipses from 4U1822-37 have shown that the central X-ray source in this system is diffused by a large Compton-thick accretion disk corona (ADC). Another binary, 4U2129-47, also displays a partial eclipse and contains ...

Accretion disks are associated with such diverse objects as planetary systems, Be stars, and spiral galaxies. However, their structure is poorly defined by existng observational data. This study was an attempt to gather specific structural information about the disks in Algol-type binary ...

Numerical simulations of accretion of planetary embryos from small planetesimals are described. In the terrestrial region, runaway growth proceeds as a wave propagating outward, producing an 'oligarchy' of embryos. The efficiency of accretion, i.e. the mass loss due to fragmentation, depends on the initial size of the planetesimals. In the outer region of ...

As the dense molecular cloud that was the precursor of our Solar System was collapsing to form a protosun and the surrounding solar-nebula accretion disk, infalling interstellar grains were heated much more effectively by radiation from the forming protosun than by radiation from the disk's ...

As the dense molecular cloud that was the precursor of our Solar System was collapsing to form a protosun and the surrounding solar-nebula accretion disk, infalling interstellar grains were heated much more effectively by radiation from the forming protosun than by radiation from the disk's ...

Hyperaccreting neutron stars or magnetar disks cooled via neutrino emission can be candidates of gamma-ray burst (GRB) central engines. The strong field >=1015-1016 G of a magnetar can play a significant role in affecting the disk properties and even lead to the funnel accretion process. In this paper, we investigate the effects of ...

Hyperaccreting neutron stars or magnetar disks cooled via neutrino emission can be candidates of gamma-ray burst (GRB) central engines. The strong field {>=}10{sup 15}-10{sup 16} G of a magnetar can play a significant role in affecting the disk properties and even lead to the funnel accretion process. In this paper, we ...

We simulate the evolution of the circumstellar and circumbinary disks in a system configured to appear similar to that observed for the GG Tau A binary. We find that mass transfer onto the circumstellar disks is episodic with maximal transfer rates which change from orbit to orbit, but which occur following each apoapse passage. ...

A model involving binary mass transfer and accretion onto main sequence stars is developed to explain the brightest known stars in external galaxies, the Hubble-Sandage variables. The similarity in spectral properties between the Hubble-Sandage variables and cataclysmic variables and the extreme disparity in their luminosities are presented as evidence for the essential ...

A maximum likelihood analysis of the NGC 4258 maser positions and velocities reveals a ~2 ? deviation from Keplerian motion in the projected rotation curve of the high-velocity features, corresponding to a ~9 km s-1, or 0.8%, flattening of the LOS velocities with respect to Keplerian motion over the range of the high-velocity masers. While there are a number of potential explanations for this ...

Recent discoveries of compact (sizes lsimR sun) debris disks around more than a dozen metal-rich white dwarfs (WDs) suggest that pollution of these stars with metals may be caused by accretion of high-Z material from the disk. But the mechanism responsible for efficient transfer of mass from a particulate disk to ...

Modeling of the x-ray spectra of the Galactic superluminal jet sources GRS 1915+105 and GRO J1655-40 reveals a three-layered atmospheric structure in the inner region of their accretion disks. Above the cold and optically thick disk with a temperature of 0.2 to 0.5 kiloelectron volts, there is a warm layer with a temperature of 1.0 to ...

We present Suzaku and XMM observations of the high-mass X-ray pulsar LMC X-4 at different phases in its superorbital cycle, which is due to the precession of a warped accretion disk. The superorbital period and phase for each observation is determined accurately using RXTE ASM data. At all superorbital phases, the broadband X-ray spectra are described by a ...

We show that changes in the orientation of the inner accretion disk of Cygnus X-1 affect the shape of the broad Fe K{alpha} emission line emitted from this object, in such a way that eV-level spectral resolution observations (such as those that will be carried out by the ASTRO-E2 satellite) can be used to analyze the dynamics of the ...

The stability and evolution of windy accretion disks is investigated in detail. The basic disk evolution equations are briefly recapitulated, and an idealized analytic treatment of the wind and viscosity is used to show that steady disk flow is indeed unstable for sufficiently large ratio of the mass loss rate in ...

Jul 20, 2009... protoplanetary disks, radiative transfer, T-TAURI DISKS, ACCRETION DISKS, YOUNG OBJECTS, CIRCUMSTELLAR DISKS, STARS, GROWTH, EARTH, DUST ...

... studies to, eg, measure inner disk truncation radii, probe the nature of the disk accretion process, and chart the evolution in the gas content of disks. ...

The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was to bring together workers on accretion disks in the western Gulf region (Texas and Louisiana). Part 2 presents the workshop program, a list of poster pres...

With the discovery that Alfven waves can be strongly unstable in a magnetized accretion disk, it can be expected to explain the turbulence necessary to drive accretion in these disks. The instability of non-axisymmetric Alfven waves is studied using analy...

Geometrically thin, optically thick, turbulent accretion disks are believed to surround many stars. Some of them are the compact components of close binaries, while the others are throught to be T Tauri stars. These accretion disks must be magnetized obje...

The influence of accretion disk instabilities on the UV fluxes of Seyfert 1 galaxies was studied. The observed characteristic timescales of variability are consistent with the interpretation that most of the UV radiation originates in an accretion disk, a...

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...

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...

Mar 12, 2005 ... Accretion Disk Simulation Credit: Michael Owen, John Blondin ... Such accretion disks power bright x-ray sources within our own galaxy. ...

Through numerical simulations using a hydrodynamic grid code, we show that a spiral density wave can be generated in inner annuli of a non-magnetic Cataclysmic Variable secondary-to-primary mass ratio q=M2/M1=0.4 system where M1=0.8 solar masses. The wave is entirely within the plane of the disk and it retrogradely precesses. We introduce the source to ...

The Lyman edge region in the spectra of 11 high-redshift quasars is studied using data designed to detect broadened Lyman edge absorption predicted by thermal models of the 'big blue bump' continuum component, especially thin accretion disks. Three objects have broadened, partial edges near the systemic redshifts, as ...

Accretional temperature profiles for Saturn�s large moon Titan are used to determine the conditions needed for accretion to avoid global melting as a function of the timing, duration, and nebular conditions of Titan�s accretion. We find that Titan can accrete undifferentiated in a �gas-starved� ...

Although there has yet been no undisputed discovery of a still-forming planet embedded in a gaseous protoplanetary disk, the cleared inner holes of transitional disks may be signposts of young planets. Here, we show that the subset of accreting transitional disks with wide, optically thin inner holes of 15 AU or ...

Nov 9, 2003 ... Consequently accretion disks have fundamental roles in the formation of planets, stars and compact objects, and are the engines driving the ...

... Understanding of accretion disks, accretion flows, X-ray induced winds, compact obect evolution are all in a primitive state. ...

... unique opportunities to study the details of the accretion flow in the cases of normal white dwarfs with accretion disks and magnetic white dwarfs. ...

Radial oscillations resulting from axisymmetric perturbations in viscous accretion disks surrounding

A possible accretion model associated with the ionization instability of quasar disks is proposed to

We present results of 3D simulations of MHD instabilities at the accretion disk-magnetosphere boundary. The instability is Rayleigh-Taylor, and develops for a fairly broad range of accretion rates and stellar rotation rates and magnetic fields. It produces tall, thin tongues of plasma that penetrate the magnetosphere in the equatorial ...

Massive stars produce so much light that the radiation pressure they exert on the gas and dust around them is stronger than their gravitational attraction, a condition that has long been expected to prevent them from growing by accretion. We present three-dimensional radiation-hydrodynamic simulations of the collapse of a massive prestellar core and find that radiation ...

The question of the nature of the ultraviolet and X-ray radiation field of cataclysmic binaries is addressed. The spectrum and luminosity of this radiation are important in determining the mass transfer rate and energy budget of the system and in studies of the ejecta surrounding novae. In many systems, the soft X-ray luminosity is approx.10/sup 2/--10/sup ...

Thermal conduction between a cool accretion disk and a hot inner corona can result in either evaporation of the disk or condensation of the hot corona. At low mass accretion rates, evaporation dominates and can completely remove the inner disk. At higher mass accretion ...

The ubiquity of accretion disks around pre-main sequence and young main sequence stars having the potential to form planetary systems is now well established. However, unknown is an accurate estimate of the fraction of single stars with disks that have pr...

Consideration is given to the Kant-Laplace hypothesis that the sun once had a ring system from which the planets condensed. It is suggested that the theory is supported by the IRAS observation of an accretion disk around Vega, which implies that ordinary stars are surrounded by a disk during and immediately after ...

How are accretion disks in Seyfert Galaxies oriented relative to the disk of the spiral galaxy which hosts them? This angle, ?, serves as a link between the innermost workings of the black hole plus fueling accretion disk and the larger galaxy, either as the memory of the activity-provoking ...

This site offers a powerpoint presentation describing astronomers current theory on the formation of our solar system. It contains slides describing star formation, protostars, the accretion of propoplanetary disks, the formation of gas giants and terrestrial planets, and the formation of bodies beyond the planets.

The collisional origin of the Moon is considered. The angular momentum of the Earth-Moon system is less than sufficient to spin the Earth to rotational instability. Nevertheless the mass of the body striking a tangential blow to the protoearth, imparting the angular momentum of the Earth-Moon system to the protoearth is examined.

The spectral evolution of accretion disks in X-ray binaries containing black holes is studied, based

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 22, 2011 ... Title: The Production of Jets From Magnetized Accretion Disks: Simulation of the Blandford-Payne Mechanism. Authors: Meier, D. ...

Jan 22, 2011 ... Title: The Production of Jets From Magnetic Accretion Disks: Simulation of the Blandford-Payne Mechanism. Authors: Meier, David L. ...

of a collimated jet ejected from the center of the accretion disk. The jet velocity is a strong function of the strength of the initial magnetic field: ...

The standard model for accretion disks (e.g., Pringle, 1981; Lin and Papaloizou, 1985) parameterizes

Feb 23, 2004 ... "Accretion disks are known to flow around many objects in the universe ... Under normal conditions, accretion disks appear far too minute to ...

Jan 31, 2005 ... KERRBB is a multi-temperature blackbody model for a thin, steady state, general relativistic accretion disk around a Kerr black hole. ...

The thesis consists of an introduction and summary, and five research papers. The introduction and summary provides the background in accretion disk physics and magnetohydrodynamics. The research papers describe numerical studies of magnetohydrodynamical ...

First � Previous � Next � Last � Index � Home � Text. Long-term Periodicities and Accretion Disks. Slide 4 of 22.

Jan 22, 2010 ... Many astrophysical objects, including neutron stars and accretion disks, are powered by a combination of very strong magnetic fields and ...

... Title : Evidence for Residual Material in Accretion Disk Gaps: CO Fundamental Emission from the T Tauri Spectroscopic Binary DQ Tauri. ...

Jun 11, 2010 ... Relativistic Illumination Law from Accretion Disks ... Relativistic Iron Fluorescent Line from Accretion Disks ...

Quasar Jets and Accretion Disks. Questions: " Does the most compact optical emission from an AGN come from an accretion disk or from a relativistic jet? ...

Binary Black Holes, Accretion Disks and Relativistic. Jets: Photocenters of Nearby AGN and Quasars. Principal Investigator: Ann E. Wehrle (Interferometry ...

Accretion Disk Coronae were first suggested to explain the incomplete eclipses and shallow profiles observed from some Low Mass X-ray Binaries (White and ...

Sep 4, 1998 ... In the case of a HMXB with a large ( $\\mathrel{\\hbox{\\rlap{\\hbox{\\lower4pt\\ ) magnetic field the accretion disk cannot extend all the way down to ...