We have studied the long-term variability of LMC X-3 in optical light curves spanning 6yr, in order to search for optical signatures which could confirm or refute the suggestion that the `modulation' is the result of accretion-rate variability rather than accretion-disc precession. We find that there is no stable period in the optical ...

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 superhump peaks. The elliptical ...

We numerically study the long-term evolution of the accretion disc around the neutron star in a coplanar Be/X-ray binary with a short period and a moderate eccentricity. From three-dimensional smoothed particle hydrodynamics simulations, we find that the disc evolves through three distinct phases, each characterized by different mass-accretion patterns. In ...

We study gas accretion onto intermediate mass black holes regulated by radiation feedback. We utilize the hydrodynamical code ZEUS-MP with the addition of a ray-tracing module. Our 1D and 2D simulations provide insight into how heating by X-ray and UV radiation influences the gas accretion rate. This allows us to ...

Observations of T Tauri stars and young brown dwarfs suggest that the accretion rates of their disks

Young stars can produce X-rays by different mechanisms: Coronal activity, accretion shocks and shocks in outflows. We propose to observe two targets within one field-of-view (FOV): SU Aur is accreting mass from a disk and shows violent coronal activity. We will study the time evolution of stellar flares on time scales from seconds to minutes using the high ...

X-ray timing of the accretion-powered pulsations during the 2003 outburst of the accreting millisecond pulsar XTE J1814-338 has revealed variation in the pulse time of arrival residuals. These can be interpreted in several ways, including spin-down and wandering of the fuel impact point around the magnetic pole. In this Letter we show that the burst ...

formation of massive stars via accretion. A necessary condition for accre- ... constraints on the accretion rate necessary to produce high mass stars and ...

large radius with `low' a.m. (e.g. from interstellar medium) but still has far too much a.m. to accrete. Capture rate is an upper limit to the accretion ...

Bain's model for the calculation of ice accretion rates was compared with meteorological flight data. The Bain model for the determination of the ice accretion rate on cylindrical rods is extended to the calculation of the accretion shape and velocity in ...

Bain's model for the calculation of ice accretion rates was compared with meteorological flight data. The Bain model for the determination of the ice accretion rate on cylindrical rods was extended to the calculation of the accretion shape and velocity in...

On the basis of data from an energy-conserving three-dimensional general relativistic MHD simulation, we predict the statistical character of variability in the coronal luminosity from accreting black holes. When the inner boundary of the corona is defined to be the electron scattering photosphere, its location depends only on the mass accretion ...

... accretion rates and total accretion on structures are given, and extracts from US and Canadian codes for ice and wind loads on structures are ...

We investigate the spectral energy distribution (SED) in the super-critical disk accretion flows around the black holes, by solving the multi-frequency radiation transfer as well as the energy equations of radiation and gas. Here, special attention is paid on the photon-trapping effects, that is, photons diffuse towards not only the vertical direction but also radial ...

We present phase-resolved infrared and optical spectrophotometry of the intermediate polar EX Hya supplemented by archival ultraviolet data. The spin-modulated emission from the accretion funnel and the emission from the accretion disk or ring contain substantial optically thin components. The white dwarf dominates the unmodulated flux ...

Magnetospheric accretion is an important process for a wide range of astrophysical systems and may play a role in the formation of gas giant planets. Extending the formalism describing stellar magnetospheric accretion into the planetary regime, we demonstrate that magnetospheric processes may govern accretion onto young gas giants in ...

A model for the 0.3-1.2 Hz optical quasi-periodic oscillations (QPOs) observed in a number of AM Her-type binary systems has been developed. It is suggested that the observed optical modulation is the result of shock oscillations induced by nonsteady accretion flows. It is shown that time-dependent models of radiative shock waves in nonsteady ...

Axisymmetric magnetohydrodynamic MHD simulations of disk accreting magnetized stars at the propeller stage have shown some quasi-periodic oscillations QPOs of the inner radius of the disk of the accretion rate at the star -s surface of outflow of matter in form of jets and of the angular momentum fluxes flowing in or out of the star ...

... Pagination or Media Count : 15. ... note is to review and synthesize the available scientific literature concerning vertical accretion rates in Louisiana ...

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 ...

We report on the discovery of variable circular polarization in the SW Sex star LS Pegasi. The observed modulation has an amplitude of ~0.3 % and a period of 29.6 minutes, which we assume as the spin period of the magnetic white dwarf. We also detected periodic flaring in the blue wing of Hbeta, with a period of 33.5 minutes. The difference between both frequencies is just the ...

The ROSAT observations were part of an extensive multiwavelength campaign of the X-ray, pulsar system Her X-1/HZ Her conducted in 1993 August. The source was found in an anomalous low state detected only once before. Characteristics observed during anomalous low states include a substantial, unexpected drop in flux at X-ray energies, with no change in absorbing column density; an increase in the ...

A unified theory of active galactic nuclei, based on the physics of accretion flows around massive black holes, is described. The accretion modes are dependent on the ratio of accretion rate to the mass of the hole. The spectral characteristics and radiative efficiency for the ion tori, thin disks, and radiation ...

We have determined the helium abundance and isotopic composition of seafloor carbonate sediments from the flanks of the Ontong Java Plateau, western equatorial Pacific Ocean (ODP Site 806). These results provide a two million year record of the burial flux of extraterrestrial 3 He, which we believe is a proxy for the terrestrial accretion rate of ...

We present the first results of a global axisymmetric simulation of accretion on to rotating magnetized stars from a turbulent accretion disc, where the turbulence is driven by the magnetorotational instability (MRI). We observed that the angular momentum is transported outwards by the magnetic stress and accretion ...

We present the first results of a global axisymmetric simulation of accretion on to rotating magnetized stars from a turbulent accretion disc, where the turbulence is driven by the magnetorotational instability (MRI). We observed that the angular momentum is transported outwards by the magnetic stress and accretion ...

We consider time-dependent accretion onto magnetized white dwarfs. A detailed description of a numerical method of solution to the hydrodynamical equations is given. The postshock flow is cooled by optically thin bremsstrahlung and is thermally unstable. As a result the shock height undergoes periodic oscillations. We consider the properties of this oscillation as a function ...

The experimental study of snow accretion on overhead power transmission lines was carried out to obtain data on accretion rates using the artificial snow accretion test equipment and a high speed camera. We evaluated the accretion rate relative to temperature and wind ...

We find long-term evolution of the ? class from the study of X-ray timing and spectral analysis of the Galactic microquasar GRS 1915+105 during two outburst activities, observed by the proportional counter array (PCA) and the High Energy X-ray Timing Experiment on-board Rossi X-ray Timing Explorer. The class is characterized by unusual periodic-like variation in intensity. With the passage of ...

Gamma ray modulation in AGN by interaction with X�rays from an accretion disk hot spot W. Bednarek interactions with X�rays emitted by a hot spot in the inner part of the accretion disk. As the hot spot orbits originates in a relatively small hot spot rotating on the surface of the inner accretion disk. If the ...

Collimated relativistic outflows-also known as jets-are amongst the most energetic phenomena in the Universe. They are associated with supermassive black holes in distant active galactic nuclei, accreting stellar-mass black holes and neutron stars in binary systems and are believed to be responsible for gamma-ray bursts. The physics of these jets, however, remains something of ...

The present study of hypercritical accretion flows onto neutron stars considers steady-state, spherically symmetric flows whose accretion rate range is characterized by the carrying away of gravitational-accretion energy by neutrinos. The models used encompass pair production, radiation diffusion, and general ...

Aug 4, 2011 ... Propagating fluctuations in the mass accretion rate of a precessing flow as a power spectral model for black hole binaries ...

We consider the problem of the flow produced by the accretion of gas from a rotating cloud onto a point gravitational source. It is shown that, for a cloud initially in uniform rotation, the effect of accretion is to produce a Taylor column in the cloud parallel to the rotation axis. Only gas within the column is accreted; the gas ...

Series of photometric CCD observations of the asynchronous polar BY Cam in a low accretion state (R = 14m 16m) were made on the K-380 telescope at the Crimean Astrophysical Observatory (CrAO) over 100 hours in the course of 31 nights during 2004 2005. A period of P 1 = 0.137120�0.000002 days was found for the variations in the brightness, along with less significant periods ...

The report deals with the question of whether mass accretion on a star can cause pulsational instability by itself. The principal result is a formula for the effect of accretion on the growth (or decay) rate of a radial pulsation mode. Application of this...

Models were developed to simulate planet formation. Three major phases are characterized in the simulations: (1) planetesimal accretion rate, which dominates that of gas, rapidly increases owing to runaway accretion, then decreases as the planet's feeding...

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. Application is made to DQ Herculis.

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...

Spherically symmetric, steady state accretion of an ionized hydrogen plasma onto a neutron star is considered for accretion rates which exceed a critical rate at which the Eddington limiting luminosity is produced. The coupled hydrodynamic and frequency integrated, radiative transfer equations are solved for ...

Context. High resolution X-ray spectroscopy has revealed soft X-rays from high density plasma in classical T Tauri stars (CTTSs), probably arising from the accretion shock region. However, the mass accretion rates derived from the X-ray observations are consistently lower than those derived from UV/optical/NIR studies. Aims: We aim to ...

Mass accretion onto (proto-)stars at high accretion rates \\dot{M}_* > 10^{-4} M_{&sun;} yr^{-1} is expected in massive star formation. We study the evolution of massive protostars at such high rates by numerically solving the stellar structure equations. In this paper, we examine the evolution via disk ...

Abstract. The accretion process onto a magnetized isolated neutron star, which captures material from the interstellar medium, is discussed. The evolutionary track of such a star can be presented as a sequence of four states: ejector, supersonic propeller, subsonic propeller, andsteady accretor. Ishowthatsubsonic propeller ? accretor transition does not occur as long as the ...

The rate of accretion of the interstellar medium onto a star is discussed. It is shown that this is a complex, fractionated process. The relative abundances of heavy elements accreting onto the star are very different from the abundances in the ambient medium. These accretion rates are ...

The current status of the physics of accretion disks in close binary stars is reviewed, with an emphasis on the hydrodynamic overreflection instability, which is a factor leading to the accretion disk turbulence. The estimated turbulent viscosity coefficients are in good agreement with observations and explain the high angular momentum transfer ...

The mass accretion rate of transonic spherical accretion flow onto compact objects such as black holes is known as the Bondi accretion rate, which is determined only by the density and the temperature of gas at the outer boundary. A rotating accretion flow has angular ...

The hydrodynamics of axisymmetric accretion flow in stellar wind-fed X-ray sources is investigated, including momentum deposition by radiation, as well as radiative heating and cooling by Compton and bremsstrahlung processes. The results of two-dimensional numerical simulations for mass accretion rates ranging from 0.02 to 0.4 of the ...

The spectral evolution of accretion disks in X-ray binaries containing black holes is studied, based on the disk instability model. The thermal transition of the outer portions of the disk controls the mass flow rate into the inner portions of the disk, thus modulating the soft X-ray flux which is thought to arise from the inner disk. ...

In the accretion disk around a black hole or a neutron star, the radiative viscosity will much exceed the viscosity of the fully ionized gas. The Reynolds number, depending strongly on the accretion rate, will reach a minimum in the zone where the bulk of the energy is released. Thermal instability will set in, altering the local ...

The development of galaxy clusters is discussed basing on our Supermodel, that expresses in full the entropy-modulated, hydrostatic equilibrium of the intracluster plasma in the DM gravitational wells. We relate central entropy levels to energy injections by AGNs or deep mergers, and the outer entropy distribution to the accretion ...

The results of external counting after intravenous administration of Sr/ sup 85/ in 1O cases of vertebral fractures are shown. The possibilities and limitations of this method in calculating the local bone accretion rate in spine fractures are discussed. (auth)

Effects of a new triple-? reaction rate on the ignition of carbon-oxygen white dwarfs accreting helium in a binary systems have been investigated. The ignition points determine the properties of a thermonuclear explosion of a Type la supernova. We examine the cases of different accretion rates of helium and ...

... early review, Buddemeier and Kinzie (1976) concluded that coral growth rates and reef accretion were not directly linked, but others argue that lower coral growth rates impede reef accretion at high latitu...

The effects of a new triple-? reaction rate on the ignition of carbon-oxygen white dwarfs accreting helium in a binary system have been investigated. The ignition points determine the properties of a thermonuclear explosion of a Type Ia supernova. We examine the cases of different accretion rates of helium and ...

The rate at which planetesimals in a uniform surface density disk collide with, and are (assumed to be) accreted by, a massive protoplanet is calculated. The collision cross-section of a protoplanet is enhanced relative to its geometric cross-section due ...

We aim to monitor T Tauri star disk emission features and jet outflow morphologies to determine how these features vary with disk accretion rate, and how and when the outflow responds to major accretion events. Young stars are surrounded by circumstellar disks through which they accrete mass. Magneto-centrifugal ...

We introduce a prescription for the luminosity from accreting protostars into smoothed particle hydrodynamics simulation and apply the method to simulations of five primordial minihaloes generated from cosmological initial conditions. We find that accretion luminosity delays fragmentation within the haloes but does not prevent it. In haloes that slowly ...

The polarized radiation from accretion shocks with a three-dimensional structure are calculated for the first time. It is shown that, because of inhomogeneities along the flow lines, accretion columns with a uniform accretion rate across the column can also produce flat optical/IR spectra as has been noted ...

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 frequency is crossed by ...

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 rates, and we have ...

Accretion onto and nova events on the surface of a degenerate cold one-solar-mass iron white dwarf are investigated. It is found that, during accretion, hydrogen diffuses deeper into the core than its CNO catalysts, suggesting that the thermonuclear runaway occurs not at the innermost radius achieved by the hydrogen but farther out where the CNO abundance ...

accreting star. Roughly half the known X�ray novae contain BH candidates and the rest contain NSs. X of the accreting star. As discussed in the Introduction, the accretion rate in a typical X�ray nova spans a wide in which the compact accreting primary stars are too massive to be neutron ...

It is investigated whether Uranus models with higher values of the total planetary ice to rock ratio

... 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 ...

A numerical study of the time variation of the angular momentum and mass capture rates for a central

The necessary conditions for the production of strong thermonuclear runaways in the hibernation scenario are identified and explored. It is found that a reduction in the accretion rate by a factor of about 100, for a period longer than a few thousand years, is generally sufficient to ensure nova-type outbursts, even in the presence of rather high ...

Black holes grow by accreting matter from their surroundings. However, angular momentum provides an efficient natural barrier to accretion and so only the lowest angular momentum material will be available to feed the black holes. The standard subgrid model for black hole accretion in galaxy formation simulations - based on the ...

Earth Planets Space, 56, 67�79, 2004 The global accretion rate of extraterrestrial materials periods, noble gas, interplanetary dust particle. 1. Introduction The accretion rate of extraterrestrial of the extraterrestrial and terrestrial environments. The influx of interplanetary dust to the Earth at present has ...

We present a novel method to measure the accretion rate of radio emitting X-ray binaries (XRBs) and active galactic nuclei (AGN) independently of the X-ray luminosity. The radio emission of the jet is used as a tracer for the accretion rate and is normalized using sources of known accretion ...

A large body of recent work points towards feedback processes related to the active accretion of matter onto supermassive black holes in the centers of most massive galaxies as being one of the primary regulatory processes for pc to Mpc scales in the Universe. We seek to close the gap in our knowledge of the physics behind active galactic nuclei (AGN) feedback processes by ...

The Rossi X-ray Timing Explorer has observed a wide range of sources and is producing valuable science. Its broad-band sensitivity has been key in the observations of both compact, stellar, and nebular objects. RXTE is ideally suited for observing X-rays from both galactic and extragalactic black holes. The range of accretion rates, masses, and possibly ...

Star formation is such a complex process that accurate numerical tools are needed to quantitatively examine the mass distribution and accretion of fragments in collapsing, turbulent, magnetized gas clouds. To enable a numerical treatment of this regime, we implemented sink particles in the adaptive mesh refinement (AMR) hydrodynamics code FLASH. Sink particles are created in ...

Neutron stars in close binary star systems often accrete matter from their companion stars. Thermonuclear ignition of the accreted material in the atmosphere of the neutron star leads to a thermonuclear explosion which is observed as an X-ray burst occurring periodically between hours and days depending on the accretion ...

The hydrostatic evolution of a carbon-oxygen white dwarf (COWD) experiencing accretion of matter from its companion, a second COWD, is calculated for accretion rates ranging from 10 to the -8th to 10 to the -5th solar masses per year. It is shown that, for accretion rates less than (3.3 + or - ...

The hydrostatic evolution of a carbon-oxygen white dwarf (COWD) experiencing accretion of matter from its companion, a second COWD, is calculated for accretion rates ranging from 10 to the -8th to 10 to the -5th solar masses per year. It is shown that, for accretion rates less than (3.3 + or - ...

We present a new way of looking at the very long-term evolution of gamma-ray bursts (GRBs) in which the disk of material surrounding the putative black hole powering the GRB jet modulates the mass flow, and hence the efficacy of the process that extracts rotational energy from the black hole and inner accretion disk. The pre-Swift paradigm of achromatic, ...

We use fractional integrals to generalize the description of hydrodynamic accretion in fractal media. The fractional continuous medium model allows the generalization of the equations of balance of mass density and momentum density. These make it possible to consider the general case of spherical hydrodynamic accretion on to a gravitating mass embedded in ...

Highly nonstationary accretion onto a magnetized neutron star from a surrounding accretion disc is considered. Nonstationary accretion has been considered before in terms of droplets or rain or as a necessary consequence of instabilities in the accretion column flow. Here, the extreme of very large units is ...

A model for emission of the hard photons of gamma bursts is presented. The model assumes accretion at nearly the Eddington limited rate onto a neutron star without magnetic a field. Initially soft photons are heated as they are compressed between the accreting matter and the star. A large electric field due to relatively small charge ...

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 stellar light reprocessing and an ultraviolet excess from the ...

We review recent results from the X-ray timing of accreting millisecond pulsars in LMXBs. This is the first time a timing analysis is performed on accreting millisecond pulsars, and for the first time we can obtain information on the behavior of a very fast pulsar subject to accretion torques. We find both spin-up and spin-down ...

We use a suite of cosmological hydrodynamic simulations to systematically quantify the accretion rates of baryons into dark matter haloes and the resulting baryon mass fractions, as a function of halo mass, redshift and baryon type (including cold and hot gas). We find that the net baryonic accretion rates through ...

The discovery of orbitally-modulated, periodic X-ray pulsations from Cen ...... Ariel 5 discovered 103 s pulsations from A 0535+26 in 1975 (Rosenberg et al. ...

... index to significant articles, news items, and ... incorporates several new physical elements: (1 ... MOMENTS, RADIO SOURCES(ASTRONOMY), X RAY ...

We study the effect of radiative feedback on accretion onto intermediate-mass black holes (IMBHs) using the hydrodynamical code ZEUS-MP with a radiative transfer algorithm. In this paper, the first of a series, we assume accretion from a uniformly dense gas with zero angular momentum and extremely low metallicity. Our one-dimensional (1D) and 2D ...

The recent very long baseline interferometry (VLBI) observation of the Galactic center black hole candidate Sgr A* at 1.3 mm shows source structure on event-horizon scales. This detection enables a direct comparison of the emission region with models of the accretion flow onto the black hole. We present the first results from time-dependent radiative transfer of general ...

Mass accretion onto (proto-)stars at high accretion rates M-dot{sub *}> 10{sup -4} M{sub sun} yr{sup -1} is expected in massive star formation. We study the evolution of massive protostars at such high rates by numerically solving the stellar structure equations. In this paper, we examine the evolution via ...

The growth of a black hole by radiation accretion in the early Universe is analyzed in the particular case in which the inflow of radiation is purely radial. This is done by generalizing the Einstein-Strauss vacuole model to the case of a radiation-filled universe. It is shown that, under this circumstance, the black hole tends to grow at the same rate as ...

The transport of angular momentum in the outward direction is the fundamental requirement for accretion to proceed in an accretion disk. This objective can be achieved if the accretion flow is turbulent. Instabilities are one of the sources for the turbulence. We study a differentially rotating compressive flow in the presence of ...

We present accretion rates for selected samples of nova-like variables having IUE archival spectra and distances uniformly determined using an infrared method by Knigge. A comparison with accretion rates derived independently with a multiparametric optimization modeling approach by Puebla et al. is carried out. The ...

We present accretion rates for selected samples of nova-like variables having IUE archival spectra and distances uniformly determined using an infrared method by Knigge (2006). A comparison with accretion rates derived independently with a multi-parametric optimization modeling approach by Puebla et al.(2007) is ...

Formation of massive stars by accretion requires a high accretion rate of \\dot{M}_* > 10^{-4} M_{&sun;} yr^{-1} to overcome the radiation pressure barrier of the forming stars. Here, we study evolution of protostars accreting at such high rates by solving the structure of the central ...

... regional coastal slope, rate of relative sea-level rise, shoreline erosion and accretion rates, tide range and ... ...

We present X-shooter observations of two brown dwarf candidates. We focus on the determination of stellar parameters and their errors. The targets, an accreting class II and a non-accreting class III objects, are members of the ? Orionis star-forming region. We derive the spectroscopic spectral types from the VIS spectrum and the stellar parameters. We ...

We consider the effect of accretion of radiation in the early Universe on primordial black holes in Brans-Dicke theory. The rate of growth of a primordial black hole due to accretion of radiation in Brans-Dicke theory is considerably smaller than the rate of growth of the cosmological horizon, thus making available ...

The relativistic accretion rate of dark matter by a black hole is revisited. Under the assumption that the phase space density indicator, Q={rho}{sub {infinity}}/{sigma}{sub {infinity}}{sup 3}, remains constant during the inflow, the derived accretion rate can be higher up to 5 orders of magnitude than the ...

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 ...

During mass exchange in binary systems the star which is receiving mass increases its volume. This effect is estimated by evolutionary calculations for different (constant) accretion rates. It is shown the chance that the two stars do not come in contact ...

The author provides a review of observations in the optical, UV (HST), and EUV (EUVE and Chandra LETG) of the rapid periodic oscillations of nonmagnetic, disk-accreting, high mass-accretion rate cataclysmic variables (CVs), with particular emphasis on the...

Calculations of the velocity field in an accretion disk show that matter may flow in the disk not only toward but also away from the central object. The rates of flow are determined, and the geometry of hydrodynamic motions in nonstationary disks is discussed.

A model for emission of the hard photons of gamma bursts is presented. The model assumes accretion at nearly the Eddington limited rate onto a neutron star without a magnetic field. Initially soft photons are heated as they are compressed between the accr...

A model for emission of the hard photons of gamma bursts is presented. The model assumes accretion at nearly the Eddington limited rate onto a neutron star without magnetic a field. Initially soft photons are heated as they are compressed between the accr...

Approximately 100 years of historical shoreline changes on the coastal beaches of Southwestern Washington have been mapped, and the rates of erosion and/or accretion have been calculated. These data show that, in general, the Washington coastline has been...

We investigate the role of the accretion rate in determining the outcome of the accretion of hydrogen-rich material onto a 1.25 M/sub sun/ C/O white dwarf. It is found that there is an upper limit to the mass accretion rate that leads to a nova outburst. The upper limit is between 10/sup -8/ ...

The purpose of this grant is to study parametric instability. The simplest example of parametric instability is a harmonic oscillator with a periodic modulation of the spring constant. If the modulation frequency is close to twice the natural frequency of the oscillator, the amplitude of oscillation tends to grow exponentially. The growth ...

With the help of a very simple two-zone model we deomonstrate the possiblity of periodic thermal relaxation (limit cycle) oscillations in the helium burning envelope of accreting neutron stars. Physically reasonable model parameters can be chosen which yield agreement with the observed features of X-ray bursts. We suggest that this limit cycle is operative in neutron stars ...

Mergers of supermassive black hole binaries release peak power of up to approximately 10(57) erg s(-1) in gravitational waves (GWs). As the GWs propagate through ambient gas, they induce shear and a small fraction of their power is dissipated through viscosity. The dissipated heat appears as electromagnetic (EM) radiation, providing a prompt EM counterpart to the GW signal. For thin ...

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 the amount of mass that can be accreted ...

From observations collected with the ESPaDOnS spectropolarimeter, we report the discovery of magnetic fields at the surface of the mildly accreting classical T Tauri star (cTTS) V2129 Oph. Zeeman signatures are detected, both in photospheric lines and in the emission lines formed at the base of the accretion funnels linking the disc to the protostar, and ...

Steady-state models of accreting neutron stars and strange stars are presented, and their properties as a function of accretion rate are analyzed. The models have steady-state envelopes, with stationary hydrogen burning taken into account, the helium shell flashes artificially suppressed, and the crust with a large number of secondary ...

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 astrophysical objects and ...

The structure and stability of accretion disks composed of hydrogen-rich matter rotating about a central neutron star have been investigated for known sources of viscosity. Two general classes of solutions have been found. For one class the energy generated in the disk is provided by hydrogen burning, whereas for the other class the gravitational binding energy released by ...

A one-zone model is developed for analysis of properties of nuclear shell flashes on accreting degenerate dwarfs and neutron stars. The model provides a description of a steady-state nuclear burning and a linear stability analysis with a small number of algebraic equations. Time evolution of the accreted layer is described with two first order ordinary ...

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 ...

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 ...

Formation of massive stars through spherical accretion has been predicted to occur only in clouds which are nearly dust-free and can provide an extremely high accretion rate. It is shown that such severe restrictions are effectively removed with nonspherical accretion. By the effects of magnetic fields, rotation, ...

We present black hole masses and accretion rates for 182 Type 1 active galactic nuclei (AGNs) in COSMOS. We estimate masses using the scaling relations for the broad H {beta}, Mg II, and C IV emission lines in the redshift ranges 0.16 < z < 0.88, 1 < z < 2.4, and 2.7 < z < 4.9. We estimate the ...

We study the process of spinning up black holes by accretion from slim disks for a wide range of accretion rates. We show that for super-Eddington accretion rates and low values of the viscosity parameter ? ( ? 0.01) the limiting value of the dimensionless spin parameter a? can reach values ...

This paper studies the production of high-energy gamma radiation (E-gamma about 100 MeV) in the vicinity of a black hole through the collisions of accreting protons on the stable orbits. A spherical accretion with a small rate is considered as a fully computable example. If the accretion rate ...

Vertical accretion rates were determined for brackish marshes in an estuarine tributary on the Eastern Shore of Chesapeake Bay. These rates determined on the basis of the peak phase of early European settlement as recorded in pollen spectra of the marsh sediments range between 0. 18 to 0.74 cm yr?1 over approximately the last 194 years ...

New determinations of lateral crustal thickness variations at anomalous oceanic spreading centres such as Iceland have shown that the crust may be thinner at the ridge axis above the plume thickening towards the sides (Bjarnason and Schmeling, 2009). To understand this behaviour crustal accretion models have been carried out solving the conservation equations of mass, momentum ...

It is suggested that the pre-main-sequence object Z CMa is a luminous accretion disk, similar in many respects to the FU Orionis variables. Z CMa shows the broad, doubled optical absorption lines expected from a rapidly rotating accretion disk. The first overtone CO absorption detected in Z CMa is blue-shifted, suggesting line formation in a disk wind. ...

We review recent results from the X-ray timing of accreting millisecond pulsars in LMXBs. This is the first time a timing analysis is performed on accreting millisecond pulsars, and for the first time we can obtain information on the behavior of a very fast pulsar subject to accretion torques. We find both spin-up and spin-down ...

We review recent results from the X-ray timing of accreting millisecond pulsars in LMXBs. This is the first time a timing analysis is performed on accreting millisecond pulsars, and for the first time we can obtain information on the behavior of a very fast pulsar subject to accretion torques. We find both spin-up and spin-down ...

We present the photometric observations of the old nova V603 Aql with the RTT 150 Russian-Turkish telescope during eleven nights of 2001-2002. We show that the star at this time was in a state with positive superhumps and its photometric period of 0.144-0.145 day was longer than the orbital period. We found night-to-night variations in the mean brightness of the system that are consistent with ...

Current published results suggest that the maximum and the minimum kHz QPO frequencies are flux-dependent for individual sources when missionlong observations are plotted together, i.e., the maximum frequency decreases with increasing flux while the minimum frequency increases with increasing flux. A confirmation of the flux-dependences would 1) prove that the radiation force of the X-ray flux ...

We study the rate at which gas accretes on to galaxies and haloes and investigate whether the accreted gas was shocked to high temperatures before reaching a galaxy. For this purpose, we use a suite of large cosmological, hydrodynamical simulations from the OverWhelmingly Large Simulations project, which uses a modified version of the ...

The latest outburst of the recurrent nova RS Oph occurred in 2006 February. Photometric data presented here show evidence of the resumption of optical flickering, indicating re-establishment of accretion by day 241 of the outburst. Magnitude variations of up to 0.32mag in V band and 0.14mag in B band on time-scales of 600-7000s are detected. Over the two-week observational ...

The latest outburst of the recurrent nova RS Oph occurred in 2006 February. Photometric data presented here show evidence of the resumption of optical flickering, indicating re-establishment of accretion by day 241 of the outburst. Magnitude variations of up to 0.32 mag in the V-band and 0.14 mag in B on time-scales of 600-7000 s are detected. Over the two week ...

Approximately half the luminosity of a typical cataclysmic variable may emerge as an optically thick component peaking in the EUV. Observations of this component are important for understanding the energetics and accretion rates of CV's in general, as well as for understanding the physics of the accretion process. The nature ...

Slim accretion discs have a total luminosity of the order L/L(sub E) = m (proportional to) 1, where L(sub E) is the Eddington luminosity and m = M/M(sub c), where M(sub c) is a critical accretion rate, related to the Teddington one. The local stability pr...

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 the inner zone is shed, producing a corona ...

A new burst mode of MXB 1730-335, the rapid burster, as discovered by Hakucho in August 1979, is characterized by a train of long X-ray bursts whose behavior is dictated by the accretion rate. In this mode the burst luminosity reaches the Eddington limit, so that the X-ray pressure controls the accretion from a reservoir in the ...

... Accession Number : ADA207078. Title : Modulation-Rate Perception: Identification and Discrimination of Modulation Rate Using a Noise Carrier. ...

Elements heavier than hydrogen or helium that are present in the atmospheres of white dwarfs with effective temperatures lower than 25,000 K, are believed to be the result of accretion. By measuring the abundances of these elements and by assuming a steady-state accretion, we can derive the composition of the accreted matter and infer ...

We investigate further a model of the accreting millisecond X-ray pulsars we proposed earlier. In this model, the X-ray-emitting regions of these pulsars are near their spin axes but move. This is to be expected if the magnetic poles of these stars are close to their spin axes, so that accreting gas is channeled there. As the accretion ...

The cosmic star formation rate is observed to drop sharply after redshift z= 2. We use two large, cosmological, smoothed particle hydrodynamics simulations to investigate how this decline is related to the evolution of gas accretion and to outflows driven by active galactic nuclei (AGN). We find that the drop in the star formation rate ...

The cosmic star formation rate is observed to drop sharply after redshift z=2. We use a large, cosmological, smoothed particle hydrodynamics simulation to investigate how this decline is related to the evolution of gas accretion and to outflows driven by active galactic nuclei (AGN). We find that the drop in the star formation rate ...

Recently, Ida et al. made an N-body simulation of lunar accretion from a protolunar disk formed by a giant impact. One of their important conclusions is that the accretion time of the Moon is as short as one month. Such rapid accretion is a necessary consequence of the high surface density of a lunar mass disk ...

If an isolated black hole is massive enough and if it accretes matter at a fast enough rate, the outer parts of the accretion disk will become self-gravitating and may become unstable, disintegrating into fragments which could form separate stars. The fragmentation would produce around the black hole a ring of gas and stars which would ...

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 surfaces of constant entropy coincide to ...

The coagulation and transportation of grains in a turbulent accretion solar nebula has been numerically studied. Compared with the case of a laminar nebula, the turbulence enhances the growth rate. The grains diffuse radially through the nebula owing to turbulent diffusion. The accreted interstellar grains form the reservoir, from ...

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 solar masses fit observations of very large ...

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, star formation, supernova feedback, and BH ...

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 outburst, as the mass accretion ...

The intent of this paper is to point out that the accretion of a ghost condensate by black holes could be extremely efficient. We analyze steady-state spherically symmetric flows of the ghost fluid in the gravitational field of a Schwarzschild black hole and calculate the accretion rate. Unlike minimally coupled scalar field or ...

The intent of this letter is to point out that the accretion of a ghost condensate by black holes could be extremely efficient. We analyze steady-state spherically symmetric flows of the ghost fluid in the gravitational field of a Schwarzschild black hole and calculate the accretion rate. Unlike minimally coupled scalar field or ...

A dark-matter-only Horizon Project simulation is used to investigate the environment and redshift dependences of accretion on to both haloes and subhaloes. These objects grow in the simulation via mergers and via accretion of diffuse non-halo material, and we measure the combined signal from these two modes of accretion. It is found ...

We report the discovery of periodic variations of the 6.7GHz methanol maser flux in source G22.356+0.066. The data were taken with the Torun 32m telescope as a part of monitoring programme of a large sample of high mass star forming regions. The methanol outbursts have a periodicity of ~178 days and a duration at half maximum of ~25 days. Time shifts between the flux curves from different features ...

We implemented sink particles in the Adaptive Mesh Refinement (AMR) code FLASH to model the gravitational collapse and accretion in turbulent molecular clouds and cores. Sink particles are frequently used to measure properties of star formation in numerical simulations, such as the star formation rate and efficiency, and the mass distribution of stars. We ...

From observations collected with the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope (CFHT) and with the NARVAL spectropolarimeter at the T�lescope Bernard Lyot (TBL), we report the detection of Zeeman signatures on the prototypical classical T Tauri star AA Tau, both in photospheric lines and accretion-powered emission lines. Using time series of ...

RS Ophiuchi is a recurrent nova system that experiences outbursts every ~20 years, implying accretion at a high rate onto a massive white dwarf. However, previous X-ray observations of the system in quiescence have detected only faint emission that is difficult to reconcile with the high accretion rate (>2 � ...

We study energy dependencies of quasi-periodic oscillations (QPOs) from a number of black hole X-ray binaries. The selected sources were observed by RXTE at time periods close to state transitions and showed QPOs in the 1-10 Hz range. We have constructed QPO rms energy spectra, which provide information about underlying physical process leading to QPO generation. These spectra show an interesting ...

Tracking loops and modulation formats for DSN telemetry rates in the tens of ... subcarriers should not be used and suppressed carrier modulation should be ...

... of oil spill and clean-up on dominant US Gulf Coast marsh ... sediment deposition in subsiding coastal salt marshes, Terrebonne Bay, Louisiana: The ...

We describe the systematics of the DHR's temporal behavior, by exploring its ... In addition, we note that for large accretion rates the DHR has periodic ...

... Abstract : Prairie potholes are small, shallow, ponded depressions of glacial origin (Sloan 1972) comprising approximately 1 million of wetlands in ...

For many years it has been recognized that ice accretion processes depend on flow effects over the model, on droplet trajectories, on the rate of water ...

Phenomenological fits to the hard X-ray spectrum of AM Herculis left unexplained the high equivalent

Dec 31, 2008 ... The line widths are influenced by rotation of the star via the Doppler effect. Since the spin rates of many of these accreting neutron stars ...

The hot thermal accretion disks of the 1970s are studied and consideration is given to the effects of electron-positron pairs, which were originally neglected. It is found that disks cooled by internally produced photons have a critical accretion rate above which equilibrium is not possible in a radial annulus centered around r = 10 ...

... at slow-spreading centers by comparing axial crustal structure with that on conjugate flanks of the slow-spreading Mid-Atlantic Ridge (MAR) (full rate ...

... for Altitudes up to 10,000 Feet ... The average ice accretion rate appears to be inde- pendent of altitude between 2000 and 10,000 feet AGI,. 17?. ...

We propose a simplified model of outflow/jet driven by the Blandford-Payne (BP) process from advection-dominated accretion flows (ADAF) and derive the expressions of the BP power and disk luminosity based on the conservation laws of mass, angular momentum and energy. We fit the 2-10 keV luminosity and kinetic power of 15 active galactic nucleus (AGNs) of sub-Eddington ...

We show how accretion rate governs the physical properties of broad-line, narrow-line, and lineless active galactic nuclei (AGNs). We avoid the systematic errors plaguing previous studies of AGN accretion rate by using accurate accretion luminosities from well-sampled multiwavelength SEDs from ...

This module examines Infant Mortality Rates (IMR) and some of the factors related to infant mortality.

Hydration-rind dating techniques have been employed to determine the relative chronologies of the Waho Shelf Sediments (hydration rate used is 2.91 micron/1000 yrs). These deposits are volcanic in origin. Rates of manganese accretion were determined to be...

Pycnonuclear fusion processes take place at extreme density conditions of ?>10^10 g/cm^3, anticipated for the core of white dwarfs or the crust of neutron stars. A formalism was developed for predicting pycnonuclear reaction rates for neutron rich nuclei in the carbon to magnesium range. The reaction rates have been used to simulate pycnonuclear burning ...

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 magnetic field configuration. The effect of the magnetic field on ...

The influence of gas accretion in determining the shape of the initial stellar mass function is investigated. Stars are assumed to form from protostellar condensations which, having fragmented out of a gas cloud, begin to accrete material from their environment. Within protocluster clouds this accretion phase is assumed to continue ...

Kilohertz QPOs have now been detected in more than twenty accreting neutron stars in low-mass binary systems. Two such QPOs are usually detected in each star. The two detected in the 401 Hz accretion-powered X-ray pulsar SAX J1808.4-3658 have a frequency separation consistent with half its 401 Hz stellar spin frequency ? spin. Two kilohertz QPOs have also ...

The growth of galaxies is driven by two processes: mergers with other galaxies and smooth accretion of intergalactic gas. The relative share of this two processes depends on the environment (rich cluster or field), and determines the morphological evolution of the galaxy. In this work we focus on the properties of accretion onto galaxies. Through numerical ...

... THE RATING OF DELTA SIGMA MODULATING SYSTEMS, WITH CONSTANT ERRORS, BURST ERRORS AND TANDEM LINKS, IN A FREE ...

... Accession Number : AD0869977. Title : Performance Rating for Analogue and Digital Modulation Methods. Descriptive Note : Technical rept.,. ...

Analog message transmission by optimum angle modulation system and rate distortion function deriving

Herbig Ae/Be stars(HAeBes) are young stellar objects of spectral class F2 through B0, with the central star often surrounded by a circumstellar disk of gas and dust. They are the higher mass analogs to T Tauri stars. The interaction between the star and the disk is not well understood, nor is the disk structure. The central star will often accrete mass from the disk, and the ...

We study the mass flow rate through a disc resulting from a varying mass-supply rate. Variable mass-supply rate occurs, for example, during disc state transitions, and in interacting eccentric binaries. It is, however, damped by the viscosity of the disc. Here, we calculate this damping in detail. We derive an analytical description of ...

We present accretion rates for a large number of solar-type stars in the Cep OB2 region, based on U-band observations. Our study comprises 95 members of the {approx}4 Myr old cluster Tr 37 (including 20 'transition' objects (TOs)), as well as the only classical T Tauri star (CTTS) in the {approx}12 Myr old cluster NGC 7160. The stars show ...

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 particular, we investigate the ...

The protostellar mass function (PMF) is the present-day mass function of the protostars in a region of star formation. It is determined by the initial mass function weighted by the accretion time. The PMF thus depends on the accretion history of protostars and in principle provides a powerful tool for observationally distinguishing different protostellar ...

Analysis of thick, radiation pressure dominated (super-Eddington) accretion disks has proven to be difficult. Purely analytical methods have not yet been adequate to determine the structure of the disk and associated jet. The work presented here circumvents the analytical problems by using a numerical method; the results are based on a series of numerical simulations of disk ...

In massive star formation (gsim 40 M sun) by core accretion, the direct stellar radiation pressure acting on the dust particles exceeds the gravitational force and interferes with mass accretion at the dust sublimation front, the first absorption site. Ram pressure generated by high accretion rates of 10-3 M sun ...

We examine the nucleosynthesis products that are produced in the outflow from rapidly accreting disks. We find that the type of element synthesis varies dramatically with the degree of neutrino trapping in the disk and therefore the accretion rate of the disk. Disks with relatively high accretion ...

We examine the nucleosynthesis products that are produced in the outflow from rapidly accreting disks. We find that the type of element synthesis varies dramatically with the degree of neutrino trapping in the disk and therefore the accretion rate of the disk. Disks with relatively high accretion ...

Recent evidence has shown that the NASA/Lewis Ice Accretion Model, LEWICE, does not predict accurate ice shapes for certain glaze ice conditions. This paper will present the methodology used to make a first attempt at improving the ice accretion prediction in these regimes. Importance is given to the correlations for heat transfer coefficient and ice ...

Extended radio galaxies (RGs) have traditionally been classified into Fanaroff-Riley (FR) I/II types, based on the ratio r of the separation between the brightest regions on either sides of the host galaxy and the total size of the radio source. We examine the distribution of various physical properties as a function of r of 1040 extended RGs at z<0.3. About 2/3 of the RGs are lobe dominated ...

Recent (6-12 months) marsh sediment accretion and accumulation rates were measured with feldspar marker horizons in the vicinity of natural waterways and man-made canals with spoil banks in the rapidly subsiding environment of coastal Louisiana. Annual accretion rates in a Spartina alterniflora salt marsh in the ...

This paper examines the deceleration of accreting material in the strongly magnetized plasma atmosphere of an X-ray pulsar, for accretion rates less than 0.1 times the Eddington flux. The previous work on accretion, flow deceleration is extended to nonisothermal atmospheres. A rough model of radiative processes in ...

Superbursts are rare thermonuclear flashes from accreting neutron stars. One condition for ignition is a sufficiently high temperature of the neutron star crust, which is heated during accretion. Most superbursts take place when the neutron star was accreting continuously above 10% of the Eddington limit for more then 10 years. In 2005 ...

Neutron viscosity is investigated as a possible mechanism for the dissipation of kinetic energy into luminosity in the innermost parts of accretion disks around compact objects. Simplified models are presented of the self-consistent, steady-state accretion flows in which viscosity is provided by neutron collisions with accreting ions. ...

Star-forming disc galaxies such as the Milky Way need to accrete >~1 Msolar of gas each year to sustain their star formation. This gas accretion is likely to come from the cooling of the hot corona, however it is still not clear how this process can take place. We present simulations supporting the idea that this cooling and the subsequent ...

We review recent results of our group on X-ray timing of accreting millisecond pulsars in LMXBs. The good quality of the RXTE data allow us to obtain information on the behavior of a very fast pulsar subject to accretion torques. We find both spin-up and spin-down behaviors, from which, using available models for the accretion torques, ...

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 ...

Neutrinos from core collapse supernovae can be emitted from a rapidly accreting disk surrounding a black hole, instead of the canonical protoneutron star. For galactic events, detector count rates are considerable and in fact can be in the thousands for Super-Kamiokande. The rate of occurrence of these accreting ...

We construct Super-Eddington Slim discs models around both stellar and supermassive black holes by allowing the formation of a porous layer with a reduced effective opacity. Unlike the standard scenario in which the discs become thick, super-Eddington discs remain slim. In addition, they accelerate a significant wind with a 'thick disc' geometry. We show that above about 1.5 times the standard ...

Vertical accretion and sediment accumulation rates were determined from the distribution of /sup 137/Cs in cores collected from fresh water, intermediate, brackish, and salt marshes in the Barataria Basin, Louisiana. Vertical accretion rates vary from about 1.3 cm.yr/sup -1/ in levee areas to 0.7 in backmarshes. ...

By means of the accretion induced magnetic field evolution model of neutron star in low mass X-ray binary, the star spin frequency evolution has been studied, and we find that the star spin frequency is almost independent of the mass accretion rate, initial magnetic field and initial period, when the star magnetosphere evolves less ...

We study proton-rich nucleosynthesis in windlike outflows from {gamma}-ray bursts accretion disks with the aim of determining if such outflows are a site of the nup process. The efficacy of this nup process depends on thermodynamic and hydrodynamic factors. We discuss the importance of the entropy of the material, the outflow rate, the initial ejection ...

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 self-consistent disk model. It is shown ...

Bounds are placed on the growth rates of dynamical instability in shear flows in accretion discs and tori. Ft is shown that the critical layer lies in the flow even when the boundaries are free for flows in accretion discs, cylinders and isentropic, constant angular momentum tori (for which the relativistic effects are also ...