Accretion Disks around Stars and the Process of Planet Formation National Radio Astronomy. This process is regulated by ejecting gas in "jet-like" outflows. II. Planets form later from the remnants of the disk. Planets may only form when conditions around the star are "just right." III. Planets have been

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 ...

The supercritical wind theory of Papers II and III is applied to winds driven by accretion phenomena. An expression for the total luminosity LT is derived in terms of the accretion rate dotMT and injection radius r?. When applied specifically to accretion disks, the theory becomes the supercritical counterpart to standard subcritical ...

X-ray illuminated accretion disks. We show how the most relevant atomic features in the spectra depend on the assumed properties of the irradiated gas. ...

KQ Mon is classified as a nova-like variable with an uncertain orbital period of 0.128 d. Optical spectra (Zwitter, T. & Munari, U.1994, A&AS, 107, 503) reveal no emission lines but strong Balmer absorption features. High speed flickering has been observed indicative of accretion. IUE spectra reveal deep absorption lines due to C III, C II, Si III, Si IV, C IV, He ...

Radiative winds and jets from luminous accretion disks/tori are reviewed. Among various models of astrophysical jets, plasma outflows emanating from accretion disks/tori and accelerated by the radiation pressure is the most promising one. Here explained are the roles of radiation pressure force ...

We 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, ...

We investigate the launching and stability of extragalactic jets through magnetohydrodynamic simulations of jet evolution. In these simulations, a small scale equilibrium magnetic corona is twisted by a differentially rotating accretion disk. Two-dimensional calculations show the formation of a collimated outflow. This ...

We consider hot accretion disk outflows from black hole-neutron star mergers in the context of the nucleosynthesis they produce. We begin with a three-dimensional numerical model of a black hole-neutron star merger and calculate the neutrino and antineutrino fluxes emitted from the resulting accretion ...

To better understand the physical properties of accretion disks in high-mass star formation, we present a study of a dozen high-mass accretion disk candidates observed at high spatial resolution with the Australia Telescope Compact Array (ATCA) in the high-excitation (4,4) and (5,5) lines of NH{sub 3}. All of our ...

Young stellar objects radiate large numbers of keV-photons that are able to penetrate significant columns of gas and thus ionize and heat circumstellar material, including the accretion disks and outflows of very young stars. The unshielded ionization rates are high. At a distance of 1 AU from a young stellar object with a moderately ...

To study the outflows from accretion disks, we solve the set of hydrodynamic equations for accretion disks in spherical coordinates (r?phi) to obtain the explicit structure along the ?-direction. Using self-similar assumptions in the radial direction, we change the equations to a set of ...

Steady state models of magnetized accretion disks that power centrifugally driven outflows are presented. Self-similar solutions for Keplerian disks that are dominated by ambipolar diffusion are constructed and the analogous solutions for resistive disks are presented. In each case, it is shown that one can obtain steady state field ...

The understanding of accretion processes and in particular of massive accretion disks is one of the most important topics in high-mass star formation. Based on our successful ATCA disk studies of high mass star formation, we now propose to investigate higher J inversion transitions of NH3 at high angular resolution (~1'') to complement our NH3 (4,4) and ...

Various papers on accretion disks (ADs) and magnetic fields in astrophysics are presented. Individual topics addressed include: relevance of magnetic fields to stars and ADs, nonlinear breakup of the sun's toroidal field, accretion and particle acceleration by spiral shock wages, MHD flows in ADs and jets, slender flux tubes in ADs, magnetic fields in the ...

The first VLBI images of H2O maser emission in the Circinus Galaxy AGN show both an accretion disk and outflow 0.1 to 1 pc from the central engine. The maser traces a warped, edge-on accretion disk between radii of about 0.1 and 0.4 pc that is bound by a 1.3�106 Msolar central mass. The ...

The properties of external accretion disks (disks with a central source of angular momentum) are explored both analytically and numerically. An illustrative example of the effect of a disk of material around a binary star on the stellar separation is considered. A Greens-function-type solution is considered in which an initial ring of matter is put in ...

The basic characteristics of line-driven winds from UV accretion disks were investigated analytically and numerically. Stellar winds have been compared with the outflow from a disk surrounding a supermassive black hole. It is found that in the approximation of vertically streaming radiation close to the disk photosphere, the existence ...

The authors have investigated both analytically and numerically the basic characteristics of line-driven winds from UV accretion disks. Stellar winds have been compared with the outflow from a disk surrounding a supermassive black hole. The authors find that in the approximation of vertically streaming radiation close to the disk ...

Recent studies of different X-ray binaries (XRBs) have shown a clear correlation between the radio and X-ray emission. We present evidence of a close relationship found between the radio and X-ray emission at different epochs for GRS 1915+105, using observations from the Ryle Telescope and Rossi X-ray Timing Explorer satellite. The strongest correlation was found during the hard state (also known ...

Rapidly-accreting black holes and young, rapidly-rotating magnetars ('proto-magnetars') are two possible central engines for gamma-ray bursts (GRBs). The midplane of neutrino-cooled accretion disks and the surface of proto-magnetars are both neutron-rich, with a neutron-to-proton ratio n|p>>1. If a large neutron fraction is ...

Observational evidence suggests long-duration, collapsar-type gamma-ray bursts (GRBs) may have been more common in the early universe. These events are thought to be powered by accretion disks around black holes (AD-BHs). While GRBs require AD-BHs, not all AD-BHs will power bursts and therefore their formation will be more common than GRBs themselves. ...

We report the completion of a survey of radio-loud active galactic nuclei (AGNs) begun in an earlier paper with the main goal of finding and studying broad, double-peaked Balmer lines. We present H? spectra of 13 more broad-lined objects, including three with double-peaked H? profiles. The final sample includes 106 radio-loud AGNs. In our final census 20% of objects have H? lines with double peaks ...

Context. Direct observations of accretion disks around high-mass young stellar objects would help to discriminate between different models of formation of massive stars. However, given the complexity of massive star forming regions, such studies are still limited in number. Additionally, there is still no general consensus on the molecular tracers to be ...

We calculate the structure of an effectively optically thin and geometrically thin accretion disk in

A general relativistic model for the formation and acceleration of lowmass-loaded jets from systems containing accreting black holes is presented. The model is based on previous numerical results and theoretical studies in the Newtonian regime, but modified to include the effects of space-time curvature in the vicinity of the event horizon of a spinning black hole. It is argued that the boundary ...

Time-resolved spectroscopy covering half an orbit and one eclipse during an outburst of the dwarf nova IP Peg are presented and compared with quiescent data. The outburst spectra show strong Balmer and He II 4686 A emission lines that are atypical of outbursting dwarf novae. Double-peaked velocity profiles and rotational distortions during eclipse show that the lines arise ...

The spectrum of Gamma rays from the decay of Pi dey is sensitive to the ... X- Ray Reflected Spectra from Accretion Disk Models. II. Diagnostic Tools for X-Ray ... This study demonstrates the ability of the model to generate recurrent 3D ...

We present spectra for a sample of 14 FUors and two T Tauri stars observed with Spitzer or ISO. Based on the appearance of the 10 ?m silicate feature, we define two categories of FUors. Objects showing the silicate feature in absorption (Category 1) are still embedded in a circumstellar envelope. The shape of the silicate bands is in good agreement with typical dust compositions of the ISM. Only ...

We develop a numerical scheme and code for estimating the energy and momentum transfer via neutrino pair annihilation, bearing in mind the application to the collapsar models of gamma-ray bursts (GRBs). To calculate the neutrino flux illuminated from the accretion disk, we perform a ray-tracing calculation in the framework of special relativity. Using ...

Classical T Tauri stars undergo magnetospheric accretion, power outflows, and possess the physical and chemical conditions in their disks to give rise to planet formation. Existing high resolution FUV spectra verify that this spectral region offers unique diagnostics of these processes, which have the potential to significantly advance our understanding of the interaction of a ...

Aims: We present near-infrared spectroscopy of the forbidden emission line (FEL) and molecular hydrogen emission line (MHEL) regions at the bases of Herbig-Haro (HH) jets from seven embedded protostars: SVS 13 (the HH 7-11 progenitor), HH 26-IRS, HH 34-IRS, HH 72-IRS, HH 83-IRS, HH 300-IRS (IRAS 04239+2436) and HH 999-IRS (IRAS 06047-1117) Methods: The integral field spectrograph, SINFONI, on the ...

Optical data from Osterbrock (1977, 1982), together with data from the literature, including IUE observations, have been used to describe the physical conditions in the nucleus of the Seyfert 1 galaxy NGC 7469. The ultraviolet excess emission over a power-law component cannot be explained by Balmer continuum and Fe II emission alone, suggesting also emission from a blackbody ...

The results of a grid of non-Local thermodynamic equilibrium (LTE) accretion disk models are presented. These models were computed by a program which calculates the radiative transfer at positions in an accretion disk characterized by a local temperature and midplane density. The models cover a range of ...

The results of a grid of non-Local thermodynamic equilibrium (LTE) accretion disk models are presented. These models were computed by a program which calculates the radiative transfer at positions in an accretion disk characterized by a local temperature and midplane density. The models cover a range of ...

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 rates such as M?=10 Msolar s-1 can ...

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 rates such as {dot M} = 10 M ...

We review the results from multi-dimensional, time-dependent simulations of gas dynamics in AGN. We will focus on two types of outflows powered by radiation emitted from the AGN central engine: (i) outflows driven from the innermost part of an accretion disk and (2) outflows driven from a ...

Cygnus X-1 was observed in the high state at the conjunction orbital phase (0) with the Chandra High Energy Transmission Grating (HETG). Strong and asymmetric absorption lines of cighly ionized species were detected, such as Fe xxv, Fe XXIV, Fe XXIII, Si ...

The outbursts of dwarf novae are suggested as being due to the liberation of energy in the accretion disk surrounding the white dwarf component following unstable mass outflow by the red companion. The periodicities observed in dwarf novae near maximum light are shown to be consistent with periodic eclipses of temperature ...

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

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 ...

The formation of low mass stars takes place with the assistance of an accretion disk that transports gas and dust from the envelope of the system to the star, and a jet that removes angular momentum and allows accretion to proceed. In the radio, these ionized jets can be studied very close to the star via the thermal (free-free) emission they produce and ...

Ultraviolet resonance lines appear to be powerful tools for diagnostics and study of the outflows from cataclysmic variable stars. The origin of these winds and their geometry are not known at present. In order to compare observed lines from the IUE database with synthetic line profiles from accretion disk winds, we have developed a ...

Over the last number of years, spectroscopic studies have strongly supported the assertion that protostellar accretion and outflow activity persist to the lowest masses. Indeed, previous to this work, the existence of three brown dwarf (BD) outflows had been confirmed by us. In this paper, we present the results of our latest investigation of BD ...

Using data from the Rossi X-Ray Timing Explorer, we investigate the spectral evolution along a "Z" track and a "?" track on the hardness-intensity diagrams of the first transient Z source XTE J1701�462. The spectral analyses suggest that the inner disk radius depends on the mass accretion rate, in agreement with the model prediction, R_in \\propto {\\dot{M}_disk}^{2/7}, for a ...

We present direct evidence, from adaptive-optics near-infrared imaging, of the jets in the Galactic microquasar SS433 interacting with enhanced wind-outflow off the accretion disk that surrounds the black hole in this system. Radiant quantities of gas are transported significant distances away from the black hole approximately ...

Jets and outflows are observed around a wide variety of accreting objects and seem to be a near-ubiquitous feature of accretion disks. Large-scale magnetic fields are often thought necessary for jet formation, but a longstanding puzzle is that the turbulence which is responsible for inward disk accretion should be even more efficient ...

We present new far-ultraviolet observations of the young M8 brown dwarf 2MASS J12073346-3932539, which is surrounded by an accretion disk. The data were obtained using the Hubble Space Telescope-Cosmic Origins Spectrograph. Moderate-resolution spectra (R? 17,000-18,000) obtained in the 1150-1750 � and 2770-2830 � bandpasses reveal H2 emission excited ...

We present new far-ultraviolet observations of the young M8 brown dwarf 2MASS J12073346-3932539, which is surrounded by an accretion disk. The data were obtained using the Hubble Space Telescope-Cosmic Origins Spectrograph. Moderate-resolution spectra (R{approx} 17,000-18,000) obtained in the 1150-1750 A and 2770-2830 A bandpasses reveal H{sub 2} emission ...

Hydromagnetic disk winds have great potential as a general theory for the production and collimation of astrophysical jets in both protostellar and black hole environments. We first review the analytic stationary theory of these outflows as well as recent numerical simulations of MHD disk winds. We then focus on simulations that we have done on winds from magnetized disks ...

Gamma-ray bursts, while rare, may be important contributors to galactic nucleosynthesis. Here we consider the types of nucleosynthesis that can occur as material is ejected from a gamma-ray burst accretion disk. We calculate the composition of material within the disk as it dissociates into protons and neutrons and then use a parameterized ...

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

We present 2.5-dimensional time-dependent simulations of the nonlinear evolution of nonrelativistic outflows from Keplerian accretion disks orbiting low-mass protostars or black holes accreting at sub-Eddington rates. The gas is ejected from the surface of the disk (which is a fixed platform in these simulations) into a cold corona in ...

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 ...

We present observations of the embedded massive young stellar object (YSO) candidate 08576nr292, obtained with X-shooter and SINFONI on the ESO Very Large Telescope (VLT). The flux-calibrated, medium-resolution X-shooter spectrum (300-2500 nm) includes over 300 emission lines, but no (photospheric) absorption lines, and is consistent with a reddened disk spectrum. Among the emission lines are ...

Aims:We investigate the dense gas, the outflows, and the continuum emission from the massive twin cores NGC 6334I and I(N) at high spatial resolution. Methods: We imaged the region with the Australia Telescope Compact Array (ATCA) at 3.4 mm wavelength in continuum, as well as CH3CN(5_K{-}4_K) and HCN(1-0) spectral line emission. Results: While the continuum emission in NGC ...

Cold steady-state disk wind theory from near Keplerian accretion disks requires a large scale magnetic field at near equipartition strength. However the minimum magnetization has never been tested. We investigate the time evolution of an accretion disk threaded by a weak vertical magnetic field. The strength of the ...

Aims: Cold steady-state disk wind theory from near Keplerian accretion disks requires a large scale magnetic field at near equipartition strength. However the minimum magnetization has never been tested with time dependent simulations. We investigate the time evolution of a Shakura-Sunyaev accretion disk threaded ...

In this Letter we investigate the properties of advection-dominated accretion flows (ADAFs) fed by the evaporation of a Shakura-Sunyaev accretion disk (SSD). In our picture, the ADAF fills the central cavity evacuated by the SSD and extends beyond the transition radius into a coronal region. We find that, because of global angular momentum conservation, a ...

Stars with masses in the range 1-8 solar masses (M(\\circ)) live ordinary lives for approximately 10(9)-10(10) years, but die extraordinary deaths. First, during their death throes as asymptotic giant branch (AGB) stars they eject, over 10(4)-10(5) years, half or more of their mass in slowly expanding, spherical winds, and then, in a short (a few 100-1,000 years) and poorly understood phase, they ...

Models of accretion disks around a star in a binary system predict that the disk will have a retrograde precession with a period a factor of ~10 times the orbital period. If the star+disk system ejects a bipolar outflow, this outflow will be subject to the effects of both the orbital motion and the precession. We ...

Models of accretion disks around a star in a binary system predict that the disk will have a retrograde precession with a period a factor of approx10 times the orbital period. If the star+disk system ejects a bipolar outflow, this outflow will be subject to the effects of both the orbital motion and the precession. ...

We have used the VLA A-configuration at lambda 20 cm to obtain new high-resolution (1\\farcs5) flux and polarization images of the large-scale, twisted jets in NGC 4258, a galaxy of particular interest because its nucleus houses the best observed case of an accretion disk around a supermassive black hole. We have also analyzed recently archived ...

Context. Our knowledge of circumstellar disks has traditionally been based on studies of dust. However, gas dominates the disk mass and its study is key to our understanding of accretion, outflows, and ultimately planet formation. The Spitzer Space Telescope provides access to gas emission lines in the mid-infrared, providing crucial new diagnostics of the physical conditions ...

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 of disks in cataclysmic variables are optically thin in the ...

For the first time ever, we derive equations governing the time evolution of fully relativistic slim accretion disks in the Kerr metric and numerically construct their detailed non-stationary models. We discuss applications of these general results to a possible limit-cycle behavior of thermally unstable disks. Our equations and numerical method are ...

A new generation of sensitive X-ray measurements are indicating that the existence of X-ray attenuation column densities, NH>1024 cm-2, is quite common among broad absorption line quasars (BALQSOs). This is significant to the geometry of the broad absorption line (BAL) outflow. In particular, such an X-ray shield also shields equatorial accretion ...

The thermal equilibrum structure and dynamical behavior of externally irradiated accretion disks are investigated. For radiative disks only the surface layer is heated, while for convective disks the heat penetrates deeply into the disk. For sufficiently strong radiation and given irradiation flux F(irr), the disk is completely stabilized against thermal ...

In the accretion disks of quiescent dwarf novae, Doppler mapping studies reveal that Balmer emission lines increase sharply toward the center of the disk, with surface brightnesses scaling roughly as R exp {minus}3/2 varies as Omega(Kep). Similarly, among chromospherically active stars the H-alpha and Ca II H and K emission cores are ...

The nucleosynthesis and nuclear energy generation in thick accretion disks around massive black holes are examined in detail. Calculations are presented and discussed for disk parameters relevant for QSOs and AGN. It is found that, depending on the disk parameters, various nuclear processes can take place in thick accretion ...

We show how direct microlensing-reverberation analysis performed on two well-known quasars (Q2237, the Einstein Cross, and Q0957, the Twin) can be used to observe the inner structure of two quasars which are in significantly different spectral states. These observations allow us to measure the detailed internal structure of Q2237 in a radio-quiet high-soft state, and compare it to Q0957 in a ...

Compact object mergers have long been speculated to be a possible site of r-process nucleosynthesis. While most attention has been focused on the cold decompression of neutron star matter ejected from the merger, other sites within the merger likely contribute to its nucleosynthetic output. Here we consider hot outflows from the accretion ...

Compact object mergers have long been speculated to be a possible site of r-process nucleosynthesis. While most attention has been focused on the cold decompression of neutron star matter ejected from the merger, other sites within the merger likely contribute to its nucleosynthetic output. Here we consider hot outflows from the accretion ...

It is now widely accepted that most galaxies undergo an active phase, during which a central super-massive black hole generates vast radiant luminosities through the gravitational accretion of gas. Winds launched from a rotating accretion disk surrounding the black hole are thought to play a critical role, allowing the disk to shed angular momentum that ...

Accretion disks and astrophysical jets are used to model many active astrophysical objects, viz., young stars, relativistic stars, and active galactic nuclei.The problem of jet acceleration and collimation is central for understanding the physics of these objects. There is now a general consensus that jet acceleration is the result of an interplay between ...

We show that a moderately massive disk (10/sup -5/--10/sup -2/ M/sub sun/) can cause the Lense-Thirring precession of the compact object (neutron star or black hole) at its center. The inner regions of the disk (r< or approx. =10/sup 8/ cm) align with the equator of an will precess at the same rate as the compact object. We propose that this disk-driven precession produces the 164 day period in ...

We present fully self-consistent calculations of the spectra emitted by accretion disks in active galactic nuclei. We treat the inner, radiation-pressure-dominated regions of standard alpha-disks. Incoherent Compton scattering and emission/absorption of radiation by hydrogen and helium are included in compting the vertical temperature structure within the ...

The spectra of dwarf novae show broad absorption lines in outburst and strong emission lines during the quiescent state. Simplified calculations are presented for idealized disk models that demonstrate that these features can be attributed to radiative properties of accretion disks. Using these models, it is shown that the absorption lines are generated ...

We present radial profiles of the H-beta line of the accretion disks for the cataclysmic variables presented in the ApJS Doppler Tomography Atlas (August 1994 issue). These profiles are based upon time-resolved spectrophotometry of the H-beta, H-gamma, and He II lines. The profiles cover 4 dwarf novae, 10 novalike CVs, 3 classical ...

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 the wind to the central accretion rate. ...

We present the results of X-ray spectral analysis of two mini-BAL QSOs, PG 1126-041 and PG 1351+640, aimed at getting insights into the physics of quasar outflows. We find strong X-ray spectral variability on timescales of years. These variations can be well reproduced by variations of physical properties as the covering factor and column density of ionized gas along the line ...

We have obtained infrared colors and limiting magnitudes from 1.25-4.8 micrometers for a sample of 26 of the cm continuum radio sources located in the core of the rho Oph molecular cloud. Their colors demonstrate that the majority of the sources appear to be heavily reddened objects surrounded by circumstellar accretion disks. In these cases the radio ...

Light curves from a growing number of Gamma Ray Bursts (GRBs) indicate that GRBs copiously produce radioactive Ni moving outward at fractions of the speed of light. We calculate nuclear abundances of elements accompanying the outflowing Ni under the assumption that this Ni originates from a wind blown off of a viscous accretion disk. ...

We discuss the application of meridionally self-similar models to winds and jets from hot coronae, in particular in the central region of accretion disks. A summary of how they may help understanding the evolution of jets from young stars is outlined. Then we discuss their application to the classification of AGN jets and extension to the relativistic ...

We present our numerical results of two-dimensional magnetohydrodynamic (MHD) simulations of the collapse of rotating massive stars in light of the collapsar model of gamma-ray bursts (GRBs). Pushed by recent evolution calculations of GRB progenitors, we focus on lower angular momentum of the central core than those taken mostly in previous studies. By performing special relativistic simulations ...

The broad-line region (BLR) disappears in many low-luminosity active galactic nuclei (AGNs), the reason of which is still controversial. The BLRs in AGNs are believed to be associated with the outflows from the accretion disks. Most of the low-luminosity AGNs contain advection-dominated accretion flows (ADAFs) which are very hot and ...

We report the discovery of TWA 30B, a wide (~3400 AU), co-moving M dwarf companion to the nearby (~42 pc) young star TWA 30. Companionship is confirmed from their statistically consistent proper motions and radial velocities (RVs), as well as a chance alignment probability of only 0.08%. Like TWA 30A, the spectrum of TWA 30B shows signatures of an actively accreting ...

We present results from new optical and UV spectroscopy of the unusual binary system SS 433, and we discuss the relationship of the particular spectral components that we observe to the properties of the binary. These spectral components include1. The continuum spectrum, which we associate with flux from the super-Eddington accretion disk and the dense ...

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 ...

We report on the results of a three-year program of coordinated X-ray and optical monitoring of the narrow-line Seyfert 1 galaxy NGC 4051. The rapid continuum variations observed in the X-ray spectra are not detected in the optical, although the time-averaged X-ray and optical continuum fluxes are well-correlated. Variations in the flux of the broad Hbeta line are found to lag behind the optical ...

We report on a three-year program of coordinated X-ray and optical monitoring of the Narrow-Line Seyfert 1 galaxy NGC 4051. The rapid continuum variations observed in the X-ray spectra are not detected in the optical, although the X-ray and optical continuum fluxes are correlated on time scales of many weeks and longer. Variations in the flux of the broad H-beta line are found to lag behind the ...

the disk. That is, the gas was assumed to be highly supersonic. Figure 7 shows the averaged Mach number for the infalling wind as it impacts the disk. On average, the gas is indeed supersonic, but, particularly.--- Plot of the Mach number, averaged over OE and the two sides of the disk, of the gas impacting

. Figure 7 shows the averaged Mach number for the infalling wind as it impacts the disk. On average . #12; { 11 { Fig. 7.| Plot of the Mach number, averaged over #30; and the two sides of the disk, of the gas for the two runs are strongly correlated. Thus, the average rate of mass falling onto the disk is independent

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 mass transfer and formation of ...

Aims: We investigate the influence of turbulent viscosity on the collapse of a rotating molecular cloud core with axial symmetry, in particular, on the first and second collapse phase, as well as the evolution of the second (protostellar) core during its first accretion period. By using extensive numerical calculations, we monitor the intricate interactions between the newly formed protostar and ...

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...

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...

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...

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...

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

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

We develop a numerical scheme and code for estimating the energy and momentum transfer via neutrino pair annihilation (? + {\\bar{?}} ? e^{-}+ e^{+}), bearing in mind the application to the collapsar models of gamma-ray bursts (GRBs). To calculate the neutrino flux illuminated from the accretion disk, we perform a ray-tracing calculation in the framework ...

During the T Tauri phase, there is a differentially rotating region attached to the top of the stellar convective layer connecting the star with the accretion disk that rotates significantly faster than the stellar surface; rotation periods during the TT phase are about 7-8 days (?_* = 0.8-0.9 day^{-1}) while the Keplerian frequency is: ?_k = 11.1 day^{-1} ...

I present new insights about accretion and ejection physics in low-mass X-ray binaries based on high-resolution Chandra HETGS studies of accretion disk winds in the microquasar GRS 1915+105. First, using 10 years of Chandra observations to probe the long-term connection between accretion disk winds and relativistic ...

We analyze the Chandra High Energy Transmission Grating Spectrometer observation of the Seyfert 2 AGN IRAS 18325-5926. We detect a v = -360+41 -66 km s-1 blueshifted ionized absorber in the X-ray spectrum, with photoionization parameter log ? = 2.0+0.1 -0.1 and hydrogen column density N H = 1.55+0.75 -0.38 � 1021 cm-2. The absorber may be a photoionized wind originating in the obscuring ...

We present radiation hydrodynamics simulations of the collapse of massive pre-stellar cores. We treat frequency dependent radiative feedback from stellar evolution and accretion luminosity at a numerical resolution down to 1.27 AU. In the 2D approximation of axially symmetric simulations, it is possible for the first time to simulate the whole accretion phase of several 105 yr for the forming ...

The origin of cosmic magnetic (B) fields remains an open question. It is generally believed that very weak primordial B fields are amplified by dynamo processes, but it appears unlikely that the amplification proceeds fast enough to account for the fields presently observed in galaxies and galaxy clusters. In an alternative scenario, cosmic B fields are generated near the inner edges of ...

Q Cygni (Nova Cygni 1876) is the third-oldest old novae (after WY Sge and V841 Oph), with a long orbital period of 10.08 hr and spectroscopic peculiarities in the optical, including the presence of variable wind outflow revealed by optical P Cygni profiles in the He I lines and H??. We have carried out a synthetic spectral analysis of a far-ultraviolet IUE archival spectrum of ...

The origin of cosmic magnetic (B) fields remains an open question. It is generally believed that very weak primordial B fields are amplified by dynamo processes, but it appears unlikely that the amplification proceeds fast enough to account for the fields presently observed in galaxies and galaxy clusters. In an alternative scenario, cosmic B fields are generated near the inner edges of ...

The UV spectra of nova-like variables are dominated by emission from the accretion disk, modified by scattering in a wind emanating from the disk. Here, we model the spectra of RW Tri and UX UMa, the only two eclipsing nova-like variables which have been observed with the Hubble Space Telescope in the far-ultraviolet, in an attempt to constrain the ...

We propose that the magnetic fields in the accretion disks of active galactic nuclei (AGNs) are generated by azimuthal electric currents due to the difference between the plasma electron and ion velocities that arises when the electrons are retarded by interactions with the AGN photons (the Poynting - Robertson battery). This process provides a unique ...

The origin of cosmicmagnetic (B) fields remains an open question. It is generally believed that very weak primordial B fields are amplified by dynamo processes, but it appears unlikely that the amplification proceeds fast enough to account for the fields presently observed in galaxies and galaxy clusters. In an alternative scenario, cosmic B fields are generated near the inner edges of ...

We present the ultraviolet-optical-infrared spectral energy distribution of the low inclination novalike cataclysmic variable (CV) V592 Cassiopeiae, including new mid-infrared observations from 3.5 to 24 ?m obtained with the Spitzer Space Telescope. At wavelengths shortward of 8 ?m, the spectral energy distribution of V592 Cas is dominated by the steady state accretion ...

Young stars are thought to accumulate most of their mass through an accretion disk, which channels the gas and dust of a collapsing cloud onto the central protostellar object. The rotational and magnetic forces in the star-disk system often produce high-velocity jets of outflowing gas. These jets can in principle be used to study the ...

In the present work we discuss how the strength of magnetic fields determines the characteristics of solutions in models where the collimated outflow and the accretion disk are treated consistently. We perform a complete analysis of the range of magnetic field by non-relativistic 2.5 dimension numerical simulations using the PLUTO ...

It is well known that there is mass outflow in cataclysmic variables, since IUE observations show P Cyg profiles of various high-excitation lines of C IV and S IV. It is proposed here that these outflows are hydromagnetic winds from accretion disks. The winds extract angular momentum from these systems and ...

Collimated outflows (jets) are ubiquitous in the universe, appearing around sources as diverse as protostars and extragalactic supermassive black holes. Jets are thought to be magnetically collimated, and launched from a magnetized accretion disk surrounding a compact gravitating object. We have developed the first laboratory ...

A survey for molecular outflows was carried out by mapping the CO J=2-1 line toward a sample of 69 luminous IRAS point sources. Sixty objects have IRAS luminosities from 103 to 105 Lsolar and are associated with dense gas traced by NH3, identifying them as high-mass star-forming regions. Among 69 sources, 65 sources have data that are suitable for outflow ...

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

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

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 ...

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 ...

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 ...

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

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

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

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 ...

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, ...

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 ...

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, ...

We present the results of a uniform and systematic search for blueshifted Fe K absorption lines in the X-ray spectra of five bright broad-line radio galaxies observed with Suzaku. We detect, for the first time in radio-loud active galactic nuclei (AGNs) at X-rays, several absorption lines at energies greater than 7 keV in three out of five sources, namely, 3C 111, 3C 120, and 3C 390.3. The lines ...

We perform axisymmetric relativistic magnetohydrodynamic simulations to investigate the acceleration and collimation of jets and outflows from disks around compact objects. Newtonian gravity is added to the relativistic treatment in order to establish the physical boundary condition of an underlying accretion disk in centrifugal and ...

We report results of several large surveys for water maser emission among Active Galactic Nuclei with the 100-m Green Bank Telescope and the two NASA Deep Space Network 70-m antennas at Tidbinbilla, Australia and at Robledo, Spain. We detected 23 new sources, which resulted in a 60% increase in the number of then known nuclear water maser sources. Eight new detections show the characteristic ...

Aims: In this paper we aim to determine the structure on 100 AU scales of the massive young stellar object W33A, using interferometric observations in the mid-infrared. This emission could be caused by a variety of elements, for example, the inner protostellar envelope, outflow cavity walls, or a dusty or gaseous accretion disk. ...

The IUE data base is used to analyze the UV line shapes of cataclysmic variables RW Sex, RW Tri, and V Sge. Observed lines are compared to synthetic line profiles computed using a model of rotating bi-conical winds from accretion disks. The wind model calculates the wind ionization structure self-consistently including photoionization from the disk and ...

We examine theoretically the behaviour of the inner accretion disk in GRS 1915+105 when soft X-ray dips are present in the X-ray light curve. We assume the presence of a radial shock in the accretion disk, as in some of the Two Component Advective Flow (TCAF) solutions. We discuss the behaviour of the flux tubes ...

Low-mass X-ray binaries (LMXBs) are systems in which a low-mass companion transfers mass via Roche-lobe overflow onto a black hole (BH) or a weakly magnetized neutron star (NS). It is believed that both the solid surface and the magnetic field of an NS can affect the accretion flow and show some observable effects. Using the disk emission dominant data, we compare the disk evolution of the two ...

We study the two-dimensional, time-dependent MHD of radiation-driven winds from luminous accretion disks initially threaded by a purely axial magnetic field. The radiation force is mediated primarily by spectral lines. We use ideal MHD to compute the evolution of Keplerian disks, varying the magnetic field strengths and the luminosity of the disk, the ...

The so-called `dusty torus', an obscuring medium surrounding the black hole accretion disk, is an essential component of the Unified Model for Active Galactic Nuclei (AGNs) invoked to explain the diversity of AGN phenomenology. One promising source for the dusty torus is a dynamical wind from the accretion disk ...

We present the results of an effort to model recent HST eclipse observations of the C IV 1550 A resonance line in the high-inclination nova-like cataclysmic variable UX UMa. Assuming this line to be predominantly wind-formed, we are able to roughly reproduce the shapes and strengths of the observed line profiles (both away from and during eclipse) within the framework of a simple kinematic model ...

Collimated outflows (jets) are ubiquitous in astrophysics appearing around sources as diverse as newly formed stars and extragalactic supermassive blackholes. In all cases these jets are believed to be launched from magnetized accretion disks surrounding a central gravitating source. Understanding astrophysical ...

Narayan and Yi (1994, AAA 064.083) found that the Bernoulli parameter is a positive constant in advection-dominated accretion flows, thereby mass outflow being inevitable. We find, however, that their conclusion depends critically on their assumptions required to derive their self-similar solutions (i.e., substantial infall velocity, comparable to the rotational velocity, or ...

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

The status of work concerned with understanding the angular momentum transport mechanisms as applied

Neutron viscosity is investigated as a possible mechanism for the dissipation of kinetic energy into

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 ...

We investigate p-process nucleosynthesis in a supercritical accretion disk around a compact object of 1.4 Msolar. Supercritical accretion is expected to occur in a supernova (SN) with fallback material accreting onto a nascent compact object. We find that appreciable amounts of p-nuclei are synthesized via the p-process in the disk when the accretion rate ...

Aims:We report on the discovery of J0644+3344, a bright, deeply-eclipsing cataclysmic variable (CV) binary. Methods: Optical photometric and spectroscopic observations were obtained to determine the nature and characteristics of this CV. Results: Spectral signatures of both binary components and an accretion disk can be seen at optical wavelengths. The ...

Optical data together with data from the literature, including IUE observations, have been used to describe the physical conditions in the nucleus of the Seyfert 1 galaxy NGC 7469. The ultraviolet excess emission, over a power-law component, cannot be explained by Balmer continuum emission alone, suggesting also emission from a blackbody with T = 20000K, respresenting the ...