WorldWideScience

Sample records for accretion disk winds

  1. Wind-driven Accretion in Transitional Protostellar Disks

    CERN Document Server

    Wang, Lile

    2016-01-01

    Transitional protostellar disks have inner cavities heavily depleted in dust and gas, yet most show signs of ongoing accretion, often at rates comparable to full disks. We show that recent constraints on the gas surface density in a few well-studied disk cavities imply that the accretion speed is at least transsonic. We propose that this is the natural result of accretion driven by magnetized winds. Typical physical conditions of the gas inside such cavities are estimated for plausible X-ray and FUV radiation fields. The gas is molecular and predominantly neutral, with a dimensionless ambipolar parameter in the right general range for wind solutions of the type developed by K\\"onigl, Wardle, and others. That is to say, the density of ions and electrons is sufficient for moderately good coupling to the magnetic field, but not so good that the magnetic flux need be dragged inward by the accreting neutrals.

  2. WIND-ACCRETION DISKS IN WIDE BINARIES, SECOND-GENERATION PROTOPLANETARY DISKS, AND ACCRETION ONTO WHITE DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Perets, Hagai B. [Technion-Israel Institute of Technology, Haifa (Israel); Kenyon, Scott J., E-mail: hperets@physics.technion.ac.il [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2013-02-20

    Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long-term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind accretion leads to long-lived stable disks over the lifetime of the asymptotic giant branch donor star. The disks have masses of a few times 10{sup -5}-10{sup -3} M {sub Sun }, with surface density and temperature profiles that follow broken power laws. The total mass in the disk scales approximately linearly with the viscosity parameter used. Roughly, 50%-80% of the mass falling into the disk accretes onto the central star; the rest flows out through the outer edge of the disk into the stellar wind of the primary. For systems with large accretion rates, the secondary accretes as much as 0.1 M {sub Sun }. When the secondary is a white dwarf, accretion naturally leads to nova and supernova eruptions. For all types of secondary star, the surface density and temperature profiles of massive disks resemble structures observed in protoplanetary disks, suggesting that coordinated observational programs might improve our understanding of uncertain disk physics.

  3. Wind-driven Accretion in Transitional Protostellar Disks

    Science.gov (United States)

    Wang, Lile; Goodman, Jeremy J.

    2017-01-01

    Transitional protostellar disks have inner cavities that are heavily depleted in dust and gas, yet most of them show signs of ongoing accretion, often at rates comparable to full disks. We show that recent constraints on the gas surface density in a few well-studied disk cavities suggest that the accretion speed is at least transsonic. We propose that this is the natural result of accretion driven by magnetized winds. Typical physical conditions of the gas inside these cavities are estimated for plausible X-ray and FUV radiation fields. The gas near the midplane is molecular and predominantly neutral, with a dimensionless ambipolar parameter in the right general range for wind solutions of the type developed by Königl, Wardle, and others. That is to say, the density of ions and electrons is sufficient for moderately good coupling to the magnetic field, but it is not so good that the magnetic flux needs to be dragged inward by the accreting neutrals.

  4. Hydrodynamic Models of Line-Driven Accretion Disk Winds II Adiabatic Winds from Nonisothermal Disks

    CERN Document Server

    Pereyra, N A; Blondin, J M; Pereyra, Nicolas Antonio; Kallman, Timothy R.; Blondin, John M.

    2000-01-01

    We present here numerical hydrodynamic simulations of line-driven accretion disk winds in cataclysmic variable systems. We calculate wind mass-loss rate, terminal velocities, and line profiles for CIV (1550 A) for various viewing angles. The models are 2.5-dimensional, include an energy balance condition, and calculate the radiation field as a function of position near an optically thick accretion disk. The model results show that centrifugal forces produce collisions of streamlines in the disk wind which in turn generate an enhanced density region, underlining the necessity of two dimensional calculations where these forces may be represented. For disk luminosity Ldisk = Lsun, white dwarf mass Mwd = 0.6 Msun, and white dwarf radii Rwd = 0.01 Rsun, we obtain a wind mass-loss rate of dMwind/dt = 8.0E-12 Msun/yr, and a terminal velocity of ~3000 km/s. The line profiles we obtain are consistent with observations in their general form, in particular in the maximum absorption at roughly half the terminal velocity ...

  5. Chemical evolution of protoplanetary disks - the effects of viscous accretion, turbulent mixing and disk winds

    CERN Document Server

    Heinzeller, Dominikus; Walsh, Catherine; Millar, Tom J

    2011-01-01

    We calculate the chemical evolution of protoplanetary disks considering radial viscous accretion, vertical turbulent mixing and vertical disk winds. We study the effects on the disk chemical structure when different models for the formation of molecular hydrogen on dust grains are adopted. Our gas-phase chemistry is extracted from the UMIST Database for Astrochemistry (Rate06) to which we have added detailed gas-grain interactions. We use our chemical model results to generate synthetic near- and mid-infrared LTE line emission spectra and compare these with recent Spitzer observations. Our results show that if H2 formation on warm grains is taken into consideration, the H2O and OH abundances in the disk surface increase significantly. We find the radial accretion flow strongly influences the molecular abundances, with those in the cold midplane layers particularly affected. On the other hand, we show that diffusive turbulent mixing affects the disk chemistry in the warm molecular layers, influencing the line ...

  6. Brackett γ radiation from the inner gaseous accretion disk, magnetosphere, and disk wind region of Herbig AeBe stars

    Science.gov (United States)

    Tambovtseva, L. V.; Grinin, V. P.; Weigelt, G.

    2016-05-01

    Various disk and outflow components such as the magnetosphere, the disk wind, the gaseous accretion disk, and other regions may contribute to the hydrogen line emission of young Herbig AeBe stars. Non-LTE modeling was performed to show the influence of the model parameters of each emitting region on the intensity and shape of the Brγ line profile, to present the spatial brightness distribution of each component, and to compare the contribution of each component to the total line emission. The modeling shows that the disk wind is the dominant contributor to the Brγ line rather than the magnetosphere and inner gaseous accretion disk. The contribution of the disk wind region to the Hα line is also considered.

  7. Abbott Wave-Triggered Runaway in Line-Driven Winds from Stars and Accretion Disks

    OpenAIRE

    2001-01-01

    Line-driven winds from stars and accretion disks are accelerated by scattering in numerous line transitions. The wind is believed to adopt a unique critical solution, out of the infinite variety of shallow and steep solutions. We study the inherent dynamics of the transition towards the critical wind. A new runaway wind mechanism is analyzed in terms of radiative-acoustic (Abbott) waves which are responsible for shaping the wind velocity law and fixing the mass loss. Three different flow type...

  8. Accretion disk winds in active galactic nuclei: X-ray observations, models, and feedback

    CERN Document Server

    Tombesi, Francesco

    2016-01-01

    Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. A strong support of this "quasar mode" feedback came from the recent X-ray observation of a mildly relativistic accretion disk wind in a ultraluminous infrared galaxy (ULIRG) and its connection with a large-scale molecular outflow, providing a direct link between the SMBH and the gas out of which stars form. Spectroscopic observations, especially in the X-ray band, show that such accretion disk winds may be common in local AGN and quasars. However, their origin and characteristics are still not fully understood. Detailed theoretical models and simulations focused on radiation, magnetohydrodynamic (MHD) or a combination of these two processes to investigate the possible acceleration mechanisms and the dynamics of these winds. Some of these models have been dir...

  9. Wind from black hole accretion disk as the driver of a molecular outflow in a galaxy

    CERN Document Server

    Tombesi, F; Veilleux, S; Reeves, J N; Gonzalez-Alfonso, E; Reynolds, C S

    2015-01-01

    Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. Recent observations of large-scale molecular outflows in ultra-luminous infrared galaxies (ULIRGs) have provided the evidence to support these studies, as they directly trace the gas out of which stars form. Theoretical models suggest an origin of these outflows as energy-conserving flows driven by fast AGN accretion disk winds. Previous claims of a connection between large-scale molecular outflows and AGN activity in ULIRGs were incomplete because they were lacking the detection of the putative inner wind. Conversely, studies of powerful AGN accretion disk winds to date have focused only on X-ray observations of local Seyferts and a few higher redshift quasars. Here we show the clear detection of a powerful AGN accretion disk wind with a mildly relativistic ...

  10. Accretion disk winds as the jet suppression mechanism in the microquasar GRS 1915+105.

    Science.gov (United States)

    Neilsen, Joseph; Lee, Julia C

    2009-03-26

    Stellar-mass black holes with relativistic jets, also known as microquasars, mimic the behaviour of quasars and active galactic nuclei. Because timescales around stellar-mass black holes are orders of magnitude smaller than those around more distant supermassive black holes, microquasars are ideal nearby 'laboratories' for studying the evolution of accretion disks and jet formation in black-hole systems. Whereas studies of black holes have revealed a complex array of accretion activity, the mechanisms that trigger and suppress jet formation remain a mystery. Here we report the presence of a broad emission line in the faint, hard states and narrow absorption lines in the bright, soft states of the microquasar GRS 1915+105. ('Hard' and 'soft' denote the character of the emitted X-rays.) Because the hard states exhibit prominent radio jets, we argue that the broad emission line arises when the jet illuminates the inner accretion disk. The jet is weak or absent during the soft states, and we show that the absorption lines originate when the powerful radiation field around the black hole drives a hot wind off the accretion disk. Our analysis shows that this wind carries enough mass away from the disk to halt the flow of matter into the radio jet.

  11. New insights on the accretion disk-winds connection in radio-loud AGNs from Suzaku

    CERN Document Server

    Tombesi, F; Reeves, J N; Braito, V; Cappi, M; Reynolds, C S; Mushotzky, R F

    2011-01-01

    From the spectral analysis of long Suzaku observations of five radio-loud AGNs we have been able to discover the presence of ultra-fast outflows with velocities ~0.1c in three of them, namely 3C 111, 3C 120 and 3C 390.3. They are consistent with being accretion disk winds/outflows. We also performed a follow-up on 3C 111 to monitor its outflow on ~7days time-scales and detected an anti-correlated variability of a possible relativistic emission line with respect to blue-shifted Fe K features, following a flux increase. This provides the first direct evidence for an accretion disk-wind connection in an AGN. The mass outflow rate of these outflows can be comparable to the accretion rate and their mechanical power can correspond to a significant fraction of the bolometric luminosity and is comparable to their typical jet power. Therefore, they can possibly play a significant role in the expected feedback from AGNs and can give us further clues on the relation between the accretion disk and the formation of winds/...

  12. Modelling Accretion Disk and Stellar Wind Interactions: the Case of Sgr A*

    CERN Document Server

    Christie, I M; Mimica, P; Giannios, D

    2016-01-01

    Sgr A* is an ideal target to study low-luminosity accreting systems. It has been recently proposed that properties of the accretion flow around Sgr A* can be probed through its interactions with the stellar wind of nearby massive stars belonging to the S-cluster. When a star intercepts the accretion disk, the ram and thermal pressures of the disk terminate the stellar wind leading to the formation of a bow shock structure. Here, a semi-analytical model is constructed which describes the geometry of the termination shock formed in the wind. With the employment of numerical hydrodynamic simulations, this model is both verified and extended to a region prone to Kelvin-Helmholtz instabilities. Because the characteristic wind and stellar velocities are in $\\sim10^{8}$ cm s$^{-1}$ range, the shocked wind may produce detectable X-rays via thermal bremsstrahlung emission. The application of this model to the pericenter passage of S2, the brightest member of the S-cluster, shows that the shocked wind produces roughly ...

  13. Regulation of black-hole accretion by a disk wind during a violent outburst of V404 Cygni.

    Science.gov (United States)

    Muñoz-Darias, T; Casares, J; Mata Sánchez, D; Fender, R P; Armas Padilla, M; Linares, M; Ponti, G; Charles, P A; Mooley, K P; Rodriguez, J

    2016-06-02

    Accretion of matter onto black holes is universally associated with strong radiative feedback and powerful outflows. In particular, black-hole transients have outflows whose properties are strongly coupled to those of the accretion flow. This includes X-ray winds of ionized material, expelled from the accretion disk encircling the black hole, and collimated radio jets. Very recently, a distinct optical variability pattern has been reported in the transient stellar-mass black hole V404 Cygni, and interpreted as disrupted mass flow into the inner regions of its large accretion disk. Here we report observations of a sustained outer accretion disk wind in V404 Cyg, which is unlike any seen hitherto. We find that the outflowing wind is neutral, has a large covering factor, expands at one per cent of the speed of light and triggers a nebular phase once accretion drops sharply and the ejecta become optically thin. The large expelled mass (>10(-8) solar masses) indicates that the outburst was prematurely ended when a sizeable fraction of the outer disk was depleted by the wind, detaching the inner regions from the rest of the disk. The luminous, but brief, accretion phases shown by transients with large accretion disks imply that this outflow is probably a fundamental ingredient in regulating mass accretion onto black holes.

  14. New Insights on the Accretion Disk-Winds Connection in Radio-Loud AGNs from Suzaku

    Science.gov (United States)

    Tombesi, F.; Sambruna, R. M.; Reeves, J. N.; Braito, V.; Cappi, M.; Reynolds, S.; Mushotzky, R. F.

    2011-01-01

    From the spectral analysis of long Suzaku observations of five radio-loud AGNs we have been able to discover the presence of ultra-fast outflows with velocities ,,approx.0.1 c in three of them, namely 3C III, 3C 120 and 3C 390.3. They are consistent with being accretion disk winds/outflows. We also performed a follow-up on 3C III to monitor its outflow on approx.7 days time-scales and detected an anti-correlated variability of a possible relativistic emission line with respect to blue-shifted Fe K features, following a flux increase. This provides the first direct evidence for an accretion disc-wind connection in an AGN. The mass outflow rate of these outflows can be comparable to the accretion rate and their mechanical power can correspond to a significant fraction of the bolometric luminosity and is comparable to their typical jet power. Therefore, they can possibly play a significant role in the expected feedback from AGNs and can give us further clues on the relation between the accretion disk and the formation of winds/jets.

  15. Modeling X-ray Absorbers in AGNs with MHD-Driven Accretion-Disk Winds

    Science.gov (United States)

    Fukumura, Keigo; Kazanas, D.; Shrader, C. R.; Tombesi, F.; Contopoulos, J.; Behar, E.

    2013-04-01

    We have proposed a systematic view of the observed X-ray absorbers, namely warm absorbers (WAs) in soft X-ray and highly-ionized ultra-fast outflows (UFOs), in the context of magnetically-driven accretion-disk wind models. While potentially complicated by variability and thermal instability in these energetic outflows, in this simplistic model we have calculated 2D kinematic field as well as density and ionization structure of the wind with density profile of 1/r corresponding to a constant column distribution per decade of ionization parameter. In particular we show semi-analytically that the inner layer of the disk-wind manifests itself as the strongly-ionized fast outflows while the outer layer is identified as the moderately-ionized absorbers. The computed characteristics of these two apparently distinct absorbers are consistent with X-ray data (i.e. a factor of ~100 difference in column and ionization parameters as well as low wind velocity vs. near-relativistic flow). With the predicted contour curves for these wind parameters one can constrain allowed regions for the presence of WAs and UFOs.The model further implies that the UFO's gas pressure is comparable to that of the observed radio jet in 3C111 suggesting that the magnetized disk-wind with density profile of 1/r is a viable agent to help sustain such a self-collimated jet at small radii.

  16. The Accretion Disk Wind in the Black Hole GRS 1915+105

    CERN Document Server

    Miller, J M; Fabian, A C; Gallo, E; Kaastra, J; Kallman, T; King, A L; Proga, D; Reynolds, C S; Zoghbi, A

    2016-01-01

    We report on a 120 ks Chandra/HETG spectrum of the black hole GRS 1915+105. The observation was made during an extended and bright soft state in June, 2015. An extremely rich disk wind absorption spectrum is detected, similar to that observed at lower sensitivity in 2007. The very high resolution of the third-order spectrum reveals four components to the disk wind in the Fe K band alone; the fastest has a blue-shift of v = 0.03c. Broadened re-emission from the wind is also detected in the first-order spectrum, giving rise to clear accretion disk P Cygni profiles. Dynamical modeling of the re-emission spectrum gives wind launching radii of r ~ 10^(2-4) GM/c^2. Wind density values of n ~ 10^(13-16) cm^-3 are then required by the ionization parameter formalism. The small launching radii, high density values, and inferred high mass outflow rates signal a role for magnetic driving. With simple, reasonable assumptions, the wind properties constrain the magnitude of the emergent magnetic field to B ~ 10^(3-4) Gauss ...

  17. Magnetically Driven Accretion Disk Winds and Ultra-fast Outflows in PG 1211+143

    Science.gov (United States)

    Fukumura, Keigo; Tombesi, Francesco; Kazanas, Demosthenes; Shrader, Chris; Behar, Ehud; Contopoulos, Ioannis

    2015-05-01

    We present a study of X-ray ionization of MHD accretion-disk winds in an effort to constrain the physics underlying the highly ionized ultra-fast outflows (UFOs) inferred by X-ray absorbers often detected in various sub classes of Seyfert active galactic nuclei (AGNs). Our primary focus is to show that magnetically driven outflows are indeed physically plausible candidates for the observed outflows accounting for the AGN absorption properties of the present X-ray spectroscopic observations. Employing a stratified MHD wind launched across the entire AGN accretion disk, we calculate its X-ray ionization and the ensuing X-ray absorption-line spectra. Assuming an appropriate ionizing AGN spectrum, we apply our MHD winds to model the absorption features in an XMM-Newton/EPIC spectrum of the narrow-line Seyfert, PG 1211+143. We find, through identifying the detected features with Fe Kα transitions, that the absorber has a characteristic ionization parameter of log (ξc[erg cm s-1]) ≃ 5-6 and a column density on the order of NH ≃ 1023 cm-2 outflowing at a characteristic velocity of vc/c ≃ 0.1-0.2 (where c is the speed of light). The best-fit model favors its radial location at rc ≃ 200 Ro (Ro is the black hole’s innermost stable circular orbit), with an inner wind truncation radius at Rt ≃ 30 Ro. The overall K-shell feature in the data is suggested to be dominated by Fe xxv with very little contribution from Fe xxvi and weakly ionized iron, which is in good agreement with a series of earlier analyses of the UFOs in various AGNs, including PG 1211+143.

  18. MAGNETICALLY DRIVEN ACCRETION DISK WINDS AND ULTRA-FAST OUTFLOWS IN PG 1211+143

    Energy Technology Data Exchange (ETDEWEB)

    Fukumura, Keigo [James Madison University, Harrisonburg, VA 22807 (United States); Tombesi, Francesco; Kazanas, Demosthenes; Shrader, Chris [Astrophysics Science Division, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Behar, Ehud [Department of Physics, Technion, Haifa 32000 (Israel); Contopoulos, Ioannis, E-mail: fukumukx@jmu.edu [Research Center for Astronomy, Academy of Athens, Athens 11527 (Greece)

    2015-05-20

    We present a study of X-ray ionization of MHD accretion-disk winds in an effort to constrain the physics underlying the highly ionized ultra-fast outflows (UFOs) inferred by X-ray absorbers often detected in various sub classes of Seyfert active galactic nuclei (AGNs). Our primary focus is to show that magnetically driven outflows are indeed physically plausible candidates for the observed outflows accounting for the AGN absorption properties of the present X-ray spectroscopic observations. Employing a stratified MHD wind launched across the entire AGN accretion disk, we calculate its X-ray ionization and the ensuing X-ray absorption-line spectra. Assuming an appropriate ionizing AGN spectrum, we apply our MHD winds to model the absorption features in an XMM-Newton/EPIC spectrum of the narrow-line Seyfert, PG 1211+143. We find, through identifying the detected features with Fe Kα transitions, that the absorber has a characteristic ionization parameter of log (ξ{sub c}[erg cm s{sup −1}]) ≃ 5–6 and a column density on the order of N{sub H} ≃ 10{sup 23} cm{sup −2} outflowing at a characteristic velocity of v{sub c}/c ≃ 0.1–0.2 (where c is the speed of light). The best-fit model favors its radial location at r{sub c} ≃ 200 R{sub o} (R{sub o} is the black hole’s innermost stable circular orbit), with an inner wind truncation radius at R{sub t} ≃ 30 R{sub o}. The overall K-shell feature in the data is suggested to be dominated by Fe xxv with very little contribution from Fe xxvi and weakly ionized iron, which is in good agreement with a series of earlier analyses of the UFOs in various AGNs, including PG 1211+143.

  19. Abbott Wave-Triggered Runaway in Line-Driven Winds from Stars and Accretion Disks

    CERN Document Server

    Feldmeier, A; Feldmeier, Achim; Shlosman, Isaac

    2001-01-01

    Line-driven winds from stars and accretion disks are accelerated by scattering in numerous line transitions. The wind is believed to adopt a unique critical solution, out of the infinite variety of shallow and steep solutions. We study the inherent dynamics of the transition towards the critical wind. A new runaway wind mechanism is analyzed in terms of radiative-acoustic (Abbott) waves which are responsible for shaping the wind velocity law and fixing the mass loss. Three different flow types result, depending on the location of perturbations. First, if the shallow solution is perturbed sufficiently far downstream, a single critical point forms in the flow, which is a barrier for Abbott waves, and the solution tends to the critical one. Second, if the shallow solution is perturbed upstream from this critical point, mass overloading results, and the critical point is shifted inwards. This wind exhibits a broad, stationary region of decelerating flow and its velocity law has kinks. Third, for perturbations eve...

  20. AGN Unification, X-Ray Absorbers and Accretion Disk MHD Winds

    Science.gov (United States)

    Kazanas, Demos

    2011-01-01

    We present the 2D photoionization structure of the MHD winds of AGN accretion disks. We focus our attention on a specific subset of winds, those with poloidal currents that lead to density profiles n(r) \\propto 1/r. We employ the code XSTAR to compute the local ionization balance, emissivities and opacity which are then used in the self-consistent transfer of radiation and ionization of a host of ionic species of a large number of elements over then entire poloidal plane. Particular attention is paid to the Absorption Measure Distribution (AMD), namely their hydrogen-equivalent column of these ions per logarithmic 7 interval, dN_H/dlog ? (? = L/n(r)r(sup 2) is the ionization parameter), which provides a measure of the winds' radial density profiles. For the given density profile, AMD is found to be independent of ?, in good agreement with analyses of Chandra and XMM data, suggesting the specific profile as a fundamental AGN property. Furthermore, the ratio of equatorial to polar column densities of these winds is \\simeq 10(exp 4); as such, it is shown they serve as the "torus" necessary for AGN unification with phenomenology consistent with the observations. The same winds are also shown to reproduce the observed columns and velocities of C IV and Fe XXV of SAL QSOs once the proper ionizing spectra and inclination angles are employed.

  1. Non-linear variability in microquasars in relation with the winds from their accretion disks

    CERN Document Server

    Janiuk, Agnieszka; Sukova, Petra; Capitanio, Fiamma; Bianchi, Stefano; Kowalski, Wojtek

    2016-01-01

    The microquasar IGR J17091, which is the recently discovered analogue of the well known source GRS 1915+105, exhibits quasi-periodic outbursts, with a period of 5-70 seconds, and regular amplitudes, referred to as "heartbeat state". We argue that these states are plausibly explained by accretion disk instability, driven by the dominant radiation pressure. Using our GLobal Accretion DIsk Simulation hydrodynamical code, we model these outbursts quantitatively. We also find a correlation between the presence of massive outflows launched from the accretion disk and the stabilization of its oscillations. We verify the theoretical predictions with the available timing and spectral observations. Furthermore, we postulate that the underlying non-linear differential equations that govern the evolution of an accretion disk are responsible for the variability pattern of several other microquasars, including XTE J1550-564, GX 339-4, and GRO J1655-40. This is based on the signatures of deterministic chaos in the observed ...

  2. Self-Similar Force-Free Wind From an Accretion Disk

    CERN Document Server

    Narayan, R; Farmer, A J; Narayan, Ramesh; Kinney, Jonathan C. Mc; Farmer, Alison J.

    2006-01-01

    We consider a self-similar force-free wind flowing out of an infinitely thin disk located in the equatorial plane. On the disk plane, we assume that the magnetic stream function $P$ scales as $P\\propto R^\

  3. Accretion Disk Evolution with Wind Infall; 2, Results of 3D Hydrodynamical Simulations with an Illustrative Application to Sgr $A^{*}$

    CERN Document Server

    Coker, R F; Falcke, H; Coker, Robert F.; Melia, Fulvio; Falcke, Heino

    1999-01-01

    In the first paper of this series, using analytic tools, we examined how the evolution and structure of a massive accretion disk may be influenced by the deposition of mass and angular momentum by an infalling Bondi-Hoyle wind. Such a mass influx impacts the long-term behavior of the disk by providing additional sources of viscosity and heating. Here, we make improvements over this earlier work by incorporating the results of 3D hydrodynamical simulations of the large scale accretion from an ambient medium into the disk evolution equations developed previously. We discuss two models, one with the axis of the disk parallel to, and the second with the axis oriented perpendicular to the large scale Bondi-Hoyle flow. We find that the mass inflow rate onto the disk within logarithmic annuli is roughly constant with radius and that the impacting wind carries much less specific angular momentum than Keplerian. We also find, in general, that the infrared spectrum of a wind-fed disk system is steeper than that of a Sh...

  4. Migration of Extrasolar Planets: Effects from X-Wind Accretion Disks

    CERN Document Server

    Adams, Fred C; Lizano, Susana

    2009-01-01

    Magnetic fields are dragged in from the interstellar medium during the gravitational collapse that forms star/disk systems. Consideration of mean field magnetohydrodynamics (MHD) in these disks shows that magnetic effects produce subkeplerian rotation curves and truncate the inner disk. This letter explores the ramifications of these predicted disk properties for the migration of extrasolar planets. Subkeplerian flow in gaseous disks drives a new migration mechanism for embedded planets and modifies the gap opening processes for larger planets. This subkeplerian migration mechanism dominates over Type I migration for sufficiently small planets (m_P < 1 M_\\earth) and/or close orbits (r < 1 AU). Although the inclusion of subkeplerian torques shortens the total migration time by only a moderate amount, the mass accreted by migrating planetary cores is significantly reduced. Truncation of the inner disk edge (for typical system parameters) naturally explains final planetary orbits with periods P=4 days. Pla...

  5. On the gas content of transitional disks: a VLT/X-Shooter study of accretion and winds

    CERN Document Server

    Manara, C F; Natta, A; Rosotti, G; Benisty, M; Ercolano, B; Ricci, L

    2014-01-01

    Transitional disks (TDs) are thought to be a late evolutionary stage of protoplanetary disks with dust depleted inner regions. The mechanism responsible for this depletion is still under debate. To constrain the models it is mandatory to have a good understanding of the properties of the gas content of the inner disk. Using X-Shooter broad band -UV to NIR- medium resolution spectroscopy we derive the stellar, accretion, and wind properties of a sample of 22 TDs. The analysis of these properties allows us to put strong constraints on the gas content in a region very close to the star (<0.2 AU) which is not accessible with any other observational technique. We fit the spectra with a self-consistent procedure to derive simultaneously SpT,Av,and mass accretion rates (Macc) of the targets. From forbidden emission lines we derive the wind properties of the targets. Comparing our findings to values for cTTs, we find that Macc and wind properties of 80% of the TDs in our sample, which is strongly biased towards st...

  6. The structure and appearance of winds from supercritical accretion disks. II - Dynamical theory of supercritical winds

    Science.gov (United States)

    Meier, D. L.

    1982-01-01

    A general analytic theory is presented of winds driven by super-Eddington luminosities. The relevant parameters are the mass of the central object, the radius at which the luminosity and matter are injected, the ratio of the free-fall time to the heating time at this radius, and the total luminosity injected at the radius. Several different regimes of dynamical wind structure are identified, and the analytic expressions are shown to agree with the numerical results in Meier (1979) in the appropriate case. It is noted that, in its general form, the theory is the optically thick (to electron scattering) counterpart to optically thin radiation pressure-driven stellar winds.

  7. Magnetically-Driven Accretion-Disk Winds and Ultra-Fast Outflows in PG1211+143

    CERN Document Server

    Fukumura, Keigo; Kazanas, Demosthenes; Shrader, Chris; Behar, Ehud; Contopoulos, Ioannis

    2015-01-01

    We present a study of X-ray ionization of magnetohydrodynamic (MHD) accretion-disk winds in an effort to constrain the physics underlying the highly-ionized ultra-fast outflows (UFOs) inferred by X-ray absorbers often detected in various sub-classes of Seyfert active galactic nuclei (AGNs). Our primary focus is to show that magnetically-driven outflows are indeed physically plausible candidates for the observed outflows accounting for the AGN absorption properties of the present X-ray spectroscopic observations. Employing a stratified MHD wind launched across the entire AGN accretion disk, we calculate its X-ray ionization and the ensuing X-ray absorption line spectra. Assuming an appropriate ionizing AGN spectrum, we apply our MHD winds to model the absorption features in an {\\it XMM-Newton}/EPIC spectrum of the narrow-line Seyfert, \\pg. We find, through identifying the detected features with Fe K$\\alpha$ transitions, that the absorber has a characteristic ionization parameter of $\\log (\\xi_c [erg~cm~s$^{-1}...

  8. Disk wind and magnetospheric accretion in emission from the Herbig Ae star MWC 480

    Science.gov (United States)

    Tambovtseva, L. V.; Grinin, V. P.; Potravnov, I. S.; Mkrtichian, D. E.

    2016-09-01

    The young Herbig Ae star MWC 480 (HD 31648) is one of the comprehensively spectroscopically studied stars in the ultraviolet, optical, and infrared spectral ranges. Using non-LTE modeling of its hydrogen spectrum, we have calculated the contribution to the hydrogen emission from such important regions of the circumstellar environment as the disk wind and the magnetosphere. We have used our own observations of the stellar spectrum performed with the 2.4-m telescope at the Thai National Observatory to quantitatively check our theoretical calculations. In addition, all of the visible and infrared spectra available in the literature have been used for a qualitative comparison. The modeling results have revealed a significant role of the magneto-centrifugal disk wind in the formation of atomic hydrogen emission. The cause of the emission line variability in the spectrum ofMWC 480 is discussed.

  9. Stratified Magnetically Driven Accretion-disk Winds and Their Relations to Jets

    Science.gov (United States)

    Fukumura, Keigo; Tombesi, Francesco; Kazanas, Demosthenes; Shrader, Chris; Behar, Ehud; Contopoulos, Ioannis

    2014-01-01

    We explore the poloidal structure of two-dimensional magnetohydrodynamic (MHD) winds in relation to their potential association with the X-ray warm absorbers (WAs) and the highly ionized ultra-fast outflows (UFOs) in active galactic nuclei (AGNs), in a single unifying approach. We present the density n(r, θ), ionization parameter ξ(r, θ), and velocity structure v(r, θ) of such ionized winds for typical values of their fluid-to-magnetic flux ratio, F, and specific angular momentum, H, for which wind solutions become super-Alfvénic. We explore the geometrical shape of winds for different values of these parameters and delineate the values that produce the widest and narrowest opening angles of these winds, quantities necessary in the determination of the statistics of AGN obscuration. We find that winds with smaller H show a poloidal geometry of narrower opening angles with their Alfvén surface at lower inclination angles and therefore they produce the highest line of sight (LoS) velocities for observers at higher latitudes with the respect to the disk plane. We further note a physical and spatial correlation between the X-ray WAs and UFOs that form along the same LoS to the observer but at different radii, r, and distinct values of n, ξ, and v consistent with the latest spectroscopic data of radio-quiet Seyfert galaxies. We also show that, at least in the case of 3C 111, the winds' pressure is sufficient to contain the relativistic plasma responsible for its radio emission. Stratified MHD disk winds could therefore serve as a unique means to understand and unify the diverse AGN outflows.

  10. Stratified magnetically driven accretion-disk winds and their relations to jets

    Energy Technology Data Exchange (ETDEWEB)

    Fukumura, Keigo [University of Maryland, Baltimore County (UMBC/CRESST), Baltimore, MD 21250 (United States); Tombesi, Francesco; Kazanas, Demosthenes; Shrader, Chris [Astrophysics Science Division, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Behar, Ehud [Department of Physics, Technion, Haifa 32000 (Israel); Contopoulos, Ioannis, E-mail: fukumukx@jmu.edu [Research Center for Astronomy, Academy of Athens, Athens 11527 (Greece)

    2014-01-10

    We explore the poloidal structure of two-dimensional magnetohydrodynamic (MHD) winds in relation to their potential association with the X-ray warm absorbers (WAs) and the highly ionized ultra-fast outflows (UFOs) in active galactic nuclei (AGNs), in a single unifying approach. We present the density n(r, θ), ionization parameter ξ(r, θ), and velocity structure v(r, θ) of such ionized winds for typical values of their fluid-to-magnetic flux ratio, F, and specific angular momentum, H, for which wind solutions become super-Alfvénic. We explore the geometrical shape of winds for different values of these parameters and delineate the values that produce the widest and narrowest opening angles of these winds, quantities necessary in the determination of the statistics of AGN obscuration. We find that winds with smaller H show a poloidal geometry of narrower opening angles with their Alfvén surface at lower inclination angles and therefore they produce the highest line of sight (LoS) velocities for observers at higher latitudes with the respect to the disk plane. We further note a physical and spatial correlation between the X-ray WAs and UFOs that form along the same LoS to the observer but at different radii, r, and distinct values of n, ξ, and v consistent with the latest spectroscopic data of radio-quiet Seyfert galaxies. We also show that, at least in the case of 3C 111, the winds' pressure is sufficient to contain the relativistic plasma responsible for its radio emission. Stratified MHD disk winds could therefore serve as a unique means to understand and unify the diverse AGN outflows.

  11. Stratified Magnetically Driven Accretion-Disk Winds and Their Relations To Jets

    Science.gov (United States)

    Fukumura, Keigo; Tombesi, Francesco; Kazanas, Demosthenes; Shrader, Chris; Behar, Ehud; Contopoulos, Ioannis

    2013-01-01

    We explore the poloidal structure of two-dimensional magnetohydrodynamic (MHD) winds in relation to their potential association with the X-ray warm absorbers (WAs) and the highly ionized ultra-fast outflows (UFOs) in active galactic nuclei (AGNs), in a single unifying approach. We present the density n(r, theta), ionization parameter xi(r, theta), and velocity structure v(r, theta) of such ionized winds for typical values of their fluid-to-magnetic flux ratio, F, and specific angular momentum, H, for which wind solutions become super-Alfvenic. We explore the geometrical shape of winds for different values of these parameters and delineate the values that produce the widest and narrowest opening angles of these winds, quantities necessary in the determination of the statistics of AGN obscuration. We find that winds with smaller H show a poloidal geometry of narrower opening angles with their Alfv´en surface at lower inclination angles and therefore they produce the highest line of sight (LoS) velocities for observers at higher latitudes with the respect to the disk plane. We further note a physical and spatial correlation between the X-ray WAs and UFOs that form along the same LoS to the observer but at different radii, r, and distinct values of n, xi, and v consistent with the latest spectroscopic data of radio-quiet Seyfert galaxies. We also show that, at least in the case of 3C 111, the winds' pressure is sufficient to contain the relativistic plasma responsible for its radio emission. Stratified MHD disk winds could therefore serve as a unique means to understand and unify the diverse AGN outflows.

  12. The impact of accretion disk winds on the X-ray spectrum of AGN: Part 2 - XSCORT + Hydrodynamic Simulations

    CERN Document Server

    Schurch, N J; Proga, D

    2008-01-01

    abridged: We use XSCORT, together with the hydrodynamic accretion disc wind simulation from Proga & Kallman (2004), to calculate the impact that the accretion disk wind has on the X-ray spectrum from a 1E8 solar mass black hole Active Galactic Nuclei (AGN) accreting at 0.5 L/L_Edd. The properties of the resulting spectra depend on viewing angle and clearly reflect the distinct regions apparent in the original hydrodynamic simulation. Very equatorial lines-of-sight (l.o.s) are dominated by Compton scattering and nearly-neutral absorption. Polar l.o.s result in largely featureless spectra. Finally, l.o.s that intersect the transition region between these extremes have a wide range of absorption features imprinted on the spectrum. Both polar and transition region l.o.s produce spectra that show highly-ionized, blue-shifted, Fe absorption features that are qualitatively similar to features observed in the X-ray spectra of a growing number of AGN. The spectra presented here clearly demonstrate that current sim...

  13. Magnetohydrodynamic Origin of Jets from Accretion Disks

    CERN Document Server

    Lovelace, R V E; Koldoba, A V

    1999-01-01

    A review is made of recent magnetohydrodynamic (MHD) theory and simulations of origin of jets from accretion disks. Many compact astrophysical objects emit powerful, highly-collimated, oppositely directed jets. Included are the extra galactic radio jets of active galaxies and quasars, and old compact stars in binaries, and emission line jets in young stellar objects. It is widely thought that these different jets arise from rotating, conducting accretion disks threaded by an ordered magnetic field. The twisting of the magnetic field by the rotation of the disk drives the jets by magnetically extracting matter, angular momentum, and energy from the accretion disk. Two main regimes have been discussed theoretically, hydromagnetic winds which have a significant mass flux, and Poynting flux jets where the mass flux is negligible. Over the past several years, exciting new developments on models of jets have come from progress in MHD simulations which now allow the study of the origin - the acceleration and collima...

  14. Ringed accretion disks: equilibrium configurations

    CERN Document Server

    Pugliese, D

    2015-01-01

    We investigate a model of ringed accretion disk, made up by several rings rotating around a supermassive Kerr black hole attractor. Each toroid of the ringed disk is governed by the General Relativity hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. Properties of the tori can be then determined by an appropriately defined effective potential reflecting the background Kerr geometry and the centrifugal effects. The ringed disks could be created in various regimes during the evolution of matter configurations around supermassive black holes. Therefore, both corotating and counterrotating rings have to be considered as being a constituent of the ringed disk. We provide constraints on the model parameters for the existence and stability of various ringed configurations and discuss occurrence of accretion onto the Kerr black hole and possible launching of jets from the ringed disk. We demonstrate that various ringed disks can be characterized by a maximum number of rings. We pr...

  15. Poynting Jets from Accretion Disks

    CERN Document Server

    Lovelace, R V E; Ustyugova, G V; Romanova, M M; Colgate, S A

    2002-01-01

    The powerful narrow jets observed to emanate from many compact accreting objects may arise from the twisting of a magnetic field threading a differentially rotating accretion disk which acts to magnetically extract angular momentum and energy from the disk. Two main regimes have been discussed, {\\it hydromagnetic outflows}, which have a significant mass flux and have energy and angular momentum carried by both the matter and the electromagnetic field and, Poynting outflows, where the mass flux is negligible and energy and angular momentum are carried predominantly by the electromagnetic field. Here we consider a Keplerian disk initially threaded by a dipole-like magnetic field and we present solutions of the force-free Grad-Shafranov equation for the coronal plasma. We find solutions with Poynting jets where there is a continuous outflow of energy and toroidal magnetic flux from the disk into the external space. This behavior contradicts the commonly accepted ``theorem'' of Solar plasma physics that the motio...

  16. RINGED ACCRETION DISKS: EQUILIBRIUM CONFIGURATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Pugliese, D.; Stuchlík, Z., E-mail: d.pugliese.physics@gmail.com, E-mail: zdenek.stuchlik@physics.cz [Institute of Physics and Research Centre of Theoretical Physics and Astrophysics, Faculty of Philosophy and Science, Silesian University in Opava, Bezručovo náměstí 13, CZ-74601 Opava (Czech Republic)

    2015-12-15

    We investigate a model of a ringed accretion disk, made up by several rings rotating around a supermassive Kerr black hole attractor. Each toroid of the ringed disk is governed by the general relativity hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. Properties of the tori can then be determined by an appropriately defined effective potential reflecting the background Kerr geometry and the centrifugal effects. The ringed disks could be created in various regimes during the evolution of matter configurations around supermassive black holes. Therefore, both corotating and counterrotating rings have to be considered as being a constituent of the ringed disk. We provide constraints on the model parameters for the existence and stability of various ringed configurations and discuss occurrence of accretion onto the Kerr black hole and possible launching of jets from the ringed disk. We demonstrate that various ringed disks can be characterized by a maximum number of rings. We present also a perturbation analysis based on evolution of the oscillating components of the ringed disk. The dynamics of the unstable phases of the ringed disk evolution seems to be promising in relation to high-energy phenomena demonstrated in active galactic nuclei.

  17. Evolution and precession of accretion disk in tidal disruption events

    Directory of Open Access Journals (Sweden)

    Matzner C.D.

    2012-12-01

    Full Text Available In a supermassive black hole (BH tidal disruption event (TDE, the tidally disrupted star feeds the BH via an accretion disk. Most often it is assumed that the accretion rate history, hence the emission light curve, tracks the rate at which new debris mass falls back onto the disk, notably the t−5/3 power law. But this is not the case when the disk evolution due to viscous spreading - the driving force for accretion - is carefully considered. We construct a simple analytical model that comprehensively describes the accretion rate history across 4 different phases of the disk evolution, in the presence of mass fallback and disk wind loss. Accretion rate evolves differently in those phases which are governed by how the disk heat energy is carried away, early on by advection and later by radiation. The accretion rate can decline as steeply as t−5/3 only if copious disk wind loss is present during the early advection-cooled phase. Later, the accretion rate history is t−8/7 or shallower. These have great implications on the TDE flare light curve. A TDE accretion disk is most likely misaligned with the equatorial plane of the spinning BH. Moreover, in the TDE the accretion rate is super- or near-Eddington thus the disk is geometrically thick, for which case the BH’s frame dragging effect may cause the disk precess as a solid body, which may manifest itself as quasi-periodic signal in the TDE light curve. Our disk evolution model predicts the disk precession period increases with time, typically as ∝ t. The results are applied to the recently jetted TDE flare Swift transient J1644 + 57 which shows numerous, quasi-periodic dips in its long-term X-ray light curve. As the current TDE sample increases, the identification of the disk precession signature provides a unique way of measuring BH spin and studying BH accretion physics.

  18. Stratified Magnetically-Driven Accretion-Disk Winds and Their Relations to Jets

    CERN Document Server

    Fukumura, Keigo; Kazanas, Demosthenes; Shrader, Chris; Behar, Ehud; Contopoulos, Ioannis

    2013-01-01

    We explore the poloidal structure of two-dimensional (2D) MHD winds in relation to their potential association with the X-ray warm absorbers (WAs) and the highly-ionized ultra-fast outflows (UFOs) in AGN, in a single unifying approach. We present the density $n(r,\\theta)$, ionization parameter $\\xi(r,\\theta)$, and velocity structure $v(r,\\theta)$ of such ionized winds for typical values of their fluid-to-magnetic flux ratio, $F$, and specific angular momentum, $H$, for which wind solutions become super-\\Alfvenic. We explore the geometrical shape of winds for different values of these parameters and delineate the values that produce the widest and narrowest opening angles of these winds, quantities necessary in the determination of the statistics of AGN obscuration. We find that winds with smaller $H$ show a poloidal geometry of narrower opening angles with their \\Alfven\\ surface at lower inclination angles and therefore they produce the highest line of sight (LoS) velocities for observers at higher latitudes ...

  19. Regulation of black-hole accretion by a disk wind during a violent outburst of V404 Cygni

    CERN Document Server

    Muñoz-Darias, T; Sánchez, D Mata; Fender, R P; Padilla, M Armas; Linares, M; Ponti, G; Charles, P A; Mooley, K P; Rodriguez, J

    2016-01-01

    Accretion of matter onto black holes is universally associated with strong radiative feedback and powerful outflows. In particular, black hole transients show outflows whose properties are strongly coupled to those of the accretion flow. This includes X-ray winds of ionized material, expelled from the accretion disc encircling the black hole, and collimated radio jets. Very recently, a distinct optical variability pattern has been reported in the transient black hole transient V404 Cyg, and interpreted as disrupted mass flow into the inner regions of its large accretion disc. Here, we report on the discovery of a sustained outer accretion disc wind in V404 Cyg, which is unlike any seen previously. We find that the outflowing wind is neutral, has a large covering factor, expands at 1% of the speed of light and triggers a nebular phase once accretion sharply drops and the ejecta become optically thin. The large expelled mass (> 10^-8 Msun) indicates that the outburst was prematurely ended when a sizeable fracti...

  20. Evolution of Accretion Disks in Tidal Disruption Events

    CERN Document Server

    Shen, Rong-Feng

    2013-01-01

    In a stellar tidal disruption event (TDE), an accretion disk forms as the stellar debris returns and circularizes. Rather than being confined within the circularizing radius, the disk can spread to larger radii to conserve angular momentum. An outer spreading disk is a source of matter for re-accretion at rates which can exceed the later stellar fall-back rate, although a disk wind can suppress its contribution to the central black hole accretion rate. A spreading disk is detectible through a break in the central accretion rate history, or, at longer wavelengths, by its own emission. Moreover, as an angular momentum reservoir, it can broadcast its existence by affecting the disk precession rate. Because these features depend on the disk's internal viscosity and the nature of wind produced in its early, advection-dominated phase, they are useful probes of transient disk physics. To model the evolution of TDE disk size and accretion rate, we account for the possibility of thermal instability for accretion rates...

  1. Theory of Disk Accretion onto Magnetic Stars

    CERN Document Server

    Lai, Dong

    2014-01-01

    Disk accretion onto magnetic stars occurs in a variety of systems, including accreting neutron stars (with both high and low magnetic fields), white dwarfs, and protostars. We review some of the key physical processes in magnetosphere-disk interaction, highlighting the theoretical uncertainties. We also discuss some applications to the observations of accreting neutron stars and protostellar systems, as well as possible connections to protoplanetary disks and exoplanets.

  2. Theory of Disk Accretion onto Magnetic Stars

    Directory of Open Access Journals (Sweden)

    Lai Dong

    2014-01-01

    Full Text Available Disk accretion onto magnetic stars occurs in a variety of systems, including accreting neutron stars (with both high and low magnetic fields, white dwarfs, and protostars. We review some of the key physical processes in magnetosphere-disk interaction, highlighting the theoretical uncertainties. We also discuss some applications to the observations of accreting neutron star and protostellar systems, as well as possible connections to protoplanetary disks and exoplanets.

  3. Global Models for Embedded, Accreting Protostellar Disks

    CERN Document Server

    Kratter, Kaitlin M; Krumholz, Mark R

    2007-01-01

    Most analytic work to date on protostellar disks has focused on disks in isolation from their environments. However, observations are now beginning to probe the earliest, most embedded phases of star formation, during which disks are rapidly accreting from their parent cores and cannot be modeled in isolation. We present a simple, one-zone model of protostellar accretion disks with high mass infall rates. Our model combines a self-consistent calculation of disk temperatures with an approximate treatment of angular momentum transport via several mechanisms. We use this model to survey the properties of protostellar disks across a wide range of stellar masses and evolutionary times, and make predictions for disks' masses, sizes, spiral structure, and fragmentation that will be directly testable by future large-scale surveys of deeply embedded disks. We define a dimensionless accretion-rotation parameter which, in conjunction with the disk's temperature, controls the disk evolution. We track the dominant mode of...

  4. Foundations of Black Hole Accretion Disk Theory.

    Science.gov (United States)

    Abramowicz, Marek A; Fragile, P Chris

    2013-01-01

    This review covers the main aspects of black hole accretion disk theory. We begin with the view that one of the main goals of the theory is to better understand the nature of black holes themselves. In this light we discuss how accretion disks might reveal some of the unique signatures of strong gravity: the event horizon, the innermost stable circular orbit, and the ergosphere. We then review, from a first-principles perspective, the physical processes at play in accretion disks. This leads us to the four primary accretion disk models that we review: Polish doughnuts (thick disks), Shakura-Sunyaev (thin) disks, slim disks, and advection-dominated accretion flows (ADAFs). After presenting the models we discuss issues of stability, oscillations, and jets. Following our review of the analytic work, we take a parallel approach in reviewing numerical studies of black hole accretion disks. We finish with a few select applications that highlight particular astrophysical applications: measurements of black hole mass and spin, black hole vs. neutron star accretion disks, black hole accretion disk spectral states, and quasi-periodic oscillations (QPOs).

  5. Winds from disks in compact binaries

    Energy Technology Data Exchange (ETDEWEB)

    Mauche, C.W.

    1993-10-27

    We herein present an observational and theoretical review of the winds of compact binaries. After a brief consideration of the accretion disk coronae and winds of X-ray binaries, the review concentrates on the winds of cataclysmic variables (CVs). Specifically, we consider the related problems of the geometry and mass-loss rate of the winds of CVs, their ionization state and variability, and the results from studies of eclipsing CVs. Finally, the properties of bona fide accretion disk wind models are reviewed.

  6. Two-dimensional vortices and accretion disks

    NARCIS (Netherlands)

    Nauta, Michiel Doede

    2001-01-01

    Observations show that there are disks around certain stars that slowly rain down on the central (compact) object: accretion disks. The rate of depletion of the disk might be slow but is still larger than was expected on theoretical grounds. That is why it has been suggested that the disks are tu

  7. Discovery of very high velocity outflow in V Hydra - Wind from an accretion disk in a binary?

    Science.gov (United States)

    Sahai, R.; Wannier, P. G.

    1988-01-01

    High-resolution observations of lines from the CO v = 1-0 vibration-rotation band at 4.6 microns, taken with the FTS/KPNO 4-m telescope, are reported for the carbon-rich red giant V Hydra, which is surrounded by an extended expanding molecular envelope resulting from extensive mass loss. The spectrum shows, in addition to the expected absorption at the outflow velocity of the envelope, absorption extending up to 120 km/s bluewards of the stellar velocity. A comparison of the spectrum observed at two epochs shows that the high-velocity absorption features change with time. It is suggested that the observed high-velocity features in V Hydra arise in a high-velocity polar outflow from an accretion disk in a binary system, as proposed in the mass-loss model for bipolar envelopes by Morris (1988).

  8. Interaction of Accretion Shocks with Winds

    Indian Academy of Sciences (India)

    Kinsuk Acharya; Sandip K. Chakrabarti; D. Molteni

    2002-03-01

    Accretion shocks are known to oscillate in presence of cooling processes in the disk. This oscillation may also cause quasi-periodic oscillations of black holes. In the presence of strong winds, these shocks have oscillations in vertical direction as well.We show examples of shock oscillations under the influence of both the effects. When the shocks are absent and the flow is cooler, the wind becomes weaker and the vertical oscillation becomes negligible.

  9. Accretion disks in Algols: progenitors and evolution

    CERN Document Server

    Van Rensbergen, W

    2016-01-01

    There are only a few Algols with measured accretion disk parameters. These measurements provide additional constraints for tracing the origin of individual systems, narrowing down the initial parameter space. We investigate the origin and evolution of 6 Algol systems with accretion disks to find the initial parameters and evolutionary constraints for them. With a modified binary evolution code, series of close binary evolution are calculated to obtain the best match for observed individual systems. Initial parameters for 6 Algol systems with accretion disks were determined matching both the present system parameters and the observed disk characteristics. When RLOF starts during core hydrogen burning of the donor, the disk lifetime was found to be short. The disk luminosity is comparable to the luminosity of the gainer during a large fraction of the disk lifetime.

  10. Magneto-thermal Disk Winds from Protoplanetary Disks

    Science.gov (United States)

    Bai, Xue-Ning; Ye, Jiani; Goodman, Jeremy; Yuan, Feng

    2016-02-01

    The global evolution and dispersal of protoplanetary disks (PPDs) are governed by disk angular-momentum transport and mass-loss processes. Recent numerical studies suggest that angular-momentum transport in the inner region of PPDs is largely driven by magnetized disk wind, yet the wind mass-loss rate remains unconstrained. On the other hand, disk mass loss has conventionally been attributed to photoevaporation, where external heating on the disk surface drives a thermal wind. We unify the two scenarios by developing a one-dimensional model of magnetized disk winds with a simple treatment of thermodynamics as a proxy for external heating. The wind properties largely depend on (1) the magnetic field strength at the wind base, characterized by the poloidal Alfvén speed vAp, (2) the sound speed cs near the wind base, and (3) how rapidly poloidal field lines diverge (achieve {R}-2 scaling). When {v}{Ap}\\gg {c}{{s}}, corotation is enforced near the wind base, resulting in centrifugal acceleration. Otherwise, the wind is accelerated mainly by the pressure of the toroidal magnetic field. In both cases, the dominant role played by magnetic forces likely yields wind outflow rates that exceed purely hydrodynamical mechanisms. For typical PPD accretion-rate and wind-launching conditions, we expect vAp to be comparable to cs at the wind base. The resulting wind is heavily loaded, with a total wind mass-loss rate likely reaching a considerable fraction of the wind-driven accretion rate. Implications for modeling global disk evolution and planet formation are also discussed.

  11. Phase transitions and He-synthesis driven winds in neutrino cooled accretion disks: prospects for late flares in short gamma-ray bursts

    CERN Document Server

    Lee, William H; Diego-Lopez-Camara,

    2009-01-01

    We consider the long term evolution of debris following the tidal disruption of compact stars in the context of short gamma ray bursts (SGRBs). The initial encounter impulsively creates a hot, dense, neutrino-cooled disk capable of powering the prompt emission. After a long delay, we find that powerful winds are launched from the surface of the disk, driven by the recombination of free nucleons into alpha-particles. The associated energy release depletes the mass supply and eventually shuts off activity of the central engine. As a result, the luminosity and mass accretion rate deviate from the earlier self-similar behavior expected for an isolated ring with efficient cooling. This then enables a secondary episode of delayed activity to become prominent as an observable signature, when material in the tidal tails produced by the initial encounter returns to the vicinity of the central object. The time scale of the new accretion event can reach tens of seconds to minutes, depending on the details of the system....

  12. Generalized Similarity for Accretion/Decretion Disks

    Science.gov (United States)

    Rafikov, Roman R.

    2016-10-01

    Decretion (or external) disks are gas disks freely expanding to large radii due to their internal stresses. They are expected to naturally arise in tidal disruption events, around Be stars, in mass-losing post-main-sequence binaries, as a result of supernova fallback, etc. Their evolution is theoretically understood in two regimes: when the central object does not exert torque on the disk (a standard assumption for conventional accretion disks) or when no mass inflow (or outflow) occurs at the disk center. However, many astrophysical objects—circumbinary disks, Be stars, neutron stars accreting in a propeller regime, etc.—feature non-zero torque simultaneously with the non-zero accretion (or ejection of mass) at the disk center. We provide a general description for the evolution of such disks (both linear and nonlinear) in the self-similar regime, to which the disk should asymptotically converge with time. We identify a similarity parameter λ, which is uniquely related to the degree, to which the central mass accretion is suppressed by the non-zero central torque. The known decretion disk solutions correspond to the two discrete values of λ, while our new solutions cover a continuum of its physically allowed values, corresponding to either accretion or mass ejection by the central object. A direct relationship between λ and central \\dot{M} and torque is also established. We describe the time evolution of the various disk characteristics for different λ, and show that the observable properties (spectrum and luminosity evolution) of the decretion disks, in general, are different from the standard accretion disks with no central torque.

  13. Accretion disks around a mass with quadrupole

    CERN Document Server

    Abishev, Medeu; Quevedo, Hernando; Toktarbay, Saken

    2015-01-01

    We consider the stability properties of test particles moving along circular orbits around a mass with quadrupole. We show that the quadrupole modifies drastically the properties of an accretion disk made of such test particles.

  14. The large scale magnetic fields of thin accretion disks

    CERN Document Server

    Cao, Xinwu

    2013-01-01

    Large scale magnetic field threading an accretion disk is a key ingredient in the jet formation model. The most attractive scenario for the origin of such a large scale field is the advection of the field by the gas in the accretion disk from the interstellar medium or a companion star. However, it is realized that outward diffusion of the accreted field is fast compared to the inward accretion velocity in a geometrically thin accretion disk if the value of the Prandtl number Pm is around unity. In this work, we revisit this problem considering the angular momentum of the disk is removed predominantly by the magnetically driven outflows. The radial velocity of the disk is significantly increased due to the presence of the outflows. Using a simplified model for the vertical disk structure, we find that even moderately weak fields can cause sufficient angular momentum loss via a magnetic wind to balance outward diffusion. There are two equilibrium points, one at low field strengths corresponding to a plasma-bet...

  15. Gas dynamics for accretion disk simulations

    Science.gov (United States)

    Whitehurst, R.

    1994-01-01

    The behavior of accretion disks can largely be understood in terms of the basic physical processes of mass, energy, and momentum conservation. Despite this, detailed modeling of these systems using modern computational techniques is challenging and controversial. Disturbing differences exist between methods used widely in astrophysics, namely Eulerian finite-difference techniques and particle codes such as SPH. Therefore neither technique is fully satisfactory for accretion disk simulations. This paper describes a new fully Lagrangian method designed to resolve these difficulties.

  16. Reverberation Mapping of AGN Accretion Disks

    Science.gov (United States)

    Fausnaugh, Michael; AGN STORM Collaboration

    2017-01-01

    I will discuss new reverberation mapping results that allow us to investigate the temperature structure of AGN accretion disks. By measuring time-delays between broad-band continuum light curves, we can determine the size of the disk as a function of wavelength. I will discuss the detection of continuum lags in NGC 5548 reported by the AGN STORM project and implications for the accretion disk. I will also present evidence for continuum lags in two other AGN for which we recently measured black hole masses from continuum-Hbeta reverberations. The mass measurements allow us to compare the continuum lags to predictions from standard thin disk theory, and our results indicate that the accretion disks are larger than the simplest expectations.

  17. MHD Turbulence in Accretion Disk Boundary Layers

    CERN Document Server

    Chan, Chi-kwan

    2012-01-01

    The physical modeling of the accretion disk boundary layer, the region where the disk meets the surface of the accreting star, usually relies on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear viscosity, widely adopted in astrophysics, satisfies this assumption by construction. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability is inefficient in this inner disk region. I will discuss the results of a recent study on the generation of hydromagnetic stresses and energy density in the boundary layer around a weakly magnetized star. Our findings suggest that although magnetic energy density can be significantly amplified in this region, angular momentum transport is rather inefficient. This seems consistent with the results obtained in numerical simulations...

  18. Accretion, Outflows, and Winds of Magnetized Stars

    CERN Document Server

    Romanova, M M

    2016-01-01

    Many types of stars have strong magnetic fields that can dynamically influence the flow of circumstellar matter. In stars with accretion disks, the stellar magnetic field can truncate the inner disk and determine the paths that matter can take to flow onto the star. These paths are different in stars with different magnetospheres and periods of rotation. External field lines of the magnetosphere may inflate and produce favorable conditions for outflows from the disk-magnetosphere boundary. Outflows can be particularly strong in the propeller regime, wherein a star rotates more rapidly than the inner disk. Outflows may also form at the disk-magnetosphere boundary of slowly rotating stars, if the magnetosphere is compressed by the accreting matter. In isolated, strongly magnetized stars, the magnetic field can influence formation and/or propagation of stellar wind outflows. Winds from low-mass, solar-type stars may be either thermally or magnetically driven, while winds from massive, luminous O and B type stars...

  19. Accretion of solid materials onto circumplanetary disks from protoplanetary disks

    Energy Technology Data Exchange (ETDEWEB)

    Tanigawa, Takayuki [Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819 (Japan); Maruta, Akito; Machida, Masahiro N., E-mail: tanigawa@pop.lowtem.hokudai.ac.jp [Department of Earth and Planetary Sciences, Kyushu University, Fukuoka 812-8581 (Japan)

    2014-04-01

    We investigate the accretion of solid materials onto circumplanetary disks from heliocentric orbits rotating in protoplanetary disks, which is a key process for the formation of regular satellite systems. In the late stage of the gas-capturing phase of giant planet formation, the accreting gas from protoplanetary disks forms circumplanetary disks. Since the accretion flow toward the circumplanetary disks affects the particle motion through gas drag force, we use hydrodynamic simulation data for the gas drag term to calculate the motion of solid materials. We consider a wide range of size for the solid particles (10{sup –2}-10{sup 6} m), and find that the accretion efficiency of the solid particles peaks around 10 m sized particles because energy dissipation of drag with circum-planetary disk gas in this size regime is most effective. The efficiency for particles larger than 10 m becomes lower because gas drag becomes less effective. For particles smaller than 10 m, the efficiency is lower because the particles are strongly coupled with the background gas flow, which prevents particles from accretion. We also find that the distance from the planet where the particles are captured by the circumplanetary disks is in a narrow range and well described as a function of the particle size.

  20. Early dust evolution in protostellar accretion disks

    OpenAIRE

    2000-01-01

    We investigate dust dynamics and evolution during the formation of a protostellar accretion disk around intermediate mass stars via 2D numerical simulations. Using three different detailed dust models, compact spherical particles, fractal BPCA grains, and BCCA grains, we find that even during the early collapse and the first 10,000 yr of dynamical disk evolution, the initial dust size distribution is strongly modified. Close to the disk's midplane coagulation produces dust particles of sizes ...

  1. Disks, accretion and outflows of brown dwarfs

    CERN Document Server

    Joergens, V; Liu, Y; Pascucci, I; Whelan, E; Alcala, J; Biazzo, K; Costigan, G; Gully-Santiago, M; Henning, Th; Natta, A; Rigliaco, E; Rodriguez-Ledesma, V; Sicilia-Aguilar, A; Tottle, J; Wolf, S

    2012-01-01

    Characterization of the properties of young brown dwarfs are important to constraining the formation of objects at the extreme low-mass end of the IMF. While young brown dwarfs share many properties with solar-mass T Tauri stars, differences may be used as tests of how the physics of accretion/outflow and disk chemistry/dissipation depend on the mass of the central object. This article summarizes the presentations and discussions during the splinter session on 'Disks, accretion and outflows of brown dwarfs' held at the CoolStars17 conference in Barcelona in June 2012. Recent results in the field of brown dwarf disks and outflows include the determination of brown dwarf disk masses and geometries based on Herschel far-IR photometry (70-160 um), accretion properties based on X-Shooter spectra, and new outflow detections in the very low-mass regime.

  2. Generalized Similarity for Accretion/Decretion Disks

    CERN Document Server

    Rafikov, Roman R

    2016-01-01

    Decretion (or external) disks are gas disks freely expanding to large radii due to their internal stresses. They are expected to naturally arise in tidal disruption events, around Be stars, in mass-losing post main sequence binaries, as a result of supernova fallback, etc. Their evolution is theoretically understood in two regimes: when the central object does not exert torque on the disk (a standard assumption for conventional accretion disks) or when no mass inflow (or outflow) occurs at the disk center. However, many astrophysical objects - circumbinary disks, Be stars, neutron stars accreting in a propeller regime, etc. - feature non-zero torque simultaneously with the non-zero accretion (or ejection of mass) at the disk center. We provide a general description for the evolution of such disks (both linear and non-linear) in the self-similar regime, to which the disk should asymptotically converge with time. We identify a similarity parameter $\\lambda$, which is uniquely related to the degree, to which the...

  3. Sub-Keplerian accretion onto circumstellar disks

    CERN Document Server

    Visser, R

    2010-01-01

    Models of the formation, evolution and photoevaporation of circumstellar disks are an essential ingredient in many theories of the formation of planetary systems. The ratio of disk mass over stellar mass in the circumstellar phase of a disk is largely determined by the angular momentum of the original cloud core from which the system was formed. While full 3D or 2D axisymmetric hydrodynamical models of accretion onto the disk automatically treat all aspects of angular momentum, this is not so trivial for 1D and semi-2D viscous disk models. Since 1D and semi-2D disk models are still very useful for long-term evolutionary modelling of disks with relatively little numerical effort, we investigate how the 2D nature of accretion affects the formation and evolution of the disk in such models. A proper treatment of this problem requires a correction for the sub-Keplerian velocity at which accretion takes place. We develop an update of our semi-2D time-dependent disk evolution model to properly treat the effects of s...

  4. Advection of magnetic flux by accretion disks around neutron stars

    Science.gov (United States)

    Flores-Tulian, S.; Reisenegger, A.

    The aim of our research is to address why millisecond pulsars have relatively weak surface magnetic fields, of about 10^8 G, with a narrow spread. We propose that the accretion of plasma from the companion star fully screens the original neutron star field, but the accretion disk carries additional magnetic flux from the companion star, or itself can generate field by means of dynamo processes. For a strongly magnetized star, the field prevents the disk from approaching the star. The accretion is along the field lines and deposits the matter on the polar cap. Then, the accreted plasma flows, dragging with itself the magnetic field lines, from the pole to the equator (Payne & Melatos 2004). In a following stage, when the star becomes non-magnetic, because the field has been buried, the disk touches the star. We suggest that some effective mechanism of magnetic flux transport such as that proposed by Spruit & Uzdensky 2005 (or Bisnovatyi-Kogan & Lovelace 2007), operates and necessarily leads to a "strongly magnetized disk''. It becomes laminar because the magneto-rotational instability saturates (it is considered to be responsible for turbulence in the disk), and the magnetic difussivity is negligible. Then, the loss of angular momentum allowing the accretion is only caused by the magneto-centrifugal disk-wind (Blandford & Payne 1982). Meanwhile, the wind-driven transport of the magnetic flux by the disk re-magnetizes the star. This process continues until the Lorentz force due to the star's magnetic field forbids any further accretion of matter and magnetic flux, in the Ideal Magneto-Hydro-Dynamics approach. Additional of material can fall onto the star (but at lower rate) if some instability process sets in, allowing the diffusion of mass through the magnetic field lines (e.g the Interchange Instability, Spruit & Taam 1990). All these processes might lead to an asymptotic magnetic field of 10^8 G,as is inferred from observations. We are developing a self

  5. Earth, Moon, Sun, and CV Accretion Disks

    CERN Document Server

    Montgomery, M M

    2009-01-01

    Net tidal torque by the secondary on a misaligned accretion disk, like the net tidal torque by the Moon and the Sun on the equatorial bulge of the spinning and tilted Earth, is suggested by others to be a source to retrograde precession in non-magnetic, accreting Cataclysmic Variable (CV) Dwarf Novae systems that show negative superhumps in their light curves. We investigate this idea in this work. We generate a generic theoretical expression for retrograde precession in spinning disks that are misaligned with the orbital plane. Our generic theoretical expression matches that which describes the retrograde precession of Earths' equinoxes. By making appropriate assumptions, we reduce our generic theoretical expression to those generated by others, or to those used by others, to describe retrograde precession in protostellar, protoplanetary, X-ray binary, non-magnetic CV DN, quasar and black hole systems. We find that differential rotation and effects on the disk by the accretion stream must be addressed. Our a...

  6. Accretion disks in luminous young stellar objects

    CERN Document Server

    Beltran, M T

    2015-01-01

    An observational review is provided of the properties of accretion disks around young stars. It concerns the primordial disks of intermediate- and high-mass young stellar objects in embedded and optically revealed phases. The properties were derived from spatially resolved observations and therefore predominantly obtained with interferometric means, either in the radio/(sub)millimeter or in the optical/infrared wavelength regions. We make summaries and comparisons of the physical properties, kinematics, and dynamics of these circumstellar structures and delineate trends where possible. Amongst others, we report on a quadratic trend of mass accretion rates with mass from T Tauri stars to the highest mass young stellar objects and on the systematic difference in mass infall and accretion rates.

  7. On the Flaring of Jet-sustaining Accretion Disks

    CERN Document Server

    Namouni, Fathi

    2009-01-01

    Jet systems with two unequal components interact with their parent accretion disks through the asymmetric removal of linear momentum from the star-disk system. We show that as a result of this interaction, the disk's state of least energy is not made up of orbits that lie in a plane containing the star's equator as in a disk without a jet. The disk's profile has the shape of a sombrero curved in the direction of acceleration. For this novel state of minimum energy, we derive the temperature profile of thin disks. The flaring geometry caused by the sombrero profile increases the disk temperature especially in its outer regions. The jet-induced acceleration disturbs the vertical equilibrium of the disk leading to mass loss in the form of a secondary wind emanating from the upper face of the disk. Jet time variability causes the disk to radially expand or contract depending on whether the induced acceleration increases or decreases. Jet time variability also excites vertical motion and eccentric distortions in t...

  8. Structures of magnetized thin accretion disks

    Institute of Scientific and Technical Information of China (English)

    LI; xiaoqing(李晓卿); JI; Haisheng(季海生)

    2002-01-01

    We investigate the magnetohydrodynamic (MHD) process in thin accretion disks. Therelevant momentum as well as magnetic reduction equations in the thin disk approximation areincluded. On the basis of these equations, we examine numerically the stationary structures, includingdistributions of the surface mass density, temperature and flow velocities of a disk around a youngstellar object (YSO). The numerical results are as follows: (i) There should be an upper limit to themagnitude of magnetic field, such an upper limit corresponds to the equipartition field. For relevantmagnitude of magnetic field of the disk's interior the disk remains approximately Keplerian. (ii) Thedistribution of effective temperature T(r) is a smoothly decreasing function of radius with power 1 corresponding to the observed radiation flux density, provided that the magnetic fieldindex γ= -1/2,is suitably chosen.

  9. FITDisk: Cataclysmic Variable Accretion Disk Demonstration Tool

    Science.gov (United States)

    Wood, Matthew A.; Dolence, J.

    2013-05-01

    FITDisk models accretion disk phenomena using a fully three-dimensional hydrodynamics calculation, and data can either be visualized as they are computed or stored to hard drive for later playback at a fast frame rate. Simulations are visualized using OpenGL graphics and the viewing angle can be changed interactively. Pseudo light curves of simulated systems can be plotted along with the associated Fourier amplitude spectrum. It provides an easy to use graphical user interface as well as 3-D interactive graphics. The code computes the evolution of a CV accretion disk, visualizes results in real time, records and plays back simulations, and generates and plots pseudo light curves and associated power spectra.

  10. Turbulent Comptonization in Black Hole Accretion Disks

    CERN Document Server

    Socrates, A; Blaes, Omer M; Socrates, Aristotle; Davis, Shane W.; Blaes, Omer

    2004-01-01

    In the inner-most regions of radiation pressure supported accretion disks, the turbulent magnetic pressure may greatly exceed that of the gas. If this is the case, it is possible for bulk Alfvenic motions driven by the magnetorotational instability (MRI) to surpass the electron thermal velocity. Bulk rather than thermal Comptonization may then be the dominant radiative process which mediates gravitational energy release. For sufficiently large turbulent stresses, we show that turbulent Comptonization produces a significant contribution to the far-UV and X-ray emission of black hole accretion disks. The existence of this spectral component provides a means of obtaining direct observational constraints on the nature of the turbulence itself. We describe how this component may affect the spectral energy distributions and variability properties of X-ray binaries and active galactic nuclei.

  11. Viscous Stability of Relativistic Keplerian Accretion Disks

    CERN Document Server

    Ghosh, P

    1998-01-01

    We investigate the viscous stability of thin, Keplerian accretion disks in regions where general relativistic (GR) effects are essential. For gas pressure dominated (GPD) disks, we show that the Newtonian conclusion that such disks are viscously stable is reversed by GR modifications in the behaviors of viscous stress and surface density over a significantly large annular region not far from the innermost stable orbit at $r=\\rms$. For slowly-rotating central objects, this region spans a range of radii $14\\lo r\\lo 19$ in units of the central object's mass $M$. For radiation pressure dominated (RPD) disks, the Newtonian conclusion that they are viscously unstable remains valid after including the above GR modifications, except in a very small annulus around $r\\approx 14M$, which has a negligible influence. Inclusion of the stabilizing effect of the mass-inflow through the disk's inner edge via a GR analogue of Roche-lobe overflow adds a small, stable region around \\rms~for RPD disks, but leaves GPD disks unchan...

  12. Disk Accretion Onto High-Mass Planets

    CERN Document Server

    Lubow, S H; Artymowicz, P

    1999-01-01

    We analyze the nonlinear, two-dimensional response of a gaseous, viscous protoplanetary disk to the presence of a planet of one Jupiter mass (1 M_J) and greater that orbits a 1 solar mass star by using the ZEUS hydrodynamics code with high resolution near the planet's Roche lobe. The planet is assumed to be in a circular orbit about the central star and is not allowed to migrate. A gap is formed about the orbit of the planet, but there is a nonaxisymmetric flow through the gap and onto the planet. The gap partitions the disk into an inner (outer) disk that extends inside (outside) the planet's orbit. For a 1 M_J planet and typical disk parameters, the accretion through the gap onto the planet is highly efficient. For typical disk parameters, the mass doubling time scale is less than 10^5 years, considerably shorter than the disk lifetime. Following shocks near the L1 and L2 Lagrange points, disk material enters the Roche lobe in the form of two gas streams. Shocks occur within the Roche lobe as the gas stream...

  13. Accretion Disks around Young Low Mass Stars

    Directory of Open Access Journals (Sweden)

    Paola D´Alessio

    2001-01-01

    Full Text Available In the past decade, it has become clear that almost half of the low mass pre-main sequence stars are surrounded by disks, which are responsible for the observed infrared and optical-UV excess emission. The characterization of the structure of circumstellar disks is a crucial step towards understanding the early stellar evolution and planet formation. The thesis summarized here presents physical models of the detailed structure of accretion disks surrounding T Tauri stars. The disks are assumed to be in steady state, in vertical hydrostatic equilibrium, and with a turbulent viscosity described by the alpha-prescription. We consider different heating mechanisms: viscous dissipation, heating by cosmic rays and radioactive decay, irradiation by the central star or irradiation by an infalling envelope. The energy is transported in the vertical direction by radiation, convection and the turbulent flux. Give n the disk structure, we calculate its emission by integrating the radiative transfer equation for an arbitrary orientation of the disk relative to the line of sight. Spectral energy distributions (SEDs and images are compared with observations, and disk properties can be inferred or constrained.

  14. Stability of black hole accretion disks

    Directory of Open Access Journals (Sweden)

    Czerny B.

    2012-12-01

    Full Text Available We discuss the issues of stability of accretion disks that may undergo the limit-cycle oscillations due to the two main types of thermal-viscous instabilities. These are induced either by the domination of radiation pressure in the innermost regions close to the central black hole, or by the partial ionization of hydrogen in the zone of appropriate temperatures. These physical processes may lead to the intermittent activity in AGN on timescales between hundreds and millions of years. We list a number of observational facts that support the idea of the cyclic activity in high accretion rate sources. We conclude however that the observed features of quasars may provide only indirect signatures of the underlying instabilities. Also, the support from the sources with stellar mass black holes, whose variability timescales are observationally feasible, is limited to a few cases of the microquasars. Therefore we consider a number of plausible mechanisms of stabilization of the limit cycle oscillations in high accretion rate accretion disks. The newly found is the stabilizing effect of the stochastic viscosity fluctuations.

  15. Bondi-Hoyle-Lyttleton Accretion onto a Protoplanetary Disk

    CERN Document Server

    Moeckel, Nickolas

    2009-01-01

    Young stellar systems orbiting in the potential of their birth cluster can accrete from the dense molecular interstellar medium during the period between the star's birth and the dispersal of the cluster's gas. Over this time, which may span several Myr, the amount of material accreted can rival the amount in the initial protoplanetary disk; the potential importance of this `tail-end' accretion for planet formation was recently highlighted by Throop & Bally (2008). While accretion onto a point mass is successfully modeled by the classical Bondi-Hoyle-Lyttleton solutions, the more complicated case of accretion onto a star-disk system defies analytic solution. In this paper we investigate via direct hydrodynamic simulations the accretion of dense interstellar material onto a star with an associated gaseous protoplanetary disk. We discuss the changes to the structure of the accretion flow caused by the disk, and vice versa. We find that immersion in a dense accretion flow can redistribute disk material such ...

  16. GRS 1915+105 in "Soft State": Nature of Accretion Disk Wind and Origin of X-Ray Emission

    CERN Document Server

    Ueda, Yoshihiro; Remillard, Ronald

    2009-01-01

    We present the results from simultaneous Chandra HETGS and RXTE observations of the microquasar GRS 1915+105 in its quasi-stable "soft state" (or State A) performed on 2007 August 14, several days after the state transition from "hard state" (State C). The X-ray flux increased with spectral hardening around the middle of the Chandra observation, after which the 67 Hz QPO became significant. The HETGS spectra reveal at least 32 narrow absorption lines from highly ionized ions including Ne, Mg, Si, S, Ar, Ca, Cr, Mn, Fe, whose features are the deepest among those ever observed with Chandra from this source. We find that the absorber has outflow velocities of ~150 and ~500 km s^{-1} with a line-of-sight velocity dispersion of ~70 and ~200 km s^{-1} for the Si XIV and Fe XXVI ions, respectively. The larger velocity and its dispersion in heavier ions indicate that the wind has a non-uniform dynamical structure along the line-of-sight. The location of the absorber is estimated at ~(1-3)x10^5 r_g (r_g is the gravita...

  17. Waves and Instabilities in Accretion Disks MHD Spectroscopic Analysis

    CERN Document Server

    Keppens, R; Goedbloed, J P

    2002-01-01

    A complete analytical and numerical treatment of all magnetohydrodynamic waves and instabilities for radially stratified, magnetized accretion disks is presented. The instabilities are a possible source of anomalous transport. While recovering results on known hydrodynamicand both weak- and strong-field magnetohydrodynamic perturbations, the full magnetohydrodynamic spectra for a realistic accretion disk model demonstrates a much richer variety of instabilities accessible to the plasma than previously realized. We show that both weakly and strongly magnetized accretion disks are prone to strong non-axisymmetric instabilities.The ability to characterize all waves arising in accretion disks holds great promise for magnetohydrodynamic spectroscopic analysis.

  18. A Wind Accretion Model for HLX-1

    CERN Document Server

    Miller, M Coleman; Maccarone, Thomas J

    2014-01-01

    The brightest ultraluminous X-ray source currently known, HLX-1, has been observed to undergo five outburst cycles. The periodicity of these outbursts, and their high inferred maximum accretion rates of $\\sim{\\rm few}\\times 10^{-4} M_\\odot {\\rm yr}^{-1}$, naturally suggest Roche lobe overflow at the pericenter of an eccentric orbit. It is, however, difficult for the Roche lobe overflow model to explain the apparent trend of decreasing decay times over the different outbursts while the integrated luminosity also drops. Thus if the trend is real rather than simply being a reflection of the complex physics of accretion disks, a different scenario may be necessary. We present a speculative model in which, within the last decade, a high-mass giant star had most of its envelope tidally stripped by the $\\sim 10^{4-5} M_\\odot$ black hole in HLX-1, and the remaining core plus low-mass hydrogen envelope now feeds the hole with a strong wind. This model can explain the short decay time of the disk, and could explain the...

  19. Viscosity prescription for gravitationally unstable accretion disks

    CERN Document Server

    Rafikov, Roman R

    2015-01-01

    Gravitationally unstable accretion disks emerge in a variety of astrophysical contexts - giant planet formation, FU Orioni outbursts, feeding of AGNs, and the origin of Pop III stars. When a gravitationally unstable disk is unable to cool rapidly it settles into a quasi-stationary, fluctuating gravitoturbulent state, in which its Toomre Q remains close to a constant value Q_0~1. Here we develop an analytical formalism describing the evolution of such a disk, which is based on the assumptions of Q=Q_0 and local thermal equilibrium. Our approach works in the presence of additional sources of angular momentum transport (e.g. MRI), as well as external irradiation. Thermal balance dictates a unique value of the gravitoturbulent stress \\alpha_{gt} driving disk evolution, which is a function of the local surface density and angular frequency. We compare this approach with other commonly used gravitoturbulent viscosity prescriptions, which specify the explicit dependence of stress \\alpha_{gt} on Toomre Q in an ad hoc...

  20. Stability of accretion disk around rotating black holes

    CERN Document Server

    Mukhopadhyay, B

    2004-01-01

    I discuss the stability of accretion disks when the black hole is considered to be rotating. I show, how the fluid properties get changed for different choices of angular momentum of black holes. I treat the problem in pseudo-Newtonian approach with a suitable potential from Kerr geometry. When the angular momentum of a black hole is considered to be significant, the valid disk parameter region affects and a disk may become unstable. Also the possibility of shock in an accretion disk around rotating black holes is checked. When the black hole is chosen to be rotating, the sonic locations of the accretion disk get shifted or disappear, making the disk unstable by means of loosing entropy. To bring the disk in a stable situation, the angular momentum of the accreting matter has to be reduced/enhanced (for co/counter-rotating disk) by means of some physical process.

  1. SPIN EVOLUTION OF ACCRETING YOUNG STARS. II. EFFECT OF ACCRETION-POWERED STELLAR WINDS

    Energy Technology Data Exchange (ETDEWEB)

    Matt, Sean P. [Laboratoire AIM Paris-Saclay, CEA/Irfu Universite Paris-Diderot CNRS/INSU, 91191 Gif-sur-Yvette (France); Pinzon, Giovanni [Observatorio Astronomico Nacional, Facultad de Ciencias, Universidad Nacional de Colombia, Bogota (Colombia); Greene, Thomas P. [NASA Ames Research Center, M.S. 245-6, Moffett Field, CA 94035-1000 (United States); Pudritz, Ralph E., E-mail: sean.matt@cea.fr, E-mail: thomas.p.greene@nasa.gov, E-mail: gapinzone@unal.edu.co, E-mail: pudritz@physics.mcmaster.ca [Physics and Astronomy Department, McMaster University, Hamilton, ON L8S 4M1 (Canada)

    2012-01-20

    We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effect of a spin-down torque that arises from an accretion-powered stellar wind (APSW). For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1-10 days in the age range of 1-3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to stars with the lowest accretion rates, strongest magnetic fields, and/or highest stellar wind mass outflow rates. We also make a direct, quantitative comparison between the APSW scenario and the two types of disk-locking models (namely, the X-wind and Ghosh and Lamb type models) and identify some remaining theoretical issues for understanding young star spins.

  2. MHD Disk Winds and Planetary Nebulae I. Existence and Applicability

    CERN Document Server

    Frank, A; Blackman, E G

    2002-01-01

    Winds from accretion disks have been proposed as the driving source for precessing jets and extreme bipolar morphologies in Planetary Nebulae (PNe) and proto-PNe (pPNe). In this paper we address the applicability of self-consistent MHD disk wind models to PNe and pPNe. We first review the basic features of magneto-centrifugal launching disk wind models adapting results from previously published non-self similar calculations of Peltier & Pudritz (1992). We then estimate the relevant conditions whichshould occur in PNe and pPNe accretion disks that form via binary interactions. Finally, examining conditions on dimensionless parameters needed for magneto-centrifugal disk wind models we show that such winds can recover the observed momentum and energy input rates for PNe and pPNe. High accretion rates are required in thelatter case (M_a approx 10^{-4} \\mdot) and we find that the observed total energy and momentum in pPNe can be recovered with disk wind models using existing disk formation scenarios

  3. Magneto centrifugal winds from accretion discs around black hole binaries

    CERN Document Server

    Chakravorty, S; Ferreira, J; Henri, G; Belmont, R; Clavel, M; Corbel, S; Rodriguez, J; Coriat, M; Drappeau, S; Malzac, J

    2016-01-01

    We want to test if self-similar magneto-hydrodynamic (MHD) accretion-ejection models can explain the observational results for accretion disk winds in BHBs. In our models, the density at the base of the outflow, from the accretion disk, is not a free parameter, but is determined by solving the full set of dynamical MHD equations without neglecting any physical term. Different MHD solutions were generated for different values of (a) the disk aspect ratio ($\\varepsilon$) and (b) the ejection efficiency ($p$). We generated two kinds of MHD solutions depending on the absence (cold solution) or presence (warm solution) of heating at the disk surface. The cold MHD solutions are found to be inadequate to account for winds due to their low ejection efficiency. The warm solutions can have sufficiently high values of $p (\\gtrsim 0.1)$ which is required to explain the observed physical quantities in the wind. The heating (required at the disk surface for the warm solutions) could be due to the illumination which would b...

  4. Deceleration Effect of Magnetic Field on Black Hole Accretion Disks

    Institute of Scientific and Technical Information of China (English)

    WANG Ding-Xiong

    2000-01-01

    The deceleration effect of magnetic field near the horizon of a spinning black hole (BH) of accretion disk is investigated in the Blandford-Znajek (BZ) process. It is shown that rates of change with respect to time for both the angular velocities of BH horizon and accreting particles at the inner edge of an accretion disk are reduced in the BZ process, behaving with non-monotonous evolution characteristics. This result implies that the magnetic field near the BH horizon has & deceleration effect not only on the spinning BH but also on the surrounding accretion disk.

  5. Power Spectrum Density of Stochastic Oscillating Accretion Disk

    Indian Academy of Sciences (India)

    G. B. Long; J. W. Ou; Y. G. Zheng

    2016-06-01

    In this paper, we employ a stochastic oscillating accretion disk model for the power spectral index and variability of BL Lac object S5 0716+714. In the model, we assume that there is a relativistic oscillation of thin accretion disks and it interacts with an external thermal bath through a friction force and a random force. We simulate the light curve and the power spectrum density (PSD) at (i) over-damped, (ii) critically damped and (iii) under-damped cases, respectively. Our results show that the simulated PSD curves depend on the intrinsic property of the accretion disk, and it could be produced in a wide interval ranging from 0.94 to 2.05 by changing the friction coefficient in a stochastic oscillating accretion disk model. We argue that accretion disk stochastic oscillating could be a possible interpretation for observed PSD variability.

  6. Vertical Structure of Magnetized Accretion Disks around Young Stars

    CERN Document Server

    Lizano, S; Boehler, Y; D'Alessio, P

    2015-01-01

    We model the vertical structure of magnetized accretion disks subject to viscous and resistive heating, and irradiation by the central star. We apply our formalism to the radial structure of magnetized accretion disks threaded by a poloidal magnetic field dragged during the process of star formation developed by Shu and coworkers. We consider disks around low mass protostars, T Tauri, and FU Orionis stars. We consider two levels of disk magnetization, $\\lambda_{sys} = 4$ (strongly magnetized disks), and $\\lambda_{sys} = 12$ (weakly magnetized disks). The rotation rates of strongly magnetized disks have large deviations from Keplerian rotation. In these models, resistive heating dominates the thermal structure for the FU Ori disk. The T Tauri disk is very thin and cold because it is strongly compressed by magnetic pressure; it may be too thin compared with observations. Instead, in the weakly magnetized disks, rotation velocities are close to Keplerian, and resistive heating is always less than 7\\% of the visc...

  7. Accretion disks around black holes with account of magnetic fields

    CERN Document Server

    Bisnovatyi-Kogan, G S

    2004-01-01

    Accretion disks are observed in young stars, cataclysmic variables, binary X-ray sources et al. Accretion disk theory was first developed as a theory with the local heat balance, where the whole energy produced by a viscous heating was emitted to the sides of the disk. Important part of this theory was the phenomenological treatment of the turbulent viscosity, known the `` alpha'' prescription, where the $(r \\phi)$ component of the stress tensor was connected with the pressure as $\\alpha P$. Sources of turbulence in the accretion disk are discussed, including hydrodynamic turbulence, convection and magnetic field role. Optically thin solution and advective disks are considered. Related problems of mass ejection from magnetized accretion disks and jet formation are discussed.

  8. Disk Winds Driven by Magnetorotational Instability and Dispersal of Proto-Planetary Disks

    CERN Document Server

    Suzuki, T K

    2008-01-01

    By performing local three-dimensional MHD simulations of stratified accretion disks, we investigate disk winds driven by MHD turbulence. Initially given weak vertical magnetic fields are effectively amplified by magnetorotational instability and winding due to differential rotation. Large scale channel flows develop most effectively at 1.5 - 2 times the scale heights where the magnetic pressure is comparable to but slightly smaller than the gas pressure. The breakup of these channel flows drives structured disk winds by transporting the Poynting flux to the gas. These features are universally observed in the simulations of various initial fields. This disk wind process should play an essential role in the dynamical evaporation of proto-planetary disks. The breakup of channel flows also excites the momentum fluxes associated with Alfvenic and (magneto-)sonic waves toward the mid-plane, which possibly contribute to the sedimentation of small dust grains in protoplanetary disks.

  9. Magnetic fields in primordial accretion disks

    Science.gov (United States)

    Latif, M. A.; Schleicher, D. R. G.

    2016-01-01

    Magnetic fields are considered a vital ingredient of contemporary star formation and may have been important during the formation of the first stars in the presence of an efficient amplification mechanism. Initial seed fields are provided via plasma fluctuations and are subsequently amplified by the small-scale dynamo, leading to a strong, tangled magnetic field. We explore how the magnetic field provided by the small-scale dynamo is further amplified via the α-Ω dynamo in a protostellar disk and assess its implications. For this purpose, we consider two characteristic cases, a typical Pop. III star with 10M⊙ and an accretion rate of 10-3M⊙ yr-1, and a supermassive star with 105M⊙ and an accretion rate of 10-1M⊙ yr-1. For the 10M⊙ Pop. III star, we find that coherent magnetic fields can be produced on scales of at least 100 AU, which are sufficient to drive a jet with a luminosity of 100L⊙ and a mass outflow rate of 10-3.7M⊙ yr-1. For the supermassive star, the dynamical timescales in its environment are even shorter, implying smaller orbital timescales and an efficient magnetization out to at least 1000 AU. The jet luminosity corresponds to ~106.0L⊙ and a mass outflow rate of 10-2.1M⊙ yr-1. We expect that the feedback from the supermassive star can have a relevant impact on its host galaxy.

  10. Magnetic fields in primordial accretion disks

    CERN Document Server

    Latif, Muhammad A

    2016-01-01

    Magnetic fields are considered as a vital ingredient of contemporary star formation, and may have been important during the formation of the first stars in the presence of an efficient amplification mechanism. Initial seed fields are provided via plasma fluctuations, and are subsequently amplified by the small-scale dynamo, leading to a strong tangled magnetic field. Here we explore how the magnetic field provided by the small-scale dynamo is further amplified via the $\\alpha-\\Omega$ dynamo in a protostellar disk and assess its implications. For this purpose, we consider two characteristic cases, a typical Pop.~III star with $10$~M$_\\odot$ and an accretion rate of $10^{-3}$~M$_\\odot$~yr$^{-1}$, and a supermassive star with $10^5$~M$_\\odot$ and an accretion rate of $10^{-1}$~M$_\\odot$~yr$^{-1}$. For the $10$~M$_\\odot$ Pop.~III star, we find that coherent magnetic fields can be produced on scales of at least $100$~AU, which are sufficient to drive a jet with a luminosity of $100$~L$_\\odot$ and a mass outflow ra...

  11. Evolution of Thick Accretion Disks Produced by Tidal Disruption Events

    CERN Document Server

    Ulmer, A

    1997-01-01

    Geometrically thick disks may form after tidal disruption events, and rapid accretion may lead to short flares followed by long-term, lower-level emission. Using a novel accretion disk code which relies primarily on global conservation laws and the assumption that viscosity is everywhere positive, a broad range of physically allowed evolutionary sequences of thick disks is investigated. The main result is that accretion in the thick disk phase can consume only a fraction of the initial disk material before the disk cools and becomes thin. This fraction is ~0.5-0.9 for disruptions around 10^6 to 10^7 M_ødot black holes and is sensitive to the mean angular momentum of the disk. The residual material will accrete in some form of thin disk over a longer period of time. The initial thick disk phase may reduce the dimming timescale of the disk by a factor of ~2 from estimates based on thin disks alone. Assuming an 0.5 M_ødot initial thick disk, even if the thin disks become advection dominated, the black hole mas...

  12. Building massive compact planetesimal disks from the accretion of pebbles

    CERN Document Server

    Moriarty, John

    2015-01-01

    We present a model in which planetesimal disks are built from the combination of planetesimal formation and accretion of radially drifting pebbles onto existing planetesimals. In this model, the rate of accretion of pebbles onto planetesimals quickly outpaces the rate of direct planetesimal formation in the inner disk. This allows for the formation of a high mass inner disk without the need for enhanced planetesimal formation or a massive protoplanetary disk. Our proposed mechanism for planetesimal disk growth does not require any special conditions to operate. Consequently, we expect that high mass planetesimal disks form naturally in nearly all systems. The extent of this growth is controlled by the total mass in pebbles that drifts through the inner disk. Anything that reduces the rate or duration of pebble delivery will correspondingly reduce the final mass of the planetesimal disk. Therefore, we expect that low mass stars (with less massive protoplanetary disks), low metallicity stars and stars with gian...

  13. Photon Bubbles and the Vertical Structure of Accretion Disks

    CERN Document Server

    Begelman, M C

    2006-01-01

    We consider the effects of "photon bubble" shock trains on the vertical structure of radiation pressure-dominated accretion disks. These density inhomogeneities are expected to develop spontaneously in radiation-dominated accretion disks where magnetic pressure exceeds gas pressure, even in the presence of magnetorotational instability. They increase the rate at which radiation escapes from the disk, and may allow disks to exceed the Eddington limit by a substantial factor. We first generalize the theory of photon bubbles to include the effects of finite optical depths and radiation damping. Modifications to the diffusion law at low optical depth tend to fill in the low-density regions of photon bubbles, while radiation damping inhibits the formation of photon bubbles at large radii, small accretion rates, and small heights above the equatorial plane. Accretion disks dominated by photon bubble transport may reach luminosities of 10 to >100 times the Eddington limit (L_E), depending on the mass of the central ...

  14. Circumplanetary disks around young giant planets: a comparison between core-accretion and disk instability

    CERN Document Server

    Szulágyi, J; Quinn, T

    2016-01-01

    Circumplanetary disks can be found around forming giant planets, regardless of whether core accretion or gravitational instability built the planet. We carried out state-of-the-art hydrodynamical simulations of the circumplanetary disks for both formation scenarios, using as similar initial conditions as possible to unveil possible intrinsic differences in the circumplanetary disk mass and temperature between the two formation mechanisms. We found that the circumplanetary disks mass linearly scales with the circumstellar disk mass. Therefore, in an equally massive protoplanetary disk, the circumplanetary disks formed in the disk instability model can be only a factor of eight more massive than their core-accretion counterparts. On the other hand, the bulk circumplanetary disk temperature differs by more than an order of magnitude between the two cases. The subdisks around planets formed by gravitational instability have a characteristic temperature below 100 K, while the core accretion circumplanetary disks a...

  15. Accretion in Radiative Equipartition (AiRE) Disks

    CERN Document Server

    Yazdi, Yasaman K

    2016-01-01

    Standard accretion disk theory (Shakura & Sunyaev 1973) predicts that the total pressure in disks at typical (sub-)Eddington accretion rates becomes radiation pressure dominated. However, radiation pressure dominated disks are thermally unstable. Since these disks are observed in approximate steady state over the instability time-scale, our accretion models in the radiation pressure dominated regime (i.e. inner disk) need to be modified. Here, we present a modification to the SS model, where radiation pressure is in equipartition with gas pressure in the inner region. We call these flows Accretion in Radiative Equipartition (AiRE) Disks. We introduce the basic features of AiRE disks and show how they modify disk properties such as the Toomre parameter and central temperature. We then show that the accretion rate of AiRE disks is limited from above and below, by Toomre and nodal sonic point instabilities, respectively. The former leads to a strict upper limit on the mass of supermassive black holes as a fu...

  16. Forming an O Star via Disk Accretion?

    Science.gov (United States)

    Qiu, Keping; Zhang, Qizhou; Beuther, Henrik; Fallscheer, Cassandra

    2012-09-01

    We present a study of outflow, infall, and rotation in a ~105 L ⊙ star-forming region, IRAS 18360-0537, with Submillimeter Array and IRAM 30 m observations. The 1.3 mm continuum map shows a 0.5 pc dust ridge, of which the central compact part has a mass of ~80 M ⊙ and harbors two condensations, MM1 and MM2. The CO (2-1) and SiO (5-4) maps reveal a biconical outflow centered at MM1, which is a hot molecular core (HMC) with a gas temperature of 320 ± 50 K and a mass of ~13 M ⊙. The outflow has a gas mass of 54 M ⊙ and a dynamical timescale of 8 × 103 yr. The kinematics of the HMC are probed by high-excitation CH3OH and CH3CN lines, which are detected at subarcsecond resolution and unveil a velocity gradient perpendicular to the outflow axis, suggesting a disk-like rotation of the HMC. An infalling envelope around the HMC is evidenced by CN lines exhibiting a profound inverse P Cygni profile, and the estimated mass infall rate, 1.5 × 10-3 M ⊙ yr-1, is well comparable to that inferred from the mass outflow rate. A more detailed investigation of the kinematics of the dense gas around the HMC is obtained from the 13CO and C18O (2-1) lines; the position-velocity diagrams of the two lines are consistent with the model of a free-falling and Keplerian-like rotating envelope. The observations suggest that the protostar of a current mass ~10 M ⊙ embedded within MM1 will develop into an O star via disk accretion and envelope infall.

  17. FORMING AN O STAR VIA DISK ACCRETION?

    Energy Technology Data Exchange (ETDEWEB)

    Qiu Keping [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany); Zhang Qizhou [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Beuther, Henrik; Fallscheer, Cassandra, E-mail: kqiu@mpifr-bonn.mpg.de [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)

    2012-09-10

    We present a study of outflow, infall, and rotation in a {approx}10{sup 5} L{sub Sun} star-forming region, IRAS 18360-0537, with Submillimeter Array and IRAM 30 m observations. The 1.3 mm continuum map shows a 0.5 pc dust ridge, of which the central compact part has a mass of {approx}80 M{sub Sun} and harbors two condensations, MM1 and MM2. The CO (2-1) and SiO (5-4) maps reveal a biconical outflow centered at MM1, which is a hot molecular core (HMC) with a gas temperature of 320 {+-} 50 K and a mass of {approx}13 M{sub Sun }. The outflow has a gas mass of 54 M{sub Sun} and a dynamical timescale of 8 Multiplication-Sign 10{sup 3} yr. The kinematics of the HMC are probed by high-excitation CH{sub 3}OH and CH{sub 3}CN lines, which are detected at subarcsecond resolution and unveil a velocity gradient perpendicular to the outflow axis, suggesting a disk-like rotation of the HMC. An infalling envelope around the HMC is evidenced by CN lines exhibiting a profound inverse P Cygni profile, and the estimated mass infall rate, 1.5 Multiplication-Sign 10{sup -3} M{sub Sun} yr{sup -1}, is well comparable to that inferred from the mass outflow rate. A more detailed investigation of the kinematics of the dense gas around the HMC is obtained from the {sup 13}CO and C{sup 18}O (2-1) lines; the position-velocity diagrams of the two lines are consistent with the model of a free-falling and Keplerian-like rotating envelope. The observations suggest that the protostar of a current mass {approx}10 M{sub Sun} embedded within MM1 will develop into an O star via disk accretion and envelope infall.

  18. Transonic properties of the accretion disk around compact objects

    CERN Document Server

    Mukhopadhyay, Banibrata

    2008-01-01

    An accretion flow is necessarily transonic around a black hole. However, around a neutron star it may or may not be transonic, depending on the inner disk boundary conditions influenced by the neutron star. I will discuss various transonic behavior of the disk fluid in general relativistic (or pseudo general relativistic) framework. I will address that there are four types of sonic/critical point possible to form in an accretion disk. It will be shown that how the fluid properties including location of sonic points vary with angular momentum of the compact object which controls the overall disk dynamics and outflows.

  19. Magnetic flux stabilizing thin accretion disks

    CERN Document Server

    Sadowski, Aleksander

    2016-01-01

    We calculate the minimal amount of large-scale poloidal magnetic field that has to thread the inner, radiation-over-gas pressure dominated region of a thin disk for its thermal stability. Such a net field amplifies the magnetization of the saturated turbulent state and makes it locally stable. For a $10 M_\\odot$ black hole the minimal magnetic flux is $10^{24}(\\dot M/\\dot M_{\\rm Edd})^{20/21}\\,\\rm G\\cdot cm^{2}$. This amount is compared with the amount of uniform magnetic flux that can be provided by the companion star -- estimated to be in the range $10^{22}-10^{24}\\,\\rm G\\cdot cm^2$. If accretion rate is large enough, the companion is not able to provide the required amount and such a system, if still sub-Eddington, must be thermally unstable. The peculiar variability of GRS 1915+105, an X-ray binary with the exceptionally high BH mass and near-Eddington luminosity, may result from the shortage of large scale poloidal field of uniform polarity.

  20. Theory of disk accretion onto supermassive black holes

    CERN Document Server

    Armitage, P J

    2004-01-01

    Accretion onto supermassive black holes produces both the dramatic phenomena associated with active galactic nuclei and the underwhelming displays seen in the Galactic Center and most other nearby galaxies. I review selected aspects of the current theoretical understanding of black hole accretion, emphasizing the role of magnetohydrodynamic turbulence and gravitational instabilities in driving the actual accretion and the importance of the efficacy of cooling in determining the structure and observational appearance of the accretion flow. Ongoing investigations into the dynamics of the plunging region, the origin of variability in the accretion process, and the evolution of warped, twisted, or eccentric disks are summarized.

  1. Three Dimensional MHD Simulation of Circumbinary Accretion Disks -2. Net Accretion Rate

    CERN Document Server

    Shi, Ji-Ming

    2015-01-01

    When an accretion disk surrounds a binary rotating in the same sense, the binary exerts strong torques on the gas. Analytic work in the 1D approximation indicated that these torques sharply diminish or even eliminate accretion from the disk onto the binary. However, recent 2D and 3D simulational work has shown at most modest diminution. We present new MHD simulations demonstrating that for binaries with mass ratios of 1 and 0.1 there is essentially no difference between the accretion rate at large radius in the disk and the accretion rate onto the binary. To resolve the discrepancy with earlier analytic estimates, we identify the small subset of gas trajectories traveling from the inner edge of the disk to the binary and show how the full accretion rate is concentrated onto them.

  2. The S2 star as a probe of the accretion disk of Sgr A*

    CERN Document Server

    Giannios, Dimitrios

    2013-01-01

    How accretion proceeds around the massive black hole in the Galactic center and other highly sub-Eddington accretors remains poorly understood. The orbit of the S2 star in the Galactic center passes through the accretion disk of the massive black hole and any observational signature from such interaction may be used as an accretion probe. Because of its early stellar type, S2 is expected to possess a fairly powerful wind. We show here that the ram pressure of the accretion disk shocks the stellar wind fairly close to the star. The shocked fluid reaches a temperature of ~ 1 keV and cools efficiently through optically thin, thermal bremsstrahlung emission. The radiation from the shocked wind peaks around the epoch of the pericenter passage of the star at a luminosity potentially comparable to the quiescent emission detected from Sgr A*. Detection of shocked wind radiation can constrain the density of the accretion disk at a distance of several thousands of gravitational radii from the black hole.

  3. A New Approach to Evolution of Black Hole Accretion Disks

    Institute of Scientific and Technical Information of China (English)

    WANG Ding-Xiong; LEI Wei-Hua; XIAO Kan

    2000-01-01

    Evolution of black hole (BH) accretion disks is investigated by a new approach, in which the evolution of the central BH can be derived in terms of BH spin directly, and the evolution characteristics of the concerning BH parameters are shown more easily and obviously. As an example, the unusual evolution characteristics of angular velocity of BH horizon and that of accreting particles at the inner edge of the disk are derived by considering the Blandford-Znajek process.

  4. TLUSTY: Stellar Atmospheres, Accretion Disks, and Spectroscopic Diagnostics

    Science.gov (United States)

    Hubeny, Ivan; Lanz, Thierry

    2011-09-01

    TLUSTY is a user-oriented package written in FORTRAN77 for modeling stellar atmospheres and accretion disks and wide range of spectroscopic diagnostics. In the program's maximum configuration, the user may start from scratch and calculate a model atmosphere of a chosen degree of complexity, and end with a synthetic spectrum in a wavelength region of interest for an arbitrary stellar rotation and an arbitrary instrumental profile. The user may also model the vertical structure of annuli of an accretion disk.

  5. Angular Momentum Transport in Quasi-Keplerian Accretion Disks

    Indian Academy of Sciences (India)

    Prasad Subramanian; B. S. Pujari; Peter A. Becker

    2004-03-01

    We reexamine arguments advanced by Hayashi & Matsuda (2001), who claim that several simple, physically motivated derivations based on mean free path theory for calculating the viscous torque in a quasi-Keplerian accretion disk yield results that are inconsistent with the generally accepted model. If correct, the ideas proposed by Hayashi & Matsuda would radically alter our understanding of the nature of the angular momentum transport in the disk, which is a central feature of accretion disk theory. However, in this paper we point out several fallacies in their arguments and show that there indeed exists a simple derivation based on mean free path theory that yields an expression for the viscous torque that is proportional to the radial derivative of the angular velocity in the accretion disk, as expected. The derivation is based on the analysis of the epicyclic motion of gas parcels in adjacent eddies in the disk.

  6. High mass accretion disks: ATCA's potential for deep impact II

    Science.gov (United States)

    Walsh, Andrew; Beuther, Henrik; Longmore, Steven; Fallscheer, Cassandra

    2010-10-01

    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 (5,5) data obtained last year. Last year's data showed a number of regions with clear rotational profiles, but no flattened structures that would indicate an edge-on accretion disk. We interpret our results to show rotating surrounding envelopes of any accretion disks. We were not able to see the accretion disks themselves because the (4,4) and (5,5) lines are optically thick. With observations of NH3 (7,7) and (8,8), which occur under even more extreme conditions than (4,4) or (5,5), we hope to peer through the surrounding envelope to see the accretion disks.

  7. Disk Accretion of Tidally Disrupted Rocky Bodies onto White Dwarfs

    Science.gov (United States)

    Feng, Wanda; Desch, Steven; Turner, Neal; Kalyaan, Anusha

    2016-06-01

    About 1/3 of white dwarfs (WDs) are polluted with heavy elements (e.g., Koester et al., 2014; Zuckerman et al., 2010) that should sediment out of their atmospheres on astronomically short timescales unless replenished by accretion from a reservoir, at rates that for many WDs must exceed ~1010 g/s (Farihi et al., 2010). Direct accretion of planetesimals is too improbable and Poynting-Robertson drag of dust is too slow (due to the low luminosity of WDs) (Jura, 2003), so it is often assumed that WDs accrete from a disk of gas and solid particles, fed by tidal disruption of planeteismals inside the WD Roche limit (e.g. Debes et al., 2012; Rafikov, 2011a, 2011b). A few such gaseous disks have been directly observed, through emission from Ca II atoms in the disk (e.g. Manser et al., 2016; Wilson et al. 2014). Models successfully explain the accretion rates of metals onto the WD, provided the gaseous disk viscously spreads at rates consistent with a partially suppressed magnetorotational instability (Rafikov, 2011a, 2011b). However, these models currently do not explore the likely extent of the magnetorotational instability in disks by calculating the degree of ionization, or suppression by strong magnetic field.We present a 1-D model of a gaseous WD disk accretion, to assess the extent of the magnetorotational instability in WD disks. The composition of the disk, the ionization and recombination mechanisms, and the degree of ionization of the disk are explored. Magnetic field strengths consistent with WD dipolar magnetic fields are assumed. Elsasser numbers are calculated as a function of radius in the WD disk. The rate of viscous spreading is calculated, and the model of Rafikov (2011a, 2011b) updated to compute likely accretion rates of metals onto WDs.

  8. Nucleosynthesis in the accretion disks of Type II collapsars

    CERN Document Server

    Banerjee, Indrani

    2013-01-01

    We investigate nucleosynthesis inside the gamma-ray burst (GRB) accretion disks formed by the Type II collapsars. In these collapsars, the core collapse of massive stars first leads to the formation of a proto-neutron star and a mild supernova explosion is driven. However, this supernova ejecta lack momentum and falls back onto the neutron star which gets transformed to a stellar mass black hole. In order to study the hydrodynamics and nucleosynthesis of such an accretion disk formed from the fallback material of the supernova ejecta, we use the well established hydrodynamic models. In such a disk neutrino cooling becomes important in the inner disk where the temperature and density are higher. Higher the accretion rate (dot{M}), higher is the density and temperature in the disks. In this work we deal with accretion disks with relatively low accretion rates: 0.001 M_sun s^{-1} \\lesssim dot{M} \\lesssim 0.01 M_sun s^{-1} and hence these disks are predominantly advection dominated. We use He-rich and Si-rich abu...

  9. Ice Accretion on Wind Turbine Blades

    DEFF Research Database (Denmark)

    Hudecz, Adriána; Koss, Holger; Hansen, Martin Otto Laver

    2013-01-01

    forces were monitored as ice was building up on the airfoil for glaze, rime and mixed ice. In the first part of the numerical analysis, the resulted ice profiles of the wind tunnel tests were compared to profiles estimated by using the 2D ice accretion code TURBICE. In the second part, Ansys Fluent......In this paper, both experimental and numerical simulations of the effects of ice accretion on a NACA 64-618 airfoil section with 7° angle of attack are presented. The wind tunnel tests were conducted in a closed-circuit climatic wind tunnel at Force Technology in Denmark. The changes of aerodynamic...

  10. Viscous Instability Triggered by Layered Accretion in Protoplanetary Disks

    CERN Document Server

    Hasegawa, Yasuhiro

    2015-01-01

    Layered accretion is one of the inevitable ingredients in protoplanetary disks when disk turbulence is excited by magnetorotational instabilities (MRIs). In the accretion, disk surfaces where MRIs fully operate have a high value of disk accretion rate ($\\dot{M}$), while the disk midplane where MRIs are generally quenched ends up with a low value of $\\dot{M}$. Significant progress on understanding MRIs has recently been made by a number of dedicated MHD simulations, which requires improvement of the classical treatment of $\\alpha$ in 1D disk models. To this end, we obtain a new expression of $\\alpha$ by utilizing an empirical formula that is derived from recent MHD simulations of stratified disks with Ohmic diffusion. It is interesting that this new formulation can be regarded as a general extension of the classical $\\alpha$. Armed with the new $\\alpha$, we perform a linear stability analysis of protoplanetary disks that undergo layered accretion, and find that a viscous instability can occur around the outer ...

  11. Disk Accretion of Tidally Disrupted Rocky Bodies onto White Dwarfs

    Science.gov (United States)

    Feng, W.; Desch, S.

    2017-03-01

    The prevailing model for the pollution of white dwarf photospheres invokes accretion from a disk of gas and solid particles, fed by tidal disruption of rocky bodies inside the Roche radius. Current models can successfully explain the accretion rates of metals onto white dwarfs, provided the gaseous disks viscously spread at rates consistent with a partially suppressed magnetorotational instability (Metzger et al. 2012); however, these models do not explore the extent of the magnetorotational instability in disks by calculating the degree of ionization. We present ionization fractions for thermal and non-thermal processes to assess the extent of the magnetorotational instability in white dwarf disks. We determine that the disk viscosity parameter α can be as high as 0.1 in white disks, implying that the magnetorotational instability must be carefully modeled.

  12. On the gravitational stability of gravito-turbulent accretion disks

    CERN Document Server

    Lin, Min-Kai

    2016-01-01

    Low mass, self-gravitating accretion disks admit quasi-steady, `gravito-turbulent' states in which cooling balances turbulent viscous heating. However, numerical simulations show that gravito-turbulence cannot be sustained beyond dynamical timescales when the cooling rate or corresponding turbulent viscosity is too large. The result is disk fragmentation. We motivate and quantify an interpretation of disk fragmentation as the inability to maintain gravito-turbulence due to formal secondary instabilities driven by: 1) cooling, which reduces pressure support; and/or 2) viscosity, which reduces rotational support. We analyze the gravitational stability of viscous, non-adiabatic accretion disks with internal heating, external irradiation, and cooling. We consider parameterized cooling functions in 2D and 3D disks, as well as radiative diffusion in 3D. We show that generally there is no critical cooling rate/viscosity below which the disk is formally stable, although interesting limits appear for unstable modes wi...

  13. Smearing of mass accretion rate variation by viscous processes in accretion disks in compact binary systems

    Science.gov (United States)

    Ghosh, A.; Chakrabarti, Sandip K.

    2016-09-01

    Variation of mass supply rate from the companion can be smeared out by viscous processes inside an accretion disk. Hence, by the time the flow reaches the inner edge, the variation in X-rays need not reflect the true variation of the mass supply rate at the outer edge. However, if the viscosity fluctuates around a mean value, one would expect the viscous time scale t_{{visc}} also to spread around a mean value. In high mass X-ray binaries, which are thought to be primarily wind-fed, the size of the viscous Keplerian disk is smaller and thus such a spread could be lower as compared to the low mass X-ray binaries which are primarily fed by Roche lobe overflow. If there is an increasing or decreasing trend in viscosity, the interval between enhanced emission would be modified systematically. In the absence of a detailed knowledge about the variation of mass supply rates at the outer edge, we study ideal circumstances where modulation must take place exactly in orbital time scales, such as when there is an ellipticity in the orbit. We study a few compact binaries using long term All Sky monitor (ASM) data (1.5-12 keV) of Rossi X-ray Timing Explorer (RXTE) and all sky survey data (15-50 keV) of Swift satellites by different methods to look for such smearing effects and to infer what these results can tell us about the viscous processes inside the respective disks. We employ three different methods to seek imprints of periodicity on the X-ray variation and found that in all the cases, the location of the peak in the power density spectra is consistent with the orbital frequencies. Interestingly, in high mass X-ray binaries the peaks are sharp with high rms values, consistent with a small Keplerian disk in a wind fed system. However, in low mass X-ray binaries with larger Keplerian disk component, the peaks are spreaded out with much lower rms values. X-ray reflections, or superhump phenomena which may also cause such X-ray modulations would not be affected by the size of

  14. Accretion Does Not Drive the Turbulence in Galactic Disks

    CERN Document Server

    Hopkins, Philip F; Murray, Norman

    2013-01-01

    Rapid accretion of cold gas plays a crucial role in getting gas into galaxies. It has been suggested that this accretion proceeds along narrow streams that might also directly drive the turbulence in galactic gas, dynamical disturbances, and bulge formation. In cosmological simulations, however, it is impossible to isolate and hence disentangle the effect of accretion from internal instabilities and mergers. Moreover, in most cosmological simulations, the phase structure and turbulence in the ISM arising from stellar feedback are treated in a sub-grid manner, so that feedback cannot generate ISM turbulence. In this paper we therefore test the effects of cold streams in extremely high-resolution simulations of otherwise isolated galaxy disks using detailed models for star formation and feedback; we then include or exclude mock cold flows falling onto the galaxies with accretion rates, velocities and geometry set to maximize their effect on the disk. We find: (1) Turbulent velocity dispersions in gas disks are ...

  15. Implications of the β Lyrae accretion disk rim Teff

    Science.gov (United States)

    Linnell, A. P.

    2000-12-01

    Photometric evidence indicates that the massive gainer in the β Lyrae system is hidden from the observer by a thick accretion disk (Linnell, Hubeny, & Harmanec, 1998, ApJ, 509, 379). It is believed that the gainer approximates a main sequence star of Teff= 30000K. Spectroscopic analysis by Balachrandan et al. (1986, MNRAS, 219, 479) establishes a Teff of 13,300K for the donor. System synthetic spectra, fitted via the BINSYN suite to spectrophotometric scan data and IUE spectra, establish a mean rim Teff of 9000K. Assuming conservative mass transfer, Harmanec & Scholz (1993, A&A, 279, 131) use the rate of period change to derive a mass transfer rate of 20x10-6M⊙ yr-1. Connecting the rim Teff to the accretion disk face Teff with the Hubeny theory (Hubeny & Plavec 1991, AJ, 102, 1156) and using the standard accretion disk relations (Frank, King & Raine), the adopted mass transfer rate predicts a rim Teff of 4500K. The BINSYN-derived 9000K rim Teff would require a mass transfer rate 30 times larger than the adopted value. The observed rate of period change excludes such a large mass transfer rate. The bolometric luminosity of the rim, from the BINSYN model, is 5.6x1036erg sec-1. The bolometric luminosity of the gainer, on the adopted model, is 9.8x1037erg sec-1. Thus, the luminosity of the rim is 6% of the luminosity of the gainer. On the BINSYN model, the accretion disk covers 26% of the sky, as seen by the gainer. Absorption of radiation from the gainer, and its reradiation by the accretion disk, could explain the derived Teff of the rim. The conclusion is that the β Lyrae accretion disk structure must be strongly affected by radiation from the hot gainer (unseen by the observer) at the center of the accretion disk.

  16. Accretion and destruction of planetesimals in turbulent disks

    CERN Document Server

    Ida, Shigeru; Morbidelli, Alessandro

    2008-01-01

    We study the conditions for collisions between planetesimals to be accretional or disruptive in turbulent disks, through analytical arguments based on fluid dynamical simulations and orbital integrations. In turbulent disks, the velocity dispersion of planetesimals is pumped up by random gravitational perturbations from density fluctuations of the disk gas. When the velocity dispersion is larger than the planetesimals' surface escape velocity, collisions between planetesimals do not result in accretion, and may even lead to their destruction. In disks with a surface density equal to that of the ``minimum mass solar nebula'' and with nominal MRI turbulence, we find that accretion proceeds only for planetesimals with sizes above $\\sim 300$ km at 1AU and $\\sim 1000$ km at 5AU. We find that accretion is facilitated in disks with smaller masses. However, at 5AU and for nominal turbulence strength, km-sized planetesimals are in a highly erosive regime even for a disk mass as small as a fraction of the mass of Jupit...

  17. Evidence of the Link between Broad Emission Line Regions and Accretion Disks in Active Galactic Nuclei

    Institute of Scientific and Technical Information of China (English)

    Yun Xu; Xin-Wu Cao

    2007-01-01

    There is observational evidence that broad-line regions (BLRs) exist in most active galactic nuclei (AGNs), but their origin is still unclear. One scenario is that the BLRs originate from winds accelerated from the hot coronae of the disks, and the winds are suppressed when the black hole is accreting at low rates. This model predicts a relation between (m) ((m) = (M)/(M)Edd) and the FWHM of broad emission lines. We estimate the central black hole masses for a sample of bright AGNs by using their broad Hβ line-widths and optical luminosities. The dimensionless accretion rates (m) = (M)/(M)Edd are derived from the optical continuum luminosities by using two different models: using an empirical relation between the bolometric luminosity Lbol and the optical luminosity ((m) = Lbol/LEdd, a fixed radiative efficiency is adopted); and calculating the optical spectra of accretion disks as a function of (m). We find a significant correlation between the derived (m) and the observed line width of Hβ,FWHM∝ (m)-0.37, which almost overlaps the disk-corona model calculations, if the viscosity α≈ 0.1 - 0.2 is adopted. Our results provide strong evidence for the physical link between the BLRs and accretion disks in AGNs.

  18. Accretion Disks Around Binary Black Holes: A Quasistationary Model

    CERN Document Server

    Liu, Yuk Tung

    2010-01-01

    Tidal torques acting on a gaseous accretion disk around a binary black hole can create a gap in the disk near the orbital radius. At late times, when the binary inspiral timescale due to gravitational wave emission becomes shorter than the viscous timescale in the disk, the binary decouples from the disk and eventually merges. Prior to decoupling the balance between tidal and viscous torques drives the disk to a quasistationary equilibrium state, perturbed slightly by small amplitude, spiral density waves emanating from the edges of the gap. We consider a black hole binary with a companion of smaller mass and construct a simple Newtonian model for a geometrically thin, Keplerian disk in the orbital plane of the binary. We solve the disk evolution equations in steady state to determine the quasistationary, (orbit-averaged) surface density profile prior to decoupling. We use our solution, which is analytic up to simple quadratures, to compute the electromagnetic flux and approximate radiation spectrum during th...

  19. Spin Evolution of Accreting Young Stars. II. Effect of Accretion-Powered Stellar Winds

    CERN Document Server

    Matt, Sean P; Greene, Thomas P; Pudritz, Ralph E

    2011-01-01

    We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effect of a spin-down torque that arises from an accretion-powered stellar wind. For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1--10 days in the age range of 1--3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to s...

  20. Angular Momentum Transport in Accretion Disks

    DEFF Research Database (Denmark)

    E. Pessah, Martin; Chan, Chi-kwan; Psaltis, Dimitrios;

    2007-01-01

    if the resolution were set equal to the natural dissipation scale in astrophysical disks. We conclude that, in order for MRI-driven turbulent angular momentum transport to be able to account for the large value of the effective alpha viscosity inferred observationally, the disk must be threaded by a significant...

  1. Evolution of an Accretion Disk in Binary Black Hole Systems

    CERN Document Server

    Kimura, Shigeo S; Toma, Kenji

    2016-01-01

    We investigate evolution of an accretion disk in binary black hole (BBH) systems, the importance of which is now increasing due to its close relationship to possible electromagnetic counterparts of the gravitational waves (GWs) from mergers of BBHs. Perna et al. (2016) proposed a novel evolutionary scenario of an accretion disk in BBHs in which a disk eventually becomes "dead", i.e., the magnetorotational instability (MRI) becomes inactive. In their scenario, the dead disk survives until {\\it a few seconds before} the merger event. We improve the dead disk model and propose another scenario, taking account of effects of the tidal torque from the companion and the critical ionization degree for MRI activation more carefully. We find that the mass of the dead disk is much lower than that in the Perna's scenario. When the binary separation sufficiently becomes small, the tidal heating reactivates MRI and mass accretion onto the black hole (BH). We also find that this disk "revival" happens {\\it many years before...

  2. Cooling of young stars growing by disk accretion

    CERN Document Server

    Rafikov, Roman

    2007-01-01

    In the initial formation stages young stars must acquire a significant fraction of their mass by accretion from a circumstellar disk that forms in the center of a collapsing protostellar cloud. Throughout this period mass accretion rates through the disk can reach 10^{-6}-10^{-5} M_Sun/yr leading to substantial energy release in the vicinity of stellar surface. We study the impact of irradiation of the stellar surface produced by the hot inner disk on properties of accreting fully convective low-mass stars, and also look at objects such as young brown dwarfs and giant planets. At high accretion rates irradiation raises the surface temperature of the equatorial region above the photospheric temperature T_0 that a star would have in the absence of accretion. The high-latitude (polar) parts of the stellar surface, where disk irradiation is weak, preserve their temperature at the level of T_0. In strongly irradiated regions an almost isothermal outer radiative zone forms on top of the fully convective interior, l...

  3. On Hydromagnetic Stresses in Accretion Disk Boundary Layers

    DEFF Research Database (Denmark)

    Pessah, Martin Elias; Chan, Chi-kwan

    2012-01-01

    Detailed calculations of the physical structure of accretion disk boundary layers, and thus their inferred observational properties, rely on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear...... viscosity satisfies this assumption by construction. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability (MRI) is inefficient in disk regions where...... with angular frequencies that increase outward in the shearing-sheet framework. We isolate the modes that are unrelated to the standard MRI and provide analytic solutions for the long-term evolution of the resulting shearing MHD waves. We show that, although the energy density of these waves can be amplified...

  4. Wave Propagation in Accretion Disks with Self-Gravity

    Institute of Scientific and Technical Information of China (English)

    LIU Xiao-Ci; YANG Lan-Tian; WU Shao-Ping; DING Shi-Xue

    2001-01-01

    We extend the research by Lubow and Pringle of axisymmetric waves in accretion disks to the case where self gravity of disks should be considered. We derive and analyse the dispersion relations with the effect of self-gravity. Results show that self-gravity extends the forbidden region of the wave propagation: for high frequency p-modes, self-gravity makes the wavelength shorter and the group velocity larger; for low frequency g-modes, the effect is opposite.

  5. Massive accretion disks: ATCA's potential for deep impact

    Science.gov (United States)

    Beuther, Henrik; Longmore, Steven; Walsh, Andrew; Fallscheer, Cassandra

    2008-04-01

    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-pilot study of IRAS18089-1732 (Beuther & Walsh, ApJL in press), we now propose to investigate a larger sample of eleven disk candidates at high angular resolution (<1'') in the highly excited NH3(4,4)/(5,5) lines. These lines trace the densest and warmest regions and are hence well suited to isolate the accretion disks from their envelopes. The observation will reveal the kinematics of the rotating structures and allow us to differentiate whether the expected disks are in Keplerian rotation like their low-mass counterparts or not. Furthermore, the chosen line pair is well suited to investigate the temperature structure of the regions. Combining the kinematic and temperature information, we will derive detailed physical models of the rotation structures in young massive star-forming regions. Investigating a larger sample is the only way to characterize massive disks in a general way important for a comprehensive understanding of massive star formation. The ATCA with its excellent spatial resolution and sensitivity has the potential to make considerable impact in this field.

  6. Turbulent Comptonization in Relativistic Accretion Disks

    CERN Document Server

    Socrates, A; Blaes, Omer M; Socrates, Aristotle; Davis, Shane W.; Blaes, Omer

    2006-01-01

    Turbulent Comptonization, a potentially important damping and radiation mechanism in relativistic accretion flows, is discussed. Particular emphasis is placed on the physical basis, relative importance, and thermodynamics of turbulent Comptonization. The effects of metal-absorption opacity on the spectral component resulting from turbulent Comptonization is considered as well.

  7. Magneto-thermal Disk Wind from Protoplanetary Disks

    CERN Document Server

    Bai, Xue-Ning; Goodman, Jeremy; Yuan, Feng

    2015-01-01

    Global evolution and dispersal of protoplanetary disks (PPDs) is governed by disk angular momentum transport and mass-loss processes. Recent numerical studies suggest that angular momentum transport in the inner region of PPDs is largely driven by magnetized disk wind, yet the wind mass-loss rate remains unconstrained. On the other hand, disk mass loss has conventionally been attributed to photoevaporation, where external heating on the disk surface drives a thermal wind. We unify the two scenarios by developing a 1D model of magnetized disk winds with a simple treatment of thermodynamics as a proxy for external heating. The wind properties largely depend on 1) the magnetic field strength at the wind base, characterized by the poloidal Alfv\\'en speed $v_{Ap}$, 2) the sound speed $c_s$ near the wind base, and 3) how rapidly poloidal field lines diverge (achieve $R^{-2}$ scaling). When $v_{Ap}\\gg c_s$, corotation is enforced near the wind base, resulting in centrifugal acceleration. Otherwise, the wind is accel...

  8. Observational Signatures of Tilted Black Hole Accretion Disks from Simulations

    CERN Document Server

    Dexter, Jason

    2011-01-01

    Geometrically thick accretion flows may be present in black hole X-ray binaries observed in the low/hard state and in low-luminosity active galactic nuclei. Unlike in geometrically thin disks, the angular momentum axis in these sources is not expected to align with the black hole spin axis. We compute images from three-dimensional general relativistic magnetohydrodynamic simulations of misaligned (tilted) accretion flows using relativistic radiative transfer, and compare the estimated locations of the radiation edge with expectations from their aligned (untilted) counterparts. The radiation edge in the tilted simulations is independent of black hole spin for a tilt of 15 degrees, in stark contrast to the results for untilted simulations, which agree with the monotonic dependence on spin expected from thin accretion disk theory. Synthetic emission line profiles from the tilted simulations depend strongly on the observer's azimuth, and exhibit unique features such as broad "blue wings." Coupled with precession,...

  9. Radial Transport and Meridional Circulation in Accretion Disks

    Science.gov (United States)

    Philippov, Alexander A.; Rafikov, Roman R.

    2017-03-01

    Radial transport of particles, elements and fluid driven by internal stresses in three-dimensional (3D) astrophysical accretion disks is an important phenomenon, potentially relevant for the outward dust transport in protoplanetary disks, origin of the refractory particles in comets, isotopic equilibration in the Earth–Moon system, etc. To gain better insight into these processes, we explore the dependence of meridional circulation in 3D disks with shear viscosity on their thermal stratification, and demonstrate a strong effect of the latter on the radial flow. Previous locally isothermal studies have normally found a pattern of the radial outflow near the midplane, switching to inflow higher up. Here we show, both analytically and numerically, that a flow that is inward at all altitudes is possible in disks with entropy and temperature steeply increasing with height. Such thermodynamic conditions may be typical in the optically thin, viscously heated accretion disks. Disks in which these conditions do not hold should feature radial outflow near the midplane, as long as their internal stress is provided by the shear viscosity. Our results can also be used for designing hydrodynamical disk simulations with a prescribed pattern of the meridional circulation.

  10. Tilted Thick-Disk Accretion onto a Kerr Black Hole

    Energy Technology Data Exchange (ETDEWEB)

    Fragile, P C; Anninos, P

    2003-12-12

    We present the first results from fully general relativistic numerical studies of thick-disk accretion onto a rapidly-rotating (Kerr) black hole with a spin axis that is tilted (not aligned) with the angular momentum vector of the disk. We initialize the problem with the solution for an aligned, constant angular momentum, accreting thick disk around a black hole with spin a/M = J/M{sup 2} = +0.9 (prograde disk). The black hole is then instantaneously tilted, through a change in the metric, by an angle {beta}{sub 0}. In this Letter we report results with {beta}{sub 0} = 0, 15, and 30{sup o}. The disk is allowed to respond to the Lense-Thirring precession of the tilted black hole. We find that the disk settles into a quasi-static, twisted, warped configuration with Lense-Thirring precession dominating out to a radius analogous to the Bardeen-Petterson transition in tilted Keplerian disks.

  11. Rossby Wave Instability of Keplerian Accretion Disks

    CERN Document Server

    Lovelace, R V E; Colgate, S A; Nelson, A F

    1999-01-01

    We find a linear instability of non-axisymmetric Rossby waves in a thin non-magnetized Keplerian disk when there is a local maximum in the radial profile of a key function ${\\cal L}(r) \\equiv {\\cal F}(r) S^{2/\\Gamma}(r)$, where ${\\cal F}^{-1} = \\hat {\\bf z}\\cdot ({\\bf \

  12. Jets and Accretion Disks in X-ray Binaries

    Science.gov (United States)

    Tomsick, John

    The outflow of material in the form of jets is a common phenomenon in astronomical sources with accretion disks. Even though jets are seen coming from the cores of galaxies, Galactic compact objects in X-ray binaries, and stars as they are forming, we do not understand in detail what accretion disk conditions are necessary to support a relativistic jet. This proposal focuses on multi-wavelength studies of X-ray binaries in order to improve our understanding of the connection between the disk and the jet. Specifically, this proposal includes work on two approved cycle 14 Rossi X-ray Timing Explorer (RXTE) programs, an approved XMM-Newton program, as well as a synthesis study of transient black hole X-ray binaries using archival RXTE and radio data. We plan to use X-ray spectral and timing properties to determine the disk properties during the re-activation of the compact jet (as seen in the radio and infrared) during the decays of black hole transient outbursts, to determine how the inner disk properties change at low mass accretion rates, and to use RXTE along with multi-wavelength observations to constrain the jet properties required for the microquasar Cygnus~X-3 to produce high- energy emission. Due to the ubiquity of jets in astrophysical settings, these science topics are relevant to NASA programs dealing with the origin, structure, evolution, and destiny of the Universe, and especially to understanding phenomena near black holes.

  13. Rossby Wave Instability of Thin Accretion Disks - III. Nonlinear Simulations

    CERN Document Server

    Li, H; Wendroff, B; Liska, R

    2000-01-01

    (abridged) We study the nonlinear evolution of the Rossby wave instability in thin disks using global 2D hydrodynamic simulations. The key questions we are addressing in this paper are: (1) What happens when the instability becomes nonlinear? Specifically, does it lead to vortex formation? (2) What is the detailed behavior of a vortex? (3) Can the instability sustain itself and can the vortex last a long time? Among various initial equilibria that we have examined, we generally find that there are three stages of the disk evolution: (1) The exponential growth of the initial small amplitude perturbations. This is in excellent agreement with the linear theory; (2) The production of large scale vortices and their interactions with the background flow, including shocks. Significant accretion is observed due to these vortices. (3) The coupling of Rossby waves/vortices with global spiral waves, which facilitates further accretion throughout the whole disk. Even after more than 20 revolutions at the radius of vortic...

  14. Nucleosynthesis in Advective Accretion Disks Around Galactic and Extra-Galactic Black Holes

    CERN Document Server

    Mukhopadhyay, B

    1998-01-01

    We compute the nucleosynthesis of materials inside advective disks around black holes. We show that composition of incoming matter can change significantly depending on the accretion rate and accretion disks. These works are improvements on the earlier works in thick accretion disks of Chakrabarti, Jin & Arnett (1987) in presence of advection in the flow.

  15. Advection/diffusion of large scale magnetic field in accretion disks

    Directory of Open Access Journals (Sweden)

    R. V. E. Lovelace

    2009-02-01

    Full Text Available Activity of the nuclei of galaxies and stellar mass systems involving disk accretion to black holes is thought to be due to (1 a small-scale turbulent magnetic field in the disk (due to the magneto-rotational instability or MRI which gives a large viscosity enhancing accretion, and (2 a large-scale magnetic field which gives rise to matter outflows and/or electromagnetic jets from the disk which also enhances accretion. An important problem with this picture is that the enhanced viscosity is accompanied by an enhanced magnetic diffusivity which acts to prevent the build up of a significant large-scale field. Recent work has pointed out that the disk's surface layers are non-turbulent and thus highly conducting (or non-diffusive because the MRI is suppressed high in the disk where the magnetic and radiation pressures are larger than the thermal pressure. Here, we calculate the vertical (z profiles of the stationary accretion flows (with radial and azimuthal components, and the profiles of the large-scale, magnetic field taking into account the turbulent viscosity and diffusivity due to the MRI and the fact that the turbulence vanishes at the surface of the disk. We derive a sixth-order differential equation for the radial flow velocity vr(z which depends mainly on the midplane thermal to magnetic pressure ratio β>1 and the Prandtl number of the turbulence P=viscosity/diffusivity. Boundary conditions at the disk surface take into account a possible magnetic wind or jet and allow for a surface current in the highly conducting surface layer. The stationary solutions we find indicate that a weak (β>1 large-scale field does not diffuse away as suggested by earlier work.

  16. Hydrodynamical wind in magnetized accretion flows with convection

    Institute of Scientific and Technical Information of China (English)

    Shahram Abbassi; Amin Mosallanezhad

    2012-01-01

    The existence of outflow and magnetic fields in the inner region of hot accretion flows has been confirmed by observations and numerical magnetohydrodynamic (MHD) simulations.We present self-similar solutions for radiatively inefficient accretion flows (RIAFs) around black holes in the presence of outflow and a global magnetic field.The influence of outflow is taken into account by adopting a radius that depends on mass accretion rate M = M0(r/r0)s with s > 0.We also consider convection through a mixing length formula to calculate convection parameter αcon.Moreover we consider the additional magnetic field parameters βr,φ,z [= cr2,φ,z/(2cs2)],where c2r,φ,z are the Alfvén sound speeds in three directions of cylindrical coordinates.Our numerical results show that by increasing all components of the magnetic field,the surface density and rotational velocity increase,but the sound speed and radial infall velocity of the disk decrease.We have also found that the existence of wind will lead to reduction of surface density as well as rotational velocity.Moreover,the radial velocity,sound speed,advection parameter and the vertical thickness of the disk will increase when outflow becomes important in the RIAF.

  17. Gas accretion from halos to disks: observations, curiosities, and problems

    CERN Document Server

    Elmegreen, Bruce G

    2015-01-01

    Accretion of gas from the cosmic web to galaxy halos and ultimately their disks is a prediction of modern cosmological models but is rarely observed directly or at the full rate expected from star formation. Here we illustrate possible large-scale cosmic HI accretion onto the nearby dwarf starburst galaxy IC10, observed with the VLA and GBT. We also suggest that cosmic accretion is the origin of sharp metallicity drops in the starburst regions of other dwarf galaxies, as observed with the 10-m GTC. Finally, we question the importance of cosmic accretion in normal dwarf irregulars, for which a recent study of their far-outer regions sees no need for, or evidence of, continuing gas buildup.

  18. The growth of supermassive black holes fed by accretion disks

    CERN Document Server

    Armijo, M A Montesinos

    2010-01-01

    Supermassive black holes are probably present in the centre of the majority of the galaxies. There is a consensus that these exotic objects are formed by the growth of seeds either by accreting mass from a circumnuclear disk and/or by coalescences during merger episodes. The mass fraction of the disk captured by the central object and the related timescale are still open questions, as well as how these quantities depend on parameters like the initial mass of the disk or the seed or on the angular momentum transport mechanism. This paper is addressed to these particular aspects of the accretion disk evolution and of the growth of seeds. The time-dependent hydrodynamic equations were solved numerically for an axi-symmetric disk in which the gravitational potential includes contributions both from the central object and from the disk itself. The numerical code is based on a Eulerian formalism, using a finite difference method of second-order, according to the Van Leer upwind algorithm on a staggered mesh. The pr...

  19. Bulk Comptonization by Turbulence in Accretion Disks

    CERN Document Server

    Kaufman, J

    2016-01-01

    Radiation pressure dominated accretion discs around compact objects may have turbulent velocities that greatly exceed the electron thermal velocities within the disc. Bulk Comptonization by the turbulence may therefore dominate over thermal Comptonization in determining the emergent spectrum. Bulk Comptonization by divergenceless turbulence is due to radiation viscous dissipation only. It can be treated as thermal Comptonization by solving the Kompaneets equation with an equivalent "wave" temperature, which is a weighted sum over the power present at each scale in the turbulent cascade. Bulk Comptonization by turbulence with non-zero divergence is due to both pressure work and radiation viscous dissipation. Pressure work has negligible effect on photon spectra in the limit of optically thin turbulence, and in this limit radiation viscous dissipation alone can be treated as thermal Comptonization with a temperature equivalent to the full turbulent power. In the limit of extremely optically thick turbulence, ra...

  20. Self-collimated axial jets from thin accretion disks

    CERN Document Server

    Tirabassi, Giulio; Carlevaro, Nakia; Benini, Riccardo

    2012-01-01

    We show how an appropriate stationary crystalline structure of the magnetic field can induce a partial fragmentation of the accretion disk, generating an axial jet composed of hot rising plasma twisted in a funnel-like structure by the rotation of the system. The most important feature of the obtained jet is its high degree of collimation, naturally arising from the condition for its existence. The presence of non-zero dissipative effects allows the plasma ejection throughout the axial jet and the predicted values of the accretion rate are in agreement with observations.

  1. The response of relativistic outflowing gas to the inner accretion disk of a black hole.

    Science.gov (United States)

    Parker, Michael L; Pinto, Ciro; Fabian, Andrew C; Lohfink, Anne; Buisson, Douglas J K; Alston, William N; Kara, Erin; Cackett, Edward M; Chiang, Chia-Ying; Dauser, Thomas; De Marco, Barbara; Gallo, Luigi C; Garcia, Javier; Harrison, Fiona A; King, Ashley L; Middleton, Matthew J; Miller, Jon M; Miniutti, Giovanni; Reynolds, Christopher S; Uttley, Phil; Vasudevan, Ranjan; Walton, Dominic J; Wilkins, Daniel R; Zoghbi, Abderahmen

    2017-03-01

    The brightness of an active galactic nucleus is set by the gas falling onto it from the galaxy, and the gas infall rate is regulated by the brightness of the active galactic nucleus; this feedback loop is the process by which supermassive black holes in the centres of galaxies may moderate the growth of their hosts. Gas outflows (in the form of disk winds) release huge quantities of energy into the interstellar medium, potentially clearing the surrounding gas. The most extreme (in terms of speed and energy) of these-the ultrafast outflows-are the subset of X-ray-detected outflows with velocities higher than 10,000 kilometres per second, believed to originate in relativistic (that is, near the speed of light) disk winds a few hundred gravitational radii from the black hole. The absorption features produced by these outflows are variable, but no clear link has been found between the behaviour of the X-ray continuum and the velocity or optical depth of the outflows, owing to the long timescales of quasar variability. Here we report the observation of multiple absorption lines from an extreme ultrafast gas flow in the X-ray spectrum of the active galactic nucleus IRAS 13224-3809, at 0.236 ± 0.006 times the speed of light (71,000 kilometres per second), where the absorption is strongly anti-correlated with the emission of X-rays from the inner regions of the accretion disk. If the gas flow is identified as a genuine outflow then it is in the fastest five per cent of such winds, and its variability is hundreds of times faster than in other variable winds, allowing us to observe in hours what would take months in a quasar. We find X-ray spectral signatures of the wind simultaneously in both low- and high-energy detectors, suggesting a single ionized outflow, linking the low- and high-energy absorption lines. That this disk wind is responding to the emission from the inner accretion disk demonstrates a connection between accretion processes occurring on very different

  2. The response of relativistic outflowing gas to the inner accretion disk of a black hole

    Science.gov (United States)

    Parker, Michael L.; Pinto, Ciro; Fabian, Andrew C.; Lohfink, Anne; Buisson, Douglas J. K.; Alston, William N.; Kara, Erin; Cackett, Edward M.; Chiang, Chia-Ying; Dauser, Thomas; De Marco, Barbara; Gallo, Luigi C.; Garcia, Javier; Harrison, Fiona A.; King, Ashley L.; Middleton, Matthew J.; Miller, Jon M.; Miniutti, Giovanni; Reynolds, Christopher S.; Uttley, Phil; Vasudevan, Ranjan; Walton, Dominic J.; Wilkins, Daniel R.; Zoghbi, Abderahmen

    2017-03-01

    The brightness of an active galactic nucleus is set by the gas falling onto it from the galaxy, and the gas infall rate is regulated by the brightness of the active galactic nucleus; this feedback loop is the process by which supermassive black holes in the centres of galaxies may moderate the growth of their hosts. Gas outflows (in the form of disk winds) release huge quantities of energy into the interstellar medium, potentially clearing the surrounding gas. The most extreme (in terms of speed and energy) of these—the ultrafast outflows—are the subset of X-ray-detected outflows with velocities higher than 10,000 kilometres per second, believed to originate in relativistic (that is, near the speed of light) disk winds a few hundred gravitational radii from the black hole. The absorption features produced by these outflows are variable, but no clear link has been found between the behaviour of the X-ray continuum and the velocity or optical depth of the outflows, owing to the long timescales of quasar variability. Here we report the observation of multiple absorption lines from an extreme ultrafast gas flow in the X-ray spectrum of the active galactic nucleus IRAS 13224‑3809, at 0.236 ± 0.006 times the speed of light (71,000 kilometres per second), where the absorption is strongly anti-correlated with the emission of X-rays from the inner regions of the accretion disk. If the gas flow is identified as a genuine outflow then it is in the fastest five per cent of such winds, and its variability is hundreds of times faster than in other variable winds, allowing us to observe in hours what would take months in a quasar. We find X-ray spectral signatures of the wind simultaneously in both low- and high-energy detectors, suggesting a single ionized outflow, linking the low- and high-energy absorption lines. That this disk wind is responding to the emission from the inner accretion disk demonstrates a connection between accretion processes occurring on very

  3. Accretion Outbursts in Self-gravitating Protoplanetary Disks

    CERN Document Server

    Bae, Jaehan; Zhu, Zhaohuan; Nelson, Richard P

    2014-01-01

    We improve on our previous treatments of long-term evolution of protostellar disks by explicitly solving disk self-gravity in two dimensions. The current model is an extension of the one-dimensional layered accretion disk model of Bae et al. We find that gravitational instability (GI)-induced spiral density waves heat disks via compressional heating (i.e. $P\\rm{d}V$ work), and can trigger accretion outbursts by activating the magnetorotational instability (MRI) in the magnetically inert disk dead-zone. The GI-induced spiral waves propagate well inside of gravitationally unstable region before they trigger outbursts at $R \\lesssim 1$ AU where GI cannot be sustained. This long-range propagation of waves cannot be reproduced with the previously used local $\\alpha$ treatments for GI. In our standard model where zero dead-zone residual viscosity ($\\alpha_{\\rm rd}$) is assumed, the GI-induced stress measured at the onset of outbursts is locally as large as $0.01$ in terms of the generic $\\alpha$ parameter. However,...

  4. Magnetospheres and Disk Accretion in Herbig Ae/Be Stars

    CERN Document Server

    Muzerolle, J; Calvet, N; Hartmann, L

    2004-01-01

    We present evidence of magnetically-mediated disk accretion in Herbig Ae/Be stars. Magnetospheric accretion models of Balmer and sodium profiles calculated with appropriate stellar and rotational parameters are in qualitative agreement with the observed profiles of the Herbig Ae star UX Ori, and yield a mass accretion rate of ~ 10^{-8} Msun/yr. If more recent indications of an extremely large rotation rate for this object are correct, the magnetic field geometry must deviate from that of a standard dipole in order to produce line emission consistent with observed flux levels. Models of the associated accretion shock qualitatively explain the observed distribution of excess fluxes in the Balmer discontinuity for a large ensemble of Herbig Ae/Be stars, and imply typically small mass accretion rates, < 10^{-7} Msun/yr. In order for accretion to proceed onto the star, significant amounts of gas must exist inside the dust destruction radius, which is potentially problematic for recently advocated scenarios of "...

  5. Accretion Disk Line Emission in AGN a Devil's Advocacy

    CERN Document Server

    Sulentic, J W; Dultzin-Hacyan, D

    1998-01-01

    We review the evidence for AGN optical and X-ray broad line emission from an accretion disk. We argue that there is little, if any, statistical evidence to support this assertion. The inconsistency is strongest for the rare class of Balmer profiles that show double peaks. The line profiles predicted by a simple illuminated disk model are often incompatible with the observations. We suggest that the Fe Kalpha line in Seyfert 1 galaxies, where a broad line is most often and most strongly detected, is actually a composite of two lines both with Gaussian profiles; one narrow/unshifted and the other broad/redshifted.

  6. Trainsient Accretion Disk and Energy Mechanism of Gamma Ray Bursts

    Institute of Scientific and Technical Information of China (English)

    LU Ye; ZHENG Guang-Sheng; ZHAO Gang; YANG Lan-Tian

    2000-01-01

    We suggest that a rotating massive black hole (106M ) located at an inactive galaxy may convert its host into a transient active phase by capturing and disrupting a star. During this period, a transient accretion disk is formed and a strong transient magnetic field can be produced in the inner boundary of the accretion disk. A large amount of rotational energy of the black hole is extracted and released in the ultra relativistic jet with a bulk Lorentz factor larger than 103 via Blandford-Znajek process. The relativistic jet energy can be converted into γ-ray radiation in the shock region located at a distance of about 1.4 × 1016 cm via the external shock mechanism.The observed properties of GRB971214 is used to illustrate our model

  7. Ring sequence decomposition of an accretion disk: the viscoresistive approach

    CERN Document Server

    Benini, Riccardo; Petitta, Jacopo

    2011-01-01

    We analyze a two dimensional viscoresistive magnetohydrodynamical (MHD) model for a thin accretion disk which reconciles the crystalline structure outlined in [Coppi(2005), Coppi and Rousseau(2006)] with real microscopic and macroscopic features of astrophysical accreting systems. In particular, we consider small dissipative effects (viscosity and resistivity, characterized by a magnetic Prandtl number of order unity), poloidal matter fluxes and a toroidal component of the magnetic field. These new ingredients allow us to set up the full equilibrium profile including the azimuthal component of the momentum conservation equation and the electron force balance relation. These two additional equations, which were identically satisfied in the original model, permit us to deal with non-zero radial and vertical matter fluxes, and the solution we construct for the global equilibrium system provides a full description of the radial and vertical dependence within the plasma disk. The main issue of our analysis is outl...

  8. Characterizing the mean-field dynamo in turbulent accretion disks

    CERN Document Server

    Gressel, Oliver

    2015-01-01

    The formation and evolution of a wide class of astrophysical objects is governed by turbulent, magnetized accretion disks. Understanding their secular dynamics is of primary importance. Apart from enabling mass accretion via the transport of angular momentum, the turbulence affects the long-term evolution of the embedded magnetic flux, which in turn regulates the efficiency of the transport. In this paper, we take a comprehensive next step towards an effective mean-field model for turbulent astrophysical disks by systematically studying the key properties of magnetorotational turbulence in vertically-stratified, isothermal shearing boxes. This allows us to infer emergent properties of the ensuing chaotic flow as a function of the shear parameter as well as the amount of net-vertical flux. Using the test-field method, we furthermore characterize the mean-field dynamo coefficients that describe the long-term evolution of large-scale fields. We simultaneously infer the vertical shape and the spectral scale depen...

  9. Local Dynamical Instabilities in Magnetized, Radiation Pressure Supported Accretion Disks

    CERN Document Server

    Blaes, Omer M; Blaes, Omer; Socrates, Aristotle

    2000-01-01

    We present a general linear dispersion relation which describes the coupled behavior of magnetorotational, photon bubble, and convective instabilities in weakly magnetized, differentially rotating accretion disks. We presume the accretion disks to be geometrically thin and supported vertically by radiation pressure. We fully incorporate the effects of a nonzero radiative diffusion length on the linear modes. In an equilibrium with purely vertical magnetic field, the vertical magnetorotational modes are completely unaffected by compressibility, stratification, and radiative diffusion. However, in the presence of azimuthal fields, which are expected in differentially rotating flows, the growth rate of all magnetorotational modes can be reduced substantially below the orbital frequency. This occurs if diffusion destroys radiation sound waves on the length scale of the instability, and the magnetic energy density of the azimuthal component exceeds the non-radiative thermal energy density. While sluggish in this c...

  10. Forming an O Star via Disk Accretion?

    CERN Document Server

    Qiu, Keping; Beuther, Henrik; Fallscheer, Cassandra

    2012-01-01

    We present a study of outflow, infall, and rotation in a ~10^5 Lsun (solar luminosity) star-forming region, IRAS 18360-0537, with Submillimeter Array (SMA) and IRAM 30m observations. The 1.3 mm continuum map shows a 0.5 pc dust ridge, of which the central compact part has a mass of ~80 Msun (solar mass) and harbors two condensations, MM1 and MM2. The CO (2--1) and SiO (5--4) maps reveal a biconical outflow centered at MM1, which is a hot molecular core (HMC) with a gas temperature of 320+/-50 K and a mass of ~13 Msun. The outflow has a gas mass of 54 Msun and a dynamical timescale of 8,000 yr. The kinematics of the HMC is probed by high-excitation CH3OH and CH3CN lines, which are detected at sub-arcsecond resolution and unveil a velocity gradient perpendicular to the outflow axis, suggesting a disk-like rotation of the HMC. An infalling envelope around the HMC is evidenced by CN lines exhibiting a profound inverse P-Cygni profile, and the estimated mass infall rate, 1.5x10^{-3} Msun/yr, is well comparable to ...

  11. Accretion Disks and Dynamos: Toward a Unified Mean Field Theory

    CERN Document Server

    Blackman, Eric G

    2012-01-01

    Conversion of gravitational energy into radiation near stars and compact objects in accretion disks the origin of large scale magnetic fields in astrophysical rotators have long been distinct topics of active research in astrophysics. In semi-analytic work on both problems it has been useful to presume large scale symmetries, which necessarily results in mean field theories; magnetohydrodynamic turbulence makes the underlying systems locally asymmetric and highly nonlinear. Synergy between theory and simulations should aim for the development of practical, semi-analytic mean field models that capture the essential physics and can be used for observational modeling. Mean field dynamo (MFD) theory and alpha-viscosity accretion disc theory have exemplified such distinct pursuits. Both are presently incomplete, but 21st century MFD theory has nonlinear predictive power compared to 20th century MFD. in contrast, alpha-viscosity accretion theory is still in a 20th century state. In fact, insights from MFD theory ar...

  12. Acceleration and Collimation of Relativistic Magnetohydrodynamic Disk Winds

    Science.gov (United States)

    Porth, Oliver; Fendt, Christian

    2010-02-01

    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 pressure equilibrium. The fiducial disk surface (respectively a slow disk wind) is prescribed as boundary condition for the outflow. We apply this technique for the first time in the context of relativistic jets. The strength of this approach is that it allows us to run a parameter study in order to investigate how the accretion disk conditions govern the outflow formation. Substantial effort has been made to implement a current-free, numerical outflow boundary condition in order to avoid artificial collimation present in the standard outflow conditions. Our simulations using the PLUTO code run for 500 inner disk rotations and on a physical grid size of 100 × 200 inner disk radii. The simulations evolve from an initial state in hydrostatic equilibrium and an initially force-free magnetic field configuration. Two options for the initial field geometries are applied—an hourglass-shaped potential magnetic field and a split monopole field. Most of our parameter runs evolve into a steady state solution which can be further analyzed concerning the physical mechanism at work. In general, we obtain collimated beams of mildly relativistic speed with Lorentz factors up to 6 and mass-weighted half-opening angles of 3-7 deg. The split-monopole initial setup usually results in less collimated outflows. The light surface of the outflow magnetosphere tends to align vertically—implying three relativistically distinct regimes in the flow—an inner subrelativistic domain close to the jet axis, a (rather narrow) relativistic jet and a surrounding subrelativistic outflow launched from the outer disk surface—similar to the spine-sheath structure

  13. Ultraluminous X-ray sources as super-Eddington accretion disks

    CERN Document Server

    Fabrika, Sergei; Atapin, Kirill

    2016-01-01

    The origin of Ultraluminous X-ray sources (ULXs) in external galaxies whose X-ray luminosities exceed those of the brightest black holes in our Galaxy by hundreds and thousands of times is mysterious. The most popular models for the ULXs involve either intermediate mass black holes (IMBHs) or stellar-mass black holes accreting at super-Eddington rates. Here we review the ULX properties, their X-ray spectra indicate a presence of hot winds in their accretion disks supposing the supercritical accretion. However, the strongest evidences come from optical spectroscopy. The spectra of the ULX counterparts are very similar to that of SS 433, the only known supercritical accretor in our Galaxy.

  14. On the X-ray heated skin of Accretion Disks

    CERN Document Server

    Nayakshin, S

    1999-01-01

    We present a simple analytical formula for the Thomson depth of the X-rayheated skin of accretion disks valid at any radius and for a broad range ofspectral indices of the incident X-rays, accretion rates and black hole masses.We expect that this formula may find useful applications in studies of geometryof the inner part of accretion flows around compact objects, and in severalother astrophysically important problems, such as the recently observed X-ray``Baldwin'' effect (i.e., monotonic decrease of Fe line's equivalent width withthe X-ray luminosity of AGN), the problem of missing Lyman edge in AGN, andline and continuum variability studies in accretion disks around compactobjects. We compute the reflected X-ray spectra for several representativecases and show that for hard X-ray spectra and large ionizing fluxes the skinrepresents a perfect mirror that does not produce any Fe lines or absorptionfeatures. At the same time, for soft X-ray spectra or small ionizing fluxes,the skin produces very strong ionized...

  15. On the Role of the Accretion Disk in Black Hole Disk-Jet Connections

    CERN Document Server

    Miller, J M; Fabian, A C; Nowak, M A; Reis, R C; Cackett, E M; Pottschmidt, K; Wilms, J

    2012-01-01

    Models of jet production in black hole systems suggest that the properties of the accretion disk - such as its mass accretion rate, inner radius, and emergent magnetic field - should drive and modulate the production of relativistic jets. Stellar-mass black holes in the "low/hard" state are an excellent laboratory in which to study disk-jet connections, but few coordinated observations are made using spectrometers that can incisively probe the inner disk. We report on a series of 20 Suzaku observations of Cygnus X-1 made in the jet-producing low/hard state. Contemporaneous radio monitoring was done using the Arcminute MicroKelvin Array radio telescope. Two important and simple results are obtained: (1) the jet (as traced by radio flux) does not appear to be modulated by changes in the inner radius of the accretion disk; and (2) the jet is sensitive to disk properties, including its flux, temperature, and ionization. Some more complex results may reveal aspects of a coupled disk-corona-jet system. A positive c...

  16. Luminosities of Disk--accreting Non--magnetic Neutron Stars

    CERN Document Server

    Thampan, A V

    2002-01-01

    Disk accretion onto a neutron star possessing a weak surface magnetic field ($B \\le 10^8$ G) provides interesting X-ray emission scenarios, and is relevant for understanding X-ray bursters and low-mass X-ray binaries (LMXBs). The standard (Newtonian) theory of disk-accretion predicts that the matter spiralling in from infinity loses one-half of its total gravitational energy in the extended disk, and the remainder in a narrow boundary layer girdling the neutron star. The ratio of the boundary layer luminosity to that from the disk ($E_{\\rm BL}/E_{\\rm D}$) is, therefore, unity. On incorporation of general relativity without rotation (Schwarzschild solution), $E_{\\rm BL}/E_{\\rm D}$ is seen to be as high as 6. We construct rotating sequences of neutron stars for three representative equations of state. We show here that for a neutron star rotating at a limit where centrifugal force balances the inward gravitational force, $E_{\\rm BL}/E_{\\rm D}\\sim 0$.

  17. Thermally Driven Winds from Radiatively Inefficient Accretion Flows

    CERN Document Server

    Kawabata, Ryoji

    2009-01-01

    Radiatively inefficient accretion flows (RIAFs) are common feature of low-luminosity accretion flows, including quiescent states of X-ray binaries and low-lunimosity active galactic nuclei. Thermally driven winds are expected from such hot accretion flows. By assuming that the flow has self-similarity structure in the radial direction, we solve the vertical structure of the wind and accretion flows simultaneously and evaluate the mass loss rates by wind. We find that the ratio of the outflow rate to the accretion rate is approximately unity for a viscosity parameter, alpha lesssim 0.1, despite some uncertainties in the angular momentum and temperature distributions. That is, the accretion rate in the RIAFs is roughly proportional to the radius. Moreover, we elucidate the effect of cooling by wind on the underneath accretion flow, finding that this effect could be important for calculating energy spectrum of the RIAF. Observational implications are briefly discussed in the context of Sgr A*.

  18. Stability of Accretion Disks in Presence of Nucleosynthesis

    CERN Document Server

    Mukhopadhyay, B; Mukhopadhyay, Banibrata; Chakrabarti, Sandip K.

    2001-01-01

    We study the effect of nuclear reaction on a thin, axisymmetric, differentially rotating, inviscid, steady accretion flow around a black hole from an analytical point of view. We find that for most of the reasonable disk parameters, when $p-p$-reaction, dissociation of deuterium and helium are taken into account, the transonic region of the disk continues to have the inner sonic point and if the temperature of the flow at the injection sonic point could be raised (by say, some heating processes) the flow would to pass through this inner sonic point. Otherwise, the flow may be unstable. We use the sonic point analysis to study the solution. In the rest of the disk parameters the inner sonic point is absent altogether and the flow will definitely be unstable.

  19. Accretion of Supersonic Winds on Boson Stars

    CERN Document Server

    Gracia-Linares, M

    2016-01-01

    We present the evolution of a supersonic wind interacting with a Boson Star (BS) and compare the resulting wind density profile with that of the shock cone formed when the wind is accreted by a non-rotating Black Hole (BH) of the same mass. The physical differences between these accretors are that a BS, unlike a BH has no horizon, it does not have a mechanical surface either and thus the wind is expected to trespass the BS. Despite these conditions, on the BS space-time the gas achieves a stationary flux with the gas accumulating in a high density elongated structure comparable to the shock cone formed behind a BH. The highest density resides in the center of the BS whereas in the case of the BH it is found on the downstream part of the BH near the event horizon. The maximum density of the gas is smaller in the BS than in the BH case. Our results indicate that the highest density of the wind is more similar on the BS to that on the BH when the BS has high self-interaction, when it is more compact and when the...

  20. Irradiation Instability at the Inner Edges of Accretion Disks

    CERN Document Server

    Fung, Jeffrey

    2014-01-01

    An instability can potentially operate in highly irradiated disks where the disk sharply transitions from being radially transparent to opaque (the 'transition region'). Such conditions may exist at the inner edges of transitional disks around T Tauri stars and accretion disks around AGNs. We derive the criterion for this instability, which we term the 'irradiation instability', or IRI. We also present the linear growth rate as a function of beta, the ratio between radiation force and gravity, and c_s, the sound speed of the disk, obtained using two methods: a semi-analytic analysis of the linearized equations and a numerical simulation using the GPU-accelerated hydrodynamical code PEnGUIn. In particular, we find that IRI occurs at beta~0.1 if the transition region extends as wide as ~0.05r, and at higher beta values if it is wider. Furthermore, in the nonlinear evolution of the instability, disks with a large beta and small c_s exhibit 'clumping': extreme local surface density enhancements, reaching a few te...

  1. Accretion from debris disks onto white dwarfs : Fingering (thermohaline) instability and derived accretion rates

    CERN Document Server

    Deal, M; Vauclair, G; Vauclair, S; Wachlin, F C

    2013-01-01

    Recent observations of a large number of DA and DB white dwarfs show evidence of debris disks, which are the remnants of old planetary systems. The infrared excess detected with \\emph{Spitzer} and the lines of heavy elements observed in their atmospheres with high-resolution spectroscopy converge on the idea that planetary material accretes onto these stars. Accretion rates have been derived by several authors with the assumption of a steady state between accretion and gravitational settling. The results are unrealistically different for DA and DB white dwarfs. When heavy matter is accreted onto stars, it induces an inverse $\\mu$-gradient that leads to fingering (thermohaline) convection. The aim of this letter is to study the impact of this specific process on the derived accretion rates in white dwarfs and on the difference between DA and DB. We solve the diffusion equation for the accreted heavy elements with a time-dependent method. The models we use have been obtained both with the IRAP code, which compu...

  2. Thin accretion disks around cold Bose–Einstein condensate stars

    Energy Technology Data Exchange (ETDEWEB)

    Dănilă, Bogdan, E-mail: bogdan.danila22@gmail.com [Department of Physics, Babes-Bolyai University, Kogalniceanu Street, Cluj-Napoca (Romania); Harko, Tiberiu, E-mail: t.harko@ucl.ac.uk [Department of Mathematics, University College London, Gower Street, WC1E 6BT, London (United Kingdom); Kovács, Zoltán, E-mail: kovacsz2013@yahoo.com [Max-Fiedler-Str. 7, 45128, Essen (Germany)

    2015-05-09

    Due to their superfluid properties some compact astrophysical objects, like neutron or quark stars, may contain a significant part of their matter in the form of a Bose–Einstein condensate (BEC). Observationally distinguishing between neutron/quark stars and BEC stars is a major challenge for this latter theoretical model. An observational possibility of indirectly distinguishing BEC stars from neutron/quark stars is through the study of the thin accretion disks around compact general relativistic objects. In the present paper, we perform a detailed comparative study of the electromagnetic and thermodynamic properties of the thin accretion disks around rapidly rotating BEC stars, neutron stars and quark stars, respectively. Due to the differences in the exterior geometry, the thermodynamic and electromagnetic properties of the disks (energy flux, temperature distribution, equilibrium radiation spectrum, and efficiency of energy conversion) are different for these classes of compact objects. Hence in this preliminary study we have pointed out some astrophysical signatures that may allow one to observationally discriminate between BEC stars and neutron/quark stars.

  3. Thin accretion disks around cold Bose-Einstein condensate stars

    Energy Technology Data Exchange (ETDEWEB)

    Danila, Bogdan [Babes-Bolyai University, Department of Physics, Cluj-Napoca (Romania); Harko, Tiberiu [University College London, Department of Mathematics, London (United Kingdom); Kovacs, Zoltan

    2015-05-15

    Due to their superfluid properties some compact astrophysical objects, like neutron or quark stars, may contain a significant part of their matter in the form of a Bose-Einstein condensate (BEC). Observationally distinguishing between neutron/quark stars and BEC stars is a major challenge for this latter theoretical model. An observational possibility of indirectly distinguishing BEC stars from neutron/quark stars is through the study of the thin accretion disks around compact general relativistic objects. In the present paper, we perform a detailed comparative study of the electromagnetic and thermodynamic properties of the thin accretion disks around rapidly rotating BEC stars, neutron stars and quark stars, respectively. Due to the differences in the exterior geometry, the thermodynamic and electromagnetic properties of the disks (energy flux, temperature distribution, equilibrium radiation spectrum, and efficiency of energy conversion) are different for these classes of compact objects. Hence in this preliminary study we have pointed out some astrophysical signatures that may allow one to observationally discriminate between BEC stars and neutron/quark stars. (orig.)

  4. On the Vertical Structure of Radiation-Dominated Accretion Disks

    CERN Document Server

    Turner, N J

    2004-01-01

    The vertical structure of black hole accretion disks in which radiation dominates the total pressure is investigated using a three-dimensional radiation-MHD calculation. The domain is a small patch of disk centered 100 Schwarzschild radii from a black hole of 10^8 Solar masses, and the stratified shearing-box approximation is used. Magneto-rotational instability converts gravitational energy to turbulent magnetic and kinetic energy. The gas is heated by magnetic dissipation and by radiation damping of the turbulence, and cooled by diffusion and advection of radiation through the vertical boundaries. The resulting structure differs in several fundamental ways from the standard Shakura-Sunyaev picture. The disk consists of three layers. At the midplane, the density is large, and the magnetic pressure and total accretion stress are less than the gas pressure. In lower-density surface layers that are optically thick, the magnetic pressure and stress are greater than the gas pressure but less than the radiation pr...

  5. Constraining MHD Disk-Winds with X-ray Absorbers

    Science.gov (United States)

    Fukumura, Keigo; Tombesi, F.; Shrader, C. R.; Kazanas, D.; Contopoulos, J.; Behar, E.

    2014-01-01

    From the state-of-the-art spectroscopic observations of active galactic nuclei (AGNs) the robust features of absorption lines (e.g. most notably by H/He-like ions), called warm absorbers (WAs), have been often detected in soft X-rays (UFOs) whose physical condition is much more extreme compared with the WAs. Motivated by these recent X-ray data we show that the magnetically- driven accretion-disk wind model is a plausible scenario to explain the characteristic property of these X-ray absorbers. As a preliminary case study we demonstrate that the wind model parameters (e.g. viewing angle and wind density) can be constrained by data from PG 1211+143 at a statistically significant level with chi-squared spectral analysis. Our wind models can thus be implemented into the standard analysis package, XSPEC, as a table spectrum model for general analysis of X-ray absorbers.

  6. Acceleration and collimation of relativistic MHD disk winds

    CERN Document Server

    Porth, O

    2009-01-01

    We perform axisymmetric relativistic magnetohydrodynamic (MHD) simulations to investigate the acceleration and collimation of jets and outflows from disks around compact objects. The fiducial disk surface (respectively a slow disk wind) is prescribed as boundary condition for the outflow. We apply this technique for the first time in the context of relativistic jets. The strength of this approach is that it allows us to run a parameter study in order to investigate how the accretion disk conditions govern the outflow formation. Our simulations using the PLUTO code run for 500 inner disk rotations and on a physical grid size of 100x200 inner disk radii. In general, we obtain collimated beams of mildly relativistic speed and mass-weighted half-opening angles of 3-7 degrees. When we increase the outflow Poynting flux by injecting an additional disk toroidal field into the inlet, Lorentz factors up to 6 are reached. These flows gain super-magnetosonic speed and remain Poynting flux dominated. The light surface of...

  7. A Simple Disk Wind Model for Broad Absorption Line Quasars

    CERN Document Server

    Higginbottom, N; Long, K S; Sim, S A; Matthews, J H

    2013-01-01

    Approximately 20% of quasi-stellar objects (QSOs) exhibit broad, blue-shifted absorption lines in their ultraviolet spectra. Such features provide clear evidence for significant outflows from these systems, most likely in the form of accretion disk winds. These winds may represent the "quasar" mode of feedback that is often invoked in galaxy formation/evolution models, and they are also key to unification scenarios for active galactic nuclei (AGN) and QSOs. To test these ideas, we construct a simple benchmark model of an equatorial, biconical accretion disk wind in a QSO and use a Monte Carlo ionization/radiative transfer code to calculate the ultraviolet spectra as a function of viewing angle. We find that for plausible outflow parameters, sightlines looking directly into the wind cone do produce broad, blue-shifted absorption features in the transitions typically seen in broad absorption line QSOs. However, our benchmark model is intrinsically X-ray weak in order to prevent overionization of the outflow, an...

  8. General relativistic spectra of accretion disks around rotating neutron stars

    CERN Document Server

    Bhattacharya, S; Thampan, A V

    2000-01-01

    General relativistic spectra from accretion disks around rotating neutron stars in the appropriate space-time geometry for several different equation of state, spin rates and mass of the compact object have been computed. The analysis involves the computation of the relativistically corrected radial temperature profiles and the effect of Doppler and gravitational red-shifts on the spectra. Light bending effects have been omitted for simplicity. The relativistic spectrum is compared with the Newtonian one and it is shown that the difference between the two is primarily due to the different radial temperature profile for the relativistic and Newtonian disk solutions. To facilitate direct comparison with observations, a simple empirical function has been presented which describes the numerically computed relativistic spectra well. This empirical function (which has three parameters including normalization) also describes the Newtonian spectrum adequately. Thus the function can in principle be used to distinguish...

  9. The Intrinsic Quasar Luminosity Function: Accounting for Accretion Disk Anisotropy

    CERN Document Server

    DiPompeo, M A; Brotherton, M S; Runnoe, J C; Green, R F

    2014-01-01

    Quasar luminosity functions are a fundamental probe of the growth and evolution of supermassive black holes. Measuring the intrinsic luminosity function is difficult in practice, due to a multitude of observational and systematic effects. As sample sizes increase and measurement errors drop, characterizing the systematic effects is becoming more important. It is well known that the continuum emission from the accretion disk of quasars is anisotropic --- in part due to its disk-like structure --- but current luminosity function calculations effectively assume isotropy over the range of unobscured lines of sight. Here, we provide the first steps in characterizing the effect of random quasar orientations and simple models of anisotropy on observed luminosity functions. We find that the effect of orientation is not insignificant and exceeds other potential corrections such as those from gravitational lensing of foreground structures. We argue that current observational constraints may overestimate the intrinsic l...

  10. Circumstellar Disks of the Most Vigorously Accreting Young Stars

    CERN Document Server

    Liu, Hauyu Baobab; Kudo, Tomoyuki; Hashimoto, Jun; Dong, Ruobing; Vorobyov, Eduard I; Pyo, Tae-Soo; Fukagawa, Misato; Tamura, Motohide; Henning, Thomas; Dunham, Michael M; Karr, Jennifer; Kusakabe, Nobuhiko; Tsuribe, Toru

    2016-01-01

    Young stellar objects (YSOs) may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. We report our high angular resolution, coronagraphic near-infrared polarization imaging observations using the High Contrast Instrument for the Subaru Next Generation Adaptive Optics (HiCIAO) of the Subaru 8.2 m Telescope, towards four YSOs which are undergoing luminous accretion outbursts. The obtained infrared images have verified the presence of several hundred AUs scale arms and arcs surrounding these YSOs. In addition, our hydrodynamics simulations and radiative transfer models further demonstrate that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation p...

  11. Effects of Fluid Instabilities on Accretion Disk Spectra

    CERN Document Server

    Davis, S W; Turner, N J; Socrates, A

    2003-01-01

    Numerical calculations and linear theory of radiation magnetohydrodynamic flows indicate that the photon bubble and magnetorotational instability (MRI) may produce large density inhomogeneities in radiation pressure supported media. We study the effects of the photon bubble instability on accretion disk spectra using 2-D Monte Carlo (MC) and 1-D Feautrier radiative transfer calculations on a snapshot of a 2-D numerical simulation domain. We find an enhancement in the thermalization of the MC spectra over that of the Feautrier calculation. In the inner-most regions of these disks, the turbulent magnetic pressure may greatly exceed that of the gas. It is then possible for bulk turbulent Alfvenic motions driven by the MRI to exceed the thermal velocity making turbulent Comptonization the dominant radiative process. We estimate the spectral distortion due to turbulent Comptonization utilizing a 1-D MC calculation.

  12. Bypass to Turbulence in Hydrodynamic Accretion Disks: An Eigenvalue Analysis

    CERN Document Server

    Mukhopadhyay, B; Narayan, R; Mukhopadhyay, Banibrata; Afshordi, Niayesh; Narayan, Ramesh

    2004-01-01

    Cold accretion disks such as those in star-forming systems, quiescent cataclysmic variables, and some active galactic nuclei, are expected to have neutral gas which does not couple well to magnetic fields. The turbulent viscosity in such disks must be hydrodynamic in origin, not magnetohydrodynamic. We investigate the growth of hydrodynamic perturbations in a linear shear flow sandwiched between two parallel walls. The unperturbed flow is similar to plane Couette flow but with a Coriolis force included. Although there are no exponentially growing eigenmodes in this system, nevertheless, because of the non-normal nature of the eigenmodes, it is possible to have a large transient growth in the energy of perturbations. For a constant angular momentum disk, we find that the perturbation with maximum growth has a wave-vector in the vertical direction. The energy grows by more than a factor of 100 for a Reynolds number R=300 and more than a factor of 1000 for R=1000. Turbulence can be easily excited in such a disk,...

  13. Silicate Dust in Evolved Protoplanetary Disks: Growth, Sedimentation, and Accretion

    CERN Document Server

    Sicilia-Aguilar, Aurora; Watson, Dan; Bohac, Chris; Henning, Thomas; Bouwman, Jeroen; 10.1086/512121

    2009-01-01

    We present the Spitzer IRS spectra for 33 young stars in Tr 37 and NGC 7160. The sample includes the high- and intermediate-mass stars with MIPS 24 microns excess, the only known active accretor in the 12 Myr-old cluster NGC 7160, and 19 low-mass stars with disks in the 4 Myr-old cluster Tr 37. We examine the 10 microns silicate feature, present in the whole sample of low-mass star and in 3 of the high- and intermediate-mass targets, and we find that PAH emission is detectable only in the Herbig Be star. We analyze the composition and size of the warm photospheric silicate grains by fitting the 10 microns silicate feature, and study the possible correlations between the silicate characteristics and the stellar and disk properties (age, SED slope, accretion rate, spectral type). We find indications of dust settling with age and of the effect of turbulent enrichment of the disk atmosphere with large grains. Crystalline grains are only small contributors to the total silicate mass in all disks, and do not seem t...

  14. Chemistry in a forming protoplanetary disk: main accretion phase

    CERN Document Server

    Yoneda, Haruaki; Furuya, Kenji; Aikawa, Yuri

    2016-01-01

    We investigate the chemistry in a radiation-hydrodynamics model of star-forming core which evolves from a cold ($\\sim 10$ K) prestellar core to the main accretion phase in $\\sim 10^5$ yr. A rotationally-supported gravitationally unstable disk is formed around a protostar. We extract the temporal variation of physical parameters in $\\sim 1.5 \\times 10^3$ SPH particles which end up in the disk, and perform post-processing calculations of the gas-grain chemistry adopting a three-phase model. Inside the disk, the SPH particles migrate both inward and outward. Since a significant fraction of volatiles such as CO can be trapped in the water-dominant ice in the three-phase model, the ice mantle composition depends not only on the current position in the disk but also on whether the dust grain has ever experienced higher temperatures than the water sublimation temperature. Stable molecules such as H$_2$O, CH$_4$, NH$_3$ and CH$_3$OH are already abundant at the onset of gravitational collapse and simply sublimated as ...

  15. Magnetized Accretion and Dead Zones in Protostellar Disks

    CERN Document Server

    Dzyurkevich, Natalia; Henning, Thomas; Kley, Wilhelm

    2013-01-01

    The edges of magnetically-dead zones in protostellar disks have been proposed as locations where density bumps may arise, trapping planetesimals and helping form planets. Magneto-rotational turbulence in magnetically-active zones provides both accretion of gas on the star and transport of mass to the dead zone. We investigate the location of the magnetically-active regions in a protostellar disk around a solar-type star, varying the disk temperature, surface density profile, and dust-to-gas ratio. We also consider stellar masses between 0.4 and 2 $M_\\odot$, with corresponding adjustments in the disk mass and temperature. The dead zone's size and shape are found using the Elsasser number criterion with conductivities including the contributions from ions, electrons, and charged fractal dust aggregates. The charged species' abundances are found using the approach proposed by S. Okuzumi. The dead zone is in most cases defined by the ambipolar diffusion. In our maps, the dead zone takes a variety of shapes, inclu...

  16. ACCRETION DISKS WITH A LARGE SCALE MAGNETIC FIELD AROUND BLACK HOLES

    Directory of Open Access Journals (Sweden)

    Gennady Bisnovatyi-Kogan

    2013-12-01

    Full Text Available We consider accretion disks around black holes at high luminosity, and the problem of the formation of a large-scale magnetic field in such disks, taking into account the non-uniform vertical structure of the disk. The structure of advective accretion disks is investigated, and conditions for the formation of optically thin regions in central parts of the accretion disk are found. The high electrical conductivity of the outer layers of the disk prevents outward diffusion of the magnetic field. This implies a stationary state with a strong magnetic field in the inner parts of the accretion disk close to the black hole, and zero radial velocity at the surface of the disk. The problem of jet collimation by magneto-torsion oscillations is investigated.

  17. Chemistry in a Forming Protoplanetary Disk: Main Accretion Phase

    Science.gov (United States)

    Yoneda, Haruaki; Tsukamoto, Yusuke; Furuya, Kenji; Aikawa, Yuri

    2016-12-01

    We investigate the chemistry in a radiation-hydrodynamics model of a star-forming core that evolves from a cold (∼10 K) prestellar core to the main accretion phase in ∼105 years. A rotationally supported gravitationally unstable disk is formed around a protostar. We extract the temporal variation of physical parameters in ∼1.5 × 103 SPH particles that end up in the disk, and perform post-processing calculations of the gas-grain chemistry adopting a three-phase model. Inside the disk, the SPH particles migrate both inward and outward. Since a significant fraction of volatiles such as CO can be trapped in the water-dominant ice in the three-phase model, the ice mantle composition depends not only on the current position in the disk, but also on whether the dust grain has ever experienced higher temperatures than the water sublimation temperature. Stable molecules such as H2O, CH4, NH3, and CH3OH are already abundant at the onset of gravitational collapse and are simply sublimated as the fluid parcels migrate inside the water snow line. On the other hand, various molecules such as carbon chains and complex organic molecules (COMs) are formed in the disk. The COMs abundance sensitively depends on the outcomes of photodissociation and diffusion rates of photofragments in bulk ice mantle. As for S-bearing species, H2S ice is abundant in the collapse phase. In the warm regions in the disk, H2S is sublimated to be destroyed, while SO, H2CS, OCS, and SO2 become abundant.

  18. Crystalline structure of accretion disks: features of a global model.

    Science.gov (United States)

    Montani, Giovanni; Benini, Riccardo

    2011-08-01

    In this paper, we develop the analysis of a two-dimensional magnetohydrodynamical configuration for an axially symmetric and rotating plasma (embedded in a dipolelike magnetic field), modeling the structure of a thin accretion disk around a compact astrophysical object. Our study investigates the global profile of the disk plasma, in order to fix the conditions for the existence of a crystalline morphology and ring sequence, as outlined by the local analysis pursued in Coppi [Phys. Plasmas 12, 7302 (2005)] and Coppi and Rousseau [Astrophys. J. 641, 458 (2006)]. In the linear regime, when the electromagnetic back-reaction of the plasma is small enough, we show the existence of an oscillating radial behavior for the flux surface function, which very closely resembles the one outlined in the local model, apart from a radial modulation of the amplitude. In the opposite limit, corresponding to a dominant back-reaction in the magnetic structure over the field of central object, we can recognize the existence of a ringlike decomposition of the disk, according to the same modulation of the magnetic flux surface, and a smoother radial decay of the disk density, with respect to the linear case. In this extreme nonlinear regime, the global model seems to predict a configuration very close to that of the local analysis, but here the thermostatic pressure, crucial for the equilibrium setting, is also radially modulated. Among the conditions requested for the validity of such a global model, the confinement of the radial coordinate within a given value sensitive to the disk temperature and to the mass of the central objet, stands; however, this condition corresponds to dealing with a thin disk configuration.

  19. The collimation of magnetic jets by disk winds

    CERN Document Server

    Globus, Noemie

    2016-01-01

    The collimation of a Poynting-flux dominated jet by a wind emanating from the surface of an accretion flow is computed using a semi-analytic model. The injection of the disk wind is treated as a boundary condition in the equatorial plane, and its evolution is followed by invoking a prescribed geometry of streamlines. Solutions are obtained for a wide range of disk wind parameters. It is found that jet collimation generally occurs when the total wind power exceeds about ten percents of the jet power. For moderate wind powers we find gradual collimation. For strong winds we find rapid collimation followed by focusing of the jet, after which it remains narrow over many Alfv\\'en crossing times before becoming conical. We estimate that in the later case the jet's magnetic field may be dissipated by the current-driven kink instability over a distance of a few hundreds gravitational radii. We apply the model to M87 and show that the observed parabolic shape of the radio jet within the Bondi radius can be reproduced ...

  20. Inner edge of accretion disks in low mass X-ray binaries

    Institute of Scientific and Technical Information of China (English)

    李向东; 汪珍如

    1995-01-01

    The magnitude of the inner edge of accretion disks in low mass X-ray binaries is controversial in theoretical considerations and observations. Using the inner boundary conditions of accretion disks the inner disk radius has been calculated by taking into account the effect of feedback radiation and the deviation of disk rotation from Keplerian. Results have been applied to the observations and possible interpretations have been proposed for the X-ray spectra and quasiperiodic oscillations.

  1. The vertical structure of T Tauri accretion disks II physical conditions in the disk

    CERN Document Server

    Malbet, F; Monin, J L

    2001-01-01

    We present a self-consistent analytical model for the computation of the physical conditions in a steady quasi-Keplerian accretion disk. The method, based on the thin disk approximation, considers the disk as concentric cylinders in which we treat the vertical transfer as in a plane-parallel medium. The formalism generalizes a work by Hubeny (1990), linking the disk temperature distribution to the local energy dissipation and leads to analytical formulae for the temperature distribution which help to understand the behaviour of the radiation propagated inside the disks. One of the main features of our new model is that it can take into account many heating sources. We apply the method first to two sources: viscous dissipation and stellar irradiation. We show that other heating sources like horizontal transfer or irradiation from the ambiant medium can also be taken into account. Using the analytical formulation in the case of a modified Shakura & Sunyaev radial distribution that allow the accretion rate t...

  2. On rapid migration and accretion within disks around supermassive black holes

    CERN Document Server

    McKernan, B; Lyra, W; Perets, H B; Winter, L M; Yaqoob, T

    2011-01-01

    Galactic nuclei should contain a cluster of stars and compact objects in the vicinity of the central supermassive black hole due to stellar evolution, minor mergers and gravitational dynamical friction. By analogy with protoplanetary migration, nuclear cluster objects (NCOs) can migrate in the accretion disks that power active galactic nuclei by exchanging angular momentum with disk gas. Here we show that an individual NCO undergoing runaway outward migration comparable to Type III protoplanetary migration can generate an accretion rate corresponding to Seyfert AGN or quasar luminosities. Multiple migrating NCOs in an AGN disk can dominate traditional viscous disk accretion and at large disk radii, ensemble NCO migration and accretion could provide sufficient heating to prevent the gravitational instability from consuming disk gas in star formation. The magnitude and energy of the X-ray soft excess observed at ~0.1-1keV in Seyfert AGN could be explained by a small population of ~10^{2}-10^{3} accreting stella...

  3. Constraints on Accretion Disk Physics in Low Luminosity Radio Galaxies

    Science.gov (United States)

    Baum, Stefi; Noel-Storr, Jacob; O'Dea, Christopher

    2008-03-01

    It is currently believed that essentially all galaxies harbor a massive black hole in their nuclei. If this is true, then it becomes hard to understand why we do not see the luminosity released by the inevitable accretion of the galaxy ISM onto the black hole in all galaxies. The differences in AGN output between the two classes of narrow-line radio galaxies (FRI and FRII) may hold the vital clue. High radio luminosity FRIIs generally show strong high-excitation narrow lines and are believed to be the obscured counterparts of radio loud quasars. Low radio luminosity FRIs by contrast have weaker, low-ionization lines and low ratios of optical to radio luminosities. A large difference in accretion rate and radiative efficiency between FRI and FRIIs would explain the difference in the optical properties and also provide a new unification between different classes of active galaxies in which the dominant parameter is accretion rate. Spitzer IRAC and MIPS observations already exist for most of a well defined sample of FRIs. However, the previously observed objects are the 'famous' ones, e.g., M87, M84, NGC315, 3C264, 3C31. Thus, the existing datasets are highly selected. Here we propose a very small request to complete the sample. We propose IRAC observations in all 4 bands, and MIPS photometry at 24 and 70 microns of 8, and 7 sources, respectively, for a total request of 1.7 hrs. These observations will complete the sample at very little cost in observing time. The large amount of existing complmentary data at multiple wavebands will greatly enhance the legacy value of the proposed observations. By completing the sample, the proposed IRAC and MIPS observations will produce a well defined and very well studied sample of nearby low luminosity radio galaxies. We will use the completed sample to investigate the properties of the accretion disk radiation, and the circumnuclear obscuring material.

  4. Crystalline Structure of Accretion Disks: Features of the Global Model

    CERN Document Server

    Montani, Giovanni

    2012-01-01

    In this paper, we develop the analysis of a two-dimensional magnetohydrodynamical configuration for an axially symmetric and rotating plasma (embedded in a dipole like magnetic field), modeling the structure of a thin accretion disk around a compact astrophysical object. Our study investigates the global profile of the disk plasma, in order to fix the conditions for the existence of a crystalline morphology and ring sequence, as outlined by the local analysis pursued in [1, 2]. In the linear regime, when the electromagnetic back-reaction of the plasma is small enough, we show the existence of an oscillating radial behavior for the flux surface function which very closely resembles the one outlined in the local model, apart from a radial modulation of the amplitude. In the opposite limit, corresponding to a dominant back-reaction in the magnetic structure over the field of central object, we can recognize the existence of a ring-like decomposition of the disk, according to the same modulation of the magnetic f...

  5. Accretion of Terrestrial Planets from Oligarchs in a Turbulent Disk

    CERN Document Server

    Ogihara, M; Morbidelli, A; Ogihara, Masahiro; Ida, Shigeru; Morbidelli, Alessandro

    2006-01-01

    We have investigated the final accretion stage of terrestrial planets from Mars-mass protoplanets that formed through oligarchic growth in a disk comparable to the minimum mass solar nebula (MMSN), through N-body simulation including random torques exerted by disk turbulence due to Magneto-Rotational-Instability. For the torques, we used the semi-analytical formula developed by Laughlin et al.(2004). The damping of orbital eccentricities (in all runs) and type-I migration (in some runs) due to the tidal interactions with disk gas are also included. We found that the orbital eccentricities pumped up by the turbulent torques and associated random walks in semimajor axes tend to delay isolation of planets, resulting in more coagulation of planets than in the case without turbulence. The eccentricities are still damped after planets become isolated. As a result, the number of final planets decreases with increase in strength of the turbulence, while Earth-mass planets with small eccentricities are still formed. I...

  6. Effects of local dissipation profiles on magnetized accretion disk spectra

    CERN Document Server

    Tao, Ted

    2013-01-01

    We present spectral calculations of non-LTE accretion disk models appropriate for high luminosity stellar mass black hole X-ray binary systems. We first use a dissipation profile based on scaling the results of shearing box simulations of Hirose et al. (2009) to a range of annuli parameters. We simultaneously scale the effective temperature, orbital frequency and surface density with luminosity and radius according to the standard \\alpha-model (Shakura & Sunyaev, 1973). This naturally brings increased dissipation to the disk surface layers (around the photospheres) at small radii and high luminosities. We find that the local spectrum transitions directly from a modified black body to a saturated Compton scattering spectrum as we increase the effective temperature and orbital frequency while decreasing midplane surface density. Next, we construct annuli models based on the parameters of a L/L_Edd=0.8 disk orbiting a 6.62 solar mass black hole using two modified dissipation profiles that explicitly put more...

  7. Numerical Simulation of Interaction between an L1 Stream and an Accretion Disk in a Close Binary System

    CERN Document Server

    Fujiwara, H; Nagae, T; Matsuda, T; Fujiwara, Hidekazu; Makita, Makoto; Nagae, Takizo; Matsuda, Takuya

    2001-01-01

    The hydrodynamic behavior of an accretion disk in a close binary system is numerically simulated. Calculation is made for a region including the compact star and the gas-supplying companion. The equation of state is that of an ideal gas characterized by the specific heat ratio $\\gamma$. Two cases with $\\gamma$ of 1.01 and 1.2 are studied. Our calculations show that the gas, flowing from the companion via a Lagrangian L1 point towards the accretion disk, forms a fine gas beam (L1 stream), which penetrates into the disk. No hot spot therefore forms in these calculations. Another fact discovered is that the gas rotating with the disk forms, on collision with the L1 stream, a bow shock wave, which may be called an L1 shock. The disk becomes hot because the L1 shock heats the disk gas in the outer parts of the disk, so that the spiral shocks wind loosely even with $\\gamma=1.01$. The L1 shock enhances the non-axisymmetry of the density distribution in the disk, and therefore the angular momentum transfer by the tid...

  8. Magnetocentrifugally Driven Flows from Young Stars and Disks. VI. Accretion with a Multipole Stellar Field

    CERN Document Server

    Mohanty, Subhanjoy

    2008-01-01

    Previous analyses of magnetospheric accretion and outflow in classical T Tauri stars (CTTSs), within the context of both the X-wind model and other theoretical scenarios, have assumed a dipolar geometry for the stellar magnetic field if it were not perturbed by the presence of an accreting, electrically conducting disk. However, CTTS surveys reveal that accretion hot spots cover a small fraction of the stellar surface, and that the net field polarization on the stellar surface is small. Both facts imply that the magnetic field generated by the star has a complex non-dipolar structure. To address this discrepancy between theory and observations, we re-examine X-wind theory without the dipole constraint. Using simple physical arguments based on the concept of trapped flux, we show that a dipole configuration is in fact not essential. Independent of the precise geometry of the stellar magnetosphere, the requirement for a certain level of trapped flux predicts a definite relationship among various CTTS observable...

  9. Magnetically elevated accretion disks in active galactic nuclei: broad emission line regions and associated star formation

    CERN Document Server

    Begelman, Mitchell C

    2016-01-01

    We propose that the accretion disks fueling active galactic nuclei are supported vertically against gravity by a strong toroidal ($\\phi-$direction) magnetic field that develops naturally as the result of an accretion disk dynamo. The magnetic pressure elevates most of the gas carrying the accretion flow at $R$ to large heights $z > 0.1 R$ and low densities, while leaving a thin dense layer containing most of the mass --- but contributing very little accretion --- around the equator. We show that such a disk model leads naturally to the formation of a broad emission line region through thermal instability. Extrapolating to larger radii, we demonstrate that local gravitational instability and associated star formation are strongly suppressed compared to standard disk models for AGN, although star formation in the equatorial zone is predicted for sufficiently high mass supply rates. This new class of accretion disk models thus appears capable of resolving two longstanding puzzles in the theory of AGN fueling: th...

  10. Using High Speed Rotating Gas to Study Angular Momentum in Accretion Disks

    Science.gov (United States)

    Berrios, William; Greess, Samuel; Merino, Enrique; Ji, Hantao

    2013-10-01

    Accretion disks are a sheet of gas and dust which surrounds black holes and quasars. The angular momentum in accretion disks is one of the biggest mysteries in astrophysics. A machine was recently built to create accretion disks in a closed chamber. In order to study this, there are several important instruments that are used: a fog machine to see the accretion disks form within the chamber, a high speed camera to observe and record the formation of the accretion disks, and Particle Image Velocimetry (PIV) to analyze velocity profile of the rotating gas and better understand this phenomenon. By collecting relevant data and subsequent computational analysis, results from a previous experiment are reproduced, expanded and the new properties observed with this experiment are characterized. A discussion of any modifications done to the machine, technical challenges and preliminary results will be presented.

  11. Spectrally resolved eclipse maps of the accretion disk in UX Ursae Majoris

    Science.gov (United States)

    Rutten, Rene G. M.; Dhillon, V. S.; Horne, Keith; Kuulkers, E.; Van Paradijs, J.

    1993-01-01

    An effort is made to observationally constrain accretion disks on the basis of light curves from the eclipsing cataclysmic variable UX Ursae Majoris, reconstructing the spectral energy distribution across the face of an accretion disk. The spectral resolution obtained suffices to reveal not only the radial dependence of absorption and emission line features within the disk, but also the spectral details of the bright spot that is formed where the accretion stream from the secondary star collides with the disk. The importance of such constraints for theoretical models is noted.

  12. You’re Cut Off: HD and MHD Simulations of Truncated Accretion Disks

    Science.gov (United States)

    Hogg, J. Drew; Reynolds, Christopher S.

    2017-01-01

    Truncated accretion disks are commonly invoked to explain the spectro-temporal variability from accreting black holes in both small systems, i.e. state transitions in galactic black hole binaries (GBHBs), and large systems, i.e. low-luminosity active galactic nuclei (LLAGNs). In the canonical truncated disk model of moderately low accretion rate systems, gas in the inner region of the accretion disk occupies a hot, radiatively inefficient phase, which leads to a geometrically thick disk, while the gas in the outer region occupies a cooler, radiatively efficient phase that resides in the standard geometrically thin disk. Observationally, there is strong empirical evidence to support this phenomenological model, but a detailed understanding of the disk behavior is lacking. We present well-resolved hydrodynamic (HD) and magnetohydrodynamic (MHD) numerical models that use a toy cooling prescription to produce the first sustained truncated accretion disks. Using these simulations, we study the dynamics, angular momentum transport, and energetics of a truncated disk in the two different regimes. We compare the behaviors of the HD and MHD disks and emphasize the need to incorporate a full MHD treatment in any discussion of truncated accretion disk evolution.

  13. Global aspects of elliptical instability in tidally distorted accretion disks

    CERN Document Server

    Ryu, D; Vishniac, E T; Ryu, Dongsu; Goodman, Jeremy; Vishniac, Ethan T

    1995-01-01

    Tidally distorted accretion disks in binary star systems are subject to a local hydrodynamic instability which excites m=1 internal waves. This instability is three dimensional and approximately incompressible. We study the global aspects of this local instability using equations derived under the shearing sheet approximation, where the effects of the azimuthal variation along distorted orbital trajectories are included in source terms which oscillate with local orbital phase. Linear analyses show that the excitation of the instability is essentially local, i.e. insensitive to radial boundary conditions. The region of rapid growth feeds waves into the region of slow or negligible growth, allowing the instability to become global. The global growth rate depends the maximum local growth rate, the size of the rapid growth region, and the local group velocity. We present an empirical expression for the global growth rate. We note that the local nature of the instability allows the excitation of waves with m\

  14. 3D Relativistic MHD Simulation of a Tilted Accretion Disk Around a Rapidly Rotating Black Hole

    CERN Document Server

    Fragile, P Chris; Blaes, Omer M; Salmonson, Jay D

    2016-01-01

    We posit that accreting compact objects, including stellar mass black holes and neutron stars as well as supermassive black holes, may undergo extended periods of accretion during which the angular momentum of the disk at large scales is misaligned with that of the compact object. In such a scenario, Lense-Thirring precession caused by the rotating compact object can dramatically affect the disk. In this presentation we describe results from a three-dimensional relativistic magnetohydrodynamic simulation of an MRI turbulent disk accreting onto a tilted rapidly rotating black hole. For this case, the disk does not achieve the commonly described Bardeen-Petterson configuration; rather, it remains nearly planar, undergoing a slow global precession. Accretion from the disk onto the hole occurs predominantly through two opposing plunging streams that start from high latitudes with respect to both the black-hole and disk midplanes. This is a consequence of the non-sphericity of the gravitational spacetime of the bl...

  15. Relativistic Effects on Neutrino Pair Annihilation above a Kerr Black Hole with the Accretion Disk

    CERN Document Server

    Asano, K; Asano, Katsuaki; Fukuyama, Takeshi

    2001-01-01

    Using idealized models of the accretion disk we investigate the relativistic effects on the energy deposition rate via neutrino pair annihilation near the rotation axis of a Kerr black hole. Neutrinos are emitted from the accretion disk. The bending of neutrino trajectories and the redshift due to the disk rotation and gravitation are taken into consideration. The Kerr parameter, $a$, affects not only neutrinos' behavior but also the inner radius of the accretion disk. When the deposition energy is mainly contributed by the neutrinos coming from the central part, the redshift effect becomes dominant as $a$ becomes large and the energy deposition rate is reduced compared with that neglecting the relativistic effects. On the other hand, for small $a$ the bending effect gets dominant and makes energy increase by factor 2 compared with that neglecting the relativistic effects. For the disk with temperature gradient, the energy deposition rate for a small inner radius of the accretion disk is smaller than that est...

  16. Modeling MHD accretion-ejection: episodic ejections of jets triggered by a mean-field disk dynamo

    Energy Technology Data Exchange (ETDEWEB)

    Stepanovs, Deniss; Fendt, Christian; Sheikhnezami, Somayeh, E-mail: deniss@stepanovs.org, E-mail: fendt@mpia.de [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)

    2014-11-20

    We present MHD simulations exploring the launching, acceleration, and collimation of jets and disk winds. The evolution of the disk structure is consistently taken into account. Extending our earlier studies, we now consider the self-generation of the magnetic field by an α{sup 2}Ω mean-field dynamo. The disk magnetization remains on a rather low level, which helps to evolve the simulations for T > 10, 000 dynamical time steps on a domain extending 1500 inner disk radii. We find the magnetic field of the inner disk to be similar to the commonly found open field structure, favoring magneto-centrifugal launching. The outer disk field is highly inclined and predominantly radial. Here, differential rotation induces a strong toroidal component, which plays a key role in outflow launching. These outflows from the outer disk are slower, denser, and less collimated. If the dynamo action is not quenched, magnetic flux is continuously generated, diffuses outward through the disk, and fills the entire disk. We have invented a toy model triggering a time-dependent mean-field dynamo. The duty cycles of this dynamo lead to episodic ejections on similar timescales. When the dynamo is suppressed as the magnetization falls below a critical value, the generation of the outflows and also accretion is inhibited. The general result is that we can steer episodic ejection and large-scale jet knots by a disk-intrinsic dynamo that is time-dependent and regenerates the jet-launching magnetic field.

  17. The intrinsic quasar luminosity function: Accounting for accretion disk anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    DiPompeo, M. A.; Myers, A. D.; Brotherton, M. S. [University of Wyoming, Department of Physics and Astronomy 3905, 1000 East University, Laramie, WY 82071 (United States); Runnoe, J. C. [Penn State University, Department of Astronomy and Astrophysics, 413 Davey Lab, University Park, PA 16802 (United States); Green, R. F. [Large Binocular Telescope Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

    2014-05-20

    Quasar luminosity functions are a fundamental probe of the growth and evolution of supermassive black holes. Measuring the intrinsic luminosity function is difficult in practice, due to a multitude of observational and systematic effects. As sample sizes increase and measurement errors drop, characterizing the systematic effects is becoming more important. It is well known that the continuum emission from the accretion disk of quasars is anisotropic—in part due to its disk-like structure—but current luminosity function calculations effectively assume isotropy over the range of unobscured lines of sight. Here, we provide the first steps in characterizing the effect of random quasar orientations and simple models of anisotropy on observed luminosity functions. We find that the effect of orientation is not insignificant and exceeds other potential corrections such as those from gravitational lensing of foreground structures. We argue that current observational constraints may overestimate the intrinsic luminosity function by as much as a factor of ∼2 on the bright end. This has implications for models of quasars and their role in the universe, such as quasars' contribution to cosmological backgrounds.

  18. A strongly truncated inner accretion disk in the Rapid Burster

    CERN Document Server

    Eijnden, J van den; Degenaar, N; Lohfink, A M; Parker, M L; Zand, J J M in 't; Fabian, A C

    2016-01-01

    The neutron star (NS) low-mass X-ray binary (LMXB) the Rapid Burster (RB; MXB 1730-335) uniquely shows both Type-I and Type-II X-ray bursts. The origin of the latter is ill-understood but has been linked to magnetospheric gating of the accretion flow. We present a spectral analysis of simultaneous Swift, NuSTAR and XMM-Newton observations of the RB during its 2015 outburst. Although a broad Fe-K line has been observed before, the high quality of our observations allows us to model this line using relativistic reflection models for the first time. We find that the disk is strongly truncated at $41.8^{+6.7}_{-5.3}$ gravitational radii ($\\sim 87$ km), which supports magnetospheric Type-II burst models and strongly disfavors models involving instabilities at the innermost stable circular orbit. Assuming that the RB magnetic field indeed truncates the disk, we find $B = (6.2 \\pm 1.5) \\times 10^8$ G, larger than typically inferred for NS LMXBs. In addition, we find a low inclination ($i = 29\\pm2^{\\rm o}$). Finally,...

  19. Modeling the Formation and Evolution of Wind-Capture Disks In Binary Systems

    Science.gov (United States)

    Huarte-Espinosa, M.; Carroll-Nellenback, J.; Nordhaus, J.; Frank, A.; Blackman, E.

    2014-04-01

    In this talk I will present results of recent models of the formation, evolution and physical properties of accretion disks formed via wind capture in binary systems. Using the AMR code AstroBEAR, we have carried out high resolution 3D simulations that follow a stellar mass secondary in the co-rotating frame as it orbits a wind producing AGB primary. A resolution criteria, based on considerations of Bondi-Hoyle flows, must be met in order to properly resolve the formation of accretion disks around the secondary. We then compare simulations of binaries with three different orbital radii (10, 15, 20 AU). Disks are formed in all three cases, however the size of the disk and, most importantly, its accretion rate decreases with orbital radii. In addition, the shape of the orbital motions of material within the disk becomes increasingly elliptical with increasing binary separation. The flow is mildly unsteady with "fluttering" around the bow shock observed. The disks are generally well aligned with the orbital plane after a few binary orbits. We do not observe the presence of any large scale, violent instabilities (such as the flip-flop mode). For the first time it is observed that the wind component that is accreted towards the secondary has a vortex tube-like structure. In the context of AGB binary systems that might be precursors to Pre-Planetary and Planetary Nebula, we find that the wind accretion rates at the chosen orbital separations are generally too small to produce the most powerful outflows observed in these systems if the companions are main sequence stars but marginally capable if the companions are white dwarfs. It is likely that many of the more powerful PPN and PN involve closer binaries than the ones considered here.

  20. Growth of a Protostar and a Young Circumstellar Disk with High Mass Accretion Rate onto the Disk

    CERN Document Server

    Ohtani, Takuya

    2013-01-01

    The growing process of both a young protostar and a circumstellar disk is investigated. Viscous evolution of a disk around a single star is considered with a model where a disk increases its mass by dynamically accreting envelope and simultaneously loses its mass via viscous accretion onto the central star. We focus on the circumstellar disk with high mass accretion rate onto the disk $\\dot{M}=8.512c_{\\rm s}^3/G$ as a result of dynamical collapse of rotating molecular cloud core. We study the origin of the surface density distribution and the origin of the disk-to-star mass ratio by means of numerical calculations of unsteady viscous accretion disk in one-dimensional axisymmetric model. It is shown that the radial profiles of the surface density $\\Sigma$, azimuthal velocity $v_{\\phi}$, and mass accretion rate $\\dot{M}$ in the inner region approach to the quasi-steady state. Profile of the surface density distribution in the quasi-steady state is determined as a result of angular momentum transport rather than...

  1. Effects of Toroidal Magnetic Fields on the Thermal Instability of Thin Accretion Disks

    Indian Academy of Sciences (India)

    Sheng-Ming Zheng; Feng Yuan; Wei-Min Gu; Ju-Fu Lu

    2011-03-01

    The standard thin disk model predicts that when the accretion rate is moderately high, the disk is radiation–pressure-dominated and thermally unstable. However, observations indicate the opposite, namely the disk is quite stable. We present an explanation in this work by taking into account the role of the magnetic field which was ignored in the previous analysis.

  2. Dust in the disk winds from young stars as a source of the circumstellar extinction

    CERN Document Server

    Tambovtseva, L V

    2008-01-01

    We examine a problem of the dust grains survival in the disk wind in T Tauri stars (TTSs). For consideration we choose the disk wind model described by Garcia et al. (2001), where a gas component of the wind is heated by an ambipolar diffusion up to the temperature of the order of 10$^4$ K. It is shown that the dust grains heating due to collisions with the gas atoms and electrons is inefficient in comparison with heating by the stellar radiation, and thus, dust survives even in the hot wind component. Owing to this, the disk wind may be opaque for the ultraviolet and optical radiation of the star and is capable to absorb its noticeable fraction. Calculations show that at the accretion rate $\\dot{M_a} = 10^{-8}-10^{-6} M_\\odot$ per year this fraction for TTSs may range from 20% to 40% of a total luminosity of the star correspondingly. This means that the disk wind in TTSs can play the same role as the puffed inner rim considered in the modern models of accretion disks. In Herbig Ae stars (HAEs) inner regions ...

  3. Equilibrium disks, MRI mode excitation, and steady state turbulence in global accretion disk simulations

    CERN Document Server

    Parkin, E R

    2012-01-01

    Global three dimensional magnetohydrodynamic (MHD) simulations of turbulent accretion disks are presented which start from fully equilibrium initial conditions in which the magnetic forces are accounted for and the induction equation is satisfied. The local linear theory of the magnetorotational instability (MRI) is used as a predictor of the growth of magnetic field perturbations in the global simulations. The linear growth estimates and global simulations diverge when non-linear motions - perhaps triggered by the onset of turbulence - upset the velocity perturbations used to excite the MRI. The saturated state is found to be independent of the initially excited MRI mode, showing that once the disk has expelled the initially net flux field and settled into quasi-periodic oscillations in the toroidal magnetic flux, the dynamo cycle regulates the global saturation stress level. Furthermore, time-averaged measures of converged turbulence, such as the ratio of magnetic energies, are found to be in agreement with...

  4. Magnetized Accretion-Ejection Structures 2.5D MHD simulations of continuous Ideal Jet launching from resistive accretion disks

    CERN Document Server

    Keppens, R

    2002-01-01

    We present numerical magnetohydrodynamic (MHD) simulations of a magnetized accretion disk launching trans-Alfvenic jets. These simulations, performed in a 2.5 dimensional time-dependent polytropic resistive MHD framework, model a resistive accretion disk threaded by an initial vertical magnetic field. The resistivity is only important inside the disk, and is prescribed as eta = alpha_m V_AH exp(-2Z^2/H^2), where V_A stands for Alfven speed, H is the disk scale height and the coefficient alpha_m is smaller than unity. By performing the simulations over several tens of dynamical disk timescales, we show that the launching of a collimated outflow occurs self-consistently and the ejection of matter is continuous and quasi-stationary. These are the first ever simulations of resistive accretion disks launching non-transient ideal MHD jets. Roughly 15% of accreted mass is persistently ejected. This outflow is safely characterized as a jet since the flow becomes super-fastmagnetosonic, well-collimated and reaches a q...

  5. The effect of gaseous accretion disk on dynamics of the stellar cluster in AGN

    CERN Document Server

    Shukirgaliyev, Bekdaulet

    2016-01-01

    There is a supermassive black hole, a gaseous accretion disk and compact star cluster in the center of active galactic nuclei, as known today. So the activity of AGN can be represented as the result of interaction of these three subsystems. In this work we investigate the dynamical interaction of a central star cluster surrounding a supermassive black hole and a central accretion disk. The dissipative force acting on stars in the disk leads to an asymmetry in the phase space distribution of the central star cluster due to the rotating accretion disk. In our work we present some results of Stardisk model, where we see some changes in density and phase space of central star cluster due to influence of rotating gaseous accretion disk.

  6. Non-axisymmetric Structure of Accretion Disks in Be/X-ray Binaries

    CERN Document Server

    Hayasaki, K; Hayasaki, Kimitake; Okazaki, Atsuo T.

    2004-01-01

    The non-axisymmetric structure of accretion disks around the neutron star in Be/X-ray binaries is studied by analyzing the results from three dimensional (3D) Smoothed Particle Hydrodynamics (SPH) simulations. It is found that ram pressure due to the phase-dependent mass transfer from the Be-star disk excites a one-armed, trailing spiral structure in the accretion disk around the neutron star. The spiral wave has a transient nature; it is excited around the periastron, when the material is transferred from the Be disk, and is gradually damped afterwards. It is also found that the orbital phase-dependence of the mass-accretion rate is mainly caused by the inward propagation of the spiral wave excited in the accretion disk.

  7. Numerical Simulation of Rotating Accretion Disk Around the Schwarzschild Black Hole Using GRH Code

    CERN Document Server

    Donmez, O

    2006-01-01

    The 2D time dependent solution of thin accretion disk in a close binary system have been presented on the equatorial plane around the Schwarzschild black hole. To do that, the special part of the General Relativistic Hydrodynamical(GRH) equations are solved using High Resolution Shock Capturing (HRSC) schemes. The spiral shock waves on the accretion disk are modeled using perfect fluid equation of state with adiabatic indices $\\gamma = 1.05, 1.2$ and 5/3. The results show that the spiral shock waves are created for gammas except the case $\\gamma=5/3$. These results consistent with results from Newtonian hydrodynamic code except close to black hole. Newtonian approximation does not give good solution while matter closes to black hole. Our simulations illustrate that the spiral shock waves are created close to black hole and the location of inner radius of spiral shock wave is around $10M$ and it depends on the specific heat rates. We also find that the smaller $\\gamma$ is the more tightly the spiral winds.

  8. Correlations among Jet, Accretion Disk, and Broad Line Region of Flat Spectrum Radio Quasars

    CERN Document Server

    Zhang, Jin; He, Jian-Jian; Liang, En-Wei; Zhang, Shuang-Nan

    2015-01-01

    The SEDs of 18 GeV FSRQs are collected and compiled from literature, in which both the jet emission and the accretion disk radiation can be observed, in order to investigate the correlations among their jet power (P_jet), accretion disk luminosity (L_disk), and luminosity of broad line region (BLR, L_BLR). On the basis of the SED fits with the jet radiation and accretion disk radiation models, we calculate P_jet and L_disk. No correlation between P_jet with either L_disk or L_BLR is found. With a sub-sample of L_BLR for 13 GeV FSRQs, it is observed that L_BLR is strongly correlated with their L_disk. We also study the BLR covering factors of the GeV FSRQs in our sample, averagely which are smaller than that of the large samples of radio-loud and radio-quiet quasars. P_jet of some GeV FSRQs is higher than L_disk, but P_jet of all the GeV FSRQs is lower than the accretion power of black hole (BH), which is estimated by \\dot{M}c^2=L_disk/0.1, indicating that the total accretion power of BH is sufficient to drive...

  9. Nucleosynthesis in the gamma-ray burst accretion disks and associated outflows

    CERN Document Server

    Banerjee, Indrani

    2013-01-01

    We investigate nucleosynthesis inside the gamma-ray burst (GRB) accretion disks formed by the Type II collapsars and outflows launched from these disks. We deal with accretion disks having relatively low accretion rates: 0.001 M_sun s^{-1} <~ Mdot <~ 0.01 M_sun s^{-1} and hence they are predominantly advection dominated. We report the synthesis of several unusual nuclei like 31P, 39K, 43Sc, 35Cl and various isotopes of titanium, vanadium, chromium, manganese and copper in the disk. We also confirm that isotopes of iron, cobalt, nickel, argon, calcium, sulphur and silicon get synthesized in the disk, as shown by previous authors. Much of these heavy elements thus synthesized are ejected from the disk and survive in the outflows. Indeed, emission lines of many of these heavy elements have been observed in the X-ray afterglows of several GRBs.

  10. Magnetically elevated accretion disks in active galactic nuclei: broad emission line regions and associated star formation

    Science.gov (United States)

    Begelman, Mitchell C.; Silk, Joseph

    2016-10-01

    We propose that the accretion disks fueling active galactic nuclei are supported vertically against gravity by a strong toroidal (φ -direction) magnetic field that develops naturally as the result of an accretion disk dynamo. The magnetic pressure elevates most of the gas carrying the accretion flow at R to large heights z ˜ 0.1 R and low densities, while leaving a thin dense layer containing most of the mass - but contributing very little accretion - around the equator. We show that such a disk model leads naturally to the formation of a broad emission line region through thermal instability. Extrapolating to larger radii, we demonstrate that local gravitational instability and associated star formation are strongly suppressed compared to standard disk models for AGN, although star formation in the equatorial zone is predicted for sufficiently high mass supply rates. This new class of accretion disk models thus appears capable of resolving two longstanding puzzles in the theory of AGN fueling: the formation of broad emission line regions and the suppression of fragmentation thought to inhibit accretion at the required rates. We show that the disk of stars that formed in the Galactic Center a few million years ago could have resulted from an episode of magnetically elevated accretion at ˜0.1 of the Eddington limit.

  11. Smearing of mass accretion rate variation by viscous processes in accretion disks in compact binary systems

    CERN Document Server

    Ghosh, Arindam

    2016-01-01

    Variation of mass supply rate from the companion can be smeared out by viscous processes inside an accretion disk. By the time the flow reaches the inner edge, the variation in X-rays needs not reflect the true variation of the rate at the outer edge. However, if the viscosity fluctuates around a mean value, one would expect the viscous time scale also to spread around a mean value. In HMXBs, the size of the viscous Keplerian disk is smaller & thus such a spread could be lower as compared to the LMXBs. If there is an increasing or decreasing trend in viscosity, the interval between enhanced emission would be modified systematically. In the absence of a full knowledge about the variation of mass supply rates at the outer edge, we study ideal circumstances where modulation must take place exactly in orbital time scales when there is an ellipticity in the orbit. We study a few compact binaries using long term RXTE/ASM(1.5-12 keV) & Swift/BAT(15-50keV) data to look for such effects & to infer what the...

  12. The Formation and Evolution of Wind-Capture Disks In Binary Systems

    CERN Document Server

    Huarte-Espinosa, Martin; Nordhaus, Jason; Frank, Adam; Blackman, Eric G

    2012-01-01

    We study the formation, evolution and physical properties of accretion disks formed via wind capture in binary systems. Using the AMR code AstroBEAR, we have carried out high resolution 3D simulations that follow a stellar mass secondary in the co-rotating frame as it orbits a wind producing AGB primary. We first derive a resolution criteria, based on considerations of Bondi-Hoyle flows, that must be met in order to properly resolve the formation of accretion disks around the secondary. We then compare simulations of binaries with three different orbital radii (10, 15, 20 AU). Disks are formed in all three cases, however the size of the disk and, most importantly, its accretion rate decreases with orbital radii. In addition, the shape of the orbital motions of material within the disk becomes increasingly elliptical with increasing binary separation. The flow is mildly unsteady with "fluttering" around the bow shock observed. The disks are generally well aligned with the orbital plane after a few binary orbit...

  13. On the Virialization of Disk Winds: Implications for the Black Hole Mass Estimates in AGN

    CERN Document Server

    Kashi, Amit; Nagamine, Kentaro; Greene, Jenny; Barth, Aaron J

    2013-01-01

    [abbreviated] Estimating the mass of a supermassive black hole (SMBH) in an active galactic nucleus (AGN) usually relies on the assumption that the broad line region (BLR) is virialized. However, this assumption seems invalid in BLR models that consists of an accretion disk and its wind. The disk is likely Keplerian and therefore virialized. However, the wind material must, beyond a certain point, be dominated by an outward force that is stronger than gravity. Here, we analyze hydrodynamic simulations of four different disk winds: an isothermal wind, a thermal wind from an X-ray heated disk, and two line-driven winds, one with and the other without X-ray heating and cooling. For each model, we check whether gravity governs the flow properties, by computing and analyzing the volume-integrated quantities that appear in the virial theorem: internal, kinetic, and gravitational energies, We find that in the first two models, the winds are non-virialized whereas the two line-driven disk winds are virialized up to a...

  14. Evidence for Magnetically Driven Protoplanetary Disk Winds

    Science.gov (United States)

    Simon, Molly; Pascucci, Ilaria; Edwards, Suzan; Feng, Wanda; Rigliaco, Elisabetta; Gorti, Uma; Hollenbach, David J.; Tuttle Keane, James

    2017-01-01

    We present Keck high resolution (~7km/s) optical spectra from a sample of 32 pre-main sequence T-Tauri stars in Taurus-Auriga plus TW Hya. We focus on low-excitation forbidden emission lines like the [O I] 6300 Å and 5577 Å lines, whose high-velocity component, with blueshifts between ~30 - 150 km/s, is known to trace fast outflowing material in the form of jets (e.g. Hartigan et al. 1995). The origin of the low-velocity component (LVC), with blueshifts on the order of ~5 km/s, has been long debated. We demonstrate that the LVC can be described by a combination of a broad and a narrow line emitting region. We show that the broad line emitting region is very common, arises within ~0.5 AU from the star, and shows the expected disk wind signature, i.e. larger blueshifts associated with narrower lines and lower disc inclinations. Such winds must be magnetically driven given that the emitting region is well inside the gravitational potential well of the central star. The origin of the narrow line emitting region remains difficult to assess, in particular we cannot exclude that it traces a thermally driven (photoevaporative) wind. Disk winds, both thermally and magnetically driven, might play a major role in the evolution and eventual dispersal of protoplanetary material, which has implications for solar system architectures and planet formation more generally. Hence, it is critical to determine the rate at which mass is lost via disk winds.

  15. Ice Accretion Prediction on Wind Turbines and Consequent Power Losses

    Science.gov (United States)

    Yirtici, Ozcan; Tuncer, Ismail H.; Ozgen, Serkan

    2016-09-01

    Ice accretion on wind turbine blades modifies the sectional profiles and causes alteration in the aerodynamic characteristic of the blades. The objective of this study is to determine performance losses on wind turbines due to the formation of ice in cold climate regions and mountainous areas where wind energy resources are found. In this study, the Blade Element Momentum method is employed together with an ice accretion prediction tool in order to estimate the ice build-up on wind turbine blades and the energy production for iced and clean blades. The predicted ice shapes of the various airfoil profiles are validated with the experimental data and it is shown that the tool developed is promising to be used in the prediction of power production losses of wind turbines.

  16. Alignment of magnetized accretion disks and relativistic jets with spinning black holes.

    Science.gov (United States)

    McKinney, Jonathan C; Tchekhovskoy, Alexander; Blandford, Roger D

    2013-01-04

    Accreting black holes (BHs) produce intense radiation and powerful relativistic jets, which are affected by the BH's spin magnitude and direction. Although thin disks might align with the BH spin axis via the Bardeen-Petterson effect, this does not apply to jet systems with thick disks. We used fully three-dimensional general relativistic magnetohydrodynamical simulations to study accreting BHs with various spin vectors and disk thicknesses and with magnetic flux reaching saturation. Our simulations reveal a "magneto-spin alignment" mechanism that causes magnetized disks and jets to align with the BH spin near BHs and to reorient with the outer disk farther away. This mechanism has implications for the evolution of BH mass and spin, BH feedback on host galaxies, and resolved BH images for the accreting BHs in SgrA* and M87.

  17. Angular momentum transport in accretion disk boundary layers around weakly magnetized stars

    DEFF Research Database (Denmark)

    Pessah, M.E.; Chan, C.-K.

    2013-01-01

    The standard model for turbulent shear viscosity in accretion disks is based on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. This implies that the turbulent stress must be negative and thus transport angular momentum inwards......, in the boundary layer where the accretion disk meets the surface of a weakly magnetized star. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability (MRI......) is inefficient in disk regions where, as expected in boundary layers, the angular frequency increases with radius. Motivated by the need of a deeper understanding of the behavior of an MHD fluid in a differentially rotating background that deviates from a Keplerian profile, we study the dynamics of MHD waves...

  18. A truncated accretion disk in the galactic black hole candidate source H1743-322

    Institute of Scientific and Technical Information of China (English)

    Kandulapati Sriram; Vivek Kumar Agrawal; Arikkala Raghurama Rao

    2009-01-01

    To investigate the geometry of the accretion disk in the source H1743-322, we have carded out a detailed X-ray temporal and spectral study using RXTE pointed observations. We have selected all data pertaining to the Steep Power Law (SPL) state during the 2003 outburst of this source. We find anti-correlated hard X-ray lags in three of the observations and the changes in the spectral and timing parameters (like the QPO fre-quency) confirm the idea of a truncated accretion disk in this source. Compiling data from similar observations of other sources, we find a correlation between the fractional change in the QPO frequency and the observed delay. We suggest that these observations indicate a definite size scale in the inner accretion disk (the radius of the truncated disk) and we explain the observed correlation using various disk parameters like Compton cooling time scale, viscous time scale etc..

  19. A truncated accretion disk in the galactic black hole source H1743-322

    CERN Document Server

    Sriram, K; Rao, A R

    2009-01-01

    To investigate the geometry of the accretion disk in the source H1743-322, we have carried out a detailed X-ray temporal and spectral study using RXTE pointed observations. We have selected all data pertaining to the Steep Power Law (SPL) state during the 2003 outburst of this source. We find anti-correlated hard X-ray lags in three of the observations and the changes in the spectral and timing parameters (like the QPO frequency) confirm the idea of a truncated accretion disk in this source. Compiling data from similar observations from other sources, we find a correlation between the fractional change in the QPO frequency and the observed delay. We suggest that these observations indicate a definite size scale in the inner accretion disk (the radius of the truncated disk) and we explain the observed correlation using various disk parameters like Compton cooling time scale, viscous time scale etc..

  20. Evolution of dynamo-generated magnetic fields in accretion disks around compact and young stars

    Science.gov (United States)

    Stepinski, Tomasz F.

    1994-01-01

    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 objects because the accreted matter, whether it comes from the companion star (binaries) or from a collapsing molecular cloud core (single young stars), carries an embedded magnetic field. In addition, most accretion disks are hot and turbulent, thus meeting the condition for the MHD turbulent dynamo to maintain and amplify any seed field magnetic field. In fact, for a disk's magnetic field to persist long enough in comparison with the disk viscous time it must be contemporaneously regenerated because the characteristic diffusion time of a magnetic field is typically much shorter than a disk's viscous time. This is true for most thin accretion disks. Consequently, studying magentic fields in thin disks is usually synonymous with studying magnetic dynamos, a fact that is not commonly recognized in the literature. Progress in studying the structure of many accretion disks was achieved mainly because most disks can be regarded as two-dimensional flows in which vertical and radial structures are largely decoupled. By analogy, in a thin disk, one may expect that vertical and radial structures of the magnetic field are decoupled because the magnetic field diffuses more rapidly to the vertical boundary of the disk than along the radius. Thus, an asymptotic method, called an adiabatic approximation, can be applied to accretion disk dynamo. We can represent the solution to the dynamo equation in the form B = Q(r)b(r,z), where Q(r) describes the field distribution along the radius, while the field distribution across the disk is included in the vector function b, which parametrically depends on r and is normalized by the condition max (b(z)) = 1. The field distribution across the disk is established rapidly, while the radial

  1. Ice accretion modeling for wind turbine rotor blades

    Energy Technology Data Exchange (ETDEWEB)

    Chocron, D.; Brahimi, T.; Paraschivoiu, I.; Bombardier, J.A. [Ecole Polytechnique de Montreal (Canada)

    1997-12-31

    The increasing application of wind energy in northern climates implies operation of wind turbines under severe atmospheric icing conditions. Such conditions are well known in the Scandinavian countries, Canada and most of Eastern European countries. An extensive study to develop a procedure for the prediction of ice accretion on wind turbines rotor blades appears to be essential for the safe and economic operation of wind turbines in these cold regions. The objective of the present paper is to develop a computer code capable of simulating the shape and amount of ice which may accumulate on horizontal axis wind turbine blades when operating in icing conditions. The resulting code is capable to predict and simulate the formation of ice in rime and glaze conditions, calculate the flow field and particle trajectories and to perform thermodynamic analysis. It also gives the possibility of studying the effect of different parameters that influence ice formation such as temperature, liquid water content, droplet diameter and accretion time. The analysis has been conducted on different typical airfoils as well as on NASA/DOE Mod-0 wind turbine. Results showed that ice accretion on wind turbines may reduce the power output by more than 20%.

  2. Does an Average White Dwarf Have Enough Mass to Prevent an Accretion Disk Tilt?

    CERN Document Server

    Montgomery, M M

    2010-01-01

    In a recent publication, we introduce the lift force as a common source to accretion disk tilt that is likely relevant to accretion disk systems. Lift is generated by slightly different supersonic gas stream speeds flowing over and under the disk at the bright spot. In this conference proceeding, we focus on whether the average white dwarf has enough mass to prevent a disk tilt in non-magnetic Cataclysmic Variables (CVs) with accretion disks. Assuming a white dwarf mass of 0.6M$_{\\odot}$ and a disk mass of 10$^{-11}$M$_{\\odot}$, we vary the secondary mass to establish theoretical minimum mass transfer rates needed to induce and maintain a disk tilt of four degrees around the line of nodes. For mass ratios in the range \\( (0.13 \\le q=M_{2}M^{-1} \\le 0.45) \\), we confirm that the secondary mass does not contribute significantly to disk tilt. We also confirm that the average white dwarf does not have enough mass to prevent a disk tilt. We find that disk tilt may be likely in low mass transfer rate systems such a...

  3. Angular Momentum in Disk Wind Revealed in the Young Star MWC 349A

    Science.gov (United States)

    Zhang, Qizhou; Claus, Brian; Watson, Linda; Moran, James

    2017-03-01

    Disk winds are thought to play a critical role in star birth. As winds extract excess angular momentum from accretion disks, matter in the disk can be transported inward to the star to fuel mass growth. However, observational evidence of wind carrying angular momentum has been very limited. We present Submillimeter Array (SMA) observations of the young star MWC 349A in the H26α and H30α recombination lines. The high signal-to-noise ratios made possible by the maser emission process allow us to constrain the relative astrometry of the maser spots to milli-arcsecond precision. Previous observations of the H30α line with the SMA and the Plateau de Bure interferometer (PdBI) showed that masers are distributed in the disk and wind. Our new high-resolution observations of the H26α line reveal differences in spatial distribution from that of the H30α line. H26α line masers in the disk are excited in a thin annulus with a radius of about 25 au, while the H30α line masers are formed in a slightly larger annulus with a radius of 30 au. This is consistent with expectations for maser excitation in the presence of an electron density variation of approximately R ‑4. In addition, the H30α and H26α line masers arise from different parts in the wind. This difference is also expected from maser theory. The wind component of both masers exhibits line-of-sight velocities that closely follow a Keplerian law. This result provides strong evidence that the disk wind extracts significant angular momentum, thereby facilitating mass accretion in the young star.

  4. Toward realistic simulations of magneto-thermal winds from weakly-ionized protoplanetary disks

    CERN Document Server

    Gressel, Oliver

    2016-01-01

    Protoplanetary disks (PPDs) accrete onto their central T Tauri star via magnetic stresses. When the effect of ambipolar diffusion (AD) is included, and in the presence of a vertical magnetic field, the disk remains laminar between 1-5 au, and a magnetocentrifugal disk wind forms that provides an important mechanism for removing angular momentum. We present global MHD simulations of PPDs that include Ohmic resistivity and AD, where the time-dependent gas-phase electron and ion fractions are computed under FUV and X-ray ionization with a simplified recombination chemistry. To investigate whether the mass loading of the wind is potentially affected by the limited vertical extent of our existing simulations, we attempt to develop a model of a realistic disk atmosphere. To this end, by accounting for stellar irradiation and diffuse reprocessing of radiation, we aim at improving our models towards more realistic thermodynamic properties.

  5. A search for the lasts gasps of disk accretion in Orion T Tauri stars

    Science.gov (United States)

    Clark, Catherine; Briceno, Cesar; Calvet, Nuria; Hernandez, Jesus

    2017-01-01

    Using the echelle mode of the Michigan/Magellan Fiber System (M2FS) on the Magellan/Clay telescope at Las Campanas Observatory, we obtained high resolution spectra (R~35000) of a sample of ~4 - 10 Myr old T Tauri stars distributed in ten 0.5 deg diameter fields in the Orion OB1 association.We present here a search for accretion signatures among a sample of weak-line T Tauri stars (WTTS). These are young stars that on the basis of their classification in low-resolution spectra, are assumed to lack a primordial disk and therefore should not be actively accreting. We look for signatures of disk accretion at modest or low levels by measuring the width at 10% height of the H-alpha profile, and looking for a redshifted absorption feature. In parallel, we determine which WTTS among the M2FS sample have infrared excesses indicating a circumstellar disk, to see which disk-bearing WTTS also show indications of accretion. We propose that such WTTS accreting at low levels are T Tauri stars at or nearing the end of their accretion phase. Our goal is to build a large sample of these objects so that we can place statistical contraints on how long the accretion phase lasts in solar-like and low-mass stars.

  6. Testing the Propagating Fluctuations Model with a Long, Global Accretion Disk Simulation

    CERN Document Server

    Hogg, J Drew

    2015-01-01

    The broad-band variability of many accreting systems displays characteristic structure; log-normal flux distributions, RMS-flux relations, and long inter-band lags. These characteristics are usually interpreted as inward propagating fluctuations in an accretion disk driven by stochasticity of the angular momentum transport mechanism. We present the first analysis of propagating fluctuations in a long-duration, high-resolution, global three-dimensional magnetohydrodynamic (MHD) simulation of a geometrically-thin ($h/r\\approx0.1$) accretion disk around a black hole. While the dynamical-timescale turbulent fluctuations in the Maxwell stresses are too rapid to drive radially-coherent fluctuations in the accretion rate, we find that the low-frequency quasi-periodic dynamo action introduces low-frequency fluctuations in the Maxwell stresses which then drive the propagating fluctuations. Examining both the mass accretion rate and emission proxies, we recover log-normality, linear RMS-flux relations, and radial coher...

  7. Numerical Simulations of Naturally Tilted, Retrogradely Precessing, Nodal Superhumping Accretion Disks

    CERN Document Server

    Montgomery, M M

    2012-01-01

    Accretion disks around black hole, neutron star, and white dwarf systems are thought to sometimes tilt, retrogradely precess, and produce hump-shaped modulations in light curves that have a period shorter than the orbital period. Although artificially rotating numerically simulated accretion disks out of the orbital plane and around the line of nodes generates these short-period superhumps and retrograde precession of the disk, no numerical code to date has been shown to produce a disk tilt naturally. In this work, we report the first naturally tilted disk in non-magnetic Cataclysmic Variables (CVs) using 3D Smoothed Particle Hydrodynamics (SPH). Our simulations show that after many hundreds of orbital periods, the disk has tilted on its own and this disk tilt is without the aid of radiation sources or magnetic fields. As the system orbits, the accretion stream strikes the bright spot (which is on the rim of the tilted disk) and flows over and under the disk on different flow paths. These different flow paths...

  8. Complex organic molecules along the accretion flow in isolated and externally irradiated protoplanetary disks

    CERN Document Server

    Walsh, Catherine; Nomura, Hideko; Millar, T J; Weaver, Susanna Widicus

    2014-01-01

    (Abridged) The birth environment of the Sun will have influenced the conditions in the pre-solar nebula, including the attainable chemical complexity, important for prebiotic chemistry. The formation and distribution of complex organic molecules (COMs) in a disk around a T Tauri star is investigated for two scenarios: (i) an isolated disk, and (ii) a disk irradiated externally by a nearby massive star. The chemistry is calculated along the accretion flow from the outer disk inwards using a comprehensive network. Two simulations are performed, one beginning with complex ices and one with simple ices only. For the isolated disk, COMs are transported without major alteration into the inner disk where they thermally desorb into the gas reaching an abundance representative of the initial assumed ice abundance. For simple ices, COMs efficiently form on grain surfaces under the conditions in the outer disk. Gas-phase COMs are released into the molecular layer via photodesorption. For the irradiated disk, complex ice...

  9. Disk Winds as an Explanation for Slowly Evolving Temperatures in Tidal Disruption Events

    CERN Document Server

    Miller, M Coleman

    2015-01-01

    Among the many intriguing aspects of optically discovered tidal disruption events is that their temperatures are lower than expected and that the temperature does not evolve as rapidly with decreasing fallback rate as would be expected in standard disk theory. We show that this can be explained qualitatively using an idea proposed by Laor & Davis in the context of normal active galactic nuclei: that larger accretion rates imply stronger winds and thus that the accretion rate through the inner disk only depends weakly on the inflow rate at the outer edge of the disk. We also show that reasonable quantitative agreement with data requires that, as has been suggested in recent papers, the circularization radius of the tidal stream is approximately equal to the semimajor axis of the most bound orbit of the debris rather than twice the pericenter distance as would be expected without rapid angular momentum redistribution. If this explanation is correct, it suggests that the evolution of tidal disruption events ...

  10. Molecule survival in magnetized protostellar disk winds. I. Chemical model and first results

    CERN Document Server

    Panoglou, D; Forets, G Pineau des; Garcia, P J V; Ferreira, J; Casse, F

    2011-01-01

    Molecular counterparts to atomic jets have been detected within 1000 AU of young stars. Reproducing them is a challenge for proposed ejection models. We explore whether molecules may survive in an MHD disk wind invoked to reproduce the kinematics and tentative rotation signatures of atomic jets in T Tauri stars. The coupled ionization, chemical and thermal evolution along dusty flow streamlines is computed for a prescribed MHD disk wind solution, using a method developed for magnetized shocks in the interstellar medium. Irradiation by wind-attenuated coronal X-rays and FUV photons from accretion hot spots is included, with self-shielding of H2 and CO. Disk accretion rates of 5e-6, 1e-6 and 1e-7 solar masses per year are considered, representative of low-mass young protostars (Class 0), evolved protostars (Class I) and very active T Tauri stars (Class II). The disk wind has an onion-like thermo-chemical structure, with streamlines launched from larger radii having lower temperature and ionisation, and higher H...

  11. A Hot and Massive Accretion Disk around the High-mass Protostar IRAS 20126+4104

    Science.gov (United States)

    Chen, Huei-Ru Vivien; Keto, Eric; Zhang, Qizhou; Sridharan, T. K.; Liu, Sheng-Yuan; Su, Yu-Nung

    2016-06-01

    We present new spectral line observations of the CH3CN molecule in the accretion disk around the massive protostar IRAS 20126+4104 with the Submillimeter Array, which, for the first time, measure the disk density, temperature, and rotational velocity with sufficient resolution (0.″37, equivalent to ˜600 au) to assess the gravitational stability of the disk through the Toomre-Q parameter. Our observations resolve the central 2000 au region that shows steeper velocity gradients with increasing upper state energy, indicating an increase in the rotational velocity of the hotter gas nearer the star. Such spin-up motions are characteristics of an accretion flow in a rotationally supported disk. We compare the observed data with synthetic image cubes produced by three-dimensional radiative transfer models describing a thin flared disk in Keplerian motion enveloped within the centrifugal radius of an angular-momentum-conserving accretion flow. Given a luminosity of 1.3 × 104 L ⊙, the optimized model gives a disk mass of 1.5 M ⊙ and a radius of 858 au rotating about a 12.0 M ⊙ protostar with a disk mass accretion rate of 3.9 × 10-5 M ⊙ yr-1. Our study finds that, in contrast to some theoretical expectations, the disk is hot and stable to fragmentation with Q > 2.8 at all radii which permits a smooth accretion flow. These results put forward the first constraints on gravitational instabilities in massive protostellar disks, which are closely connected to the formation of companion stars and planetary systems by fragmentation.

  12. Enhanced MHD transport in astrophysical accretion flows: turbulence, winds and jets

    CERN Document Server

    Dobbie, Peter B; Bicknell, Geoffrey V; Salmeron, Raquel

    2009-01-01

    Astrophysical accretion is arguably the most prevalent physical process in the Universe; it occurs during the birth and death of individual stars and plays a pivotal role in the evolution of entire galaxies. Accretion onto a black hole, in particular, is also the most efficient mechanism known in nature, converting up to 40% of accreting rest mass energy into spectacular forms such as high-energy (X-ray and gamma-ray) emission and relativistic jets. Whilst magnetic fields are thought to be ultimately responsible for these phenomena, our understanding of the microphysics of MHD turbulence in accretion flows as well as large-scale MHD outflows remains far from complete. We present a new theoretical model for astrophysical disk accretion which considers enhanced vertical transport of momentum and energy by MHD winds and jets, as well as transport resulting from MHD turbulence. We also describe new global, 3D simulations that we are currently developing to investigate the extent to which non-ideal MHD effects may...

  13. Can neutron stars have auroras ? : electromagnetic coupling process between neutron star and magnetized accretion disk

    Science.gov (United States)

    Kimura, T.; Iwakiri, W. B.; Enoto, T.; Wada, T.; Tao, C.

    2015-12-01

    In the binary neutron star system, angular momentum transfer from accretion disk to a star is essential process for spin-up/down of stars. The angular momentum transfer has been well formulated for the accretion disk strongly magnetized by the neutron star [e.g., Ghosh and Lamb, 1978, 1979a, b]. However, the electromagnetic (EM) coupling between the neutron star and accretion disk has not been self-consistently solved in the previous studies although the magnetic field lines from the star are strongly tied with the accretion disk. In this study, we applied the planet-magnetosphere coupling process established for Jupiter [Hill, 1979] to the binary neutron star system. Angular momentum distribution is solved based on the torque balance between the neutron star's surface and accretion disk coupled by the magnetic field tensions. We found the EM coupling can transfer significantly larger fraction of the angular momentum from the magnetized accretion disk to the star than the unmagnetized case. The resultant spin-up rate is estimated to ~10^-14 [sec/sec] for the nominal binary system parameters, which is comparable with or larger than the other common spin-down/up processes: e.g., the magnetic dipole radiation spin-down. The Joule heating energy dissipated in the EM coupling is estimated to be up to ~10^36 [erg/sec] for the nominal binary system parameters. The release is comparable to that of gravitation energy directly caused by the matters accreting onto the neutron star. This suggests the EM coupling at the neutron star can accompany the observable radiation as auroras with a similar manner to those at the rotating planetary magnetospheres like Jupiter, Saturn, and other gas giants.

  14. Testing the Propagating Fluctuations Model with a Long, Global Accretion Disk Simulation

    Science.gov (United States)

    Hogg, J. Drew; Reynolds, Christopher S.

    2016-07-01

    The broadband variability of many accreting systems displays characteristic structures; log-normal flux distributions, root-mean square (rms)-flux relations, and long inter-band lags. These characteristics are usually interpreted as inward propagating fluctuations of the mass accretion rate in an accretion disk driven by stochasticity of the angular momentum transport mechanism. We present the first analysis of propagating fluctuations in a long-duration, high-resolution, global three-dimensional magnetohydrodynamic (MHD) simulation of a geometrically thin (h/r ≈ 0.1) accretion disk around a black hole. While the dynamical-timescale turbulent fluctuations in the Maxwell stresses are too rapid to drive radially coherent fluctuations in the accretion rate, we find that the low-frequency quasi-periodic dynamo action introduces low-frequency fluctuations in the Maxwell stresses, which then drive the propagating fluctuations. Examining both the mass accretion rate and emission proxies, we recover log-normality, linear rms-flux relations, and radial coherence that would produce inter-band lags. Hence, we successfully relate and connect the phenomenology of propagating fluctuations to modern MHD accretion disk theory.

  15. ANISOTROPY OF X-RAY BURSTS FROM NEUTRON STARS WITH CONCAVE ACCRETION DISKS

    Energy Technology Data Exchange (ETDEWEB)

    He, C.-C. [College of Physics, Jilin University, Changchun 130012 (China); Keek, L., E-mail: jordanhe1994@gmail.com [CRESST and X-ray Astrophysics Laboratory NASA/GSFC, Greenbelt, MD 20771 (United States)

    2016-03-01

    Emission from neutron stars and accretion disks in low-mass X-ray binaries is anisotropic. The non-spherical shape of the disk as well as blocking of the neutron star by the disk make the observed flux dependent on the inclination angle of the disk with respect to the line of sight. This is of importance for the interpretation of thermonuclear X-ray bursts from neutron stars. Because part of the X-ray burst is reflected off the disk, the observed burst flux depends on the anisotropies for both direct emission from the neutron star and reflection off the disk. This influences measurements of source distance, mass accretion rate, and constraints on the neutron star’s equation of state. Previous predictions of the anisotropy factors assumed a geometrically flat disk. Detailed observations of two so-called superbursts allowed for the direct and the reflected burst fluxes to each be measured separately. The reflection fraction was much higher than what the anisotropies of a flat disk can account for. We create numerical models to calculate the anisotropy factors for different disk shapes, including concave disks. We present the anisotropy factors of the direct and reflected burst fluxes separately, as well as the anisotropy of the persistent flux. Reflection fractions substantially larger than unity are produced in the case where the inner accretion disk increases steeply in height, such that part of the star is blocked from view. Such a geometry could possibly be induced by the X-ray burst if X-ray heating causes the inner disk to puff up.

  16. Crossing the Eddington limit: examining disk spectra at high accretion rates

    CERN Document Server

    Sutton, Andrew D; Roberts, Timothy P; Middleton, Matthew J; Soria, Roberto; Done, Chris

    2016-01-01

    The faintest ultraluminous X-ray sources (ULXs), those with 0.3-10 keV luminosities 1 < L_X/10^39 < 3 erg s^-1, tend to have X-ray spectra that are disk-like but broader than expected for thin accretion disks. These `broadened disk' spectra are thought to indicate near- or mildly super-Eddington accretion onto stellar remnant black holes. Here we report that a sample of bright thermal-dominant black hole binaries, which have Eddington ratios constrained to moderate values, also show broadened disk spectra in the 0.3-10 keV band at an order of magnitude lower luminosities. This broadening would be missed in studies that only look above ~2 keV. While this may suggest that broadened disk ULXs could be powered by accretion onto massive stellar remnant black holes with close to maximal spin, we argue in favor of a scenario where they are at close to the Eddington luminosity, such that radiation pressure would be expected to result in geometrically slim, advective accretion disks. However, this implies that a...

  17. Diffusive Particle Acceleration in Shocked, Viscous Accretion Disks: Green's Function Energy Distribution

    Science.gov (United States)

    Becker, Peter A.; Das, Santabrata; Le, Truong

    2011-12-01

    The acceleration of relativistic particles in a viscous accretion disk containing a standing shock is investigated as a possible explanation for the energetic outflows observed around radio-loud black holes. The energy/space distribution of the accelerated particles is computed by solving a transport equation that includes the effects of first-order Fermi acceleration, bulk advection, spatial diffusion, and particle escape. The velocity profile of the accreting gas is described using a model for shocked viscous disks recently developed by the authors, and the corresponding Green's function distribution for the accelerated particles in the disk and the outflow is obtained using a classical method based on eigenfunction analysis. The accretion-driven, diffusive shock acceleration scenario explored here is conceptually similar to the standard model for the acceleration of cosmic rays at supernova-driven shocks. However, in the disk application, the distribution of the accelerated particles is much harder than would be expected for a plane-parallel shock with the same compression ratio. Hence the disk environment plays a key role in enhancing the efficiency of the shock acceleration process. The presence of the shock helps to stabilize the disk by reducing the Bernoulli parameter, while channeling the excess binding energy into the escaping relativistic particles. In applications to M87 and Sgr A*, we find that the kinetic power in the jet is {\\sim}0.01\\,\\dot{M} c^2, and the outflowing relativistic particles have a mean energy ~300 times larger than that of the thermal gas in the disk at the shock radius. Our results suggest that a standing shock may be an essential ingredient in accretion onto underfed black holes, helping to resolve the long-standing problem of the stability of advection-dominated accretion disks.

  18. Accretion disks before (?) the main planet formation phase

    NARCIS (Netherlands)

    Dominik, C.

    2009-01-01

    Protoplanetary disks are the sites of planet formation and therefore one of the foremost targets of future facilities in astronomy. In this review, I will discuss the main options for using JWST and concurrent facilities to study the early, gas-rich, massive phases of protoplanetary disks. We discus

  19. Critical condition for the propeller effect in systems with magnetized neutron stars accreting from geometrically thin accretion disks

    Science.gov (United States)

    Ertan, Unal

    2016-07-01

    The inner disk radius around a magnetized neutron star in the spin-down phase is usually assumed to be close to the radius at which the viscous and magnetic stresses are balanced. With different assumptions, this radius is estimated to be very close the Alfven radius. Furthermore, it is commonly assumed that the propeller mechanism can expel the matter from the system when this radius is found to be greater than the co-rotation radius. In the present work, we have shown with simple analytical calculations from the first principles that a steady-state propeller mechanism cannot be established at the radius where the viscous and the magnetic torques are balanced. We have found that a steady-state propeller phase can be built up with an inner disk radius that is at least ~10 - 30 times smaller than the Alfven radius depending on the current mass-flow rate of the disk, the field strength and the rotational period of the source. This result also indicates that the critical accretion rate for the accretion-propeller transition is orders of magnitude smaller than the rate found by equating the Alfven and the co-rotation radii. Our results are consistent with the properties of recently discovered transitional millisecond pulsars which show transitions between the rotational powered radio pulsar and the accretion powered X-ray pulsar states.

  20. Radiation hydrodynamic simulations of line-driven disk winds for ultra-fast outflows

    Science.gov (United States)

    Nomura, Mariko; Ohsuga, Ken; Takahashi, Hiroyuki R.; Wada, Keiichi; Yoshida, Tessei

    2016-02-01

    Using two-dimensional radiation hydrodynamic simulations, we investigate the origin of the ultra-fast outflows (UFOs) that are often observed in luminous active galactic nuclei (AGNs). We found that the radiation force due to the spectral lines generates strong winds (line-driven disk winds) that are launched from the inner region of accretion disks (˜30 Schwarzschild radii). A wide range of black hole masses (MBH) and Eddington ratios (ε) was investigated to study the conditions causing the line-driven winds. For MBH = 106-109 M⊙ and ε = 0.1-0.7, funnel-shaped disk winds appear, in which dense matter is accelerated outward with an opening angle of 70°-80° and with 10% of the speed of light. If we observe the wind along its direction, the velocity, the column density, and the ionization state are consistent with those of the observed UFOs. As long as obscuration by the torus does not affect the observation of X-ray bands, the UFOs could be statistically observed in about 13%-28% of the luminous AGNs, which is not inconsistent with the observed ratio (˜40%). We also found that the results are insensitive to the X-ray luminosity and the density of the disk surface. Thus, we can conclude that UFOs could exist in any luminous AGNs, such as narrow-line Seyfert 1s and quasars with ε > 0.1, with which fast line-driven winds are associated.

  1. Tidally-Driven Transport in Accretion Disks in Close Binary Systems

    CERN Document Server

    Blondin, J M

    1999-01-01

    The effects of binary tidal forces on transport within an accretion disk are studied with a time-dependent hydrodynamical model of a two-dimensional isothermal accretion disk. Tidal forces quickly truncate the accretion disk to radii of order half the average radius of the Roche lobe, and excite a two-armed spiral wave that remains stationary in the rotating reference frame of the binary system. We measure an effective alpha of order 0.1 near the outer edge of the disk in all of our models, independent of the mass ratio, Mach number, and radial density profile. However, in cold disks with high Mach number, the effective alpha drops rapidly with decreasing radius such that it falls below our threshold of measurement (roughly .001) at a radius of only one third the tidal radius. In warmer disks where the Mach numbers remain below 20, we can measure an effective alpha down to radii 10 times smaller than the maximum size of the disk.

  2. Connections Between Tilted Accretion Disks Around White Dwarfs and Substellar Companions

    CERN Document Server

    Montgomery, M M

    2010-01-01

    Accretion disks in white dwarf systems are believed to be tilted. In a recent publication, the lift force has been suggested to be a source to disk tilt, a source that is likely relevant to all accretion disk systems. Lift is generated by slightly different supersonic gas stream speeds flowing over and under the disk at the bright spot. In this conference proceeding, we focus on whether a brown dwarf donor star accreting onto a white dwarf primary has enough mass to contribute to disk tilt. We also would like to obtain whether a white dwarf - brown dwarf close binary system has enough mass to induce and maintain a disk tilt of four degrees. We adopt SDSS 103533.03+055158.4 as our model system which has a mass transfer rate of \\( (10\\pm2) \\times 10^{-12} \\) M$_{\\odot}$ yr$^{-1}$. We find that the brown dwarf in SDSS 1035 does not have enough mass to contribute to disk tilt. We find a gross magnitude of the minimum mass transfer rate to be $\\sim10^{-10}$M$_{\\odot}$yr$^{-1}$. We conclude that SDSS 1035 does not ...

  3. Connections between Tilted Accretion Disks around White Dwarfs and Substellar Companions

    CERN Document Server

    Montgomery, M M

    2011-01-01

    Accretion disks in white dwarf systems are believed to be tilted. In a recent publication, the lift force has been suggested to be a source to disk tilt, a source that is likely relevant to all accretion disk systems. Lift is generated by slightly different supersonic gas stream speeds flowing over and under the disk at the bright spot. In this conference proceeding, we focus on whether a brown dwarf donor star accreting onto a white dwarf primary has enough mass to contribute to disk tilt. We also would like to obtain whether a white dwarf - brown dwarf close binary system has enough mass to induce and maintain a disk tilt of four degrees. We adopt SDSS 103533.03+055158.4 as our model system which has a mass transfer rate of (10 \\pm 2) x 10-12 M* yr-1. We find that the brown dwarf in SDSS 1035 does not have enough mass to contribute to disk tilt. We find a gross magnitude of the minimum mass transfer rate to be - 10-10 M* yr-1 . We conclude that SDSS 1035 does not seem to have a high enough mass transfer rat...

  4. Application of the Cubed-Sphere Grid to Tilted Black-Hole Accretion Disks

    Energy Technology Data Exchange (ETDEWEB)

    Fragile, P C; Lindner, C C; Anninos, P; Salmonson, J D

    2008-09-24

    In recent work we presented the first results of global general relativistic magnetohydrodynamic (GRMHD) simulations of tilted (or misaligned) accretion disks around rotating black holes. The simulated tilted disks showed dramatic differences from comparable untilted disks, such as asymmetrical accretion onto the hole through opposing 'plunging streams' and global precession of the disk powered by a torque provided by the black hole. However, those simulations used a traditional spherical-polar grid that was purposefully underresolved along the pole, which prevented us from assessing the behavior of any jets that may have been associated with the tilted disks. To address this shortcoming we have added a block-structured 'cubed-sphere' grid option to the Cosmos++ GRMHD code, which will allow us to simultaneously resolve the disk and polar regions. Here we present our implementation of this grid and the results of a small suite of validation tests intended to demonstrate that the new grid performs as expected. The most important test in this work is a comparison of identical tilted disks, one evolved using our spherical-polar grid and the other with the cubed-sphere grid. We also demonstrate an interesting dependence of the early-time evolution of our disks on their orientation with respect to the grid alignment. This dependence arises from the differing treatment of current sheets within the disks, especially whether they are aligned with symmetry planes of the grid or not.

  5. Suppression of type I migration by disk winds

    CERN Document Server

    Ogihara, Masahiro; Guillot, Tristan

    2015-01-01

    Planets less massive than Saturn tend to rapidly migrate inward in protoplanetary disks. This is the so-called type I migration. Simulations attempting to reproduce the observed properties of exoplanets show that type I migration needs to be significantly reduced over a wide region of the disk for a long time. However, the mechanism capable of suppressing type I migration over a wide region has remained elusive. The recently found turbulence-driven disk winds offer new possibilities. We investigate the effects of disk winds on the disk profile and type I migration for a range of parameters that describe the strength of disk winds. We also examine the in situ formation of close-in super-Earths in disks that evolve through disk winds. The disk profile, which is regulated by viscous diffusion and disk winds, was derived by solving the diffusion equation. We carried out a number of simulations and plot here migration maps that indicate the type I migration rate. We also performed N-body simulations of the formati...

  6. What Kinds of Accretion Disks Are There in the Nuclei of Radio Galaxies?

    CERN Document Server

    Kaburaki, Osamu; Tamura, Naoya; Wajima, Kiyoaki

    2010-01-01

    It seems to be a widely accepted opinion that the types of accretion disks (or flows) generally realized in the nuclei of radio galaxies and in further lower mass-accretion rate nuclei are inner, hot, optically thin, radiatively inefficient accretion flows (RIAFs) surrounded by outer, cool, optically thick, standard type accretion disks. However, observational evidence for the existence of such outer cool disks in these nuclei is rather poor. Instead, recent observations sometimes suggest the existence of inner cool disks of non-standard type, which develop in the region very close to their central black holes. Taking NGC 4261 as a typical example of such light eating nuclei, for which both flux data ranging from radio to X-ray and data for the counterjet occultation are available, we examine the plausibility of such a picture for the accretion states as mentioned above, based on model predictions. It is shown that the explanation of the gap seen in the counterjet emission in terms of the free-free absorption...

  7. Occurrence of instability through the protostellar accretion disks by landing of low-mass condensations

    CERN Document Server

    Elyasi, Mahjubeh

    2016-01-01

    Low-mass condensations (LMCs) are observed inside the envelope of the collapsing molecular cloud cores. In this research, we investigate the effects of landing LMCs for occurrence of instability through the protostellar accretion disks. We consider some regions of the disk where duration of infalling and landing of the LMCs are shorter than the orbital period. In this way, we can consider the landing LMCs as density bumps and grooves in the azimuthal direction of an initial thin axisymmetric steady state self-gravitating protostellar accretion disk (nearly Keplerian). Using the linear effects of the bump quantities, we obtain a characteristic equation for growth/decay rate of bumps; we numerically solve it to find occurrence of instability. We also evaluate the minimum-growth-time-scale (MGTS) and the enhanced mass accretion rate. The results show that infalling and landing of the LMCs in the inner regions of the protostellar accretion disks can cause faster unstable modes and less enhanced accretion rates re...

  8. Atlas of Tilted Accretion Disks & Source to Negative Superhumps

    CERN Document Server

    Montgomery, M M

    2009-01-01

    Using smoothed particle hydrodynamics, we numerically simulate steady state accretion discs for Cataclysmic Variable Dwarf Novae systems that have a secondary-to-primary mass ratio (0.35 \\le q \\le 0.55). After these accretion discs have come to quasi-equilibrium, we rotate each disc out of the orbital plane by (\\delta = (1, 2, 3, 4, 5,) or (20)^{o}) to induce negative superhumps. For accretion discs tilted $5^{o}$, we generate light curves and associated Fourier transforms for an atlas on negative superhumps and retrograde precession. Our simulation results suggest that accretion discs need to be tilted more than three degrees for negative superhumps to be statistically significant. We also show that if the disc is tilted enough such that the gas stream strikes a disc face, then a dense cooling ring is generated near the radius of impact. In addition to the atlas, we study these artificially tilted accretion discs to find the source to negative superhumps. Our results suggest that the source is additional lig...

  9. Shapes and Positions of Black Hole Shadows in Accretion Disks and Spin Parameters of Black Holes

    OpenAIRE

    Takahashi, Rohta

    2004-01-01

    Can we determine a spin parameter of a black hole by observation of a black hole shadow in an accretion disk? In order to answer this question, we make a qualitative analysis and a quantitative analysis of a shape and a position of a black hole shadow casted by a rotating black hole on an optically thick accretion disk and its dependence on an angular momentum of a black hole. We have found black hole shadows with a quite similar size and a shape for largely different black hole spin paramete...

  10. Annihilation luminosity of a neutrino-cooled accretion disk in a gamma-ray burst

    Institute of Scientific and Technical Information of China (English)

    WANG Hao; LIU Tong; LU JuFu

    2009-01-01

    We discuss how the annihilation luminosity of a neutrino-cooled accretion disk in a gamma-ray burst,LW-, is determined by the disk's fundamental parameters, namely, the mass of the central black hole M,the mass accretion rate M, and the viscosity parameter α.It is shown that LW- depends mainly on M in evidence, and decreases with increasing M, but is almost independent of α. This result argues additionally that the central black hole in a gamma-ray burst must be with a stellar mass.

  11. Suppression of type I migration by disk winds

    Science.gov (United States)

    Ogihara, Masahiro; Morbidelli, Alessandro; Guillot, Tristan

    2015-12-01

    Context. Planets less massive than Saturn tend to rapidly migrate inward in protoplanetary disks. This is the so-called type I migration. Simulations attempting to reproduce the observed properties of exoplanets show that type I migration needs to be significantly reduced over a wide region of the disk for a long time. However, the mechanism capable of suppressing type I migration over a wide region has remained elusive. The recently found turbulence-driven disk winds offer new possibilities. Aims: We investigate the effects of disk winds on the disk profile and type I migration for a range of parameters that describe the strength of disk winds. We also examine the in situ formation of close-in super-Earths in disks that evolve through disk winds. Methods: The disk profile, which is regulated by viscous diffusion and disk winds, was derived by solving the diffusion equation. We carried out a number of simulations and plot here migration maps that indicate the type I migration rate. We also performed N-body simulations of the formation of close-in super-Earths from a population of planetesimals and planetary embryos. Results: We define a key parameter, Kw, which determines the ratio of strengths between the viscous diffusion and disk winds. For a wide range of Kw, the type I migration rate is presented in migration maps. These maps show that type I migration is suppressed over the whole close-in region when the effects of disk winds are relatively strong (Kw ≲ 100). From the results of N-body simulations, we see that type I migration is significantly slowed down assuming Kw = 40. We also show that the results of N-body simulations match statistical orbital distributions of close-in super-Earths.

  12. The dynamic of stellar wind accretion and the HMXB zoo

    Science.gov (United States)

    Walter, Roland; Manousakis, Antonios

    2016-07-01

    The dynamic of the accretion of stellar wind on the pulsar in Vela X-1 is dominated by unstable hydrodynamical flows. Off-states, 10^{37} erg/s flares, quasi-periodic oscillations and log normal flux distribution can all be reproduced by hydrodynamical simulations and reveal the complex motion of bow shocks moving either towards or away from the neutron star. These behaviors are enlightening the zoo of HMXB and suggest new phenomenology to be detected.

  13. The Evolution of Gas and Dust in Protoplanetary Accretion Disks

    CERN Document Server

    Birnstiel, T

    2011-01-01

    Dust constitutes only about one percent of the mass of circumstellar disks, yet it is of crucial importance for the modeling of planet formation, disk chemistry, radiative transfer and observations. The initial growth of dust from sub-micron sized grains to planetesimals and also the radial transport of dust in disks around young stars is the topic of this thesis. Circumstellar dust is subject to radial drift, vertical settling, turbulent mixing, collisional growth, fragmentation and erosion. We approach this subject from three directions: analytical calculations, numerical simulations, and comparison to observations. We describe the physical and numerical concepts that go into a model which is able to simulate the radial and size evolution of dust in a gas disk which is viscously evolving over several million years. The resulting dust size distributions are compared to our analytical predictions and a simple recipe for obtaining steady-state dust size distributions is derived. With the numerical model at han...

  14. White Dwarf Pollution by Disk Accretion of Tidally Disrupted Rocky Bodies

    Science.gov (United States)

    Feng, Wanda; Desch, Steven

    2017-01-01

    Approximately 30% of cool white dwarfs (WDs) show heavy elements which should otherwise sediment out of their atmospheres (Koester et al. 2014; Zuckerman et al. 2010). The prevailing model for the pollution of white dwarf photospheres invokes the formation of a solid disk upon a rocky body falling within the WD Roche radius, which is then transported inward by Poynting-Robertson drag (e.g., Metzger et al. 2012, Rafikov 2011). At high temperatures close to the WD, solid particles sublimate to gas that accretes onto the WD and viscously spreads outward. This concept is supported by observations of Ca II emission from WD disks (e.g., Manser et al. 2016). The model by Metzger et al. (2012) successfully explains the range in inferred mass accretion rates (10^10 g/s, Farihi et al. 2010), provided the gaseous disks viscously spread at rates consistent with a partially suppressed magnetorotational instability (MRI). However, Metzger et al. (2012) do not consider disk chemistry or dust-to-gas mixing in their model, and do not calculate the degree of ionization to explore the extent of MRI in WD disks.We present a 1-D model of a gaseous WD disk accretion, to assess the extent of the magnetorotational instability in WD disks. The disk composition is considered with changes in sublimation rate by pressure. The degree of ionization is determined by considering UV, X-ray, and high-temperature ionization. We calculate the rate of viscous spreading and accretion rates of metals onto WDs.

  15. Cold Dark Matter Substructure and Galactic Disks I: Morphological Signatures of Hierarchical SatelliteAccretion

    Energy Technology Data Exchange (ETDEWEB)

    Kazantzidis, Stelios; Bullock, James S.; Zentner, Andrew R.; Kravtsov, Andrey V.; Moustakas, Leonidas A.

    2007-12-03

    We conduct a series of high-resolution, fully self-consistent dissipation less N-body simulations to investigate the cumulative effect of substructure mergers onto thin disk galaxies in the context of the {Lambda}CDM paradigm of structure formation. Our simulation campaign is based on a hybrid approach combining cosmological simulations and controlled numerical experiments. Substructure mass functions, orbital distributions, internal structures, and accretion times are culled directly from cosmological simulations of galaxy-sized cold dark matter (CDM) halos. We demonstrate that accretions of massive subhalos onto the central regions of host halos, where the galactic disk resides, since z {approx} 1 should be common occurrences. In contrast, extremely few satellites in present-day CDM halos are likely to have a significant impact on the disk structure. This is due to the fact that massive subhalos with small orbital pericenters that are most capable of strongly perturbing the disk become either tidally disrupted or suffer substantial mass loss prior to z = 0. One host halo merger history is subsequently used to seed controlled N-body experiments of repeated satellite impacts on an initially-thin Milky Way-type disk galaxy. These simulations track the effects of six dark matter substructures, with initial masses in the range {approx} (0.7-2) x 10{sup 10} M{sub {circle_dot}} ({approx} 20-60% of the disk mass), crossing the disk in the past {approx} 8 Gyr. We show that these accretion events produce several distinctive observational signatures in the stellar disk including: a long-lived, low-surface brightness, ring-like feature in the outskirts; a significant flare; a central bar; and faint filamentary structures that (spuriously) resemble tidal streams in configuration space. The final distribution of disk stars exhibits a complex vertical structure that is well-described by a standard 'thin-thick' disk decomposition, where the 'thick' disk

  16. Quasi-static model of collimated jets and radio lobes. I. Accretion disk and jets

    Energy Technology Data Exchange (ETDEWEB)

    Colgate, Stirling A.; Li, Hui [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Fowler, T. Kenneth [University of California, Berkeley, CA 94720 (United States); Pino, Jesse [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States)

    2014-07-10

    This is the first of a series of papers showing that when an efficient dynamo can be maintained by accretion disks around supermassive black holes in active galactic nuclei, it can lead to the formation of a powerful, magnetic helix that could explain both the observed radio jet/lobe structures on very large scales and ultimately the enormous power inferred from the observed ultra-high-energy cosmic rays. In this work, we solve a set of one-dimensional equations similar to the steady-state standard accretion disk model, but now including the large-scale magnetic fields giving rises to jets. We find that the frequently made assumption that large-scale fields are frozen into the disk is fundamentally incorrect, due to the necessity for current and the accreting mass to flow perpendicular to magnetic flux surfaces. A correct treatment greatly simplifies the calculations, yielding fields that leave the disk nearly vertically with magnetic profiles uniquely determined by disk angular momentum conservation. Representative solutions of the magnetic fields in different radial regions of the disk surface are given, and they determine the overall key features in the jet structure and its dissipation, which will be the subjects of later papers.

  17. Radiation Pressure-supported Accretion Disks: Vertical Structure, Energy Advection, and Convective Stability

    CERN Document Server

    Gu, Wei-Min

    2012-01-01

    By taking into account the local energy balance per unit volume between the viscous heating and the advective cooling plus the radiative cooling, we investigate the vertical structure of radiation pressure-supported accretion disks in spherical coordinates. Our solutions show that the photosphere of the disk is close to the polar axis and therefore the disk seems to be extremely thick. However, the profile of density implies that most of the accreted matter exists in a moderate range around the equatorial plane. We show that the well-known polytropic relation between the pressure and the density is unsuitable for describing the vertical structure of radiation pressure-supported disks. More importantly, we find that the energy advection is significant even for slightly sub-Eddington accretion disks. We argue that the non-negligible advection may help to understand why the standard thin disk model is likely to be inaccurate above \\sim 0.3 Eddington luminosity, which was found by some works on the black hole spi...

  18. Spin Evolution of Accreting Young Stars. I. Effect of Magnetic Star-Disk Coupling

    CERN Document Server

    Matt, Sean P; de la Reza, Ramiro; Greene, Thomas P

    2010-01-01

    We present a model for the rotational evolution of a young, solar mass star interacting with an accretion disk. The model incorporates a description of the angular momentum transfer between the star and disk due to a magnetic connection, and includes changes in the star's mass and radius and a decreasing accretion rate. The model also includes, for the first time in a spin evolution model, the opening of the stellar magnetic field lines, as expected to arise from twisting via star-disk differential rotation. In order to isolate the effect that this has on the star-disk interaction torques, we neglect the influence of torques that may arise from open field regions connected to the star or disk. For a range of magnetic field strengths, accretion rates, and initial spin rates, we compute the stellar spin rates of pre-main-sequence stars as they evolve on the Hayashi track to an age of 3~Myr. How much the field opening affects the spin depends on the strength of the coupling of the magnetic field to the disk. For...

  19. A Hot and Massive Accretion Disk around the High-Mass Protostar IRAS 20126+4104

    CERN Document Server

    Chen, Huei-Ru Vivien; Zhang, Qizhou; Sridharan, T K; Liu, Sheng-Yuan; Su, Yu-Nung

    2016-01-01

    We present new spectral line observations of the CH3CN molecule in the accretion disk around the massive protostar IRAS 20126+4104 with the Submillimeter Array that for the first time measure the disk density, temperature, and rotational velocity with sufficient resolution (0.37", equivalent to ~600 AU) to assess the gravitational stability of the disk through the Toomre-Q parameter. Our observations resolve the central 2000 AU region that shows steeper velocity gradients with increasing upper state energy, indicating an increase in the rotational velocity of the hotter gas nearer the star. Such spin-up motions are characteristics of an accretion flow in a rotationally supported disk. We compare the observed data with synthetic image cubes produced by three-dimensional radiative transfer models describing a thin flared disk in Keplerian motion enveloped within the centrifugal radius of an angular-momentum-conserving accretion flow. Given a luminosity of 1.3x10^4 Lsun, the optimized model gives a disk mass of ...

  20. Circumbinary ring, circumstellar disks, and accretion in the binary system UY Aurigae

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Ya-Wen; Ho, Paul T. P. [Academia Sinica, Institute of Astronomy and Astrophysics, Taipei, Taiwan (China); Dutrey, Anne; Guilloteau, Stéphane; Di Folco, Emmanuel [Université de Bordeaux, Observatoire Aquitain des Sciences de l' Univers, CNRS, UMR 5804, Laboratoire d' Astrophysique de Bordeaux, 2 rue de l' Observatoire, BP 89, F-33271 Floirac Cedex (France); Piétu, Vincent; Gueth, Fréderic [IRAM, 300 rue de la piscine, F-38406 Saint Martin d' Hères Cedex (France); Beck, Tracy [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Boehler, Yann [Centro de Radioastronomìa y Astrofìsica, UNAM, Apartado Postal 3-72, 58089 Morelia, Michoacàn (Mexico); Bary, Jeff [Department of Physics and Astronomy, Colgate University, 13 Oak Drive, Hamilton, NY 13346 (United States); Simon, Michal, E-mail: ywtang@asiaa.sinica.edu.tw [Stony Brook University, Stony Brook, NY 11794-3800 (United States)

    2014-09-20

    Recent exo-planetary surveys reveal that planets can orbit and survive around binary stars. This suggests that some fraction of young binary systems which possess massive circumbinary (CB) disks may be in the midst of planet formation. However, there are very few CB disks detected. We revisit one of the known CB disks, the UY Aurigae system, and probe {sup 13}CO 2-1, C{sup 18}O 2-1, SO 5(6)-4(5) and {sup 12}CO 3-2 line emission and the thermal dust continuum. Our new results confirm the existence of the CB disk. In addition, the circumstellar (CS) disks are clearly resolved in dust continuum at 1.4 mm. The spectral indices between the wavelengths of 0.85 mm and 6 cm are found to be surprisingly low, being 1.6 for both CS disks. The deprojected separation of the binary is 1.''26 based on our 1.4 mm continuum data. This is 0.''07 (10 AU) larger than in earlier studies. Combining the fact of the variation of UY Aur B in R band, we propose that the CS disk of an undetected companion UY Aur Bb obscures UY Aur Ba. A very complex kinematical pattern inside the CB disk is observed due to a mixing of Keplerian rotation of the CB disk, the infall and outflow gas. The streaming gas accreting from the CB ring toward the CS disks and possible outflows are also identified and resolved. The SO emission is found to be at the bases of the streaming shocks. Our results suggest that the UY Aur system is undergoing an active accretion phase from the CB disk to the CS disks. The UY Aur B might also be a binary system, making the UY Aur a triple system.

  1. General relativistic hydrodynamics with Adaptive-Mesh Refinement (AMR) and modeling of accretion disks

    Science.gov (United States)

    Donmez, Orhan

    We present a general procedure to solve the General Relativistic Hydrodynamical (GRH) equations with Adaptive-Mesh Refinement (AMR) and model of an accretion disk around a black hole. To do this, the GRH equations are written in a conservative form to exploit their hyperbolic character. The numerical solutions of the general relativistic hydrodynamic equations is done by High Resolution Shock Capturing schemes (HRSC), specifically designed to solve non-linear hyperbolic systems of conservation laws. These schemes depend on the characteristic information of the system. We use Marquina fluxes with MUSCL left and right states to solve GRH equations. First, we carry out different test problems with uniform and AMR grids on the special relativistic hydrodynamics equations to verify the second order convergence of the code in 1D, 2 D and 3D. Second, we solve the GRH equations and use the general relativistic test problems to compare the numerical solutions with analytic ones. In order to this, we couple the flux part of general relativistic hydrodynamic equation with a source part using Strang splitting. The coupling of the GRH equations is carried out in a treatment which gives second order accurate solutions in space and time. The test problems examined include shock tubes, geodesic flows, and circular motion of particle around the black hole. Finally, we apply this code to the accretion disk problems around the black hole using the Schwarzschild metric at the background of the computational domain. We find spiral shocks on the accretion disk. They are observationally expected results. We also examine the star-disk interaction near a massive black hole. We find that when stars are grounded down or a hole is punched on the accretion disk, they create shock waves which destroy the accretion disk.

  2. Shock-driven Accretion in Circumplanetary Disks: Observables and Satellite Formation

    Science.gov (United States)

    Zhu, Zhaohuan; Ju, Wenhua; Stone, James M.

    2016-12-01

    Circumplanetary disks (CPDs) control the growth of planets, supply material for satellites to form, and provide observational signatures of young forming planets. We have carried out two-dimensional hydrodynamical simulations with radiative cooling to study CPDs and suggested a new mechanism to drive the disk accretion. Two spiral shocks are present in CPDs, excited by the central star. We find that spiral shocks can at least contribute to, if not dominate, the angular momentum transport and energy dissipation in CPDs. Meanwhile, dissipation and heating by spiral shocks have a positive feedback on shock-driven accretion itself. As the disk is heated up by spiral shocks, the shocks become more open, leading to more efficient angular momentum transport. This shock-driven accretion is, on the other hand, unsteady due to production and destruction of vortices in disks. After being averaged over time, a quasi-steady accretion is reached from the planet’s Hill radius all the way to the planet surface, and the disk α coefficient characterizing angular momentum transport is ˜0.001-0.02. The disk surface density ranges from 10 to 1000 g cm-2 in our simulations, which is at least three orders of magnitude smaller than the “minimum-mass subnebula” model used to study satellite formation; instead it is more consistent with the “gas-starved” satellite formation model. Finally, we calculate the millimeter flux emitted by CPDs at ALMA and EVLA wavelength bands and predict the flux for several recently discovered CPD candidates, which suggests that ALMA is capable of discovering these accreting CPDs.

  3. Modified viscosity in accretion disks. Application to Galactic black hole binaries, intermediate mass black holes and AGN

    CERN Document Server

    Grzędzielski, Mikołaj; Czerny, Bożena; Wu, Qingwen

    2016-01-01

    Black holes surrounded by accretion disks are present in the Universe in different scales of masses, from microquasars up to the Active Galactic Nuclei. The current picture of the accretion disk theory remains still ad hoc, due the complexity of the magnetic field action. In addition, the accretion disks at high Eddington rates can be radiation-pressure dominated and, according to some of the heating prescriptions, thermally unstable. The observational verification of their resulting variability patterns may shed the light on both the role of radiation pressure and magnetic field in the accretion process. We compute the structure and time evolution of an accretion disk. We supplement this model with a modified viscosity prescription, which can to some extent describe the magnetization of the disk. We study the results for a large grid of models and derive conclusions separately for different scales of black hole masses. We show the dependences between the flare, or outburst, duration, its amplitude and period...

  4. Circumstellar disks of the most vigorously accreting young stars.

    Science.gov (United States)

    Liu, Hauyu Baobab; Takami, Michihiro; Kudo, Tomoyuki; Hashimoto, Jun; Dong, Ruobing; Vorobyov, Eduard I; Pyo, Tae-Soo; Fukagawa, Misato; Tamura, Motohide; Henning, Thomas; Dunham, Michael M; Karr, Jennifer L; Kusakabe, Nobuhiko; Tsuribe, Toru

    2016-02-01

    Stars may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. Our high-resolution near-infrared imaging has verified the presence of the key associated features, large-scale arms and arcs surrounding four young stellar objects undergoing luminous outbursts. Our hydrodynamics simulations and radiative transfer models show that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation phase. The effect of those tempestuous episodes of disk evolution on star and planet formation remains to be understood.

  5. Magnetically Driven Accretion Flows in the Kerr Metric IV: Dynamical Properties of the Inner Disk

    CERN Document Server

    Krolik, J H; Hirose, S; Krolik, Julian H.; Hawley, John F.; Hirose, Shigenobu

    2004-01-01

    This paper continues the analysis of a set of general relativistic 3D MHD simulations of accreting tori in the Kerr metric with different black hole spins. We focus on bound matter inside the initial pressure maximum, where the time-averaged motion of gas is inward and an accretion disk forms. We use the flows of mass, angular momentum, and energy in order to understand dynamics in this region. The sharp reduction in accretion rate with increasing black hole spin reported in Paper I of this series is explained by a strongly spin-dependent outward flux of angular momentum conveyed electromagnetically; when a/M > 0.9, this flux can be comparable to the inward angular momentum flux carried by the matter. In all cases, there is outward electromagnetic angular momentum flux throughout the flow; in other words, contrary to the assertions of traditional accretion disk theory, there is in general no "stress edge", no surface within which the stress is zero. The retardation of accretion in the inner disk by electromag...

  6. Simulating the Formation of Massive Protostars: I. Radiative Feedback and Accretion Disks

    CERN Document Server

    Klassen, Mikhail; Kuiper, Rolf; Peters, Thomas; Banerjee, Robi

    2016-01-01

    We present radiation hydrodynamic simulations of collapsing protostellar cores with initial masses of 30, 100, and 200 M$_{\\odot}$. We follow their gravitational collapse and the formation of a massive protostar and protostellar accretion disk. We employ a new hybrid radiative feedback method blending raytracing techniques with flux-limited diffusion for a more accurate treatment of the temperature and radiative force. In each case, the disk that forms becomes Toomre-unstable and develops spiral arms. This occurs between 0.35 and 0.55 freefall times and is accompanied by an increase in the accretion rate by a factor of 2-10. Although the disk becomes unstable, no other stars are formed. In the case of our 100 and 200 M$_{\\odot}$ simulation, the star becomes highly super-Eddington and begins to drive bipolar outflow cavities that expand outwards. These radiatively-driven bubbles appear stable, and appear to be channeling gas back onto the protostellar accretion disk. Accretion proceeds strongly through the dis...

  7. Relativistic lines and reflection from the inner accretion disks around neutron stars

    NARCIS (Netherlands)

    Cackett, E.M.; Miller, J.M.; Ballantyne, D.R.; Barret, D.; Bhattacharyya, S.; Boutelier, M.; Miller, M.C.; Strohmayer, T.E.; Wijnands, R.

    2010-01-01

    A number of neutron star low-mass X-ray binaries (LMXBs) have recently been discovered to show broad, asymmetric Fe K emission lines in their X-ray spectra. These lines are generally thought to be the most prominent part of a reflection spectrum, originating in the inner part of the accretion disk w

  8. Shock-driven Accretion in Circumplanetary Disks: Observables and Satellite Formation

    CERN Document Server

    Zhu, Zhaohuan; Stone, James M

    2016-01-01

    Circumplanetary disks (CPDs) control the growth of planets, supply material for satellites to form, and provide observational signatures of young forming planets. We have carried out two dimensional hydrodynamical simulations with radiative cooling to study CPDs, and suggested a new mechanism to drive the disk accretion. Two spiral shocks are present in CPDs, excited by the central star. We find that spiral shocks can at least contribute to, if not dominate the angular momentum transport and energy dissipation in CPDs. Meanwhile, dissipation and heating by spiral shocks have a positive feedback on shock-driven accretion itself. As the disk is heated up by spiral shocks, the shocks become more open, leading to more efficient angular momentum transport. This shock driven accretion is, on the other hand, unsteady on a timescale of months/years due to production and destruction of vortices in disks. After being averaged over time, a quasi-steady accretion is reached from the planet's Hill radius all the way to th...

  9. Structure analysis of solution to equations of quasi 3-D accretion disk model

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    In this paper we discuss the problems contained in the solution to the equations of quasi 3-D accretion disk model, and point out that the angular momentum equation should not be integrated directly. Finally, we develop a criterion of the existence of a disconnected solution to this model.

  10. Wind accretion in symbiotic X-ray binaries

    CERN Document Server

    Postnov, K; González-Galán, A; Kuulkers, E; Kretschmar, P; Larsson, S; Finger, M H; Kochetkova, A; Lü, G; Yungelson, L

    2011-01-01

    The properties of wind accretion in symbiotic X-ray binaries (SyXBs) consisting of red-giant and magnetized neutron star (NS) are discussed. The spin-up/spin-down torques applied to NS are derived based on a hydrodynamic theory of quasi-spherical accretion onto magnetized NSs. In this model, a settling subsonic accretion proceeds through a hot shell formed around the NS magnetosphere. The accretion rate onto the NS is determined by the ability of the plasma to enter the magnetosphere.Due to large Reynolds numbers in the shell, the interaction of the rotating magnetosphere with plasma initiates a subsonic turbulence. The convective motions are capable of carrying the angular momentum through the shell. We carry out a population synthesis of SyXBs in the Galaxy with account for the spin evolution of magnetized NS. The Galactic number of SyXBs with bright (M_v<1) low-mass red-giant companion is found to be from \\sim 40 to 120, and their birthrate is \\sim 5\\times 10^{-5}-10^{-4} per year. According to our mode...

  11. Accretion disk dynamics. α-viscosity in self-similar self-gravitating models

    Science.gov (United States)

    Kubsch, Marcus; Illenseer, Tobias F.; Duschl, Wolfgang J.

    2016-04-01

    Aims: We investigate the suitability of α-viscosity in self-similar models for self-gravitating disks with a focus on active galactic nuclei (AGN) disks. Methods: We use a self-similar approach to simplify the partial differential equations arising from the evolution equation, which are then solved using numerical standard procedures. Results: We find a self-similar solution for the dynamical evolution of self-gravitating α-disks and derive the significant quantities. In the Keplerian part of the disk our model is consistent with standard stationary α-disk theory, and self-consistent throughout the self-gravitating regime. Positive accretion rates throughout the disk demand a high degree of self-gravitation. Combined with the temporal decline of the accretion rate and its low amount, the model prohibits the growth of large central masses. Conclusions: α-viscosity cannot account for the evolution of the whole mass spectrum of super-massive black holes (SMBH) in AGN. However, considering the involved scales it seems suitable for modelling protoplanetary disks.

  12. An extensive numerical survey of the correlation between outflow dynamics and accretion disk magnetization

    CERN Document Server

    Stepanovs, Deniss

    2016-01-01

    We investigate the accretion-ejection process of jets from magnetized accretion disks. We apply a novel approach to the jet-launching problem in order to obtain correlations between the physical properties of the jet and the underlying disk. We extend and confirm the previous works of \\citet{2009MNRAS.400..820T} and \\citet{2010A&A...512A..82M} by scanning a large parameter range for the disk magnetization, $\\mu_{\\rm D} = 10^{-3.5} ... 10^{-0.7}$. We disentangle the disk magnetization at the foot point of the outflow as the main parameter that governs the properties of the outflow. We show how the four jet integrals known from steady-state MHD are correlated to the disk magnetization at the jet foot point. This agrees with the usual findings of the steady-state theory, however, here we obtain these correlations from time-dependent simulations that include the dynamical evolution of the disk in the treatment. In particular, we obtain robust correlations between the local disk magnetization and (i)the outflo...

  13. Parsec-scale accretion and winds irradiated by a quasar

    CERN Document Server

    Dorodnitsyn, Anton; Proga, Daniel

    2015-01-01

    We present numerical simulations of properties of a parsec-scale torus exposed to illumination by the central black hole in an active galaxy (AGN). Our physical model allows to investigate the balance between the formation of winds and accretion simultaneously. Radiation-driven winds are allowed by taking into account radiation pressure due to UV and IR radiation along with X-ray heating and dust sublimation. Accretion is allowed through angular momentum transport and the solution of the equations of radiation hydrodynamics. Our methods adopt flux-limited diffusion radiation-hydrodynamics for the dusty, infrared pressure driven part of the flow, along with X-ray heating and cooling. Angular momentum transport in the accreting part of the flow is modeled using effective viscosity. Our results demonstrate that radiation pressure on dust can play an important role in shaping AGN obscuration. For example, when the luminosity illuminating the torus exceeds $L>0.01\\,L_{\\rm Edd}$, where $L_{\\rm Edd}$ is the Eddingto...

  14. Molecule survival in magnetized protostellar disk winds. II. Predicted H2O line profiles versus Herschel/HIFI observations

    CERN Document Server

    Yvart, W; Forets, G Pineau des; Ferreira, J

    2016-01-01

    We investigate whether the broad wings of H2O emission identified with Herschel towards low-mass Class 0 and Class 1 protostars may be consistent with an origin in a dusty MHD disk wind, and the constraints it would set on the underlying disk properties. We present synthetic H2O line profiles predictions for a typical MHD disk wind solution with various values of disk accretion rate, stellar mass, extension of the launching area, and view angle. We compare them in terms of line shapes and intensities with the HIFI profiles observed by the WISH Key Program. We find that a dusty MHD disk wind launched from 0.2--0.6 AU AU to 3--25 AU can reproduce to a remarkable degree the observed shapes and intensities of the broad H2O component, both in the fundamental 557 GHz line and in more excited lines. Such a model also readily reproduces the observed correlation of 557 GHz line luminosity with envelope density, if the infall rate at 1000 AU is 1--3 times the disk accretion rate in the wind ejection region. It is also ...

  15. Star formation and accretion in the circumnuclear disks of active galaxies

    CERN Document Server

    Wutschik, Stephanie; Palmer, Thomas S

    2013-01-01

    We explore the evolution of supermassive black holes (SMBH) centered in a circumnuclear disk (CND) as a function of the mass supply from the host galaxy and considering different star formation laws, which may give rise to a self-regulation via the injection of supernova-driven turbulence. A system of equations describing star formation, black hole accretion and angular momentum transport was solved for an axisymmetric disk in which the gravitational potential includes contributions from the black hole, the disk and the hosting galaxy. Our model extends the framework provided by Kawakatu et al. (2008) by separately considering the inner and outer part of the disk, and by introducing a potentially non-linear dependence of the star formation rate on the gas surface density and the turbulent velocity. The star formation recipes are calibrated using observational data for NGC 1097, while the accretion model is based on turbulent viscosity as a source of angular momentum transport in a thin viscous accretion disk....

  16. Accretion Disks Around Binary Black Holes of Unequal Mass: GRMHD Simulations Near Decoupling

    Science.gov (United States)

    Gold, Roman; Paschalidis, Vasileios; Etienne, Zachariah B.; Shapiro, Stuart L.; Pfeiffer, Harald, P.

    2013-01-01

    We report on simulations in general relativity of magnetized disks onto black hole binaries. We vary the binary mass ratio from 1:1 to 1:10 and evolve the systems when they orbit near the binary disk decoupling radius. We compare (surface) density profiles, accretion rates (relative to a single, non-spinning black hole), variability, effective alpha-stress levels and luminosities as functions of the mass ratio. We treat the disks in two limiting regimes: rapid radiative cooling and no radiative cooling. The magnetic field lines clearly reveal jets emerging from both black hole horizons and merging into one common jet at large distances. The magnetic fields give rise to much stronger shock heating than the pure hydrodynamic flows, completely alter the disk structure, and boost accretion rates and luminosities. Accretion streams near the horizons are among the densest structures; in fact, the 1:10 no-cooling evolution results in a refilling of the cavity. The typical effective temperature in the bulk of the disk is approx. 10(exp5) (M / 10(exp 8)M solar mass (exp -1/4(L/L(sub edd) (exp 1/4K) yielding characteristic thermal frequencies approx. 10 (exp 15) (M /10(exp 8)M solar mass) (exp -1/4(L/L (sub edd) (1+z) (exp -1)Hz. These systems are thus promising targets for many extragalactic optical surveys, such as LSST, WFIRST, and PanSTARRS.

  17. Reverberation Mapping of the Broad Line Region: application to a hydrodynamical line-driven disk wind solution

    CERN Document Server

    Waters, Tim; Proga, Daniel; Eracleous, Michael; Barth, Aaron J; Greene, Jenny

    2016-01-01

    The latest analysis efforts in reverberation mapping are beginning to allow reconstruction of echo images (or velocity-delay maps) that encode information about the structure and kinematics of the broad line region (BLR) in active galactic nuclei (AGNs). Such maps can constrain sophisticated physical models for the BLR. The physical picture of the BLR is often theorized to be a photoionized wind launched from the AGN accretion disk. Previously we showed that the line-driven disk wind solution found in an earlier simulation by Proga and Kallman is virialized over a large distance from the disk. This finding implies that, according to this model, black hole masses can be reliably estimated through reverberation mapping techniques. However, predictions of echo images expected from line-driven disk winds are not available. Here, after presenting the necessary radiative transfer methodology, we carry out the first calculations of such predictions. We find that the echo images are quite similar to other virialized ...

  18. Truncation of the Inner Accretion Disk Around a Black Hole at Low Luminosity

    Science.gov (United States)

    Tomsick, John A.; Yamoka, Kazutaka; Corbel, Stephane; Kaaret, Philip; Kalemci, Emrah; Migliari, Simone

    2011-01-01

    Most black hole binaries show large changes in X-ray luminosity caused primarily by variations in mass accretion rate. An important question for understanding black hole accretion and jet production is whether the inner edge of the accretion disk recedes at low accretion rate. Measurements of the location of the inner edge (R(sub in)) can be made using iron emission lines that arise due to fluorescence of iron in the disk, and these indicate that R(sub in) is very close to the black hole at high and moderate luminosities (greater than or equal to 1% of the Eddington luminosity, L(sub Edd). Here, we report on X-ray observations of the black hole GX 339-4 in the hard state by Suzaku and the Rossi X-ray Timing Explorer that extend iron line studies to 0.14% L(sub Edd) and show that R(sub in) increases by a factor of greater than 27 over the value found when GX 339-4 was bright. The exact value of R(sub in) depends on the inclination of the inner disk (i), and we derive 90% confidence limits of R(sub in) greater than 35 R(sub g) at i = 0 degrees and R(sub in) greater than 175 R(sub g) at i = 30 degrees. This provides direct evidence that the inner portion of the disk is not present at low luminosity, allowing for the possibility that the inner disk is replaced by advection- or magnetically dominated accretion flows.

  19. Accretion Disk Signatures in Type I X-Ray Bursts: Prospects for Future Missions

    Science.gov (United States)

    Keek, L.; Wolf, Z.; Ballantyne, D. R.

    2016-07-01

    Type I X-ray bursts and superbursts from accreting neutron stars illuminate the accretion disk and produce a reflection signal that evolves as the burst fades. Examining the evolution of reflection features in the spectra will provide insight into the burst-disk interaction, a potentially powerful probe of accretion disk physics. At present, reflection has been observed during only two bursts of exceptional duration. We investigate the detectability of reflection signatures with four of the latest well-studied X-ray observatory concepts: Hitomi, Neutron Star Interior Composition Explorer (NICER), Athena, and Large Observatory For X-ray Timing (LOFT). Burst spectra are modeled for different values for the flux, temperature, and the disk ionization parameter, which are representative for most known bursts and sources. The effective area and throughput of a Hitomi-like telescope are insufficient for characterizing burst reflection features. NICER and Athena will detect reflection signatures in Type I bursts with peak fluxes ≳10-7.5 erg cm-2 s-1 and also effectively constrain the reflection parameters for bright bursts with fluxes of ˜10-7 erg cm-2 s-1 in exposures of several seconds. Thus, these observatories will provide crucial new insight into the interaction of accretion flows and X-ray bursts. For sources with low line-of-sight absorption, the wide bandpass of these instruments allows for the detection of soft X-ray reflection features, which are sensitive to the disk metallicity and density. The large collecting area that is part of the LOFT design would revolutionize the field by tracing the evolution of the accretion geometry in detail throughout short bursts.

  20. Relativistic Accretion Disk Models of High State Black Hole X-ray Binary Spectra

    CERN Document Server

    Davis, S W; Hubeny, I; Turner, N J; Davis, Shane W.; Blaes, Omer M.; Hubeny, Ivan; Turner, Neal J.

    2004-01-01

    We present calculations of non-LTE, relativistic accretion disk models applicable to the high/soft state of black hole X-ray binaries. We include the effects of thermal Comptonization and bound-free and free-free opacities of all abundant ion species. We present spectra calculated for a variety of accretion rates, black hole spin parameters, disk inclinations, and stress prescriptions. We also consider nonzero inner torques on the disk, and explore different vertical dissipation profiles, including some which are motivated by recent radiation MHD simulations of magnetorotational turbulence. Bound-free metal opacity generally produces significantly less spectral hardening than previous models which only considered Compton scattering and free-free opacity. It also tends to keep the effective photosphere near the surface, resulting in spectra which are remarkably independent of the stress prescription and vertical dissipation profile, provided little dissipation occurs above the effective photosphere. We provide...

  1. Coronae as Consequence of Large Scale Magnetic Fields in Turbulent Accretion Disks

    DEFF Research Database (Denmark)

    G. Blackman, Eric; Pessah, Martin Elias

    2009-01-01

    Non-thermal X-ray emission in compact accretion engines can be interpreted to result from magnetic dissipation in an optically thin magnetized corona above an optically thick accretion disk. If coronal magnetic field originates in the disk and the disk is turbulent, then only magnetic structures...... large enough for their turbulent shredding time to exceed their buoyant rise time survive the journey to the corona. We use this concept and a physical model to constrain the minimum fraction of magnetic energy above the critical scale for buoyancy as a function of the observed coronal to bolometric...... AGN, for which of order 30 per cent of the bolometric flux is in the X-ray band, we find that more than 20 per cent of the magnetic energy must be of large enough scale to rise and dissipate in the corona....

  2. MHD Flows in Compact Astrophysical Objects Accretion, Winds and Jets

    CERN Document Server

    Beskin, Vasily S

    2010-01-01

    Accretion flows, winds and jets of compact astrophysical objects and stars are generally described within the framework of hydrodynamical and magnetohydrodynamical (MHD) flows. Analytical analysis of the problem provides profound physical insights, which are essential for interpreting and understanding the results of numerical simulations. Providing such a physical understanding of MHD Flows in Compact Astrophysical Objects is the main goal of this book, which is an updated translation of a successful Russian graduate textbook. The book provides the first detailed introduction into the method of the Grad-Shafranov equation, describing analytically the very broad class of hydrodynamical and MHD flows. It starts with the classical examples of hydrodynamical accretion onto relativistic and nonrelativistic objects. The force-free limit of the Grad-Shafranov equation allows us to analyze in detail the physics of the magnetospheres of radio pulsars and black holes, including the Blandford-Znajek process of energy e...

  3. Coronae and Winds from Irradiated Disks in X-ray binaries

    CERN Document Server

    Higginbottom, Nick

    2015-01-01

    X-ray and UV line emission in X-ray binaries can be accounted for by a hot corona. Such a corona forms through irradiation of the outer disk by radiation produced in the inner accretion flow. The same irradiation can produce a strong outflow from the disk at sufficiently large radii. Outflowing gas has been recently detected in several X-ray binaries via blue-shifted absorption lines. However, the causal connection between winds produced by irradiation and the blue-shifted absorption lines is problematic, particularly in the case of GRO J1655-40. Observations of this source imply wind densities about two orders of magnitude higher than theoretically predicted. This discrepancy does not mean that these `thermal disk-winds' cannot explain blue-shifted absorption in other systems, nor that they are unimportant as a sink of matter. Motivated by the inevitability of thermal disk-winds and wealth of data taken with current observatories such as Chandra, XMM-Newton and Suzaku, as well as the future AstroH mission, w...

  4. Unstable Disk Accretion to Magnetized Stars: First Global 3D MHD Simulations

    CERN Document Server

    Romanova, Marina M; Lovelace, Richard V E

    2007-01-01

    We report the first global three-dimensional (3D) MHD simulations of disk accretion onto a rotating magnetized star through the Rayleigh-Taylor instability. In this regime, the accreting matter typically forms 2 to 7 vertically elongated "tongues" which penetrate deep into the magnetosphere, until they are stopped by the strong field. Subsequently, the matter is channeled along the field lines to the surface of the star, forming hot spots. The number, position and shape of the hot spots vary with time, so that the light-curves associated with the hot spots are stochastic. A magnetized star may be in the stable (with funnel streams) or unstable (with random tongues) regime of accretion, and consequently have significantly different observational properties. A star may switch between these two regimes depending on the accretion rate.

  5. Patchy Accretion Disks in Ultraluminous X-ray Sources

    CERN Document Server

    Miller, J M; Barret, D; Harrison, F A; Fabian, A C; Webb, N A; Walton, D J; Rana, V

    2014-01-01

    The X-ray spectra of the most extreme ultra-luminous X-ray sources -- those with L > 1 E+40 erg/s -- remain something of a mystery. Spectral roll-over in the 5-10 keV band was originally detected in in the deepest XMM-Newton observations of the brightest sources; this is confirmed in subsequent NuSTAR spectra. This emission can be modeled via Comptonization, but with low electron temperatures (kT_e ~ 2 keV) and high optical depths (tau ~ 10) that pose numerous difficulties. Moreover, evidence of cooler thermal emission that can be fit with thin disk models persists, even in fits to joint XMM-Newton and NuSTAR observations. Using NGC 1313 X-1 as a test case, we show that a patchy disk with a multiple temperature profile may provide an excellent description of such spectra. In principle, a number of patches within a cool disk might emit over a range of temperatures, but the data only require a two-temperature profile plus standard Comptonization, or three distinct blackbody components. A mechanism such as the p...

  6. BIPOLAR JETS LAUNCHED FROM MAGNETICALLY DIFFUSIVE ACCRETION DISKS. I. EJECTION EFFICIENCY VERSUS FIELD STRENGTH AND DIFFUSIVITY

    Energy Technology Data Exchange (ETDEWEB)

    Sheikhnezami, Somayeh; Fendt, Christian; Porth, Oliver; Vaidya, Bhargav [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); Ghanbari, Jamshid, E-mail: nezami@mpia.de, E-mail: fendt@mpia.de [Department of Physics, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of)

    2012-09-20

    We investigate the launching of jets and outflows from magnetically diffusive accretion disks. Using the PLUTO code, we solve the time-dependent resistive magnetohydrodynamic equations taking into account the disk and jet evolution simultaneously. The main question we address is which kind of disks launch jets and which kind of disks do not? In particular, we study how the magnitude and distribution of the (turbulent) magnetic diffusivity affect mass loading and jet acceleration. We apply a turbulent magnetic diffusivity based on {alpha}-prescription, but also investigate examples where the scale height of diffusivity is larger than that of the disk gas pressure. We further investigate how the ejection efficiency is governed by the magnetic field strength. Our simulations last for up to 5000 dynamical timescales corresponding to 900 orbital periods of the inner disk. As a general result, we observe a continuous and robust outflow launched from the inner part of the disk, expanding into a collimated jet of superfast-magnetosonic speed. For long timescales, the disk's internal dynamics change, as due to outflow ejection and disk accretion the disk mass decreases. For magnetocentrifugally driven jets, we find that for (1) less diffusive disks, (2) a stronger magnetic field, (3) a low poloidal diffusivity, or (4) a lower numerical diffusivity (resolution), the mass loading of the outflow is increased-resulting in more powerful jets with high-mass flux. For weak magnetization, the (weak) outflow is driven by the magnetic pressure gradient. We consider in detail the advection and diffusion of magnetic flux within the disk and we find that the disk and outflow magnetization may substantially change in time. This may have severe impact on the launching and formation process-an initially highly magnetized disk may evolve into a disk of weak magnetization which cannot drive strong outflows. We further investigate the jet asymptotic velocity and the jet rotational

  7. Accretion of the Moon from non-canonical disks

    CERN Document Server

    Salmon, Julien

    2014-01-01

    Impacts that leave the Earth-Moon system with a large excess in angular momentum have recently been advocated as a means of generating a protolunar disc with a composition that is nearly identical to that of the Earth's mantle. We here investigate the accretion of the Moon from discs generated by such "non-canonical" impacts, which are typically more compact than discs produced by canonical impacts and have a higher fraction of their mass initially located inside the Roche limit. Our model predicts a similar overall accretional history for both canonical and non-canonical discs, with the Moon forming in three consecutive steps over hundreds of years. However, we find that, to yield a lunar-mass Moon, the more compact non-canonical discs must initially be more massive than implied by prior estimates, and only a few of the discs produced by impact simulations to date appear to meet this condition. Non-canonical impacts require that capture of the Moon into the evection resonance with the Sun reduced the Earth-M...

  8. Accretion disk dynamics: {\\alpha}-viscosity in self-similar self-gravitating models

    CERN Document Server

    Kubsch, Marcus; Duschl, W J

    2016-01-01

    Aims: We investigate the suitability of {\\alpha}-viscosity in self-similar models for self-gravitating disks with a focus on active galactic nuclei (AGN) disks. Methods: We use a self-similar approach to simplify the partial differential equations arising from the evolution equation, which are then solved using numerical standard procedures. Results: We find a self-similar solution for the dynamical evolution of self-gravitating {\\alpha}-disks and derive the significant quantities. In the Keplerian part of the disk our model is consistent with standard stationary {\\alpha}-disk theory, and self-consistent throughout the self-gravitating regime. Positive accretion rates throughout the disk demand a high degree of self-gravitation. Combined with the temporal decline of the accretion rate and its low amount, the model prohibits the growth of large central masses. Conclusions: {\\alpha}-viscosity cannot account for the evolution of the whole mass spectrum of super-massive black holes (SMBH) in AGN. However, conside...

  9. Resonance oscillation of radiative shock waves in accretion disks around compact objects

    CERN Document Server

    Molteni, D; Chakrabarti, S K; Molteni, Diego M; Chakrabarti, Sandip K

    1995-01-01

    We extend our previous numerical simulation of accretion disks with shock waves when cooling effects are also included. We consider bremsstrahlung and other power law processes: \\Lambda \\propto T^{\\alpha} \\rho^2 to mimic cooling in our simulation. We employ {\\it Smoothed Particle Hydrodynamics} technique as in the past. We observe that for a given angular momentum of the flow, the shock wave undergoes a steady, radial oscillation with the period is roughly equal to the cooling time. Oscillations seem to take place when the disk and cooling parameters (i.e., accretion rate, cooling process) are such that the infall time from shock is of the same order as the post-shock cooling time. The amplitude of oscillation could be up to ten percent of the distance of the shock wave from the black hole when the black hole is accreting. When the accretion is impossible due to the centrifugal barrier, the amplitude variation could be much larger. Due to the oscillation, the energy output from the disk is also seen to vary q...

  10. The evolution of a binary in a retrograde circular orbit embedded in an accretion disk

    CERN Document Server

    Ivanov, P B; Paardekooper, S -J; Polnarev, A G

    2014-01-01

    Supermassive black hole binaries may form as a consequence of galaxy mergers. Both prograde and retrograde orbits have been proposed. We study a binary of a small mass ratio, q, in a retrograde orbit immersed in and interacting with a gaseous accretion disk in order to estimate time scales for inward migration leading to coalescence and the accretion rate to the secondary component. We employ both semi-analytic methods and two dimensional numerical simulations, focusing on the case where the binary mass ratio is small but large enough to significantly perturb the disk. We develop the theory of type I migration for this case and determine conditions for gap formation finding that then inward migration occurs on a time scale equal to the time required for one half of the secondary mass to be accreted through the unperturbed disk, with accretion onto the secondary playing only a minor role. The semi-analytic and fully numerical approaches are in good agreement, the former being applicable over long time scales. ...

  11. Supersonic turbulence, filamentary accretion,and the rapid assembly of massive stars and disks

    CERN Document Server

    Banerjee, R; Anderson, D W; Banerjee, Robi; Pudritz, Ralph E.; Anderson, Dave W.

    2006-01-01

    We present a detailed computational study of the assembly of protostellar disks and massive stars in molecular clouds with supersonic turbulence. We follow the evolution of large scale filamentary structures in a cluster-forming clump down to protostellar length scales by means of very highly resolved, 3D adaptive mesh refined (AMR) simulations, and show how accretion disks and massive stars form in such environments. We find that an initially elongated cloud core which has a slight spin from oblique shocks collapses first to a filament and later develops a turbulent disk close to the center of the filament. The continued large scale flow that shocks with the filament maintains the high density and pressure within it. Material within the cooling filament undergoes gravitational collapse and an outside-in assembly of a massive protostar. Our simulations show that very high mass accretion rates of up to 10^-2 Msol/yr and high, supersonic, infall velocities result from such filamentary accretion. Accretion at th...

  12. Vertical Convection in Turbulent Accretion Disks and Light Curves of the A0620-00 1975 Outburst

    CERN Document Server

    Malanchev, Konstantin

    2015-01-01

    We present a model of the non-stationary $\\alpha$-disk with account for the irradiation and the vertical convection in the outer accretion disk where hydrogen is partially ionized. We include the viscous energy generation in the mix-length convection equations in accretion disks. The optical and X-ray light curves of X-ray nova A0620-00 are investigated in terms of this model. The turbulent viscosity parameter of the accretion disk is estimated, $\\alpha = 0.5 \\div 0.6$, which is necessary to explain the luminosity decay rate on the descending branch of the X-ray light curve for the A0620-00 1975 outburst. The secondary luminosity maximum on the light curves is explained by assuming an additional injection of matter into the accretion disk from the optical companion.

  13. Radiation Hydrodynamic Simulations of Line-Driven Disk Winds for Ultra Fast Outflows

    CERN Document Server

    Nomura, Mariko; Takahashi, Hiroyuki R; Wada, Keiichi; Yoshida, Tessei

    2015-01-01

    Using two-dimensional radiation hydrodynamic simulations, we investigate origin of the ultra fast outflows (UFOs) that are often observed in luminous active galactic nuclei (AGNs). We found that the radiation force due to the spectral lines generates strong winds (line-driven disk winds) that are launched from the inner region of accretion disks (~30 Schwarzschild radii). A wide range of black hole masses ($M_{\\rm BH}$) and Eddington ratios ($\\varepsilon$) was investigated to study conditions for causing the line-driven winds. For $M_{\\rm BH} = 10^6-10^9 M_\\odot$ and $\\varepsilon = 0.1-0.7$, funnel-shaped disk winds appear, in which dense matter is accelerated outward with an opening angle of 70-80 deg and with 10% of the light speed. If we observe the wind along its direction, the velocity, the column density, and the ionization state are consistent with those of the observed UFOs. As long as the obscuration by the torus does not affect the observations of X-ray bands, the UFOs could be statistically observe...

  14. Shrinking Galaxy Disks with Fountain-Driven Accretion from the Halo

    CERN Document Server

    Elmegreen, Bruce G; Hunter, Deidre A

    2014-01-01

    Star formation in most galaxies requires cosmic gas accretion because the gas consumption time is short compared to the Hubble time. This accretion presumably comes from a combination of infalling satellite debris, cold flows, and condensation of hot halo gas at the cool disk interface, perhaps aided by a galactic fountain. In general, the accretion will have a different specific angular momentum than the part of the disk that receives it, even if the gas comes from the nearby halo. Then the gas disk expands or shrinks over time. Here we show that condensation of halo gas at a rate proportional to the star formation rate in the fountain model will preserve an initial shape, such as an exponential, with a shrinking scale length, leaving behind a stellar disk with a slightly steeper profile of younger stars near the center. This process is slow for most galaxies, producing imperceptible radial speeds, and it may be dominated by other torques, but it could be important for Blue Compact Dwarfs, which tend to have...

  15. Outflows from accretion disks formed in neutron star mergers: effect of black hole spin

    CERN Document Server

    Fernández, Rodrigo; Metzger, Brian D; Quataert, Eliot

    2014-01-01

    The accretion disk that forms after a neutron star merger is a source of neutron-rich ejecta. The ejected material contributes to a radioactively-powered electromagnetic transient, with properties that depend sensitively on the composition of the outflow. Here we investigate how the spin of the black hole remnant influences mass ejection on the thermal and viscous timescales. To this end, we carry out two-dimensional, time-dependent hydrodynamic simulations of merger remnant accretion disks including viscous angular momentum transport and approximate neutrino self-irradiation. The gravity of the spinning black hole is included via a pseudo-Newtonian potential. We find that a disk around a spinning black hole ejects more mass, up to a factor of several, relative to the non-spinning case. The enhanced mass loss is due to energy release by accretion occurring deeper in the gravitational potential, raising the disk temperature and hence the rate of viscous heating in regions where neutrino cooling is ineffective....

  16. Accretion disk signatures in Type I X-ray Bursts: prospects for future missions

    CERN Document Server

    Keek, L; Ballantyne, D R

    2016-01-01

    Type I X-ray bursts and superbursts from accreting neutron stars illuminate the accretion disk and produce a reflection signal that evolves as the burst fades. Examining the evolution of reflection features in the spectra will give insight into the burst-disk interaction, a potentially powerful probe of accretion disk physics. At present, reflection has been observed during only two bursts of exceptional duration. We investigate the detectability of reflection signatures with four of the latest well-studied X-ray observatory concepts: Hitomi, NICER, Athena, and LOFT. Burst spectra are modeled for different values for the flux, temperature, and the disk ionization parameter, which are representative for most known bursts and sources. The effective area and through-put of a Hitomi-like telescope are insufficient for characterizing burst reflection features. NICER and Athena will detect reflection signatures in Type I bursts with peak fluxes $\\ge 10^{-7.5}$ erg cm$^{-2}$ s$^{-1}$, and also effectively constrain ...

  17. Light Curves from an MHD Simulation of a Black Hole Accretion Disk

    Science.gov (United States)

    Schnittman, Jeremy D.; Krolik, Julian H.; Hawley, John F.

    2006-11-01

    We use a relativistic ray-tracing code to calculate the light curves observed from a global, general relativistic, magnetohydrodynamic simulation of an accretion flow onto a Schwarzschild black hole. We apply three basic emission models to sample different properties of the time-dependent accretion disk. With one of these models, which assumes thermal blackbody emission and free-free absorption, we can predict qualitative features of the high-frequency power spectrum from stellar-mass black holes in the ``thermal dominant'' state. The simulated power spectrum is characterized by a power law of index Γ~3 and total rms fractional variance of ~1% near the orbital frequency at the innermost stable orbit. Initial results indicate the existence of transient QPO peaks with frequency ratios of nearly 2:3 at a 99.9% confidence limit, but they are not generic features, because at any given time they are seen only from certain observer directions. In addition, we present detailed analysis of the azimuthal structure of the accretion disk and the evolution of density perturbations in the inner disk. These ``hot-spot'' structures appear to be roughly self-similar over a range of disk radii, with a single characteristic size δφ=25deg and δr/r=0.3, and typical lifetimes Tl~0.3Torb.

  18. Binary Black Holes, Accretion Disks and Relativistic Jets: Photocenters of Nearby AGN and Quasars

    Science.gov (United States)

    Wehrle, Ann E.; Jones, Dayton L.; Meier, David L.; Piner, B. Glenn; Unwin, Stephen C.

    2004-01-01

    One of the most challenging questions in astronomy today is to understand the origin, structure, and evolution of the central engines in the nuclei of quasars and active galaxies (AGNs). The favoured theory involves the activation of relativistic jets from the fueling of a supermassive black hole through an accretion disk. In some AGN an outer optically thick, dusty torus is seen orbiting the black hole system. This torus is probably related to an inner accretion disk - black hole system that forms the actual powerhouse of the AGN. In radio-loud AGN two oppositely-directed radio jets are ejected perpendicular to the torus/disk system. Although there is a wealth of observational data on AGN, some very basic questions have not been definitively answered. The Space Interferometry Mission (SIM) will address the following three key questions about AGN. 1) Does the most compact optical emission from an AGN come from an accretion disk or from a relativistic jet? 2) Does the separation of the radio core and optical photocenter of the quasars used for the reference frame tie, change on the timescales of their photometric variability, or is the separation stable at the level of a few microarcseconds? 3) Do the cores of galaxies harbor binary supermassive black holes remaining from galaxy mergers? It is not known whether such mergers are common, and whether binaries would persist for a significant time.

  19. Kilonova Light Curves from the Disk Wind Outflows of Compact Object Mergers

    CERN Document Server

    Kasen, Daniel; Metzger, Brian

    2014-01-01

    We study the radioactively-powered transients produced by accretion disk winds following a compact object merger. Starting with the outflows generated in two-dimensional hydrodynamical disk models, we use wavelength-dependent radiative transfer calculations to generate synthetic light curves and spectra. We show that the brightness and color of the resulting kilonova transients carry information about the merger physics. In the regions of the wind where neutrino irradiation raises the electron fraction to Ye > 0.25, r-process nucleosynthesis halts before producing high-opacity, complex ions (the lanthanides). The kilonova light curves thus show two distinct components: a brief (~2 day) blue optical transient produced in the outer lanthanide-free ejecta, and a longer (~10 day) infrared transient produced in the inner, lanthanide line-blanketed region. Mergers producing a longer-lived neutron star, or a more rapidly spinning black hole, have stronger neutrino irradiation, generate more lanthanide-free ejecta, a...

  20. On the virialization of disk winds: Implications for the black hole mass estimates in active galactic nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Kashi, Amit; Proga, Daniel; Nagamine, Kentaro [Department of Physics and Astronomy, University of Nevada, Las Vegas, 4505 South Maryland Parkway, Las Vegas, NV 89154-4002 (United States); Greene, Jenny [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Barth, Aaron J., E-mail: kashia@physics.unlv.edu [Department of Physics and Astronomy, University of California, Irvine, Irvine, CA 92697 (United States)

    2013-11-20

    Estimating the mass of a supermassive black hole in an active galactic nucleus usually relies on the assumption that the broad line region (BLR) is virialized. However, this assumption seems to be invalid in BLR models that consist of an accretion disk and its wind. The disk is likely Keplerian and therefore virialized. However, beyond a certain point, the wind material must be dominated by an outward force that is stronger than gravity. Here, we analyze hydrodynamic simulations of four different disk winds: an isothermal wind, a thermal wind from an X-ray-heated disk, and two line-driven winds, one with and the other without X-ray heating and cooling. For each model, we determine whether gravity governs the flow properties by computing and analyzing the volume-integrated quantities that appear in the virial theorem: internal, kinetic, and gravitational energies. We find that in the first two models, the winds are non-virialized, whereas the two line-driven disk winds are virialized up to a relatively large distance. The line-driven winds are virialized because they accelerate slowly so that the rotational velocity is dominant and the wind base is very dense. For the two virialized winds, the so-called projected virial factor scales with inclination angle as 1/sin {sup 2} i. Finally, we demonstrate that an outflow from a Keplerian disk becomes unvirialized more slowly when it conserves the gas specific angular momentum, as in the models considered here, than when it conserves the angular velocity, as in the so-called magneto-centrifugal winds.

  1. Annihilation luminosity of a neutrino-cooled accretion disk in a gamma-ray burst

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    We discuss how the annihilation luminosity of a neutrino-cooled accretion disk in a gamma-ray burst, Lνν, is determined by the disk’s fundamental parameters, namely, the mass of the central black hole M, the mass accretion rate M, and the viscosity parameter α. It is shown that Lνν depends mainly on M in evidence, and decreases with increasing M, but is almost independent of α. This result argues additionally that the central black hole in a gamma-ray burst must be with a stellar mass.

  2. Time-Variable Accretion in the TW Hya Star/Disk System

    CERN Document Server

    Eisner, J A; Najita, J R; McCarthy, D; Kulesa, C; Swift, B J; Teske, J

    2010-01-01

    We present two epochs of observations of TW Hya from the high-dispersion near-IR spectrograph ARIES at the MMT. We detect strong emission from the Brackett gamma transition of hydrogen, indicating an accretion rate substantially larger than previously estimated using hydrogen line emission. The Brackett gamma line-strength varies across our two observed epochs. We also measure circumstellar-to-stellar flux ratios (i.e., veilings) that appear close to zero in both epochs. These findings suggest that TW Hya experiences episodes of enhanced accretion while the inner disk remains largely devoid of dust. We discuss several physical mechanisms that may explain these observations.

  3. Perspectives for the study of gas in protoplanetary disks and accretion/ejection phenomena in young stars with the near-IR spectrograph SPIROU at the CFHT

    Science.gov (United States)

    Carmona, A.; Bouvier, J.; Delfosse, X.

    2013-11-01

    Near-IR atomic and molecular transitions are powerful tools to trace the warm and hot gas in the circumstellar environment of young stars. Ro-vibrational transitions of H_2 and H_2O, and overtone transitions of CO at 2 μm centered at the stellar velocity trace hot (T˜ 1500 K) gas in the inner few AU of protoplanetary disks. H_2 near-IR lines displaying a blueshift of a few km/s probe molecular disk winds. H_2 lines presenting blueshifts of hundreds of km/s reveal hot shocked gas in jets. Atomic lines such as the HeI line at 10830 Å and the Hydrogen Paschen β and Brakett γ lines trace emission from accretion funnel flows and atomic disk winds. Bright forbidden atomic lines in the near-IR of species such as [Fe II], [N I], [S I], [S II], and [C I] trace atomic and ionized material in jets. The new near-IR high resolution spectrograph SPIROU planned for the Canada France Hawaii Telescope will offer the unique capability of combining high-spectral resolution (R˜75000) with a large wavelength coverage (0.98 to 2.35 μm) in one single exposure. This will provide us with the means of probing accretion funnel flows, winds, jets, and hot gas in the inner disk simultaneously. This opens the exiting possibility of investigating their combined behavior in time by the means of monitoring observations and systematic surveys. SPIROU will be a powerful tool to progress our understanding of the connexion between the accretion/ejection process, disk evolution, and planet formation.

  4. Accretion Disks around Black Holes: Dynamical Evolution, Meridional Circulations, and Gamma-Ray Bursts

    Science.gov (United States)

    Lee, William H.; Ramirez-Ruiz, Enrico

    2002-10-01

    We study the hydrodynamic evolution of massive accretion disks around black holes, formed when a neutron star is disrupted by a black hole in a binary system. The initial conditions are taken from three-dimensional calculations of coalescing binaries. By assuming azimuthal symmetry we are able to follow the time dependence of the disk structure for 0.2 s in cylindrical coordinates (r,z). We use an ideal gas equation of state and assume that all the dissipated energy is radiated away. The disks evolve because of viscous stresses, modeled with an α law. We study the disk structure and, in particular, the strong meridional circulations that are established and persist throughout our calculations. These consist of strong outflows along the equatorial plane that reverse direction close to the surface of the disk and converge on the accretor. In the context of gamma-ray bursts (GRBs), we estimate the energy released from the system in neutrinos and through magnetic-dominated mechanisms and find it can be as high as Eν~1052 ergs and EBZ~1051 ergs, respectively, during an estimated accretion timescale of 0.1-0.2 s. The νν annihilation is likely to produce bursts from only a short, impulsive energy input Lνν~t-5/2 and so would be unable to account for a large fraction of bursts that show complicated light curves. On the other hand, a gas mass ~0.1-0.25 Msolar survives in the orbiting debris, which enables strong magnetic fields ~1016 G to be anchored in the dense matter long enough to power short duration GRBs. We highlight the effects that the initial disk and black holes masses, viscosity, and binary mass ratio have on the evolution of the disk structure. Finally, we investigate the continuous energy injection that arises as the black hole slowly swallows the rest of the disk and discuss its consequences on the GRB afterglow emission.

  5. Evidence for a correlation between mass accretion rates onto young stars and the mass of their protoplanetary disks

    CERN Document Server

    Manara, C F; Testi, L; Natta, A; Alcalá, J M; Williams, J P; Ansdell, M; Miotello, A; van der Marel, N; Tazzari, M; Carpenter, J; Guidi, G; Mathews, G S; Oliveira, I; Prusti, T; van Dishoeck, E F

    2016-01-01

    A relation between the mass accretion rate onto the central young star and the mass of the surrounding protoplanetary disk has long been theoretically predicted and observationally sought. For the first time, we have accurately and homogeneously determined the photospheric parameters, the mass accretion rate, and the disk mass for an essentially complete sample of young stars with disks in the Lupus clouds. Our work combines the results of surveys conducted with VLT/X-Shooter and ALMA. With this dataset we are able to test a basic prediction of viscous accretion theory, the existence of a linear relation between the mass accretion rate onto the central star and the total disk mass. We find a correlation between the mass accretion rate and the disk dust mass, with a ratio that is roughly consistent with the expected viscous timescale when assuming an ISM gas-to-dust ratio. This confirms that mass accretion rates are related to the properties of the outer disk. We find no correlation between mass accretion rate...

  6. Spectral properties of accretion disks around galactic and extragalactic black holes

    CERN Document Server

    Chakrabarti, S K; Chakrabarti, Sandip K

    1995-01-01

    We study the spectral properties of a very general class of accretion disks which can be decomposed into three distinct components apart from a shock at r=r_s: (1) An optically thick Keplerian disk on the equatorial plane (r>r_s), (2) A sub-Keplerian optically thin halo above and below this Keplerian disk r>r_s and (3) A hot, optically slim, \\tau\\sim 1 postshock region rdisk. We produce radiated spectra from both the disk components as functions of the accretion rates and compare them with the spectra of galactic ...

  7. Vertical dissipation profiles and the photosphere location in thin and slim accretion disks

    CERN Document Server

    Sadovskii, A; Bursa, M; Kluzniak, W; Rozanska, A

    2009-01-01

    We calculate optically thick but geometrically thin (and slim) accretion disk models and perform a ray-tracing of photons (in the Kerr geometry) to calculate the observed disk spectra. Previously, it was a common practice to ray-trace photons assuming that they are emitted from the Kerr geometry equatorial plane, z = 0. We show that the spectra calculated with this assumption differ from these calculated under the assumption that photons are emitted from the actual surface of the disc, z = H(r). This implies that a knowledge of the location of the thin disks effective photosphere is relevant for calculating the spectra. In this paper we investigate, in terms of a simple toy model, a possible influence of the (unknown, and therefore ad hoc assumed) vertical dissipation profiles on the vertical structure of the disk and thus on the location of the effective photosphere, and on the observed spectra. For disks with moderate and high mass accretion rates (\\dot m>0.01\\dot m_C) we find that the photosphere location ...

  8. Accretion disk assembly and survival during the disruption of a neutron star by a black hole

    CERN Document Server

    Ramirez-Ruiz, E; Ramirez-Ruiz, Enrico; Lee, William H.

    2003-01-01

    We study the formation of accretion disks resulting from dynamical three dimensional binary coalescence calculations, where a neutron star is tidally disrupted before being swallowed by its black hole companion. By subsequently assuming azimuthal symmetry we are able to follow the time dependence of the disk structure for a few tenths of a second. Although the disruption of a neutron star leads to a situation where violent instabilities redistribute mass and angular momentum within a few dynamical timescales, enough gas mass remains in the orbiting debris to catalyse the extraction of energy from the hole at a rate adequate to power a short-lived gamma ray burst.

  9. 2.5-dimensional solution of the advective accretion disk:a self-similar approach

    Institute of Scientific and Technical Information of China (English)

    Shubhrangshu Ghosh; Banibrata Mukhopadhyay

    2009-01-01

    We provide a 2.5-dimensional solution to a complete set of viscous hydrodynamical equations describing accretion-induced outflows and plausible jets around black holes/compact objects. We prescribe a self-consistent advective disk-outflow coupling model, which explicitly includes the information of vertical flux. Inter-connecting dynamics of an inflow-outflow system essentially upholds the conservation laws. We provide a set of analytical family of solutions through a self-similar approach. The flow parameters of the disk-outflow system depend strongly on the viscosity parameter α and the cooling factor f.

  10. Line-driven Disk Winds in Active Galactic Nuclei: The Critical Importance of Ionization and Radiative Transfer

    CERN Document Server

    Higginbottom, Nick; Knigge, Christian; Long, Knox S; Matthews, James H; Sim, Stuart A

    2014-01-01

    Accretion disk winds are thought to produce many of the characteristic features seen in the spectra of active galactic nuclei (AGN) and quasi-stellar objects (QSOs). These outflows also represent a natural form of feedback between the central supermassive black hole and its host galaxy. The mechanism for driving this mass loss remains unknown, although radiation pressure mediated by spectral lines is a leading candidate. Here, we calculate the ionization state of, and emergent spectra for, the hydrodynamic simulation of a line-driven disk wind previously presented by Proga & Kallman (2004). To achieve this, we carry out a comprehensive Monte Carlo simulation of the radiative transfer through, and energy exchange within, the predicted outflow. We find that the wind is much more ionized than originally estimated. This is because it is much more difficult to shield any wind regions effectively when the outflow itself is allowed to reprocess and redirect ionizing photons. As a result, the wind no longer produ...

  11. Observational Limits on the Spin-down Torque of Accretion Powered Stellar Winds

    Science.gov (United States)

    Zanni, Claudio; Ferreira, Jonathan

    2011-01-01

    The rotation period of classical T Tauri stars (CTTS) represents a longstanding puzzle. While young low-mass stars show a wide range of rotation periods, many CTTS are slow rotators, spinning at a small fraction of breakup, and their rotation period does not seem to shorten, despite the fact that they are actively accreting and contracting. Matt & Pudritz proposed that the spin-down torque of a stellar wind powered by a fraction of the accretion energy would be strong enough to balance the spin-up torque due to accretion. Since this model establishes a direct relation between accretion and ejection, the observable stellar parameters (mass, radius, rotation period, magnetic field) and the accretion diagnostics (accretion shock luminosity) can be used to constrain the wind characteristics. In particular, since the accretion energy powers both the stellar wind and the shock emission, we show in this Letter how the accretion shock luminosity L UV can provide upper limits to the spin-down efficiency of the stellar wind. It is found that luminous sources with L UV >= 0.1 L sun and typical dipolar field components UV Lt 0.1 L sun) are compatible with a zero-torque condition, but the corresponding stellar winds are still very demanding in terms of mass and energy flux. We therefore conclude that accretion powered stellar winds are unlikely to be the sole mechanism to provide an efficient spin-down torque for accreting CTTS.

  12. Large-scale dynamo of accretion disks around supermassive nonrotating black holes

    Directory of Open Access Journals (Sweden)

    Poplavsky A.L.

    2006-01-01

    Full Text Available In this paper one presents an analytical model of accretion disk magnetosphere dynamics around supermassive nonrotating black holes in the centers of active galactic nuclei. Based on general relativistic equations of magneto hydrodynamics, the nonstationary solutions for time-dependent dynamo action in the accretion disks, spatial and temporal distribution of magnetic field are found. It is shown that there are two distinct stages of dynamo process: the transient and the steady-state regimes, the induction of magnetic field at t > 6:6665 x 1011GM/c3 s becomes stationary, magnetic field is located near the innermost stable circular orbit, and its value rises up to ~ 105 G. Applications of such systems with nonrotating black holes in real active galactic nuclei are discussed.

  13. Magnetorotational dynamo chimeras. The missing link to turbulent accretion disk dynamo models?

    CERN Document Server

    Riols, A; Cossu, C; Lesur, G; Ogilvie, G I; Longaretti, P-Y

    2016-01-01

    In Keplerian accretion disks, turbulence and magnetic fields may be jointly excited through a subcritical dynamo process involving the magnetorotational instability (MRI). High-resolution simulations exhibit a tendency towards statistical self-organization of MRI dynamo turbulence into large-scale cyclic dynamics. Understanding the physical origin of these structures, and whether they can be sustained and transport angular momentum efficiently in astrophysical conditions, represents a significant theoretical challenge. The discovery of simple periodic nonlinear MRI dynamo solutions has recently proven useful in this respect, and has notably served to highlight the role of turbulent magnetic diffusion in the seeming decay of the dynamics at low magnetic Prandtl number Pm (magnetic diffusivity larger than viscosity), a common regime in accretion disks. The connection between these simple structures and the statistical organization reported in turbulent simulations remained elusive, though. Here, we report the n...

  14. Optical polarimetry of PKS 2155 - 304 and constraints on accretion disk models for BL Lacertae objects

    Science.gov (United States)

    Smith, Paul S.; Sitko, Michael L.

    1991-01-01

    Optical broad-band polarimetry and photometry of the BL Lacertae object PKS 2155 - 304 during late 1990 are presented. Variability in both flux and linear polarization was moderate during this period. The optical polarization ranged from 2 to 7 percent while photometric variations were within 0.2 mag (V = 13.2-13.4). Accurate multicolor measurements were made to study any wavelength dependence of the polarization with an eye to using these data to test the model of Wandel and Urry (1991) which proposes that the UV to soft X-ray continuum of this object arises from an accretion disk. Wavelength-dependent polarization (WDP) is observed in PKS 2155 - 304. However, the polarization is always seen to decrease with wavelength when WDP is observed. This is opposite to the expected sense of WDP if the UV continuum is dominated by an accretion disk.

  15. Iron Opacity Bump Changes the Stability and Structure of Accretion Disks in Active Galactic Nuclei

    CERN Document Server

    Jiang, Yan-Fei; Stone, James

    2016-01-01

    Accretion disks around supermassive black holes have regions where the Rosseland mean opacity can be much larger than the electron scattering opacity primarily due to the large number of bound-bound transitions in iron. We study the effects of this iron opacity "bump" on the thermal stability and vertical structure of radiation pressure dominated accretion disks, utilizing three dimensional radiation magneto-hydrodynamic simulations in the local shearing box approximation. The simulations self-consistently calculate the heating due to MHD turbulence caused by magneto-rotational instability and radiative cooling by using the radiative transfer module based on a variable Eddington tensor in Athena. For a $5\\times 10^8$ solar mass black hole with $\\sim 3\\%$ of the Eddington luminosity, a model including the iron opacity bump maintains its structure for more than $10$ thermal times without showing significant signs of thermal runaway. In contrast, if only electron scattering and free-free opacity are included as ...

  16. Quasi-periodic variability and the inner radii of thin accretion disks in galactic black-hole systems

    CERN Document Server

    Matteo, T D; Matteo, Tiziana Di; Psaltis, Dimitrios

    1999-01-01

    We calculate upper bounds on the inner radii of geometrically thin accretion disks in galactic black-hole systems by relating their rapid variability properties to those of neutron stars. We infer that the inner disk radii do not exhibit large excursions between different spectral states, in contrast with the concept that the disk retreats significantly during the soft-to-hard state transition. We find that, in the hard state, the accretion disks extend down to radii less than 6-25 GM/c^2 and discuss the implications of our results for models of black-hole X-ray spectra.

  17. Bipolar jets launched from magnetically diffusive accretion disks. I. Ejection efficiency vs field strength and diffusivity

    CERN Document Server

    Sheikhnezami, Somayeh; Porth, Oliver; Vaidya, Bhargav; Ghanbari, Jamshid

    2012-01-01

    We investigate the launching of jets and outflows from magnetically diffusive accretion disks. Using the PLUTO code we solve the time-dependent resistive MHD equations taking into account the disk and jet evolution simultaneously. The main question we address is which kind of disks do launch jets and which kind of disks do not? In particular, we study how the magnitude and distribution of the (turbulent) magnetic diffusivity affect mass loading and jet acceleration. We have applied a turbulent magnetic diffusivity based on \\alpha-prescription, but have also investigate examples where the scale height of diffusivity is larger than that of the disk gas pressure. We further investigate how the ejection efficiency is governed by the magnetic field strength. Our simulations last for up to 5000 dynamical time scales corresponding to 900 orbital periods of the inner disk. As a general result we observe a continuous and robust outflow launched from the inner part of the disk, expanding into a collimated jet of super ...

  18. NuSTAR AND SUZAKU OBSERVATIONS OF THE HARD STATE IN CYGNUS X-1: LOCATING THE INNER ACCRETION DISK

    Energy Technology Data Exchange (ETDEWEB)

    Parker, M. L.; Lohfink, A.; Fabian, A. C.; Alston, W. N.; Kara, E. [Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA (United Kingdom); Tomsick, J. A.; Boggs, S. E.; Craig, W. W. [Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720-7450 (United States); Miller, J. M. [Department of Astronomy, University of Michigan, 1085 South University Avenue, West Hall 311, Ann Arbor, MI 48109-1042 (United States); Yamaoka, K. [Solar-Terrestrial Environment Laboratory, Department of Particles and Astronomy, Nagoya University, Furocho, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan); Nowak, M.; Grinberg, V. [Massachusetts Institute of Technology, Kavli Institute for Astrophysics, Cambridge, MA 02139 (United States); Christensen, F. E. [Danish Technical University, DK-2800 Lyngby (Denmark); Fürst, F.; Grefenstette, B. W.; Harrison, F. A. [California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Gandhi, P. [School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ (United Kingdom); Hailey, C. J. [Columbia University, New York, NY 10027 (United States); King, A. L. [Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, CA 94305 (United States); Stern, D. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); and others

    2015-07-20

    We present simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR ) and Suzaku observations of the X-ray binary Cygnus X-1 in the hard state. This is the first time this state has been observed in Cyg X-1 with NuSTAR, which enables us to study the reflection and broadband spectra in unprecedented detail. We confirm that the iron line cannot be fit with a combination of narrow lines and absorption features, instead requiring a relativistically blurred profile in combination with a narrow line and absorption from the companion wind. We use the reflection models of García et al. to simultaneously measure the black hole spin, disk inner radius, and coronal height in a self-consistent manner. Detailed fits to the iron line profile indicate a high level of relativistic blurring, indicative of reflection from the inner accretion disk. We find a high spin, a small inner disk radius, and a low source height and rule out truncation to greater than three gravitational radii at the 3σ confidence level. In addition, we find that the line profile has not changed greatly in the switch from soft to hard states, and that the differences are consistent with changes in the underlying reflection spectrum rather than the relativistic blurring. We find that the blurring parameters are consistent when fitting either just the iron line or the entire broadband spectrum, which is well modeled with a Comptonized continuum plus reflection model.

  19. NuSTAR and Suzaku observations of the hard state in Cygnus X-1: locating the inner accretion disk

    CERN Document Server

    Parker, M L; Miller, J M; Yamaoka, K; Lohfink, A; Nowak, M; Fabian, A C; Alston, W N; Boggs, S E; Christensen, F E; Craig, W W; Fuerst, F; Gandhi, P; Grefenstette, B W; Grinberg, V; Hailey, C J; Harrison, F A; Kara, E; King, A L; Stern, D; Walton, D J; Wilms, J; Zhang, W W

    2015-01-01

    We present simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR ) and Suzaku observations of the X-ray binary Cygnus X-1 in the hard state. This is the first time this state has been observed in Cyg X-1 with NuSTAR, which enables us to study the reflection and broad-band spectra in unprecedented detail. We confirm that the iron line cannot be fit with a combination of narrow lines and absorption features, and instead requires a relativistically blurred profile in combination with a narrow line and absorption from the companion wind. We use the reflection models of Garcia et al. (2014) to simultaneously measure the black hole spin, disk inner radius, and coronal height in a self-consistent manner. Detailed fits to the iron line profile indicate a high level of relativistic blurring, indicative of reflection from the inner accretion disk. We find a high spin, a small inner disk radius, and a low source height, and rule out truncation to greater than three gravitational radii at the 3{\\sigma} confidence le...

  20. On the stream-accretion disk interaction - Response to increased mass transfer rate

    Science.gov (United States)

    Dgani, Ruth; Livio, Mario; Soker, Noam

    1989-01-01

    The time-dependent interaction between the stream of mass from the inner Lagrangian point and the accretion disk, resulting from an increasing mass transfer rate is calculated. The calculation is fully three-dimensional, using a pseudoparticle description of the hydrodynamics. It is demonstrated that the results of such calculations, when combined with specific observations, have the potential of both determining essential parameters, such as the viscosity parameter alpha, and can distinguish between different models of dwarf nova eruptions.

  1. HST/COS Observations of Ionized Gas Accretion at the Disk-halo Interface of M33

    CERN Document Server

    Zheng, Y; Werk, J K; Putman, M E

    2016-01-01

    We report the detection of accreting ionized gas at the disk-halo interface of the nearby galaxy M33. We analyze HST/COS absorption-line spectra of seven ultraviolet-bright stars evenly distributed across the disk of M33. We find Si IV absorption components consistently redshifted relative to the bulk M33's ISM absorption along all the sightlines. The Si IV detection indicates an enriched, disk-wide, ionized gas inflow toward the disk. This inflow is most likely multi-phase as the redshifted components can also be observed in ions with lower ionization states (e.g., S II, P II, Fe II, Si II). Kinematic modeling of the inflow is consistent with an accreting layer at the disk-halo interface of M33, which has an accretion velocity of 110$^{+15}_{-20}$ km s$^{-1}$ at a distance of 1.5$^{+1.0}_{-1.0}$ kiloparsec above the disk. The modeling indicates a total mass of $\\sim3.9\\times10^7$ M$_{\\odot}$ for the accreting material at the disk-halo interface on the near side of the M33 disk , with an accretion rate of $\\s...

  2. Numerical Simulations of Accretion Flows, Jets, and Winds Around Black Holes

    Science.gov (United States)

    Narayan, Ramesh

    Accretion flows around black holes in X-ray binaries, active galactic nuclei and gamma- ray bursts are highly relativistic. This is especially true of the inner regions of these flows where the accreting gas comes close to the black hole and from where relativistic jets are launched. Understanding the properties of black holes and the effects of their associated relativistic ejections on their environment is a central goal of NASA's Astrophysics Theory program. We propose to carry out three-dimensional time-dependent numerical simulations, as well as analytical studies, focusing on two main problems: quantitatively studying the feedback effects of winds and jets ejected from AGN accretion flows on their environment, and pinning down the validity of the standard model of thin black-hole accretion disks by Novikov & Thorne (1973, NT). The PI and his team possess general relativistic magnetohydrodynamics (GRMHD) codes which are uniquely suited for simulating fully relativistic highly magnetized flows. These codes will be used to perform the following tasks: (1) To study the validity of the NT model in the region inside the innermost stable circular orbit (ISCO). On the one hand, simulations for a range of black hole spin values will be performed, in order to find the errors in spin estimates, obtained using the NT model, of black holes in X-ray binaries. On the other hand, we will look for an improved disk model using our simulation results. (2) Large-dynamic-range simulations of advection-dominated accretion flows (ADAFs) for a range of black hole spin values, to understand (i) the mass, energy and momentum output of winds and jets, which is important for understanding feedback effects on galaxy formation, and cooling flows; (ii) the relative importance of feedback through a relativistic jet versus a non-relativistic wind; and (iii) the effect of ADAF disk winds on jet collimation. The proposed research will be done by postdoctoral fellow Dr. Akshay Kulkarni and

  3. Nucleosynthesis from neutrino-dominated accretion disks in gamma-ray bursts and its application

    Directory of Open Access Journals (Sweden)

    Liu Tong

    2014-03-01

    Full Text Available We investigate the element distribution in neutrino-dominated accretion flows around black holes with the proton-rich nuclear statistical equilibrium. According to our calculations, the radial nuclei distribution (around equatorial plane is dominated by free nucleons, 4He, and 56Fe in the inner, middle, and outer region, respectively. For the vertical distribution, the heavy nuclei tend to be produced in a thin region near the disk surface, in which we find that 56Ni is dominant for the flow with low accretion rate but it would switch to 56Fe for high accretion rate. Our results imply that 56Ni produced by central engine would tend to outflow and subsequently decay to drive the bumps observed in the light curves of the core collapse supernovae.

  4. Accretion disc atmospheres and winds in low-mass X-ray binaries

    CERN Document Server

    Trigo, M Díaz

    2015-01-01

    In the last decade, X-ray spectroscopy has enabled a wealth of discoveries of photoionised absorbers in X-ray binaries. Studies of such accretion disc atmospheres and winds are of fundamental importance to understand accretion processes and possible feedback mechanisms to the environment. In this work, we review the current observational state and theoretical understanding of accretion disc atmospheres and winds in low-mass X-ray binaries, focusing on the wind launching mechanisms and on the dependence on accretion state. We conclude with issues that deserve particular attention.

  5. Anisotropic illumination of AGN's accretion disk by a non thermal source; 1, General theory and application to the Newtonian geometry

    CERN Document Server

    Henri, G

    1997-01-01

    We present a model of accretion disk where the disk luminosity is entirely due to the reprocessing of hard radiation impinging on the disk. The hard radiation itself is emitted by a hot point source above the disk, that could be physically realized by a strong shock terminating an aborted jet. This hot source contains ultrarelativistic leptons scattering the disk soft photons by Inverse Compton (IC) process. Using a simple formula to describe the IC process in an anisotropic photon field, we derive a self-consistent angular distribution of soft and hard radiation in the Newtonian geometry. The radial profile of the disk effective temperature is also univoquely determined. The high energy spectrum can be calculated for a given lepton distribution. This offers an alternative picture to the standard accretion disk emission law. We discuss the application of this model to Active Galactic Nuclei, either for reproducing individual spectra, or for predicting new scaling laws that fit better the observed statistical ...

  6. Experimental study of snow accretion on overhead transmission lines using a wind tunnel and a high-speed camera

    Science.gov (United States)

    Yasui, Mitsuru; Kagami, Jun; Ando, Hitoshi; Hamada, Yutaka

    1995-05-01

    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 velocity under simulated conditions of natural snowing and strong winds.

  7. The multipolar magnetic fields of accreting pre-main-sequence stars: B at the inner disk, B along the accretion flow, and B at the accretion shock

    CERN Document Server

    Gregory, Scott G; Hussain, Gaitee A J

    2016-01-01

    Zeeman-Doppler imaging studies have revealed the complexity of the large-scale magnetic fields of accreting pre-main-sequence stars. All have multipolar magnetic fields with the octupole component being the dominant field mode for many of the stars studied thusfar. Young accreting stars with fully convective interiors often feature simple axisymmetric magnetic fields with dipole components of order a kilo-Gauss (at least those of mass $\\gtrsim0.5\\,{\\rm M}_\\odot$), while those with substantially radiative interiors host more complex non-axisymmetric magnetic fields with dipole components of order a few 0.1 kilo-Gauss. Here, via several simple examples, we demonstrate that i). in most cases, the dipole component alone can be used to estimate the disk truncation radius (but little else); ii) due the presence of higher order magnetic field components, the field strength in the accretion spots is far in excess of that expected if a pure dipole magnetic field is assumed. (Fields of $\\sim$6$\\,{\\rm kG}$ have been mea...

  8. Spectral eclipse mapping of the accretion disk in the nova-like variable UX Ursae Majoris

    Science.gov (United States)

    Rutten, R. G. M.; Dhillon, V. S.; Horne, K.; Kuulkers, E.

    1994-01-01

    We analyze narrow-band eclipse light curves of the nova-like cataclysmic variable UX UMa, obtained from low-resolution spectra spanning lambda lambda 3600-9800 A . The light curves for narrow bands in the continuum as well as those for individual spectral lines are treated independently, and are used to construct images of the accretion disk's brightness distribution using the maximum-entropy eclipse-mapping technique. Particular attention is paid to the propagation of statistical uncertainties in the data and to how the analysis may introduce systematic errors in the final result. From the many narrrow band images we have reconstructed the spectra from isolated parts of the accretion disk. These spectra reveal that the inner disk radiates a continuum spectrum which peaks in the near UV and has the hydrogen Balmer lines in absorption (with the exception of H-alpha), whereas the outer disk is much fainter, has a much redder spectrum, and has Balmer emission lines. Our analysis reveals the presence of an uneclipsed component of the total light, whose spectrum is very red and has Balmer lines in emission. This unexpected feature of the eclipse mapping technique offers a new tool for an independent assessment of the secondary star's spectrum in eclipsing cataclysmic variables.

  9. Generation of magnetic field on the accretion disk around a proto-first-star

    Energy Technology Data Exchange (ETDEWEB)

    Shiromoto, Yuki; Susa, Hajime [Department of Physics, Konan University, Kobe 658-8501 (Japan); Hosokawa, Takashi, E-mail: susa@konan-u.ac.jp [Department of Physics and Research Center for the Early Universe, The University of Tokyo, Tokyo 113-0033 (Japan)

    2014-02-20

    The generation process of a magnetic field around a proto-first-star is studied. Utilizing the recent numerical results of proto-first-star formation based on radiation hydrodynamics simulations, we assess the magnetic field strength generated by the radiative force and the Biermann battery effect. We find that a magnetic field of ∼10{sup –9} G is generated on the surface of the accretion disk around the proto-first-star. The field strength on the accretion disk is smaller by two orders of magnitude than the critical value, above which the gravitational fragmentation of the disk is suppressed. Thus, the generated seed magnetic field hardly affect the dynamics of on-site first star formation directly, unless an efficient amplification process is taken into consideration. We also find that the generated magnetic field is continuously blown out from the disk on the outflows to the poles, that are driven by the thermal pressure of photoheated gas. The strength of the diffused magnetic field in low-density regions is ∼10{sup –14}-10{sup –13} G at n {sub H} = 10{sup 3} cm{sup –3}, which could play an important role in the next generation star formation, as well as the seeds of the magnetic field in the present-day universe.

  10. Generation of Magnetic Field on the Accretion Disk around a Proto-First-Star

    CERN Document Server

    Shiromoto, Yuki; Hosokawa, Takashi

    2014-01-01

    The generation process of magnetic field around a proto-first-star is studied. Utilizing the recent numerical result of proto-first-star formation based upon the radiation hydrodynamics simulations, we assess the magnetic field strength generated by the radiative force and the Biermann battery effect. We find that magnetic field of \\sim 10^{-9} G is generated on the surface of the accretion disk around the proto-first-star. The field strength on the accretion disk is smaller by two orders of magnitude than the critical value, above which the gravitational fragmentation of the disk is suppressed. Thus, the generated seed magnetic field hardly affect the dynamics of on-site first star formation directly, unless efficient amplification process is taken into consideration. We also find that the generated magnetic field is continuously blown out from the disk on the outflows to the poles, that are driven by the thermal pressure of photoheated gas. The strength of the diffused magnetic field in low density regions ...

  11. The Structure of the Accretion Disk in the ADC X-Ray Binary 4U 1822-371 at Optical and Ultraviolet Wavelengths

    CERN Document Server

    Bayless, Amanda J; Hynes, Robert I; Ashcraft, Teresa A; Cornell, Mark E

    2009-01-01

    The eclipsing low-mass X-ray binary 4U 1822-371 is the prototypical accretion disk corona (ADC) system. We have obtained new time-resolved UV spectroscopy of 4U 1822-371 with the Advanced Camera for Surveys/Solar Blind Channel (ACS/SBC) on the Hubble Space Telescope (HST) and new V- and J-band photometry with the 1.3-m SMARTS telescope at CTIO. We use the new data to construct its UV/optical spectral energy distribution and its orbital light curve in the UV, V, and J bands. We derive an improved ephemeris for the optical eclipses and confirm that the orbital period is changing rapidly, indicating extremely high rates of mass flow in the system; and we show that the accretion disk in the system has a strong wind with projected velocities up to 4000 km/s. We show that the disk has a vertically-extended, optically-thick component at optical wavelengths.This component extends almost to the edge of the disk and has a height equal to ~0.5 of the disk radius. As it has a low brightness temperature, we identify it as...

  12. Probing the connection between the accretion disk, outflows and the jet in 3C111

    Science.gov (United States)

    Tombesi, Francesco

    2011-10-01

    Recent XMM-Newton and Suzaku observations of 3C111 demonstrated the presence of ultra-fast outflows (UFOs) with v~0.1c and their relation with the accretion disk. Independent studies found that X-ray dips are followed by ejection of superluminal radio knots, therefore providing a proof of the disk-jet connection. We acquired evidence that UFOs are preferentially present between X-ray dips and new knots, possibly indicating also a link between disk outflows and the jet. The goal of this XMM-Newton proposal is to confirm this evidence. Given the strong correlation with X-rays, we will use an ongoing optical monitoring campaign to trigger a 90ks observation within two days of a dip to detect a UFO and we request a possible additional 60ks >15 days after to compare with the non-dipped state.

  13. The Black-Hole Accretion Disk in NGC 4258: One of Nature's Most Beautiful Dynamical Systems

    Science.gov (United States)

    Moran, J. M.

    2008-08-01

    In this talk I will summarize some of the work that the CfA group has done to study the structure of the water masers in the accretion disk of NGC 4258. A series of 18 epochs of VLBA data taken from 1997.3 to 2000.8 were used for this study. The vertical distribution of maser features in the systemic group was found to be Gaussian, as expected for hydrostatic equilibrium, with a σ-width of 5.1 microarcsec (μas). If the disk is in hydrostatic equilibrium, its temperature is about 600 K. The systemic features exhibit a small, but persistent, gradient in acceleration versus impact parameter. This characteristic may indicate the presence of a spiral density wave rotating at sub-Keplerian speed. A more precise understanding of the dynamical properties of the disk is expected to lead to a more refined estimate of the distance to the galaxy.

  14. The Black Hole Accretion Disk in NGC 4258: One of Nature's Most Beautiful Dynamical Systems

    CERN Document Server

    Moran, James M

    2008-01-01

    In this talk I will summarize some of the work that the CfA group has done to study the structure of the water masers in the accretion disk of NGC 4258. A series of 18 epochs of VLBA data taken from 1997.3 to 2000.8 were used for this study. The vertical distribution of maser features in the systemic group was found to have a Gaussian distribution, as expected for hydrostatic equilibrium, with a $\\sigma$-width of 5.1 $\\mu$as. If the disk is in hydrostatic equilibrium, its temperature is about 600K. The systemic features exhibit a small, but persistent, gradient in acceleration versus impact parameter. This characteristic may indicate the presence of a spiral density wave rotating at sub-Keplerian speed. A more precise understanding of the dynamical properties of the disk is expected to lead to a more refined estimate of the distance to the galaxy.

  15. Relativistic X-ray Lines from the Inner Accretion Disks Around Black Holes

    CERN Document Server

    Miller, J M

    2007-01-01

    Relativistic X-ray emission lines from the inner accretion disk around black holes are reviewed. Recent observations with the Chandra X-ray Observatory, X-ray Multi-Mirror Mission-Newton, and Suzaku are revealing these lines to be good probes of strong gravitational effects. A number of important observational and theoretical developments are highlighted, including evidence of black hole spin and effects such as gravitational light bending, the detection of relativistic lines in stellar-mass black holes, and evidence of orbital-timescale line flux variability. In addition, the robustness of the relativistic disk lines against absorption, scattering, and continuum effects is discussed. Finally, prospects for improved measures of black hole spin and understanding the spin history of supermassive black holes in the context of black hole-galaxy co-evolution are presented. The best data and most rigorous results strongly suggest that relativistic X-ray disk lines can drive future explorations of General Relativiti...

  16. The low-mass stellar population in the young cluster Tr37: Disk evolution, accretion, and environment

    CERN Document Server

    Sicilia-Aguilar, Aurora; Sobolev, Andrej; Getman, Konstantin; Henning, Thomas; Fang, Min

    2013-01-01

    We present a study of accretion and protoplanetary disks around M-type stars in the 4 Myr-old cluster Tr37. With a well-studied solar-type population, Tr37 is a benchmark for disk evolution. We used low-resolution spectroscopy to identify 141 members (78 new) and 64 probable members, mostly M-type stars. H\\alpha\\ emission provides information about accretion. Optical, 2MASS, Spitzer, and WISE data are used to trace the SEDs. We construct radiative transfer models to explore the structures of full-disks, pre-transition, transition, and dust-depleted disks. Including the new and previously known members, we confirm that a substantial fraction (~2/5) of disks show signs of evolution, either as radial dust evolution (transition/pre-transition disks) or as a more global evolution (low small-dust masses, dust settling, and weak/absent accretion signatures). Accretion is strongly dependent on the SED type. About half of the transition objects are consistent with no accretion, and dust-depleted disks have weak (or un...

  17. Numerical relativity simulations of thick accretion disks around tilted Kerr black holes

    CERN Document Server

    Mewes, Vassilios; Galeazzi, Filippo; Montero, Pedro J; Stergioulas, Nikolaos

    2015-01-01

    In this work we present 3D numerical relativity simulations of thick accretion disks around {\\it tilted} Kerr black holes. We investigate the evolution of three different initial disk models with a range of initial black hole spin magnitudes and tilt angles. For all the disk-to-black hole mass ratios considered ($0.044-0.16$) we observe significant black hole precession and nutation during the evolution. This indicates that for such mass ratios, neglecting the self-gravity of the disks by evolving them in a fixed background black hole spacetime is not justified. We find that the two more massive models are unstable against the Papaloizou-Pringle (PP) instability and that those PP-unstable models remain unstable for all initial spins and tilt angles considered, showing that the development of the instability is a very robust feature of such PP-unstable disks. The tilt between the black hole spin and the disk is strongly modulated during the growth of the PP instability, causing a partial global realignment of ...

  18. Accretion-Powered Stellar Winds II: Numerical Solutions for Stellar Wind Torques

    CERN Document Server

    Matt, Sean

    2008-01-01

    [Abridged] In order to explain the slow rotation observed in a large fraction of accreting pre-main-sequence stars (CTTSs), we explore the role of stellar winds in torquing down the stars. For this mechanism to be effective, the stellar winds need to have relatively high outflow rates, and thus would likely be powered by the accretion process itself. Here, we use numerical magnetohydrodynamical simulations to compute detailed 2-dimensional (axisymmetric) stellar wind solutions, in order to determine the spin down torque on the star. We explore a range of parameters relevant for CTTSs, including variations in the stellar mass, radius, spin rate, surface magnetic field strength, the mass loss rate, and wind acceleration rate. We also consider both dipole and quadrupole magnetic field geometries. Our simulations indicate that the stellar wind torque is of sufficient magnitude to be important for spinning down a ``typical'' CTTS, for a mass loss rate of $\\sim 10^{-9} M_\\odot$ yr$^{-1}$. The winds are wide-angle, ...

  19. 1H 1752 + 081: an eclipsing cataclysmic variable with a small accretion disk

    Science.gov (United States)

    Silber, Andrew D.; Remillard, Ronald A.; Horne, Keith; Bradt, Hale V.

    1994-04-01

    We announce the discovery of an eclipsing nova-like cataclysmic variable (CV) as the optical counterpart to the HEAO 1 X-ray source 1H1752 + 081. This CV has an orbital period of 1.882801 hr, a high equivalent width of H-beta, and an average mv of 16.4 out of the eclipse. A geometric model is constructed from observations of the eclipse ingress and egress in many optical bandpasses. The broad-band emission originates primarily in two regions; the disk/accretion stream 'hot spot' and a compact central component, which may be a spot on the white dwarf surface, the entire white dwarf surface or the boundary layer between the accretion disk and the white dwarf surface. Based on the durations and offsets of the two eclipses we determined the mass ratio q = 2.5 +/- 0.6 and the angle of inclination i = 77 deg +/- 2 deg. If the central component is the entire white dwarf surface the masses of the stars are M1 = 0.80 +/- 0.06 solar masses and M2 = 0.32 +/- 0.06 solar masses. The disk is faint and small (RD = 0.25 +/- 0.05 rL1, where rL1 is the distance from the primary to the L1 point), compared to other eclipsing CVs. The small disk may result from the removal of angular momentum from the accretion disk by the magnetic field of the white dwarf; this CV may be a DQ Her type with a slowly rotating white dwarf. The emission-line velocities do not show the 'Z-wave' expected from the eclipse of a Keplerian accretion disk, nor do they have the correct phasing to originate near the white dwarf. The most likely origin of the line emission is the hot spot. The secondary star is visible at wavelengths greater than or equal to 6000 A during eclipse. We estimate a spectral type approximately M6 which, together with the observed m1 = 16.94 during eclipse, results in a distance estimate of 150 +/- 27 pc.

  20. Orbital circularization of a planet accreting disk gas: the formation of distant jupiters in circular orbits based on a core accretion model

    Energy Technology Data Exchange (ETDEWEB)

    Kikuchi, Akihiro; Higuchi, Arika [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551 (Japan); Ida, Shigeru, E-mail: kikuchi.a@geo.titech.ac.jp, E-mail: higuchia@geo.titech.ac.jp, E-mail: ida@elsi.jp [Earth-Life Science Institute, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8550 (Japan)

    2014-12-10

    Recently, gas giant planets in nearly circular orbits with large semimajor axes (a ∼ 30-1000 AU) have been detected by direct imaging. We have investigated orbital evolution in a formation scenario for such planets, based on a core accretion model. (1) Icy cores accrete from planetesimals at ≲ 30 AU, (2) they are scattered outward by an emerging nearby gas giant to acquire highly eccentric orbits, and (3) their orbits are circularized through the accretion of disk gas in outer regions, where they spend most of their time. We analytically derived equations to describe the orbital circularization through gas accretion. Numerical integrations of these equations show that the eccentricity decreases by a factor of more than 5 while the planetary mass increases by a factor of 10. Because runaway gas accretion increases planetary mass by ∼10-300, the orbits are sufficiently circularized. On the other hand, a is reduced at most only by a factor of two, leaving the planets in the outer regions. If the relative velocity damping by shock is considered, the circularization slows down, but is still efficient enough. Therefore, this scenario potentially accounts for the formation of observed distant jupiters in nearly circular orbits. If the apocenter distances of the scattered cores are larger than the disk sizes, their a shrink to a quarter of the disk sizes; the a-distribution of distant giants could reflect the outer edges of the disks in a similar way that those of hot jupiters may reflect inner edges.

  1. Accretion in Evolved and Transitional Disks in Cep OB2: Looking for the Origin of the Inner Holes

    CERN Document Server

    Sicilia-Aguilar, Aurora; Hartmann, Lee

    2010-01-01

    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 ~4 Myr-old cluster Tr 37 (including 20 "transition" objects; TO), as well as the only CTTS in the ~12 Myr-old cluster NGC 7160. The stars show different disk morphologies, with the majority of them having evolved and flattened disks. The typical accretion rates are about one order of magnitude lower than in regions aged 1-2 Myr, and we find no strong correlation between disk morphology and accretion rates. Although half of the TO are not accreting, the median accretion rates of normal CTTS and accreting "transition" disks are similar (~3 10^{-9} and 2 10^{-9} Msun/yr, respectively). Comparison with other regions suggests that the TO observed at different ages do not necessarily represent the same type of objects, which is consistent with the fact that the different processes that can lead to reduced IR excess/inner disk clearing (e.g., binarity, dust coag...

  2. High-Resolution Spectroscopy in Tr37: Gas Accretion Evolution in Evolved Dusty Disks

    CERN Document Server

    Sicilia-Aguilar, A; Furezs, G; Henning, T; Dullemond, C; Brandner, W; Sicilia-Aguilar, Aurora; Hartmann, Lee; Furezs, Gabor; Henning, Thomas; Dullemond, Cornelis; Brandner, Wolfgang

    2006-01-01

    Using the Hectochelle multifiber spectrograph, we have obtained high-resolution (R~34,000) spectra in the Halpha region for a large number of stars in the 4 Myr-old cluster Tr 37, containing 146 previously known members and 26 newly identified ones. We present the Halpha line profiles of all members, compare them to our IR observations of dusty disks (2MASS/JHK + IRAC + MIPS 24 micron), use the radial velocities as a membership criterion, and calculate the rotational velocities. We find a good correlation between the accretion-broadened profiles and the presence of protoplanetary disks, noting that a small fraction of the accreting stars presents broad profiles with Halpha equivalent widths smaller than the canonical limit separating CTTS and WTTS. The number of strong accretors appears to be lower than in younger regions, and a large number of CTTS have very small accretion rates (dM/dt<10^{-9} Msun/yr). Taking into account that the spectral energy distributions are consistent with dust evolution (grain g...

  3. High energy neutrinos produced in the accretion disks by neutrons from nuclei disintegrated in the AGN jets

    CERN Document Server

    Bednarek, W

    2016-01-01

    We investigate the consequences of acceleration of nuclei in jets of active galaxies not far from the surface of an accretion disk. The nuclei can be accelerated in the re-connection regions in the jet and/or at the jet boundary, between the relativistic jet and its cocoon. It is shown that the relativistic nuclei can efficiently fragment onto specific nucleons in collisions with the disk radiation. Neutrons, directed towards the accretion disk, take a significant part of energy from the relativistic nuclei. These neutrons develop a cascade in the dense accretion disk. We calculate the neutrino spectra produced in such hadronic cascade within the accretion disk. We propose that the neutrinos produced in such scenario from the whole population of super-massive black holes in active galaxies can explain the extragalactic neutrino background recently measured by the IceCube neutrino detector, provided that $5\\%$ fraction of galaxies is AGN and a few percent of neutrons reach the accretion disk. It is predicted t...

  4. High-Frequency QPOs and Overstable Oscillations of Black-Hole Accretion Disks

    CERN Document Server

    Lai, Dong; Tsang, David; Horak, Jiri; Yu, Cong

    2012-01-01

    The physical origin of high-frequency QPOs (HFQPOs) in black-hole X-ray binaries remains an enigma despite many years of detailed observational studies. Although there exists a number of models for HFQPOs, many of these are simply "notions" or "concepts" without actual calculation derived from fluid or disk physics. Future progress requires a combination of numerical simulations and semi-analytic studies to extract physical insights. We review recent works on global oscillation modes in black-hole accretion disks, and explain how, with the help of general relativistic effects, the energy stored in the disk differential rotation can be pumped into global spiral density modes in the disk, making these modes grow to large amplitudes under certain conditions ("corotational instability"). These modes are robust in the presence of disk magnetic fields and turbulence. The computed oscillation mode frequencies are largely consistent with the observed values for HFQPOs in BH X-ray binaries. The approximate 2:3 frequen...

  5. Simulations of the Poynting--Robertson Cosmic Battery in Resistive Accretion Disks

    CERN Document Server

    Christodoulou, Dimitris M; Kazanas, Demosthenes

    2007-01-01

    We describe the results of numerical "2.5--dimensional" MHD simulations of an initially unmagnetized disk model orbiting a central point--mass and responding to the continual generation of poloidal magnetic field due to a secular source that emulates the Poynting--Robertson (PR) drag on electrons in the vicinity of a luminous stellar or compact accreting object. The fluid in the disk and in the surrounding hotter atmosphere has finite electrical conductivity and allows for the magnetic field to diffuse freely out of the areas where it is generated, while at the same time, the differential rotation of the disk twists the poloidal field and quickly induces a substantial toroidal--field component. The secular PR term has dual purpose in these simulations as the source of the magnetic field and the trigger of a magnetorotational instability (MRI) in the disk. The MRI is especially mild and does not destroy the disk because a small amount of resistivity dampens the instability efficiently. In simulations with mode...

  6. Can self-organized critical accretion disks generate a log-normal emission variability in AGN?

    Science.gov (United States)

    Kunjaya, C.; Mahasena, P.; Vierdayanti, K.; Herlie, S.

    2011-12-01

    Active Galactic Nuclei (AGN), such as Seyfert galaxies, quasars, etc., show light variations in all wavelength bands, with various amplitude and in many time scales. The variations usually look erratic, not periodic nor purely random. Many of these objects also show lognormal flux distribution and RMS-flux relation and power law frequency distribution. So far, the lognormal flux distribution of black hole objects is only observational facts without satisfactory explanation about the physical mechanism producing such distribution in the accretion disk. One of the most promising models based on cellular automaton mechanism has been successful in reproducing PSD (Power Spectral Density) of the observed objects but could not reproduce lognormal flux distribution. Such distribution requires the existence of underlying multiplicative process while the existing SOC models are based on additive processes. A modified SOC model based on cellular automaton mechanism for producing lognormal flux distribution is presented in this paper. The idea is that the energy released in the avalanche and diffusion in the accretion disk is not entirely emitted instantaneously as in the original cellular automaton model. Some part of the energy is kept in the disk and thus increase its energy content so that the next avalanche will be in higher energy condition and will release more energy. The later an avalanche occurs, the more amount of energy is emitted to the observers. This can provide multiplicative effects to the flux and produces lognormal flux distribution.

  7. Depletion of molecular gas by an accretion outburst in a protoplanetary disk

    CERN Document Server

    Banzatti, A; Bruderer, S; Muzerolle, J; Meyer, M R

    2014-01-01

    We investigate new and archival 3-5 $\\mu$m high resolution ($\\sim3$ km s$^{-1}$) spectroscopy of molecular gas in the inner disk of the young solar-mass star EX Lupi, taken during and after the strong accretion outburst of 2008. The data were obtained using the CRIRES spectrometer at the ESO Very Large Telescope in 2008 and 2014. In 2008, emission lines from CO, H$_{2}$O, and OH were detected with broad profiles tracing gas near and within the corotation radius (0.02-0.3 AU). In 2014, the spectra display marked differences. The CO lines, while still detected, are much weaker, and the H$_{2}$O and OH lines have disappeared altogether. At 3 $\\mu$m a veiled stellar photospheric spectrum is observed. Our analysis finds that the molecular gas mass in the inner disk has decreased by an order of magnitude since the outburst, matching a similar decrease in the accretion rate onto the star. We discuss these findings in the context of a rapid depletion of material accumulated beyond the disk corotation radius during qu...

  8. Correlation analysis of radio properties and accretion-disk luminosity for low luminosity AGNs

    CERN Document Server

    Su, Renzhi; Zhang, Zhen

    2016-01-01

    The correlation between the jet power and accretion disk luminosity is investigated and analyzed with our model for 7 samples of low luminosity active galactic nuclei (LLAGNs). The main results are: (1) the power-law correlation index ($P_{jet} \\propto L_{disk}^{\\mu}$) typically ranges $\\mu=0.4-0.7$ for the LLAGN samples, and there is a hint of steep index for the LLAGN sample which hosted by a high fraction of elliptical galaxies, and there are no significant correlation between the $\\mu$ and the LLAGN types (Seyfert, LINER); (2) for $\\mu \\approx$1, as noted in Liu et al., the accretion disk dominates the jet power and the black hole (BH) spin is not important, for the LLAGN samples studied in this paper we find that the $\\mu$ is significantly less than unity, implying that BH spin may play a significant role in the jet power of LLAGNs; (3) the BH spin-jet power is negatively correlated with the BH mass in our model, which means a high spin-jet efficiency in the `low' BH-mass LLAGNs; (4) an anti-correlation ...

  9. The existence of warm and optically thick dissipative coronae above accretion disks

    CERN Document Server

    Rozanska, A; Belmont, R; Czerny, B; Petrucci, P -O

    2015-01-01

    In the past years, several observations of AGN and X-ray binaries have suggested the existence of a warm T around 0.5-1 keV and optically thick, \\tau ~ 10-20, corona covering the inner parts of the accretion disk. These properties are directly derived from spectral fitting in UV to soft-X-rays using Comptonization models. However, whether such a medium can be both in radiative and hydrostatic equilibrium with an accretion disk is still uncertain. We investigate the properties of such warm, optically thick coronae and put constraints on their existence. We solve the radiative transfer equation for grey atmosphere analytically in a pure scattering medium, including local dissipation as an additional heating term in the warm corona. The temperature profile of the warm corona is calculated assuming it is cooled by Compton scattering, with the underlying dissipative disk providing photons to the corona. Our analytic calculations show that a dissipative thick, (\\tau_{cor} ~ 10-12) corona on the top of a standard ac...

  10. A model for the jet-disk connection in BH accreting systems

    CERN Document Server

    Hujeirat, A

    2003-01-01

    Based on theoretical arguments and quasi-stationary radiative MHD calculations, a model for accretion-induced jet is presented. It is argued that accretion disks around BHs consist of 1) a cold, Keplerian-rotating and weakly magnetized medium in the outer part, 2) highly advective and turbulent-free plasma inside $r_\\mm{tr} = 10-20$ Schwarzschild radii, where magnetic fields (-MFs) are pre-dominantly of large scale topology, and in excess of thermal equipartition, and 3) an ion-dominated torus in the vicinity of the hole, where MFs undergo a topological change into amonopole like-topology. The action of MFs interior to $r_\\mm{tr}$ is to initiate torsional Alfven waves (-TAWs) that extract angular momentum from disk-plasma and deposit it into the transition layer (-TL) above the between the disk, where the plasma is dissipative and tenuous. A significant fraction of the toroidal magnetic field (-TMF) reconnect in the TL, thereby virial-heating the ions and forming a two-temperature, super-Keplerian rotating, c...

  11. Long-term evolution of accretion disks around the neutron star in Be/X-ray binaries

    CERN Document Server

    Hayasaki, K; Hayasaki, Kimitake; Okazaki, Atsuo T.

    2005-01-01

    we study the long-term evolution of the accretion disk around the neutron star in Be/X-ray binaries. We confirm the earlier result by Hayasaki & Okazaki (2004) that the disk evolves via a two-stage process, which consists of the initial developing stage and the later developed stage. The peak mass-accretion rate is distributed around apastron after the disk is fully developed. This indicates that the modulation of the mass accretion rate is essentially caused by an inward propagation of the one-armed spiral wave. The X-ray luminosity peak around the apastron could provide circumstatial evidence for an persistent disk around the neutron star in Be/X-ray binaries.

  12. The Role for the Inner Disk in Mass Accretion to the Star in the Early Phase of Star Formation

    CERN Document Server

    Ohtani, Takuya; Tsuribe, Toru; Vorobyov, Eduard I

    2014-01-01

    A physical mechanism that drives FU Orionis-type outbursts is reconsidered. We study the effect of inner part of a circumstellar disk covering a region from near the central star to the radius of approximately $5$ AU (hereafter, the inner disk). Using the fluctuated mass accretion rate onto the inner disk $\\dot{M}_{\\rm out}$, we consider the viscous evolution of the inner disk and the time variability of the mass accretion rate onto the central star $\\dot{M}_{\\rm in}$ by means of numerical calculation of an unsteady viscous accretion disk in a one-dimensional axisymmetric model. First, we calculate the evolution of the inner disk assuming an oscillating $\\dot{M}_{\\rm out}$. It is shown that the time variability of $\\dot{M}_{\\rm in}$ does not coincide with $\\dot{M}_{\\rm out}$ due to viscous diffusion. Second, we investigate the properties of spontaneous outbursts with temporally constant $\\dot{M}_{\\rm out}$. Outburst occur only in a limited range of mass accretion rates onto the inner disk $10^{-10}<\\dot{M}...

  13. Crossing the Eddington Limit: Examining Disk Spectra at High Accretion Rates

    Science.gov (United States)

    Sutton, Andrew D.; Swartz, Douglas A.; Roberts, Timothy P.; Middleton, Matthew J.; Soria, Roberto; Done, Chris

    2017-02-01

    The faintest ultraluminous X-ray sources (ULXs), those with 0.3–10 keV luminosities 1thermal-dominant black hole binaries, which have Eddington ratios constrained to moderate values, also show BD spectra in the 0.3–10 keV band at an order of magnitude lower luminosities. This broadening would be missed in studies that only look above ∼ 2 {keV}. While this may suggest that BD ULXs could be powered by accretion onto massive stellar remnant black holes with close to maximal spin, we argue in favor of a scenario where they are at close to the Eddington luminosity, such that radiation pressure would be expected to result in geometrically slim, advective accretion disks. However, this implies that an additional physical mechanism is required to produce the observed broad spectra at low Eddington ratios.

  14. Linear Two-Dimensional MHD of Accretion Disks: Crystalline structure and Nernst coefficient

    CERN Document Server

    Montani, Giovanni

    2009-01-01

    We analyse the two-dimensional MHD configurations characterising the steady state of the accretion disk on a highly magnetised neutron star. The model we describe has a local character and represents the extension of the crystalline structure outlined in Coppi (2005), dealing with a local model too, when a specific accretion rate is taken into account. We limit our attention to the linearised MHD formulation of the electromagnetic back-reaction characterising the equilibrium, by fixing the structure of the radial, vertical and azimuthal profiles. Since we deal with toroidal currents only, the consistency of the model is ensured by the presence of a small collisional effect, phenomenologically described by a non-zero constant Nernst coefficient (thermal power of the plasma). Such an effect provides a proper balance of the electron force equation via non zero temperature gradients, related directly to the radial and vertical velocity components. We show that the obtained profile has the typical oscillating feat...

  15. Variabilities of Gamma-ray Bursts from Black Hole Hyper-accretion Disks

    CERN Document Server

    Lin, Da-Bin; Mu, Hui-Jun; Liu, Tong; Hou, Shu-Jin; Lv, Jing; Gu, Wei-Min; Liang, En-Wei

    2016-01-01

    The emission from black hole binaries (BHBs) and active galactic nuclei (AGNs) displays significant aperiodic variabilities. The most promising explanation for these variabilities is the propagating fluctuations in the accretion flow. It is natural to expect that the mechanism driving variabilities in BHBs and AGNs may operate in a black hole hyper-accretion disk, which is believed to power gamma-ray bursts (GRBs). We study the variabilities of jet power in GRBs based on the model of propagating fluctuations. It is found that the variabilities of jet power and the temporal profile of erratic spikes in this scenario are similar to those in observed light curves of prompt gamma-ray emission of GRBs. Our results show that the mechanism driving X-ray variabilities in BHBs and AGNs may operate in the central engine to drive the variabilities of GRBs.

  16. Measuring the Direction and Angular Velocity of a Black Hole Accretion Disk via Lagged Interferometric Covariance

    CERN Document Server

    Johnson, Michael D; Shiokawa, Hotaka; Chael, Andrew A; Doeleman, Sheperd S

    2015-01-01

    We show that interferometry can be applied to study irregular, rapidly rotating structures, as are expected in the turbulent accretion flow near a black hole. Specifically, we analyze the lagged covariance between interferometric baselines of similar lengths but slightly different orientations. We demonstrate that the peak in the lagged covariance indicates the direction and angular velocity of the flow. Importantly, measuring the direction of the flow as clockwise or counterclockwise on the sky breaks a degeneracy in accretion disk inclinations when analyzing time-averaged images alone. We explore the potential efficacy using three-dimensional, general relativistic magnetohydrodynamic (GRMHD) simulations, and we highlight several baseline pairs for the Event Horizon Telescope (EHT) that are well-suited to this application. These results indicate that the EHT is capable of determining the direction and angular velocity of the emitting material near Sgr A*, even for highly-inclined flows, and they suggest that...

  17. Accretion Disk Model of Short-Timescale Intermittent Activity in Young Radio Sources

    CERN Document Server

    Czerny, Bozena; Janiuk, Agnieszka; Nikiel-Wroczynski, Blazej; Stawarz, Lukasz

    2009-01-01

    We associate the existence of short-lived compact radio sources with the intermittent activity of the central engine caused by a radiation pressure instability within an accretion disk. Such objects may constitute a numerous sub-class of Giga-Hertz Peaked Spectrum sources, in accordance with the population studies of radio-loud active galaxies, as well as detailed investigations of their radio morphologies. We perform the model computations assuming the viscosity parametrization as proportional to a geometrical mean of the total and gas pressure. The implied timescales are consistent with the observed ages of the sources. The duration of an active phase for a moderate accretion rate is short enough (< 10^3-10^4 years) that the ejecta are confined within the host galaxy and thus these sources cannot evolve into large size radio galaxies unless they are close to the Eddington limit.

  18. A global three-dimensional radiation magneto-hydrodynamic simulation of super-eddington accretion disks

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Yan-Fei [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Stone, James M. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Davis, Shane W. [Canadian Institute for Theoretical Astrophysics. Toronto, ON M5S3H4 (Canada)

    2014-12-01

    We study super-Eddington accretion flows onto black holes using a global three-dimensional radiation magneto-hydrodynamical simulation. We solve the time-dependent radiative transfer equation for the specific intensities to accurately calculate the angular distribution of the emitted radiation. Turbulence generated by the magneto-rotational instability provides self-consistent angular momentum transfer. The simulation reaches inflow equilibrium with an accretion rate ∼220 L {sub Edd}/c {sup 2} and forms a radiation-driven outflow along the rotation axis. The mechanical energy flux carried by the outflow is ∼20% of the radiative energy flux. The total mass flux lost in the outflow is about 29% of the net accretion rate. The radiative luminosity of this flow is ∼10 L {sub Edd}. This yields a radiative efficiency ∼4.5%, which is comparable to the value in a standard thin disk model. In our simulation, vertical advection of radiation caused by magnetic buoyancy transports energy faster than photon diffusion, allowing a significant fraction of the photons to escape from the surface of the disk before being advected into the black hole. We contrast our results with the lower radiative efficiencies inferred in most models, such as the slim disk model, which neglect vertical advection. Our inferred radiative efficiencies also exceed published results from previous global numerical simulations, which did not attribute a significant role to vertical advection. We briefly discuss the implications for the growth of supermassive black holes in the early universe and describe how these results provided a basis for explaining the spectrum and population statistics of ultraluminous X-ray sources.

  19. 原太阳吸积盘结构%THE STRUCTURE OF PROTOSOLAR ACCRETION DISK

    Institute of Scientific and Technical Information of China (English)

    刘文洁; 黄克谅; 周洪楠

    2001-01-01

    计算了粘滞演化阶段原太阳吸积盘结构.采用稳态标准吸积盘模型来描述盘中湍动粘滞;忽略其径向能量传输,将垂直结构作为一维问题处理.假设盘作Keplerian较差旋转,处于流体力学平衡和局域热平衡,盘由粘滞耗散加热,能量通过对流和辐射向外传输.结果表明,对温度敏感的不透明度是决定盘结构的重要因素;原太阳吸积盘为冷的薄盘,盘中热对流不稳定性由外而内,由上而下地终结;行星的形成应首先开始于对流终结的区域.%The structure of protosolar accretion disk during viscous diffusion stage is calculated. The standard α model is used to describe the viscosity in the optically thick protosolar accretion disc. The energy transport associated with radial motions is neglected and the vertical structure is constructed by assuming a Keplerian rotation and local hydrostatic and thermal equilibrium. The disk is heated by viscous dissipation and energy is transported by convection or radiation. It is found that the dependence of opacity on temperature is important to the disk structure. For the cold protosolar accretion disc,convective instability will gradually end from the outer region to the center and from the surface to central plane. So the formation of planets should first take place in the region where convection ends.

  20. Mhd waves in stellar winds and accretion disks

    Directory of Open Access Journals (Sweden)

    M. J. Vasconcelos

    2000-01-01

    Full Text Available Las ondas de Alfv en han sido usadas para explicar el calentamiento de las coronas estelares y de la producci on de vientos estelares en varias zonas del diagrama Hertzsprung-Russell (HR. Las ondas fueron usadas como un mecanismo importante en la aceleraci on del viento de protoestrellas, de estrellas de tipos tempranos y tard os y del viento solar. Tambi en son importantes en la creaci on de inhomogeneidades, v a las inestabilidades t ermicas, en vientos de estrellas de tipo temprano. Por otro lado, el calentamiento generado por la disipaci on no lineal y turbulenta de las ondas puede ser una fuente importante de energ a para ionizar discos protoestelares, permitiendo el transporte de momento angular mediante la inestabilidad de Balbus-Hawly (BHI. Analizamos el papel de la disipaci on de ondas de Alfv en en las regiones medias e internas de los discos protoestelares (0:1 < R(AU < 1:4. Demostramos que cuando la disipaci on viscosa es insu ciente para mantener la ionizaci on requerida por la BHI, el amortiguamiento de las ondas de Alfv en puede ser una fuente alternativa de energ a para la ionizaci on.

  1. Wind interactions above accretion discs: a model for broad-line regions and collimated outflow

    Energy Technology Data Exchange (ETDEWEB)

    Smith, M.D.; Raine, D.J. (Leicester Univ. (UK). Dept. of Astronomy)

    1985-01-15

    The interaction of a wind from an active galactic nucleus with a Compton-heating-induced wind from an accretion disc is studied. The nuclear wind is taken as initially supersonic and spherically symmetric. The disc wind arises when the disc surface is exposed to a hard and powerful X-ray source. Three classes of interaction are identified in terms of the relation between the pressure on the disc surface and the corresponding thermal and ram pressures in the nuclear wind.

  2. MODELING THE Fe K LINE PROFILES IN TYPE I ACTIVE GALACTIC NUCLEI WITH A COMPTON-THICK DISK WIND

    Energy Technology Data Exchange (ETDEWEB)

    Tatum, M. M.; Turner, T. J. [Department of Physics, University of Maryland, Baltimore County, Baltimore, MD 21250 (United States); Sim, S. A. [Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston Creek, ACT 2611 (Australia); Miller, L. [Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom); Reeves, J. N.; Patrick, A. R. [Astrophysics Group, School of Physical and Geographical Sciences, Keele University, Keele, Staffordshire ST5 5BG (United Kingdom); Long, K. S. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2012-06-20

    We have modeled a small sample of Seyfert galaxies that were previously identified as having simple X-ray spectra with little intrinsic absorption. The sources in this sample all contain moderately broad components of Fe K-shell emission and are ideal candidates for testing the applicability of a Compton-thick accretion disk wind model to active galactic nucleus (AGN) emission components. Viewing angles through the wind allow the observer to see the absorption signature of the gas, whereas face-on viewing angles allow the observer to see the scattered light from the wind. We find that the Fe K emission line profiles are well described with a model of a Compton-thick accretion disk wind of solar abundances, arising tens to hundreds of gravitational radii from the central black hole. Further, the fits require a neutral component of Fe K{alpha} emission that is too narrow to arise from the inner part of the wind, and likely comes from a more distant reprocessing region. Our study demonstrates that a Compton-thick wind can have a profound effect on the observed X-ray spectrum of an AGN, even when the system is not viewed through the flow.

  3. Are broad optical balmer lines from central accretion disk in PG 1613+658?

    CERN Document Server

    Zhang, XueGuang

    2014-01-01

    In this letter, we report positive correlations between broad line width and broad line flux for the broad balmer lines of the long-term observed AGN PG 1613+658. Rather than the expected negative correlations under the widely accepted virialization assumption for AGN BLRs, the positive correlations indicate much different BLR structures of PG 1613+658 from the commonly considered BLR structures which are dominated by the equilibrium between radiation pressure and gas pressure. Therefore, accretion disk origin is preferred for the observed broad single-peaked optical balmer lines of PG 1613+658, because of the mainly gravity dominated disk-like BLRs with radial structures having few effects from radiation pressure.

  4. Beltrami state in black-hole accretion disk: A magnetofluid approach

    CERN Document Server

    Bhattacharjee, Chinmoy; Stark, David J; Mahajan, S M

    2015-01-01

    Using the magnetofluid unification framework, we show that the accretion disk plasma (embedded in the background geometry of a blackhole) can relax to a class of states known as the Beltrami-Bernoulli (BB) equilibria. Modeling the disk plasma as a Hall MHD system, we find that the space-time curvature can significantly alter the magnetic/velocity decay rate as we move away from the compact object; the velocity profiles in BB states, for example, deviate substantially from the predicted corresponding geodesic velocity profiles. These departures imply a rich interplay of plasma dynamics and general relativity revealed by examining the corresponding Bernoulli condition representing "homogeneity" of total energy. The relaxed states have their origin in the constraints provided by the two helicity invariants of Hall MHD. These helicities conspire to introduce a new oscillatory length scale into the system that is strongly influenced by relativistic and thermal effects.

  5. Global MHD Simulations of Accretion Disks in Cataclysmic Variables (CVs): I. The Importance of Spiral Shocks

    CERN Document Server

    Ju, Wenhua; Zhu, Zhaohuan

    2016-01-01

    We present results from the first global 3D MHD simulations of accretion disks in Cataclysmic Variable (CV) systems in order to investigate the relative importance of angular momentum transport via turbulence driven by the magnetorotational instability (MRI) compared to that driven by spiral shock waves. Remarkably, we find that even with vigorous MRI turbulence, spiral shocks are an important component to the overall angular momentum budget, at least when temperatures in the disk are high (so that Mach numbers are low). In order to understand the excitation, propagation, and damping of spiral density waves in our simulations more carefully, we perform a series of 2D global hydrodynamical simulations with various equation of states and both with and without mass inflow via the Lagrangian point (L1). Compared with previous similar studies, we find the following new results. 1) Linear wave dispersion relation fits the pitch angles of spiral density waves very well. 2) We demonstrate explicitly that mass accreti...

  6. Beltrami state in black-hole accretion disk: A magnetofluid approach.

    Science.gov (United States)

    Bhattacharjee, Chinmoy; Das, Rupam; Stark, David J; Mahajan, S M

    2015-12-01

    Using the magnetofluid unification framework, we show that the accretion disk plasma (embedded in the background geometry of a black hole) can relax to a class of states known as the Beltrami-Bernoulli (BB) equilibria. Modeling the disk plasma as a Hall magnetohydrodynamics (MHD) system, we find that the space-time curvature can significantly alter the magnetic (velocity) decay rates as we move away from the compact object; the velocity profiles in BB states, for example, deviate substantially from the predicted corresponding geodesic velocity profiles. These departures imply a rich interplay of plasma dynamics and general relativity revealed by examining the corresponding Bernoulli condition representing "homogeneity" of total energy. The relaxed states have their origin in the constraints provided by the two helicity invariants of Hall MHD. These helicities conspire to introduce an oscillatory length scale into the system that is strongly influenced by relativistic and thermal effects.

  7. Do Circumnuclear Dense Gas Disks Drive Mass Accretion onto Supermassive Black Holes?

    Science.gov (United States)

    Izumi, Takuma; Kawakatu, Nozomu; Kohno, Kotaro

    2016-08-01

    We present a positive correlation between the mass of dense molecular gas ({M}{{dense}}) of ˜100 pc scale circumnuclear disks (CNDs) and the black hole mass accretion rate ({\\dot{M}}{{BH}}) in a total of 10 Seyfert galaxies, based on data compiled from the literature and an archive (median aperture θ med = 220 pc). A typical {M}{{dense}} of CNDs is 107-8 {M}⊙ , estimated from the luminosity of the dense gas tracer, the HCN(1-0) emission line. Because dense molecular gas is the site of star formation, this correlation is virtually equivalent to the one between the nuclear star-formation rate and {\\dot{M}}{{BH}} revealed previously. Moreover, the {M}{{dense}}{--}{\\dot{M}}{{BH}} correlation was tighter for CND-scale gas than for the gas on kiloparsec or larger scales. This indicates that CNDs likely play an important role in fueling black holes, whereas greater than kiloparesec scale gas does not. To demonstrate a possible approach for studying the CND-scale accretion process with the Atacama Large Millimeter/submillimeter Array, we used a mass accretion model where angular momentum loss due to supernova explosions is vital. Based on the model prediction, we suggest that only the partial fraction of the mass accreted from the CND ({\\dot{M}}{{acc}}) is consumed as {\\dot{M}}{{BH}}. However, {\\dot{M}}{{acc}} agrees well with the total nuclear mass flow rate (i.e., {\\dot{M}}{{BH}} + outflow rate). Although these results are still tentative with large uncertainties, they support the view that star formation in CNDs can drive mass accretion onto supermassive black holes in Seyfert galaxies.

  8. On the difficulty of launching an outflow from an accretion disk

    CERN Document Server

    Ogilvie, G I; Ogilvie, Gordon I.; Livio, Mario

    1997-01-01

    We solve for the local vertical structure of a thin accretion disk threaded by a poloidal magnetic field. The angular velocity deviates from the Keplerian value as a result of the radial Lorentz force, but is constant on magnetic surfaces. Angular momentum transport and energy dissipation in the disk are parametrized by an alpha-prescription, and a Kramers opacity law is assumed to hold. We also determine the stability of the equilibria with respect to the magnetorotational (or Balbus-Hawley) instability. If the magnetic field is sufficiently strong, stable equilibria can be found in which the angle of inclination, i, of the magnetic field to the vertical at the surface of the disk has any value in the range [0,90 degrees). By analyzing the dynamics of a transonic outflow in the corona of the disk, we show that a certain potential difference must be overcome even when i > 30 degrees. We determine this potential difference as a function of i for increasing values of the vertical magnetic field strength. For ma...

  9. Angular Momentum Transport and Variability in Boundary Layers of Accretion Disks Driven by Global Acoustic Modes

    CERN Document Server

    Belyaev, Mikhail A; Stone, James M

    2012-01-01

    Disk accretion onto a weakly magnetized central object, e.g. a star, is inevitably accompanied by the formation of a boundary layer near the surface, in which matter slows down from the highly supersonic orbital velocity of the disk to the rotational velocity of the star. We perform high resolution 2D hydrodynamical simulations in the equatorial plane of an astrophysical boundary layer with the goal of exploring the dynamics of non-axisymmetric structures that form there. We generically find that the supersonic shear in the boundary layer excites non-axisymmetric quasi-stationary acoustic modes that are trapped between the surface of the star and a Lindblad resonance in the disk. These modes rotate in a prograde fashion, are stable for hundreds of orbital periods, and have a pattern speed that is less than and of order the rotational velocity at the inner edge of the disk. The origin of these intrinsically global modes is intimately related to the operation of a corotation amplifier in the system. Dissipation...

  10. Angular Momentum Transport in Protoplanetary and Black Hole Accretion Disks: The Role of Parasitic Modes in the Saturation of MHD Turbulence

    DEFF Research Database (Denmark)

    Pessah, Martin Elias

    2010-01-01

    The magnetorotational instability (MRI) is considered a key process for driving efficient angular momentum transport in astrophysical disks. Understanding its nonlinear saturation constitutes a fundamental problem in modern accretion disk theory. The large dynamical range in physical conditions i...

  11. C/O and Snowline Locations in Protoplanetary Disks: The Effect of Radial Drift and Viscous Gas Accretion

    CERN Document Server

    Piso, Ana-Maria A; Birnstiel, Tilman; Murray-Clay, Ruth A

    2015-01-01

    The C/O ratio is a defining feature of both gas giant atmospheric and protoplanetary disk chemistry. In disks, the C/O ratio is regulated by the presence of snowlines of major volatiles at different distances from the central star. We explore the effect of radial drift of solids and viscous gas accretion onto the central star on the snowline locations of the main C and O carriers in a protoplanetary disk, H2O, CO2 and CO, and their consequences for the C/O ratio in gas and dust throughout the disk. We determine the snowline locations for a range of fixed initial particle sizes and disk types. For our fiducial disk model, we find that grains with sizes ~0.5 cm < s < 7 m for an irradiated disk, and ~0.001 cm < s < 7 m for an evolving and viscous disk, desorb at a size-dependent location in the disk, which is independent of the particle's initial position. The snowline radius decreases for larger particles, up to sizes of ~7 m. Compared to a static disk, we find that radial drift and gas accretion in...

  12. Photoionization Models for the Inner Gaseous Disks of Herbig Be Stars: Evidence against Magnetospheric Accretion?

    Science.gov (United States)

    Patel, P.; Sigut, T. A. A.; Landstreet, J. D.

    2017-02-01

    We investigate the physical properties of the inner gaseous disks of three hot Herbig B2e stars, HD 76534, HD 114981, and HD 216629, by modeling CFHT-ESPaDOns spectra using non-LTE radiative transfer codes. We assume that the emission lines are produced in a circumstellar disk heated solely by photospheric radiation from the central star in order to test whether the optical and near-infrared emission lines can be reproduced without invoking magnetospheric accretion. The inner gaseous disk density was assumed to follow a simple power-law in the equatorial plane, and we searched for models that could reproduce observed lines of H i (Hα and Hβ), He i, Ca ii, and Fe ii. For the three stars, good matches were found for all emission line profiles individually; however, no density model based on a single power-law was able to reproduce all of the observed emission lines. Among the single power-law models, the one with the gas density varying as ∼10‑10(R */R)3 g cm‑3 in the equatorial plane of a 25 R * (0.78 au) disk did the best overall job of representing the optical emission lines of the three stars. This model implies a mass for the Hα-emitting portion of the inner gaseous disk of ∼10‑9 M *. We conclude that the optical emission line spectra of these HBe stars can be qualitatively reproduced by a ≈1 au, geometrically thin, circumstellar disk of negligible mass compared to the central star in Keplerian rotation and radiative equilibrium. Based on observations obtained at the Canada–France–Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l”Univers of the Centre National de la Recherche Scientique of France, and the University of Hawaii.

  13. Dust in the wind II: Polarization imaging from disk-born outflows

    CERN Document Server

    Marin, F

    2013-01-01

    In this second research note of a series of two, we aim to map the polarized flux emerging from a disk-born, dusty outflow as it was prescribed by Elvis (2000). His structure for quasars was achieved to unify the emission and absorption features observed in active galactic nuclei (AGN) and can be used as an alternative scenario to the typical dusty torus that is extensively used to account for AGN circumnuclear obscuration. Using Monte Carlo radiative transfer simulations, we model an obscuring outflow arising from an emitting accretion disk and examine the resulting polarization degree, polarization angle and polarized flux. Polarization cartography reveals that a disk-born outflow has a similar torus morphology in polar viewing angles, with bright polarized fluxes reprocessed onto the wind funnel. At intermediate and edge-on inclinations, the model is rather close to a double-conical wind, with higher fluxes in the cone bases. It indicates that the optically thick outflow is not efficient enough to avoid ra...

  14. The Effect of X-ray Irradiation on the Time Dependent Behaviour of Accretion Disks with Stochastic Perturbations

    CERN Document Server

    Maqbool, Bari; Iqbal, Naseer; Ahmad, Naveel

    2015-01-01

    The UV emission from X-ray binaries, is more likely to be produced by reprocessing of X-rays by the outer regions of an accretion disk. The structure of the outer disk may be altered due to the presence of X-ray irradiation and we discuss the physical regimes where this may occur and point out certain X-ray binaries where this effect may be important. The long term X-ray variability of these sources is believed to be due to stochastic fluctuations in the outer disk, which propagate inwards giving rise to accretion rate variation in the X-ray producing inner regions. The X-ray variability will induce structural variations in the outer disk which in turn may affect the inner accretion rate. To understand the qualitative behaviour of the disk in such a scenario, we adopt simplistic assumptions that the disk is fully ionised and is not warped. We develop and use a time dependent global hydrodynamical code to study the effect of a sinusoidal accretion rate perturbation introduced at a specific radius. The response...

  15. VARIABILITY OF THE ACCRETION DISK OF V926 Sco INFERRED FROM TOMOGRAPHIC ANALYSIS

    Energy Technology Data Exchange (ETDEWEB)

    Connolly, S. D. [University of Southampton, Highfield, Southampton, S017 1BJ (United Kingdom); Peris, C. S. [Department of Physics, Northeastern University, Boston, MA 02115 (United States); Vrtilek, S. D., E-mail: sdc1g08@soton.ac.u, E-mail: peris.c@husky.neu.edu, E-mail: cperis@cfa.harvard.edu, E-mail: svrtilek@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

    2013-11-10

    We present phase-resolved spectroscopic observations of the low-mass X-ray binary V926 Sco (4U 1735-44), covering the orbital period of 0.23 days, obtained with the Walter Baade 6.5 m Magellan Telescope at the Las Campanas Observatory in 2010 June and 2011 June. We use Hα radial velocities to derive a systemic velocity of –109 ± 4 km s{sup –1}. The FWHM of the lines observed in common with previous authors are significantly lower during our observations suggesting much reduced velocities in the system. The equivalent width of the Bowen fluorescence lines with respect to He II λ4686 are factors of two or more lower during our observations in comparison to those previously reported for the system, suggesting reduced irradiation of the secondary. Doppler and modulation tomography of Hα and He II λ4686 show asymmetric emission that can be attributed to a bulge in the accretion disk, as inferred from He II observations by previous authors. The X-ray fluxes from the source at times concurrent with the optical observations are significantly lower during our observations than during optical observations taken in 2003. We suggest that the system is in a lower accretion state compared to earlier observations; this explains both the lower velocities observed from the disk and the reduction of emission due to Bowen fluorescence detected from the secondary.

  16. Numerical simulation of the disk dynamics around the black hole: Bondi-Hoyle accretion

    Science.gov (United States)

    Koyuncu, Fahrettin; Dönmez, Orhan

    2014-06-01

    We have solved the General Relativistic Hydrodynamic (GRH) equations using the high resolution shock capturing scheme (HRSCS) to find out the dependency of the disk dynamics to the Mach number, adiabatic index, the black hole rotation parameter and the outer boundary of the computational domain around the non-rotating and rotating black holes. We inject the gas to computational domain at upstream and downstream regions at the same time with different initial conditions. It is found that variety of the mass accretion rates and shock cone structures strongly depend on Mach number and adiabatic index of the gas. The shock cones on the accretion disk are important physical mechanisms to trap existing oscillation modes, thereupon these trapped modes may generate strong X-rays observed by different X-ray satellites. Besides, our numerical approach also show that the shock cones produces the flip-flop oscillation around the black holes. The flip-flop instabilities which are monitored in our simulations may explain the erratic spin behavior of the compact objects (the black holes and neutron stars) seen from observed data.

  17. A Substantial Dust Disk Surrounding an Actively Accreting First-Ascent Giant Star

    CERN Document Server

    Melis, C; Song, I; Rhee, J H; Metchev, S

    2009-01-01

    We report identification of the first unambiguous example of what appears to be a new class of first-ascent giant stars that are actively accreting gas and dust and that are surrounded by substantial dusty disks. These old stars, who are nearing the end of their lives, are experiencing a rebirth into characteristics typically associated with newborn stars. The F2-type first-ascent giant star TYC 4144 329 2 is in a wide separation binary system with an otherwise normal G8 IV star, TYC 4144 329 1. From Keck near-infrared imaging and high-resolution spectroscopy we are able to determine that these two stars are $\\sim$1 Gyr old and reside at a distance of $\\sim$550 pc. One possible explanation for the origin of the accreting material is common-envelope interaction with a low-mass stellar or sub-stellar companion. The gaseous and dusty material around TYC 4144 329 2, as it is similar to the primordial disks observed around young classical T Tauri stars, could potentially give rise to a new generation of planets an...

  18. Angular momentum transport and particle acceleration during magnetorotational instability in a kinetic accretion disk.

    Science.gov (United States)

    Hoshino, Masahiro

    2015-02-13

    Angular momentum transport and particle acceleration during the magnetorotational instability (MRI) in a collisionless accretion disk are investigated using three-dimensional particle-in-cell simulation. We show that the kinetic MRI can provide not only high-energy particle acceleration but also enhancement of angular momentum transport. We find that the plasma pressure anisotropy inside the channel flow with p(∥)>p(⊥) induced by active magnetic reconnection suppresses the onset of subsequent reconnection, which, in turn, leads to high-magnetic-field saturation and enhancement of the Maxwell stress tensor of angular momentum transport. Meanwhile, during the quiescent stage of reconnection, the plasma isotropization progresses in the channel flow and the anisotropic plasma with p(⊥)>p(∥) due to the dynamo action of MRI outside the channel flow contribute to rapid reconnection and strong particle acceleration. This efficient particle acceleration and enhanced angular momentum transport in a collisionless accretion disk may explain the origin of high-energy particles observed around massive black holes.

  19. Emergence of nonlinearity and plausible turbulence in accretion disks via hydromagnetic transient growth faster than magnetorotational instability

    CERN Document Server

    Nath, Sujit K

    2016-01-01

    We investigate the evolution of hydromagnetic perturbations in a small section of accretion disks. It is known that molecular viscosity is negligible in accretion disks. Hence, it has been argued that Magnetorotational Instability (MRI) is responsible for transporting matter in the presence of weak magnetic field. However, there are some shortcomings, which question effectiveness of MRI. Now the question arises, whether other hydromagnetic effects, e.g. transient growth (TG), can play an important role to bring nonlinearity in the system, even at weak magnetic fields. Otherwise, whether MRI or TG, which is primarily responsible to reveal nonlinearity to make the flow turbulent? Our results prove explicitly that the flows with high Reynolds number (Re), which is the case of realistic astrophysical accretion disks, exhibit nonlinearity by best TG of perturbation modes faster than that by best modes producing MRI. For a fixed wavevector, MRI dominates over transient effects, only at low Re, lower than its value ...

  20. Thermal Disk Winds in X-Ray Binaries: Realistic Heating and Cooling Rates Give Rise to Slow, but Massive, Outflows

    Science.gov (United States)

    Higginbottom, N.; Proga, D.; Knigge, C.; Long, K. S.

    2017-02-01

    A number of X-ray binaries exhibit clear evidence for the presence of disk winds in the high/soft state. A promising driving mechanism for these outflows is mass loss driven by the thermal expansion of X-ray heated material in the outer disk atmosphere. Higginbottom & Proga recently demonstrated that the properties of thermally driven winds depend critically on the shape of the thermal equilibrium curve, since this determines the thermal stability of the irradiated material. For a given spectral energy distribution, the thermal equilibrium curve depends on an exact balance between the various heating and cooling mechanisms at work. Most previous work on thermally driven disk winds relied on an analytical approximation to these rates. Here, we use the photoionization code cloudy to generate realistic heating and cooling rates which we then use in a 2.5D hydrodynamic model computed in ZEUS to simulate thermal winds in a typical black hole X-ray binary. We find that these heating and cooling rates produce a significantly more complex thermal equilibrium curve, with dramatically different stability properties. The resulting flow, calculated in the optically thin limit, is qualitatively different from flows calculated using approximate analytical rates. Specifically, our thermal disk wind is much denser and slower, with a mass-loss rate that is a factor of two higher and characteristic velocities that are a factor of three lower. The low velocity of the flow—{v}\\max ≃ 200 km s‑1—may be difficult to reconcile with observations. However, the high mass-loss rate—15 × the accretion rate—is promising, since it has the potential to destabilize the disk. Thermally driven disk winds may therefore provide a mechanism for state changes.

  1. Stellar parameters and accretion rate of the transition disk star HD 142527 from X-shooter

    Energy Technology Data Exchange (ETDEWEB)

    Mendigutía, I.; Fairlamb, J.; Oudmaijer, R. D. [School of Physics and Astronomy, University of Leeds, Woodhouse Lane, Leeds LS2 9JT (United Kingdom); Montesinos, B. [Centro de Astrobiología, Departamento de Astrofísica (CSIC-INTA), ESAC Campus, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Najita, J. R. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Brittain, S. D. [Department of Physics and Astronomy, Clemson University, Clemson, SC 29634-0978 (United States); Van den Ancker, M. E., E-mail: I.Mendigutia@leeds.ac.uk [European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching b. München (Germany)

    2014-07-20

    HD 142527 is a young pre-main-sequence star with properties indicative of the presence of a giant planet and/or a low-mass stellar companion. We have analyzed an X-Shooter/Very Large Telescope spectrum to provide accurate stellar parameters and accretion rate. The analysis of the spectrum, together with constraints provided by the spectral energy distribution fitting, the distance to the star (140 ± 20 pc), and the use of evolutionary tracks and isochrones, led to the following set of parameters: T{sub eff} = 6550 ± 100 K, log g = 3.75 ± 0.10, L{sub *}/L{sub ☉} = 16.3 ± 4.5, M{sub *}/M{sub ☉} = 2.0 ± 0.3, and an age of 5.0 ± 1.5 Myr. This stellar age provides further constraints to the mass of the possible companion estimated by Biller et al., being between 0.20 and 0.35 M{sub ☉}. Stellar accretion rates obtained from UV Balmer excess modeling and optical photospheric line veiling, and from the correlations with several emission lines spanning from the UV to the near-IR, are consistent with each other. The mean value from all previous tracers is 2 (±1) × 10{sup –7} M{sub ☉} yr{sup –1}, which is within the upper limit gas flow rate from the outer to the inner disk recently provided by Cassasus et al.. This suggests that almost all gas transferred between both components of the disk is not trapped by the possible planet(s) in between but fall onto the central star, although it is discussed how the gap flow rate could be larger than previously suggested. In addition, we provide evidence showing that the stellar accretion rate of HD 142527 has increased by a factor ∼7 on a timescale of 2 to 5 yr.

  2. Stellar Parameters and Accretion Rate of the Transition Disk Star HD 142527 from X-Shooter

    Science.gov (United States)

    Mendigutía, I.; Fairlamb, J.; Montesinos, B.; Oudmaijer, R. D.; Najita, J. R.; Brittain, S. D.; van den Ancker, M. E.

    2014-07-01

    HD 142527 is a young pre-main-sequence star with properties indicative of the presence of a giant planet and/or a low-mass stellar companion. We have analyzed an X-Shooter/Very Large Telescope spectrum to provide accurate stellar parameters and accretion rate. The analysis of the spectrum, together with constraints provided by the spectral energy distribution fitting, the distance to the star (140 ± 20 pc), and the use of evolutionary tracks and isochrones, led to the following set of parameters: T eff = 6550 ± 100 K, log g = 3.75 ± 0.10, L */L ⊙ = 16.3 ± 4.5, M */M ⊙ = 2.0 ± 0.3, and an age of 5.0 ± 1.5 Myr. This stellar age provides further constraints to the mass of the possible companion estimated by Biller et al., being between 0.20 and 0.35 M ⊙. Stellar accretion rates obtained from UV Balmer excess modeling and optical photospheric line veiling, and from the correlations with several emission lines spanning from the UV to the near-IR, are consistent with each other. The mean value from all previous tracers is 2 (±1) × 10-7 M ⊙ yr-1, which is within the upper limit gas flow rate from the outer to the inner disk recently provided by Cassasus et al.. This suggests that almost all gas transferred between both components of the disk is not trapped by the possible planet(s) in between but fall onto the central star, although it is discussed how the gap flow rate could be larger than previously suggested. In addition, we provide evidence showing that the stellar accretion rate of HD 142527 has increased by a factor ~7 on a timescale of 2 to 5 yr.

  3. Magnetorotational dynamo chimeras. The missing link to turbulent accretion disk dynamo models?

    Science.gov (United States)

    Riols, A.; Rincon, F.; Cossu, C.; Lesur, G.; Ogilvie, G. I.; Longaretti, P.-Y.

    2017-02-01

    In Keplerian accretion disks, turbulence and magnetic fields may be jointly excited through a subcritical dynamo mechanisminvolving magnetorotational instability (MRI). This dynamo may notably contribute to explaining the time-variability of various accreting systems, as high-resolution simulations of MRI dynamo turbulence exhibit statistical self-organization into large-scale cyclic dynamics. However, understanding the physics underlying these statistical states and assessing their exact astrophysical relevance is theoretically challenging. The study of simple periodic nonlinear MRI dynamo solutions has recently proven useful in this respect, and has highlighted the role of turbulent magnetic diffusion in the seeming impossibility of a dynamo at low magnetic Prandtl number (Pm), a common regime in disks. Arguably though, these simple laminar structures may not be fully representative of the complex, statistically self-organized states expected in astrophysical regimes. Here, we aim at closing this seeming discrepancy by reporting the numerical discovery of exactly periodic, yet semi-statistical "chimeral MRI dynamo states" which are the organized outcome of a succession of MRI-unstable, non-axisymmetric dynamical stages of different forms and amplitudes. Interestingly, these states, while reminiscent of the statistical complexity of turbulent simulations, involve the same physical principles as simpler laminar cycles, and their analysis further confirms the theory that subcritical turbulent magnetic diffusion impedes the sustainment of an MRI dynamo at low Pm. Overall, chimera dynamo cycles therefore offer an unprecedented dual physical and statistical perspective on dynamos in rotating shear flows, which may prove useful in devising more accurate, yet intuitive mean-field models of time-dependent turbulent disk dynamos. Movies associated to Fig. 1 are available at http://www.aanda.org

  4. DETERMINATION OF CENTRAL ENGINE POSITION AND ACCRETION DISK STRUCTURE IN NGC 4261 BY CORE SHIFT MEASUREMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Haga, Takafumi; Doi, Akihiro; Murata, Yasuhiro [Department of Space and Astronautical Science, The Graduate University for Advanced Studies (SOKENDAI), 3-1-1 Yoshinodai, Chuou-ku, Sagamihara, Kanagawa, 252-5210 (Japan); Sudou, Hiroshi [Department of Mathematical and Design Engineering, Faculty of Engineering, Gifu University, 1-1 Yanagido, Gifu City 5011-1193 (Japan); Kameno, Seiji [Joint ALMA Observatory, Alonso de Córdova 3107 Vitacura, Santiago (Chile); Hada, Kazuhiro, E-mail: haga@vsop.isas.jaxa.jp [Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588 (Japan)

    2015-07-01

    We report multifrequency phase-referenced observations of the nearby radio galaxy NGC 4261, which has prominent two-sided jets, using the Very Long Baseline Array at 1.4–43 GHz. We measured radio core positions showing observing frequency dependences (known as “core shift”) in both approaching jets and counterjets. The limit of the core position as the frequency approaches infinity, which suggests a jet base, is separated by 82 ± 16 μas upstream in projection, corresponding to (310 ± 60)R{sub s} (R{sub s}: Schwarzschild radius) as a deprojected distance, from the 43 GHz core in the approaching jet. In addition, the innermost component at the counterjet side appeared to approach the same position at infinity of the frequency, indicating that cores on both sides are approaching the same position, suggesting a spatial coincidence with the central engine. Applying a phase-referencing technique, we also obtained spectral index maps, which indicate that emission from the counterjet is affected by free–free absorption (FFA). The result of the core shift profile on the counterjet also requires FFA because the core positions at 5–15 GHz cannot be explained by a simple core shift model based on synchrotron self-absorption (SSA). Our result is apparently consistent with the SSA core shift with an additional disk-like absorber over the counterjet side. Core shift and opacity profiles at the counterjet side suggest a two-component accretion: a radiatively inefficient accretion flow at the inner region and a truncated thin disk in the outer region. We proposed a possible solution about density and temperature profiles in the outer disk on the basis of the radio observation.

  5. Observational limits on the spin-down torque of Accretion Powered Stellar Winds

    CERN Document Server

    Zanni, C

    2010-01-01

    The rotation period of classical T Tauri stars (CTTS) represents a longstanding puzzle. While young low-mass stars show a wide range of rotation periods, many CTTS are slow rotators, spinning at a small fraction of break-up, and their rotation period does not seem to shorten, despite the fact that they are actively accreting and contracting. Matt & Pudritz (2005) proposed that the spin-down torque of a stellar wind powered by a fraction of the accretion energy would be strong enough to balance the spin-up torque due to accretion. Since this model establishes a direct relation between accretion and ejection, the observable stellar parameters (mass, radius, rotation period, magnetic field) and the accretion diagnostics (accretion shock luminosity), can be used to constraint the wind characteristics. In particular, since the accretion energy powers both the stellar wind and the shock emission, we show in this letter how the accretion shock luminosity L_UV can provide upper limits to the spin-down efficiency ...

  6. Enhanced accretion rates of stars on Super-massive Black Holes by star-disk interactions in galactic nuclei

    CERN Document Server

    Just, Andreas; Makukov, Maxim; Berczik, Peter; Omarov, Chingis; Spurzem, Rainer; Vilkoviskij, Emanuel Y

    2012-01-01

    We investigate the dynamical interaction of a central star cluster surrounding a super-massive black hole and a central accretion disk. The dissipative force acting on stars in the disk leads to an enhanced mass flow towards the super-massive black hole and to an asymmetry in the phase space distribution due to the rotating accretion disk. The accretion disk is considered as a stationary Keplerian rotating disk, which is vertically extended in order to employ a fully self-consistent treatment of stellar dynamics including the dissipative force originating from star-gas ram pressure effects. The stellar system is treated with a direct high-accuracy N-body integration code. A star-by-star representation, desirable in N-body simulations, cannot be extended to real particle numbers yet. Hence, we carefully discuss the scaling behavior of our model with regard to particle number and tidal accretion radius. The main idea is to find a family of models for which the ratio of two-body relaxation time and dissipation t...

  7. Structure analysis of solution to equations of quasi 3-D accretion disk model

    Institute of Scientific and Technical Information of China (English)

    WU; Mei

    2001-01-01

    [1]Frank, J., King, A., Raine, K., Accretion Power in Astrophysics, Cambridge: Cambridge University Press, 1992.[2]Lu Jufu, Abramowicz, M. A., Bimodel characteristic of accrection of black hole, Acta Astrophysica Sinica, 1988, 8(1): 1—13.[3]Shakura, N. I., Sunyaev, R. A., Black holes in binary systems: Observational appearance, A& A, 1973, 24: 337—355.[4]Spruit, H., Matsuda, T., Inoue, M. et al., Spiral shocks and accretion in discs, MNRAS, 1987, 229: 517—527.[5]Yang, R. X., Kafatos, M., Shock study in fully relativistic isothermal flows, 2, A& A, 1995, 295: 238—244.[6]Kafatos, M., Yang, R. X., Transonic inviscid disc flows in the schwarzschild metric-I, MNRAS, 1994, 268 (4): 925—937.[7]Fortner, B., Lamb, F. K., Miller, G. S., Origin of ‘normal-branch’ quasiperiodic oscillations in low-mass X-ray binary systems, Nature, 1989, 342 (14): 775—777.[8]Narayan, R., Kato, S., Honma, F., Global structure and dynamics of advection-dominated accretion flows around black holes, ApJ, 1997, 476: 49—60.[9]Chakrabarti, S., Titarchuk, L. G., Spectral properties of accretion disks around galactic and extragalactic black holes, ApJ, 1995, 455: 623—639.[10]Landu, L. D., Lifshitz, E. M., Fluid Mechanics, Bristol: f. W. Arrowsmith Ltd., 1959, 514—515.

  8. Investigating accretion disk - radio jet coupling across the stellar mass scale

    CERN Document Server

    Miller-Jones, James C A; Altamirano, Diego; Körding, Elmar G; Krimm, Hans A; Maitra, Dipankar; Remillard, Ron A; Russell, David M; Tudose, Valeriu; Dhawan, Vivek; Fender, Rob P; Heinz, Sebastian; Markoff, Sera; Migliari, Simone; Rupen, Michael P; Sarazin, Craig L

    2010-01-01

    Relationships between the X-ray and radio behavior of black hole X-ray binaries during outbursts have established a fundamental coupling between the accretion disks and radio jets in these systems. We begin by reviewing the prevailing paradigm for this disk-jet coupling, also highlighting what we know about similarities and differences with neutron star and white dwarf binaries. Until recently, this paradigm had not been directly tested with dedicated high-angular resolution radio imaging over entire outbursts. Moreover, such high-resolution monitoring campaigns had not previously targetted outbursts in which the compact object was either a neutron star or a white dwarf. To address this issue, we have embarked on the Jet Acceleration and Collimation Probe Of Transient X-Ray Binaries (JACPOT XRB) project, which aims to use high angular resolution observations to compare disk-jet coupling across the stellar mass scale, with the goal of probing the importance of the depth of the gravitational potential well, the...

  9. Properties and stability of freely propagating nonlinear density waves in accretion disks

    CERN Document Server

    Fromang, S

    2007-01-01

    In this paper, we study the propagation and stability of nonlinear sound waves in accretion disks. Using the shearing box approximation, we derive the form of these waves using a semi-analytic approach and go on to study their stability. The results are compared to those of numerical simulations performed using finite difference approaches such as employed by ZEUS as well as Godunov methods. When the wave frequency is between Omega and two Omega (where Omega is the disk orbital angular velocity), it can couple resonantly with a pair of linear inertial waves and thus undergo a parametric instability. Neglecting the disk vertical stratification, we derive an expression for the growth rate when the amplitude of the background wave is small. Good agreement is found with the results of numerical simulations performed both with finite difference and Godunov codes. During the nonlinear phase of the instability, the flow remains well organised if the amplitude of the background wave is small. However, strongly nonlin...

  10. A statistical study of the relation between soft X-ray excess and accretion disk

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    To study the origin of the soft X-ray excess,we compile a sample of 94 unobscured,radio-quiet QSOs and Seyfert galaxies with available data from GALEX and ROSAT.We find that 50 sources show strong soft X-ray excess and the other 44 show weak/no soft X-ray excess.Systematic analyses of the data indicate that the difference in soft X-rays is mainly but not only resulting from different accretion rates(in units of Eddington rate).The statistical study of the sources with soft X-ray excess shows that the strength of soft X-ray excess weakly and positively correlates with the Eddington ratio and increases with the increase of the strength of UV radiations relative to the X-rays.Provided that the UV emissions are from the thin disk,the correlations imply that the origin of soft X-ray excess is associated with the thin disk,either by means of Comptonization of the disk photons or in some other ways.

  11. Accretion dynamics and disk evolution in NGC 2264: a study based on the Corot photometric observations

    CERN Document Server

    Alencar, S H P; Guimaraes, M M; McGinnis, P T; Gameiro, J F; Bouvier, J; Aigrain, S; Flaccomio, E; Favata, F

    2010-01-01

    The young cluster NGC 2264 was observed with the Corot satellite for 23 days uninterruptedly in March 2008 with unprecedent photometric accuracy. We present here the first results of the analysis of the accreting population. We intended to look for possible light curve variability of the same nature as that observed in the classical T Tauri star AA Tau, which was attributed to a magnetically controlled inner disk warp, which is directly associated with the interaction between the stellar magnetic field and the inner disk region. We analysed the Corot light curves of 83 previously known classical T Tauri stars that belong to NGC 2264 and classified them according to their morphology. We also studied the Corot light curve morphology as a function of a Spitzer-based classification of the star-disk systems. The classification derived on the basis of the Corot light curve morphology agrees very well with the Spitzer IRAC-based classification of the systems. The percentage of AA Tau-like light curves decreases as t...

  12. Magnetic fields during the early stages of massive star formation I: Accretion and disk evolution

    CERN Document Server

    Seifried, D; Klessen, R S; Duffin, D; Pudritz, R E

    2011-01-01

    We present simulations of collapsing 100 M_\\sun mass cores in the context of massive star formation. The effect of variable initial rotational and magnetic energies on the formation of massive stars is studied in detail. We focus on accretion rates and on the question under which conditions massive Keplerian disks can form in the very early evolutionary stage of massive protostars. For this purpose, we perform 12 simulations with different initial conditions extending over a wide range in parameter space. The equations of magnetohydrodynamics (MHD) are solved under the assumption of ideal MHD. We find that the formation of Keplerian disks in the very early stages is suppressed for a mass-to-flux ratio normalised to the critical value \\mu below 10, in agreement with a series of low-mass star formation simulations. This is caused by very efficient magnetic braking resulting in a nearly instantaneous removal of angular momentum from the disk. For weak magnetic fields, corresponding to \\mu > 10, large-scale, cent...

  13. Radiation-hydrodynamic simulations of quasar disk winds

    Science.gov (United States)

    Higginbottom, N.

    2015-09-01

    Disk winds are a compelling candidate to provide geometrical unification between Broad Absorption Line QSOs (BALQSOs) and Type1 Quasars. However, the geometry of these winds, and even the driving mech- anism remain largely unknown. Progress has been made through RT simulations and theoretical analysis of simplified wind geometries but there are several outstanding issues including the problem of shielding the low ionization BAL gas from the intense X-ray radiation from the central corona, and also how to produce the strong emission lines which exemplify Type 1 Quasars. A complex, clumpy geometry may provide a solution, and a full hydrodynamic model in which such structure may well spontaneously develop is something we wish to investigate. We have already demonstrated that the previous generation of hydrodynamic models of BALQSOs suffer from the fact that radiation transfer (RT) was necessarily simplified to permit computation, thereby neglecting the effects of multiple scattering and reprocessing of photons within the wind (potentially very important processes). We have therefore embarked upon a project to marry together a RT code with a hydrodynamics code to permit full radiation hydrodynamics simulations to be carried out on QSO disk winds. Here we present details of the project and results to date.

  14. MHD Modeling of a Disk-Wind from a High-Mass Protobinary: the case of Orion Source I

    CERN Document Server

    Vaidya, B

    2012-01-01

    Very long baseline interferometry (VLBI) observations of SiO masers in Orion Source I has enabled for the first time to resolve the outflow from a high-mass protostar in the launch and collimation region. Therefore, Source I provides a unique laboratory to study mass-loss and mass-accretion in a high-mass protostar. We numerically simulate the dynamics of the disk-wind inside 100 AU from Source I. This enables us to investigate the balance of different forces (gravitational, magnetic, thermal) regulating gas dynamics in massive star formation. In this work, we adopt magnetohydrodynamic (MHD) disk-wind models to explain the observed properties of the disk-wind from Orion Source I. The central source is assumed to be a binary composed of two 10\\,$\\msun$ stars in a circular orbit with an orbital separation of 7 AU. High resolution ideal MHD wind launching simulations (which prescribe disk as a boundary) are performed using the PLUTO code. The simulations are allowed to run until a steady state is obtained. MHD d...

  15. Observations of T Tauri Disks at Sub-AU Radii: Implications for Magnetospheric Accretion and Planet Formation

    CERN Document Server

    Eisner, J A; White, R J; Akeson, R L; Sargent, A I

    2005-01-01

    We determine inner disk sizes and temperatures for four solar-type (1-2 M$_{\\odot}$) classical T Tauri stars (AS 207A, V2508 Oph, AS 205A, and PX Vul) using 2.2 $\\mu$m observations from the Keck Interferometer. Nearly contemporaneous near-IR adaptive optics imaging photometry, optical photometry, and high-dispersion optical spectroscopy are used to distinguish contributions from the inner disks and central stars in the interferometric observations. In addition, the spectroscopic and photometric data provide estimates of stellar properties, mass accretion rates, and disk co-rotation radii. We model our interferometric and photometric data in the context of geometrically flat accretion disk models with inner holes, and flared disks with puffed-up inner walls. Models incorporating puffed-up inner disk walls generally provide better fits to the data, similar to previous results for higher-mass Herbig Ae stars. Our measured inner disk sizes are larger than disk truncation radii predicted by magnetospheric accretio...

  16. Powerful, Rotating Disk Winds from Stellar-mass Black Holes

    CERN Document Server

    Miller, J M; Kaastra, J; Kallman, T; King, A L; Proga, D; Raymond, J; Reynolds, C S

    2015-01-01

    We present an analysis of ionized X-ray disk winds observed in the Fe K band of four stellar-mass black holes observed with Chandra, including 4U 1630-47, GRO J1655-40, H 1743-322, and GRS 1915+105. High-resolution photoionization grids were generated in order to model the data. Third-order gratings spectra were used to resolve complex absorption profiles into atomic effects and multiple velocity components. The Fe XXV line is found to be shaped by contributions from the intercombination line (in absorption), and the Fe XXVI line is detected as a spin-orbit doublet. The data require 2-3 absorption zones, depending on the source. The fastest components have velocities approaching or exceeding 0.01c, increasing mass outflow rates and wind kinetic power by orders of magnitude over prior single-zone models. The first-order spectra require re-emission from the wind, broadened by a degree that is loosely consistent with Keplerian orbital velocities at the photoionization radius. This suggests that disk winds are ro...

  17. Can Self Organized Critical Accretion Disks Generate a Log-normal Emission Variability in AGN?

    CERN Document Server

    Kunjaya, Chatief; Vierdayanti, Kiki; Herlie, Stefani

    2011-01-01

    Active Galactic Nuclei (AGN), such as Seyfert galaxies, quasars, etc., show light variations in all wavelength bands, with various amplitude and in many time scales. The variations usually look erratic, not periodic nor purely random. Many of these objects also show lognormal flux distribution and RMS - flux relation and power law frequency distribution. So far, the lognormal flux distribution of black hole objects is only observational facts without satisfactory explanation about the physical mechanism producing such distribution in the accretion disk. One of the most promising models based on cellular automaton mechanism has been successful in reproducing PSD (Power Spectral Density) of the observed objects but could not reproduce lognormal flux distribution. Such distribution requires the existence of underlying multiplicative process while the existing SOC models are based on additive processes. A modified SOC model based on cellular automaton mechanism for producing lognormal flux distribution is present...

  18. Extracting Energy Magnetically from Plunging Region of Black-Hole Accretion Disk

    Institute of Scientific and Technical Information of China (English)

    LIU Dong-Mei; YE Yong-Chun; WANG Ding-Xiong

    2007-01-01

    An analytical expression for the jet power extracted from the plunging region between a black hole (BH)horizon and the inner edge of the disk (hereafter the PL power) is derived based on an improved equivalent circuit in BH magnetosphere with a mapping relation between the radial coordinate of the plunging region and that of the remote astrophysical load.It is shown that the PL power is of great importance in explaining jet power and dominates over the BZ and DL powers for a wide value range of the BH spin.In addition,we show that the PL power derived in our model can be fitted with the strong jet powers of several 3CR FR I radio galaxies,which cannot be explained by virtue of the BZ mechanism.Furthermore,the condition for negative energy of the accreting particles in the plunging region is discussed with the validity of the second law of BH thermodynamics.

  19. Instability of Non-uniform Toroidal Magnetic Fields in Accretion Disks

    CERN Document Server

    Hirabayashi, Kota

    2016-01-01

    A new type of instability that is expected to drive magnetohydrodynamic (MHD) turbulence from a purely toroidal magnetic field in an accretion disk is presented. It is already known that in a differentially rotating system, the uniform toroidal magnetic field is unstable due to a magnetorotational instability (MRI) under a non-axisymmetric and vertical perturbation, while it is stable under a purely vertical perturbation. Contrary to the previous study, this paper proposes an unstable mode completely confined to the equatorial plane, driven by the expansive nature of the magnetic pressure gradient force under a non-uniform toroidal field. The basic nature of this growing eigenmode, to which we give a name "magneto-gradient driven instability", is studied using linear analysis, and the corresponding nonlinear evolution is then investigated using two-dimensional ideal MHD simulations. Although a single localized magnetic field channel alone cannot provide sufficient Maxwell stress to contribute significantly to...

  20. A pure hydrodynamic instability in shear flows and its application to astrophysical accretion disks

    CERN Document Server

    Nath, Sujit Kumar

    2016-01-01

    We provide the possible resolution for the century old problem of hydrodynamic shear flows, which are apparently stable in linear analysis but shown to be turbulent in astrophysically observed data and experiments. This mismatch is noticed in a variety of systems, from laboratory to astrophysical flows. There are so many uncountable attempts made so far to resolve this mismatch, beginning with the early work of Kelvin, Rayleigh, and Reynolds towards the end of the nineteenth century. Here we show that the presence of stochastic noise, whose inevitable presence should not be neglected in the stability analysis of shear flows, leads to pure hydrodynamic linear instability therein. This explains the origin of turbulence, which has been observed/interpreted in astrophysical accretion disks, laboratory experiments and direct numerical simulations. This is, to the best of our knowledge, the first solution to the long standing problem of hydrodynamic instability of Rayleigh stable flows.

  1. Special relativistic effects on the strength of the fluorescent $K\\alpha$ iron line from black hole accretion disks

    CERN Document Server

    Reynolds, C S

    1997-01-01

    The broad iron K$\\alpha$ emission line, commonly seen in the X-ray spectrum of Seyfert nuclei, is thought to originate when the inner accretion disk is illuminated by an active disk-corona. We show that relative motion between the disk and the X-ray emitting material can have an important influence on the observed equivalent width (EW) of this line via special relativistic aberration and Doppler effects. We suggest this may be relevant to understanding why the observed EW often exceeds the prediction of the standard X-ray reflection model. Several observational tests are suggested that could disentangle these special relativistic effects from iron abundance effects.

  2. Inner disk radius, accretion and the propeller effect in the spin-down phase of neutron stars

    CERN Document Server

    Ertan, Unal

    2015-01-01

    We have investigated the critical conditions required for an efficient steady propeller mechanism in the spin-down phases of magnetized neutron stars with optically thick accretion disks. We have shown through simple analytical calculations that: (1) the strength of the dipole field at the Alfven radius is not sufficient to sustain an efficient mass-outflow even when the magnetic dipole field lines rotate much faster than the escape speed, (2) in the spin-down phase, mass accretion onto the star could persist above a minimum disk mass-flow rate that is orders of magnitude lower than the rate corresponding to the transition between the spin-up and the spin-down states, (3) below this critical mass-flow rate, a steady propeller state could be established with a maximum inner disk radius about 25 times smaller than the Alfven radius. Our results indicate that only for spherical accretion, the inner disk radius is likely to approach the Alfven radius, and for all realistic cases, the accretion-propeller transitio...

  3. Design of Experiments Relevant to Accreting Stream-Disk Impact in Interacting Binaries

    Science.gov (United States)

    Krauland, Christine; Drake, R. P.; Kuranz, C. C.; Grosskopf, M. J.; Young, R.; Plewa, T.

    2010-05-01

    In many Cataclysmic Binary systems, mass transfer via Roche lobe overflow onto an accretion disk occurs. This produces a hot spot from the heating created by the supersonic impact of the infalling flow with the rotating accretion disk, which can produce a radiative reverse shock in the infalling flow. This collision region has many ambiguities as a radiation hydrodynamic system. Depending upon conditions, it has been argued (Armitgae & Livio, ApJ 493, 898) that the shocked region may be optically thin, thick, or intermediate, which has the potential to significantly alter its structure and emissions. Laboratory experiments have yet to produce colliding flows that create a radiative reverse shock or to produce obliquely incident colliding flows, both of which are aspects of these Binary systems. We have undertaken the design of such an experiment, aimed at the Omega-60 laser facility. The design elements include the production of postshock flows within a dense material layer or ejecta flows by release of material from a shocked layer. Obtaining a radiative reverse shock in the laboratory requires producing a sufficiently fast flow (> 100 km/s) within a material whose opacity is large enough to produce energetically significant emission from experimentally achievable layers. In this poster we will discuss the astrophysical context, the experimental design work we have done, and the challenges of implementing and diagnosing an actual experiment. This work is funded by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, by the National Laser User Facility Program in NNSA-DS and by the Predictive Sciences Academic Alliances Program in NNSA-ASC. The corresponding grant numbers are DE-FG52-09NA29548, DE-FG52-09NA29034, and DE-FC52-08NA28616.

  4. Wind tunnel measurements of wake structure and wind farm power for actuator disk model wind turbines in yaw

    Science.gov (United States)

    Howland, Michael; Bossuyt, Juliaan; Kang, Justin; Meyers, Johan; Meneveau, Charles

    2016-11-01

    Reducing wake losses in wind farms by deflecting the wakes through turbine yawing has been shown to be a feasible wind farm control approach. In this work, the deflection and morphology of wakes behind a wind turbine operating in yawed conditions are studied using wind tunnel experiments of a wind turbine modeled as a porous disk in a uniform inflow. First, by measuring velocity distributions at various downstream positions and comparing with prior studies, we confirm that the nonrotating wind turbine model in yaw generates realistic wake deflections. Second, we characterize the wake shape and make observations of what is termed a "curled wake," displaying significant spanwise asymmetry. Through the use of a 100 porous disk micro-wind farm, total wind farm power output is studied for a variety of yaw configurations. Strain gages on the tower of the porous disk models are used to measure the thrust force as a substitute for turbine power. The frequency response of these measurements goes up to the natural frequency of the model and allows studying the spatiotemporal characteristics of the power output under the effects of yawing. This work has been funded by the National Science Foundation (Grants CBET-113380 and IIA-1243482, the WINDINSPIRE project). JB and JM are supported by ERC (ActiveWindFarms, Grant No. 306471).

  5. Do Circumnuclear Dense Gas Disks Drive Mass Accretion onto Supermassive Black Holes?

    CERN Document Server

    Izumi, Takuma; Kohno, Kotaro

    2016-01-01

    We present a positive correlation between the mass of dense molecular gas ($M_{\\rm dense}$) of $\\sim 100$ pc scale circumnuclear disks (CNDs) and the black hole mass accretion rate ($\\dot{M}_{\\rm BH}$) in total 10 Seyfert galaxies, based on data compiled from the literature and an archive (median aperture $\\theta_{\\rm med}$ = 220 pc). A typical $M_{\\rm dense}$ of CNDs is 10$^{7-8}$ $M_\\odot$, estimated from the luminosity of the dense gas tracer, the HCN($1-0$) emission line. Because dense molecular gas is the site of star formation, this correlation is virtually equivalent to the one between nuclear star formation rate and $\\dot{M}_{\\rm BH}$ revealed previously. Moreover, the $M_{\\rm dense}-\\dot{M}_{\\rm BH}$ correlation was tighter for CND-scale gas than for the gas on kpc or larger scales. This indicates that CNDs likely play an important role in fueling black holes, whereas $>$kpc scale gas does not. To demonstrate a possible approach for studying the CND-scale accretion process with the Atacama Large Mill...

  6. Characterising anomalous transport in accretion disks from X-ray observations

    CERN Document Server

    Greenhough, J; Chaty, S; Dendy, R O; Rowlands, G

    2002-01-01

    Whilst direct observations of internal transport in accretion disks are not yet possible, measurement of the energy emitted from accreting astrophysical systems can provide useful information on the physical mechanisms at work. Here we examine the unbroken multi-year time variation of the total X-ray flux from three sources: Cygnus X-1, the microquasar GRS1915+105, and for comparison the nonaccreting Crab nebula. To complement previous analyses, we demonstrate that the application of advanced statistical methods to these observational time-series reveals important contrasts in the nature and scaling properties of the transport processes operating within these sources. We find the Crab signal resembles Gaussian noise; the Cygnus X-1 signal is a leptokurtic random walk whose self-similar properties persist on timescales up to three years; and the GRS1915+105 signal is similar to that from Cygnus X-1, but with self-similarity extending possibly to only a few days. This evidence of self-similarity provides a robu...

  7. Light Curves from an MHD Simulation of a Black Hole Accretion Disk

    CERN Document Server

    Schnittman, J D; Hawley, J F; Schnittman, Jeremy D.; Krolik, Julian H.; Hawley, John F.

    2006-01-01

    We use a relativistic ray-tracing code to calculate the light curves observed from a global general relativistic magneto-hydrodynamic simulation of an accretion flow onto a Schwarzschild black hole. We apply three basic emission models to sample different properties of the time-dependent accretion disk. With one of these models, which assumes thermal blackbody emission and free-free absorption, we can predict qualitative features of the high-frequency power spectrum from stellar-mass black holes in the "Thermal Dominant" state. The simulated power spectrum is characterized by a power law of index Gamma ~ 3 and total rms fractional variance of ~ 1 % near the orbital frequency at the inner-most stable orbit. Initial results indicate the existence of transient QPO peaks with frequency ratios of nearly 2:3 at a 99.9% confidence limit, but they are not generic features because at any given time they are seen only from certain observer directions. Additionally, we present detailed analysis of the azimuthal structur...

  8. MEASURING THE DIRECTION AND ANGULAR VELOCITY OF A BLACK HOLE ACCRETION DISK VIA LAGGED INTERFEROMETRIC COVARIANCE

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Michael D.; Loeb, Abraham; Shiokawa, Hotaka; Chael, Andrew A.; Doeleman, Sheperd S., E-mail: mjohnson@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2015-11-10

    We show that interferometry can be applied to study irregular, rapidly rotating structures, as are expected in the turbulent accretion flow near a black hole. Specifically, we analyze the lagged covariance between interferometric baselines of similar lengths but slightly different orientations. For a flow viewed close to face-on, we demonstrate that the peak in the lagged covariance indicates the direction and angular velocity of the emission pattern from the flow. Even for moderately inclined flows, the covariance robustly estimates the flow direction, although the estimated angular velocity can be significantly biased. Importantly, measuring the direction of the flow as clockwise or counterclockwise on the sky breaks a degeneracy in accretion disk inclinations when analyzing time-averaged images alone. We explore the potential efficacy of our technique using three-dimensional, general relativistic magnetohydrodynamic simulations, and we highlight several baseline pairs for the Event Horizon Telescope (EHT) that are well-suited to this application. These results indicate that the EHT may be capable of estimating the direction and angular velocity of the emitting material near Sgr A*, and they suggest that a rotating flow may even be utilized to improve imaging capabilities.

  9. An accretion disk swept up by a powerful thermonuclear X-ray burst

    Science.gov (United States)

    Degenaar, Nathalie

    Type-I X-ray bursts are thermonuclear explosions occurring in the surface layers of accreting neutron stars. These events are powerful probes of the physics of neutron stars and their surrounding accretion flow. Swift recently caught a very energetic type-I X-ray burst from the neutron star IGR J17062-6143 that displayed exceptional features. Firstly, the light curve of the 18 minute long X-ray burst tail shows an episode of 10 minutes with wild X-ray intensity fluctuations. Secondly, X-ray spectral analysis revealed a highly significant emission line around 1 keV, which can be interpreted as an Fe-L shell line caused by the irradiation of cold gas. Finally, the detection of significant absorption lines and edges in the Fe-K band are strongly suggestive of the presence of hot, highly ionized gas along the line of sight. None of these features are present in the persistent emission of the source. The X-ray burst of IGR J17062-6143 shows the first unambiguous detection of atomic features at CCD resolution. The timescale of the strong intensity variations, the velocity width of the Fe-L emission line, and photo-ionization modeling of the Fe-K absorption features each independently point to swept-up gas at a radius of ~1000 km from the neutron star. The unusual X-ray light curve and spectral properties could have plausibly been caused by a disruption of the accretion disk due to the super-Eddington fluxes reached during the X-ray burst.

  10. `Tail-end' Bondi-Hoyle accretion in young star clusters: Implications for disks, planets, and stars

    CERN Document Server

    Throop, Henry B

    2008-01-01

    Young stars orbiting in the gravitational potential well of forming star clusters pass through the cluster's dense molecular gas and can experience Bondi-Hoyle accretion from reservoirs outside their individual protostellar cloud cores. Accretion can occur for several million years after the stars form, but before the cluster disperses. This accretion is predominantly onto the disk and not the star. N-body simulations of stars orbiting in three young model clusters containing 30, 300, and 3000 stars are presented. The simulations include the gravitational potential of the molecular gas which smoothly disperses over time. The clusters have a star formation efficiency of 33% and a radius of 0.22 pc. We find that the disks surrounding solar-mass stars in the N=30 cluster accretes ~0.01 M_sol (~1 minimum-mass solar nebula, MMSN) per Myr. The accretion rate scales as M^2.1 for stars of mass M. The accretion rate is ~5 times lower for N=3000 cluster, due to its higher stellar velocities and higher temperature. The ...

  11. Perspectives for the study of gas in protoplanetary disks and accretion/ejection phenomena in young stars with the near-IR spectrograph SPIROU at the CFHT

    CERN Document Server

    Carmona, A; Delfosse, X

    2013-01-01

    Near-IR atomic and molecular transitions are powerful tools to trace the warm and hot gas in the circumstellar environment of young stars. Ro-vibrational transitions of H2 and H2O, and overtone transitions of CO at 2 micron centered at the stellar velocity trace hot (T~1500 K) gas in the inner few AU of protoplanetary disks. H2 near-IR lines displaying a blueshift of a few km/s probe molecular disk winds. H2 lines presenting blueshifts of hundreds of km/s reveal hot shocked gas in jets. Atomic lines such as the HeI line at 10830 A and the Hydrogen Paschen beta and Brakett gamma lines trace emission from accretion funnel flows and atomic disk winds. Bright forbidden atomic lines in the near-IR of species such as [Fe II], [N I], [S I], [S II], and [C I] trace atomic and ionized material in jets. The new near-IR high resolution spectrograph SPIROU planned for the Canada France Hawaii Telescope will offer the unique capability of combining high-spectral resolution (R~75000) with a large wavelength coverage (0.98 ...

  12. Multi-dimensional modelling of X-ray spectra for AGN accretion-disk outflows III: application to a hydrodynamical simulation

    CERN Document Server

    Sim, S A; Miller, L; Long, K S; Turner, T J

    2010-01-01

    We perform multi-dimensional radiative transfer simulations to compute spectra for a hydrodynamical simulation of a line-driven accretion disk wind from an active galactic nucleus. The synthetic spectra confirm expectations from parameterized models that a disk wind can imprint a wide variety of spectroscopic signatures including narrow absorption lines, broad emission lines and a Compton hump. The formation of these features is complex with contributions originating from many of the different structures present in the hydrodynamical simulation. In particular, spectral features are shaped both by gas in a successfully launched outflow and in complex flows where material is lifted out of the disk plane but ultimately falls back. We also confirm that the strong Fe Kalpha line can develop a weak, red-skewed line wing as a result of Compton scattering in the outflow. In addition, we demonstrate that X-ray radiation scattered and reprocessed in the flow has a pivotal part in both the spectrum formation and determi...

  13. Rossby Wave Instability of Thin Accretion Disks; 2, Detailed Linear Theory

    CERN Document Server

    Finn, J M; Colgate, S A

    1999-01-01

    In earlier work we identified a global, non-axisymmetric instability associated with the presence of an extreme in the radial profile of the key function ${\\cal L}(r) \\equiv (\\Sigma \\Omega/\\kappa^2) S^{2/\\Gamma}$ in a thin, inviscid, nonmagnetized accretion disk. Here, $\\Sigma(r)$ is the surface mass density of the disk, $\\Omega(r)$ the angular rotation rate, $S(r)$ the specific entropy, $\\Gamma$ the adiabatic index, and $\\kappa(r)$ the radial epicyclic frequency. The dispersion relation of the instability was shown to be similar to that of Rossby waves in planetary atmospheres. In this paper, we present the detailed linear theory of this Rossby wave instability and show that it exists for a wider range of conditions, specifically, for the case where there is a ``jump'' over some range of $r$ in $\\Sigma(r)$ or in the pressure $P(r)$. We elucidate the physical mechanism of this instability and its dependence on various parameters, including the magnitude of the ``bump'' or ``jump,'' the azimuthal mode number, ...

  14. The Acceleration Mechanism of Resistive MHD Jets Launched from Accretion Disks

    CERN Document Server

    Kuwabara, T; Kudoh, T; Matsumoto, R

    2004-01-01

    We analyzed the results of non-linear resistive magnetohydrodynamical (MHD) simulations of jet formation to study the acceleration mechanism of axisymmetric, resistive MHD jets. The initial state is a constant angular momentum, polytropic torus threaded by weak uniform vertical magnetic fields. The time evolution of the torus is simulated by applying the CIP-MOCCT scheme extended for resistive MHD equations. We carried out simulations up to 50 rotation period at the innermost radius of the disk created by accretion from the torus. The acceleration forces and the characteristics of resistive jets were studied by computing forces acting on Lagrangian test particles. Since the angle between the rotation axis of the disk and magnetic field lines is smaller in resistive models than in ideal MHD models, magnetocentrifugal acceleration is smaller. The effective potential along a magnetic field line has maximum around $z \\sim 0.5r_0$ in resistive models, where $r_0$ is the radius where the density of the initial toru...

  15. Detection of the Orbital Motions of Material in the Inner Accretion Disk of Mrk 766

    Science.gov (United States)

    Turner, T. J.; Miller, L.; George, I. M.; Reeves, J. N.

    2004-12-01

    Time-resolved X-ray spectroscopy has been obtained for the Seyfert galaxy Mrk 766 from XMM-Newton observations. Fe Kα emission has been detected with multiple peaks in energy that vary with time. The time variations appear as sinusoidally varying trails on the spectral-time plane, and provide direct evidence for the existence of matter orbiting a supermassive black hole. Fitting orbit models to the variations strongly indicates that the observed Fe emission originates in a small number of hotspots that are in coplanar orbits consistent with arising on an accretion disk. Taking the independently-determined value for the black hole mass of 4.3 × 106 M⊙ implies the disk is inclined at 26 ± 1o to the line of sight and emission is seen at a distance ˜ 100 gravitational radii ( ˜ 4 A.U.) from the black hole. The period and amplitude of the orbits yield a lower limit for the black hole mass of M BH > 3.6 × 105 M⊙ within a radius of 1.8 A.U.

  16. Relativistic emission lines from accreting black holes - The effect of disk truncation on line profiles

    CERN Document Server

    Müller, A; Mueller, Andreas; Camenzind, Max

    2004-01-01

    Relativistic emission lines generated by thin accretion disks around rotating black holes are an important diagnostic tool for testing gravity near the horizon. The iron K-line is of special importance for the interpretation of the X-ray emission of Seyfert galaxies, quasars and galactic X-ray binary systems. A generalized kinematic model is presented which includes radial drifts and non-Keplerian rotations for the line emitters. The resulting line profiles are obtained with an object-oriented ray tracer operating in the curved Kerr background metric. The general form of the Doppler factor is presented which includes all kinds of poloidal and toroidal motions near the horizon. The parameters of the model include the spin parameter, the inclination, the truncation and outer radius of the disk, velocity profiles for rotation and radial drift, the emissivity profile and a multi-species line-system. The red wing flux is generally reduced when radial drift is included as compared to the pure Keplerian velocity fie...

  17. The Effects of Photon Bubble Instability in Radiation-Dominated Accretion Disks

    CERN Document Server

    Turner, N J; Socrates, A; Begelman, M C; Davis, S W

    2005-01-01

    We examine the effects of photon bubble instability in radiation-dominated accretion disks such as those found around black holes in active galactic nuclei and X-ray binary star systems. Two- and 3-D numerical radiation MHD calculations of small patches of disk are used. Modes with wavelengths shorter than the gas pressure scale height grow faster than the orbital frequency in the surface layers. The fastest growth rate observed is five times the orbital frequency and occurs on nearly-vertical magnetic fields. The spectrum of linear modes agrees with a WKB analysis indicating still faster growth at unresolved scales, with a maximum proportional to the gravity and inversely proportional to the gas sound speed. Disturbances reaching non-linear amplitudes steepen into trains of shocks similar to a 1-D periodic non-linear analytic solution. Variations in propagation speed result in merging of adjacent fronts, and over time the shock spacing and amplitude increase. Growth is limited by the strength of the field, a...

  18. Stronger Reflection from Black Hole Accretion Disks in Soft X-ray States

    CERN Document Server

    Steiner, James F; Garcia, Javier A; McClintock, Jeffrey E

    2016-01-01

    We analyze 15,000 spectra of 29 stellar-mass black hole candidates collected over the 16-year mission lifetime of RXTE using a simple phenomenological model. As these black holes vary widely in luminosity and progress through a sequence of spectral states, which we broadly refer to as hard and soft, we focus on two spectral components: The Compton power law and the reflection spectrum it generates by illuminating the accretion disk. Our proxy for the strength of reflection is the equivalent width of the Fe-K line as measured with respect to the power law. A key distinction of our work is that for all states we estimate the continuum under the line by excluding the thermal disk component and using only the component that is responsible for fluorescing the Fe-K line, namely the Compton power law. We find that reflection is several times more pronounced (~3) in soft compared to hard spectral states. This is most readily caused by the dilution of the Fe line amplitude from Compton scattering in the corona, which ...

  19. The Relative Orientation of Nuclear Accretion and Galaxy Stellar Disks in Seyfert Galaxies

    CERN Document Server

    Nagar, N M

    1999-01-01

    We use the difference (delta) between the position angles of the nuclear radio emission and the host galaxy major axis to investigate the distribution of the angle (beta) between the axes of the nuclear accretion disk and the host galaxy disk in Seyfert galaxies. We provide a critical appraisal of the quality of all measurements, and find that the data are limited by observational uncertainties and biases, such as the well known deficiency of Seyfert galaxies of high inclination. There is weak evidence that the distribution of delta for Seyfert 2 galaxies may be different (at the 90% confidence level) from a uniform distribution, while the Seyfert 1 delta distribution is not significantly different from a uniform distribution or from the Seyfert 2 delta distribution. The cause of the possible non-uniformity in the distribution of delta for Seyfert 2 galaxies is discussed. Seyfert nuclei in late-type spiral galaxies may favor large values of delta (at the ~96% confidence level), while those in early-type galax...

  20. Stronger Reflection from Black Hole Accretion Disks in Soft X-Ray States

    Science.gov (United States)

    Steiner, James F.; Remillard, Ronald A.; García, Javier A.; McClintock, Jeffrey E.

    2016-10-01

    We analyze 15,000 spectra of 29 stellar-mass black hole (BH) candidates collected over the 16 year mission lifetime of Rossi X-ray Timing Explorer using a simple phenomenological model. As these BHs vary widely in luminosity and progress through a sequence of spectral states, which we broadly refer to as hard and soft, we focus on two spectral components: the Compton power law and the reflection spectrum it generates by illuminating the accretion disk. Our proxy for the strength of reflection is the equivalent width of the Fe-K line as measured with respect to the power law. A key distinction of our work is that for all states we estimate the continuum under the line by excluding the thermal disk component and using only the component that is responsible for fluorescing the Fe-K line, namely, the Compton power law. We find that reflection is several times more pronounced (˜3) in soft compared to hard spectral states. This is most readily caused by the dilution of the Fe line amplitude from Compton scattering in the corona, which has a higher optical depth in hard states. Alternatively, this could be explained by a more compact corona in soft (compared to hard) states, which would result in a higher reflection fraction.

  1. A Newly Forming Cold Flow Protogalactic Disk, a Signature of Cold Accretion from the Cosmic Web

    Science.gov (United States)

    Martin, D. Christopher; Matuszewski, Mateusz; Morrissey, Patrick; Neill, James D.; Moore, Anna; Steidel, Charles C.; Trainor, Ryan

    2016-06-01

    How galaxies form from, and are fueled by, gas from the intergalactic medium (IGM) remains one of the major unsolved problems in galaxy formation. While the classical Cold Dark Matter paradigm posits galaxies forming from cooling virialized gas, recent theory and numerical simulations have highlighted the importance of cold accretion flows—relatively cool (T ˜ few × 104 K) unshocked gas streaming along filaments into dark matter halos, including hot, massive, high-redshift halos. These flows are thought to deposit gas and angular momentum into the circumgalactic medium resulting in disk- or ring-like structures, eventually coalescing into galaxies forming at filamentary intersections. We earlier reported a bright, Lyα emitting filament near the QSO HS1549+19 at redshift z = 2.843 discovered with the Palomar Cosmic Web Imager. We now report that the bright part of this filament is an enormous (R > 100 kpc) rotating structure of hydrogen gas with a disk-like velocity profile consistent with a 4 × 1012 M ⊙ halo. The orbital time of the outer part of the what we term a “protodisk” is comparable to the virialization time and the age of the universe at this redshift. We propose that this protodisk can only have recently formed from cold gas flowing directly from the cosmic web.

  2. Numerical Simulation of Hot Accretion Flows (III): Revisiting wind properties using trajectory approach

    CERN Document Server

    Yuan, Feng; Narayan, Ramesh; Sadowski, Aleksander; Bu, Defu; Bai, Xue-Ning

    2015-01-01

    Previous MHD simulations have shown that wind must exist in black hole hot accretion flows. In this paper, we continue our study by investigating the detailed properties of wind, such as mass flux and poloidal speed, and the mechanism of wind production. For this aim, we make use of a three dimensional GRMHD simulation of hot accretion flows around a Schwarzschild black hole. The simulation is designed so that the magnetic flux is not accumulated significantly around the black hole. To distinguish real wind from turbulent outflows, we track the trajectories of the virtual Largrangian particles from simulation data. We find two types of real outflows, i.e., a quasi-relativistic jet close to the axis and a sub-relativistic wind subtending a much larger solid angle. Most of the wind originates from the surface layer of the accretion flow. The poloidal wind speed almost remains constant once they are produced, but the flux-weighted wind speed roughly follows $v_{\\rm p, wind}(r)\\approx 0.25 v_k(r)$. The mass flux ...

  3. WAVE-VORTEX MODE COUPLING IN ASTROPHYSICAL ACCRETION DISKS UNDER COMBINED RADIAL AND VERTICAL STRATIFICATION

    Energy Technology Data Exchange (ETDEWEB)

    Salhi, A. [Departement de Physique, Faculte des Sciences de Tunis, 1060 Tunis (Tunisia); Lehner, T. [LUTH, UMR 8102 CNRS, Observatoire de Paris-Meudon, 5 place de Janssen, F-92195 Meudon (France); Godeferd, F.; Cambon, C. [Laboratoire de Mecanique des Fluides et d' Acoustique, Ecole Centrale de Lyon, Universite de Lyon, UMR 5509, CNRS, INSA, UCB, F-69134 Ecully Cedex (France)

    2013-07-10

    We examine accretion disk flow under combined radial and vertical stratification utilizing a local Cartesian (or ''shearing box'') approximation. We investigate both axisymmetric and nonaxisymmetric disturbances with the Boussinesq approximation. Under axisymmetric disturbances, a new dispersion relation is derived. It reduces to the Solberg-Hoieland criterion in the case without vertical stratification. It shows that, asymptotically, stable radial and vertical stratification cannot induce any linear instability; Keplerian flow is accordingly stable. Previous investigations strongly suggest that the so-called bypass concept of turbulence (i.e., that fine-tuned disturbances of any inviscid smooth shear flow can reach arbitrarily large transient growth) can also be applied to Keplerian disks. We present an analysis of this process for three-dimensional plane-wave disturbances comoving with the shear flow of a general rotating shear flow under combined stable radial and vertical rotation. We demonstrate that large transient growth occurs for K{sub 2}/k{sub 1} >> 1 and k{sub 3} = 0 or k{sub 1} {approx} k{sub 3}, where k{sub 1}, K{sub 2}, and k{sub 3} are the azimuthal, radial, and vertical components of the initial wave vector, respectively. By using a generalized ''wave-vortex'' decomposition of the disturbance, we show that the large transient energy growth in a Keplerian disk is mainly generated by the transient dynamics of the vortex mode. The analysis of the power spectrum of total (kinetic+potential) energy in the azimuthal or vertical directions shows that the contribution coming from the vortex mode is dominant at large scales, while the contribution coming from the wave mode is important at small scales. These findings may be confirmed by appropriate numerical simulations in the high Reynolds number regime.

  4. The advection-dominated accretion flow+thin accretion disk model for two low-luminosity active galactic nuclei: M81 and NGC 4579

    Institute of Scientific and Technical Information of China (English)

    Ya-Di Xu; Xin-Wu Cao

    2009-01-01

    It was found that advection-dominated accretion flow (ADAF)+thin disk model calculations can reproduce the observed spectral energy distributions (SEDs) of two low- luminosity active galactic nuclei (AGNs), provided they are accreting at ~ 0.01 - 0.03 Eddington rates and the thin disks are truncated to ADAFs at~ 100Rs (Rs is the Schwarzschild radius) for M81 and NGC 4579 (Quataert et al. 1999). However, the black hole masses adopted in their work are about one order of magnitude lower than recent measurements on these two sources. Adopting the well estimated black hole masses, our ADAF+thin disk model calculations can reproduce the observed SEDs of these two low- luminosity AGNs, if the black hole is accreting at 2.5 × 10-4 Eddington rates with the thin disk truncated at Rtr = 120Rs for M81 ((m) = 3.3 × 10-3 and Rtr = 80Rs are required for NGC 4579). The transition zones with temperature from the thin disk with 104 - 105 to~109 - 1010 K in the ADAF will inevitably emit thermal X-ray lines, which provides a useful diagnosis of their physical properties. The observed widths of the thermal X-ray iron lines at(~)6.8 keV are consistent with Doppler broadening by Keplerian motion of the gases in the transition zones at~100Rs. We use the structure of the transition zone between the ADAF and the thin disk derived by assuming the turbulent diffusive heat mechanism to calculate their thermal X-ray line emission with the standard software package Astrophysical Plasma Emission Code (APEC). Comparing them with the equivalent widths of the observed thermal X-ray iron lines in these two sources, we find that the turbulent diffusive heat mechanism seems to be unable to reproduce the ob- served thermal X-ray line emission. The test of the evaporation model for the accretion mode transition with the observed thermal X-ray line emission is briefly discussed.

  5. Raman Scattered O VI $\\lambda$ 6825 and the Accretion Disk Emission Model in the Symbiotic Stars V1016 Cygni and HM Sagittae

    CERN Document Server

    Lee, Hee-Won

    2007-01-01

    We present the high resolution spectra of the D type symbiotic stars V1016 Cygni and HM Sagittae obtained with the Bohyunsan Optical Echelle Spectrograph (BOES), and investigate the double-peaked asymmetric profiles of the Raman scattered O VI 6825. By adopting a wind accretion disk model, we assume that the O VI emission region is described by a Keplerian thin disk. The Raman scattering occurs in a neutral region near the giant, taking in the form of a slow stellar wind, part of which is ionized by the strong UV radiation from the hot white dwarf. Using a Monte Carlo technique, we compute the line profiles that are modulated by the slow spherical stellar wind from the giant component with the ionization front approximated by a hyperboloid. In order to account for the asymmetry and the existence of a central dip in the profiles, we add an O VI resonance scattering region between the hot white dwarf and the giant star which hinders the incidence of slightly blue O VI photons upon the H I region. Overall good f...

  6. Simulations of disk galaxies with cosmic ray driven galactic winds

    CERN Document Server

    Booth, C M; Kravtsov, Andrey V; Gnedin, Nickolay Y

    2013-01-01

    We present results from high-resolution hydrodynamic simulations of isolated SMC- and Milky Way-sized galaxies that include a model for feedback from galactic cosmic rays (CRs). We find that CRs are naturally able to drive winds with mass loading factors of up to ~10 in dwarf systems. The scaling of the mass loading factor with circular velocity between the two simulated systems is consistent with \\propto v_c^{1-2} required to reproduce the faint end of the galaxy luminosity function. In addition, simulations with CR feedback reproduce both the normalization and the slope of the observed trend of wind velocity with galaxy circular velocity. We find that winds in simulations with CR feedback exhibit qualitatively different properties compared to SN driven winds, where most of the acceleration happens violently in situ near star forming sites. In contrast, the CR-driven winds are accelerated gently by the large-scale pressure gradient established by CRs diffusing from the star-forming galaxy disk out into the h...

  7. Outflowing disk winds in B[e] Supergiants

    CERN Document Server

    Cur'e, M; Cidale, L; Cur\\'{e}, Michel; Rial, Diego F.; Cidale, Lydia

    2005-01-01

    The effects of rapid rotation and bi--stability upon the density contrast between the equatorial and polar directions of a B[e] supergiant are investigated. Based on a new slow solution for different high rotational radiation--driven winds and the fact that bi--stability allows a change in the line--force parameters ($\\alpha$, $k$, and $\\delta$), the equatorial densities are about $10^2$--$10^3$ times higher than the polar ones. These values are in qualitative agreement with the observations. This calculation also permits to obtain the aperture angle of the disk.

  8. Turbulence In the Outer Regions of Protoplanetary Disks. II. Strong Accretion Driven by a Vertical Magnetic Field

    CERN Document Server

    Simon, Jacob B; Armitage, Philip J; Stone, James M; Beckwith, Kris

    2013-01-01

    We carry out a series of local, vertically stratified shearing box simulations of protoplanetary disks that include ambipolar diffusion and a net vertical magnetic field. The ambipolar diffusion profiles we employ correspond to 30AU and 100AU in a minimum mass solar nebula (MMSN) disk model, which consists of a far-UV-ionized surface layer and low-ionization disk interior. These simulations serve as a follow up to Simon et al. (2013), in which we found that without a net vertical field, the turbulent stresses that result from the magnetorotational instability (MRI) are too weak to account for observed accretion rates. The simulations in this work show a very strong dependence of the accretion stresses on the strength of the background vertical field; as the field strength increases, the stress amplitude increases. For gas to magnetic pressure ratios of 1e4 and 1e5, we find accretion rates between 1e-8 and 1e-7 solar masses per year. These accretion rates agree with observational constraints, suggesting a vert...

  9. Quasi-Periodic Oscillations and Frequencies in AN Accretion Disk and Comparison with the Numerical Results from Non-Rotating Black Hole Computed by the Grh Code

    Science.gov (United States)

    Donmez, Orhan

    The shocked wave created on the accretion disk after different physical phenomena (accretion flows with pressure gradients, star-disk interaction etc.) may be responsible observed Quasi Periodic Oscillations (QPOs) in X-ray binaries. We present the set of characteristics frequencies associated with accretion disk around the rotating and non-rotating black holes for one particle case. These persistent frequencies are results of the rotating pattern in an accretion disk. We compare the frequency's from two different numerical results for fluid flow around the non-rotating black hole with one particle case. The numerical results are taken from Refs. 1 and 2 using fully general relativistic hydrodynamical code with non-selfgravitating disk. While the first numerical result has a relativistic tori around the black hole, the second one includes one-armed spiral shock wave produced from star-disk interaction. Some physical modes presented in the QPOs can be excited in numerical simulation of relativistic tori and spiral waves on the accretion disk. The results of these different dynamical structures on the accretion disk responsible for QPOs are discussed in detail.

  10. Exploring accretion disc physics and black hole growth with regular monitoring of ultrafast AGN winds

    CERN Document Server

    Pounds, Ken; Nixon, Chris

    2016-01-01

    15 years of XMM-Newton observations have established that ultra-fast, highly ionized winds are common in radio-quiet AGN. A simple theory of Eddington-limited accretion correctly predicts the typical velocity (~0.1c) and high ionization of such winds, with observed flow energy capable of ejecting star-forming gas. With a recent extended XMM-Newton observation of the archetypal UFO, PG1211+143, revealing a more complex flow pattern, we suggest that targetted observations over the next decade offer unique potential for probing the inner accretion disc structure and SMBH growth.

  11. Do stellar winds prevent the formation of supermassive stars by accretion?

    Science.gov (United States)

    Nakauchi, Daisuke; Hosokawa, Takashi; Omukai, Kazuyuki; Saio, Hideyuki; Nomoto, Ken'ichi

    2017-03-01

    Supermassive stars (SMSs; ∼105 M⊙) formed from metal-free gas in the early Universe attract attention as progenitors of supermassive black holes observed at high redshifts. To form SMSs by accretion, central protostars must accrete at as high rates as ∼0.1-1 M⊙ yr-1. Such protostars have very extended structures with bloated envelopes, like supergiant stars, and are called supergiant protostars (SGPSs). Under the assumption of hydrostatic equilibrium, SGPSs have density-inverted layers, where the luminosity becomes locally super-Eddington, near the surface. If the envelope matter is allowed to flow out, however, a stellar wind could be launched and hinder the accretion growth of SGPSs before reaching the supermassive regime. We examine whether radiation-driven winds are launched from SGPSs by constructing steady and spherically symmetric wind solutions. We find that the wind velocity does not reach the escape velocity in any case considered. This is because once the temperature falls below ∼104 K, the opacity plummet drastically owing to the recombination of hydrogen and the acceleration ceases suddenly. This indicates that, in realistic non-steady cases, even if outflows are launched from the surface of SGPSs, they would fall back again. Such a 'wind' does not result in net mass-loss and does not prevent the growth of SGPSs. In conclusion, SGPSs will grow to SMSs and eventually collapse to massive black holes of ∼105 M⊙, as long as the rapid accretion is maintained.

  12. Sustaining star formation rates in spiral galaxies - Supernova-driven turbulent accretion disk models applied to THINGS galaxies

    CERN Document Server

    Vollmer, B

    2010-01-01

    Gas disks of spiral galaxies can be described as clumpy accretion disks without a coupling of viscosity to the actual thermal state of the gas. The model description of a turbulent disk consisting of emerging and spreading clumps (Vollmer & Beckert 2003) contains free parameters, which can be constrained by observations of molecular gas, atomic gas and the star formation rate for individual galaxies. Radial profiles of 18 nearby spiral galaxies from THINGS, HERACLES, SINGS, and GALEX data are used to compare the observed star formation efficiency, molecular fraction, and velocity dispersion to the model. The observed radially decreasing velocity dispersion can be reproduced by the model. In the framework of this model the decrease in the inner disk is due to the stellar mass distribution which dominates the gravitational potential. Introducing a radial break in the star formation efficiency into the model improves the fits significantly. This change in star formation regime is realized by replacing the fr...

  13. 3-D MHD disk wind simulations of jets and outflows from high-mass protostars

    Science.gov (United States)

    Staff, Jan E.; Tanaka, Kei; Tan, Jonathan C.; Zhang, Yichen; Liu, Mengyao

    2017-01-01

    We present the results of a series of nested, large scale, three-dimensional magnetohydrodynamics simulations of disk winds with a Blandford-Payne like magnetic field configuration, resolving scales from the stellar surface to beyond the core. The goal is to understand the structure of massive protostellar cores at various stages of their formation as the protostellar mass grows from a massive core. At each stage of a given protostellar mass, first, we study how jets and winds develop from the inner accretion disk to ~100 AU scales. We use the results from these simulations to dictate the inner boundary condition of a set of simulation extending to the core boundary at ~10,000 AU of an initially 60 solar mass core. We run separate simulations where the protostellar mass is 1, 2, 4, 8, 12, 16, and 24 Msun, and we are working on making a small grid of models in the context of the Turbulent Core Model with three different core masses and three different core surface densities. The wind is blown into the simulation box with properties derived from the previous jet simulations. We examine the opening angle of the outflow cavity and thus the star formation efficiency from the core due to outflow feedback. We find that the opening angle increases as the protostellar mass grows, but it is always less than 10 degrees, which is surprisingly small compared with previous analytic models. This is caused by the core which confines the outflow. Finally, we use our simulation results as input to a radiative transfer calculation, to compare with observations made by the SOMA survey.

  14. Clumpy wind accretion in supergiant neutron star high mass X-ray binaries

    Science.gov (United States)

    Bozzo, E.; Oskinova, L.; Feldmeier, A.; Falanga, M.

    2016-05-01

    The accretion of the stellar wind material by a compact object represents the main mechanism powering the X-ray emission in classical supergiant high mass X-ray binaries and supergiant fast X-ray transients. In this work we present the first attempt to simulate the accretion process of a fast and dense massive star wind onto a neutron star, taking into account the effects of the centrifugal and magnetic inhibition of accretion ("gating") due to the spin and magnetic field of the compact object. We made use of a radiative hydrodynamical code to model the nonstationary radiatively driven wind of an O-B supergiant star and then place a neutron star characterized by a fixed magnetic field and spin period at a certain distance from the massive companion. Our calculations follow, as a function of time (on a total timescale of several hours), the transitions of the system through all different accretion regimes that are triggered by the intrinsic variations in the density and velocity of the nonstationary wind. The X-ray luminosity released by the system is computed at each time step by taking into account the relevant physical processes occurring in the different accretion regimes. Synthetic lightcurves are derived and qualitatively compared with those observed from classical supergiant high mass X-ray binaries and supergiant fast X-ray transients. Although a number of simplifications are assumed in these calculations, we show that taking into account the effects of the centrifugal and magnetic inhibition of accretion significantly reduces the average X-ray luminosity expected for any neutron star wind-fed binary. The present model calculations suggest that long spin periods and stronger magnetic fields are favored in order to reproduce the peculiar behavior of supergiant fast X-ray transients in the X-ray domain.

  15. X-ray Reflection from Inhomogeneous Accretion Disks: II. Emission Line Variability and Implications for Reverberation Mapping

    CERN Document Server

    Ballantyne, D R; Young, A J

    2004-01-01

    One of the principal scientific objectives of the upcoming Constellation-X mission is to attempt to map the inner regions of accretion disks around black holes in Seyfert galaxies by reverberation mapping of the Fe K fluorescence line. This area of the disk is likely radiation pressure dominated and subject to various dynamical instabilities. Here, we show that density inhomogeneities in the disk atmosphere resulting from the photon bubble instability (PBI) can cause rapid changes in the X-ray reflection features, even when the illuminating flux is constant. Using a simulation of the development of the PBI, we find that, for the disk parameters chosen, the Fe K and O VIII Ly\\alpha lines vary on timescales as short as a few hundredths of an orbital time. In response to the changes in accretion disk structure, the Fe K equivalent width (EW) shows variations as large as ~100 eV. The magnitude and direction (positive or negative) of the changes depends on the ionization state of the atmosphere. The largest change...

  16. The Space Density of Extended Ultraviolet (XUV) Disks in the Local Universe and Implications for Gas Accretion on to Galaxies

    CERN Document Server

    Lemonias, Jenna J; Thilker, David; Wyder, Ted K; Martin, D Christopher; Seibert, Mark; Treyer, Marie A; Bianchi, Luciana; Heckman, Timothy M; Madore, Barry F; Rich, R Michael

    2011-01-01

    We present results of the first unbiased search for extended UV (XUV)-disk galaxies undertaken to determine the space density of such galaxies. Our sample contains 561 local (0.001 1.5 x 10^4 s) and SDSS DR7 footprints. We explore modifications to the standard classification scheme for our sample that includes both disk- and bulge-dominated galaxies. Visual classification of each galaxy in the sample reveals an XUV-disk frequency of up to 20% for the most nearby portion of our sample. On average over the entire sample (out to z=0.05) the frequency ranges from a hard limit of 4% to 14%. The GALEX imaging allows us to detect XUV-disks beyond 100 Mpc. The XUV regions around XUV-disk galaxies are consistently bluer than the main bodies. We find a surprisingly high frequency of XUV emission around luminous red (NUV-r > 5) and green valley (3 1.5-4.2 x 10^-3 Mpc^-3. Using the XUV emission as an indicator of recent gas accretion, we estimate that the cold gas accretion rate onto these galaxies is > 1.7-4.6 x 10^-3...

  17. A High-Frequency Doppler Feature in the Power Spectra of Simulated GRMHD Black Hole Accretion Disks

    CERN Document Server

    Wellons, Sarah; Psaltis, Dimitrios; Narayan, Ramesh; McClintock, Jeffrey E

    2013-01-01

    Black hole binaries exhibit a wide range of variability phenomena, from large-scale state changes to broadband noise and quasi-periodic oscillations, but the physical nature of much of this variability is poorly understood. We examine the variability properties of three GRMHD simulations of thin accretion disks around black holes of varying spin, producing light curves and power spectra as would be seen by observers. We find that the simulated power spectra show a broad feature at high frequency, which increases in amplitude with the inclination of the observer. We show that this high-frequency feature is a product of the Doppler effect and that its location is a function of the mass and spin of the black hole. This Doppler feature demonstrates that power spectral properties of the accretion disk can be tied to, and potentially used to determine, physical properties of the black hole.

  18. X-ray Reflection from Inhomogeneous Accretion Disks: I. Toy Models and Photon Bubbles

    CERN Document Server

    Ballantyne, D R; Blaes, Omer M

    2004-01-01

    Numerical simulations of the interiors of radiation dominated accretion disks show that significant density inhomogeneities can be generated in the gas. Here, we present the first results of our study on X-ray reflection spectra from such heterogeneous density structures. We consider two cases: first, we produce a number of toy models where a sharp increase or decrease in density of variable width is placed at different depths in a uniform slab. Comparing the resulting reflection spectra to those from an unaltered slab shows that the inhomogeneity can affect the emission features, in particular the Fe K and O VIII Lyalpha lines. The magnitude of any differences depends on both the parameters of the density change and the ionizing power of the illuminating radiation, but the inhomogeneity is required to be within ~2 Thomson depths of the surface to cause an effect. However, only relatively small variations in density (on the order of a few) are necessary for significant changes in the reflection features to be...

  19. The Role of Tiny Grains on the Accretion Process in Protoplanetary Disks

    CERN Document Server

    Bai, Xue-Ning

    2011-01-01

    Tiny grains such as PAHs have been thought to dramatically reduce the coupling between gas and magnetic fields in weakly ionized gas such as in protoplanetary disks (PPDs) because they provide tremendous surface area to recombine free electrons. The presence of tiny grains in PPDs thus raises the question of whether the magnetorotational instability (MRI) is able to drive rapid accretion to be consistent with observations. Charged tiny grains have similar conduction properties as ions, whose presence leads to qualitatively new behaviors in the conductivity tensor, characterized by n_bar/n_e>1, where n_e and n_bar denote the number densities of free electrons and all other charged species respectively. In particular, Ohmic conductivity becomes dominated by charged grains rather than electrons when n_bar/n_e exceeds about 10^3, and Hall and ambipolar diffusion (AD) coefficients are reduced by a factor of (n_bar/n_e)^2 in the AD dominated regime relative to that in the Ohmic regime. Applying the methodology of B...

  20. High-Density Effects in X-ray Reflection Models from Accretion Disks

    CERN Document Server

    García, Javier A; Kallman, Timothy R; Dauser, Thomas; Parker, Michael L; McClintock, Jeffrey E; Steiner, James F; Wilms, Jörn

    2016-01-01

    The current models for the X-ray reflected spectrum from accretion disks around compact objects are commonly calculated for a constant density along a few Thomson depths from in the direction normal to the irradiated surface. In this models an important simplification is adopted, that is that the ionization structure of the material is completely governed by the the ratio of the incident flux to the gas density (i.e., the ionization parameter $\\xi$. In this setup the value of the density is is typically fixed at $n=10^{15}$ cm$^{-3}$, as it is assumed that the ionization state of the gas is the same for equal values of $\\xi$. In this paper we explore the limitations of this assumption by computing the reflected spectra for various values of the gas density. We show that for large values ($n \\gtrsim 10^{17}$ cm$^{-3}$) the high-density effects become important, significantly modifying the reflected spectrum. The main observed effect is a large increase of thermal emission at soft energies (below $\\sim2$ keV), ...

  1. An ALMA Constraint on the GSC 6214-210 B Circum-Substellar Accretion Disk Mass

    CERN Document Server

    Bowler, Brendan P; Kraus, Adam L; Ireland, Michael J; Herczeg, Gregory; Ricci, Luca; Carpenter, John; Brown, Michael E

    2015-01-01

    We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of GSC 6214-210 A and B, a solar-mass member of the 5-10 Myr Upper Scorpius association with a 15 $\\pm$ 2 Mjup companion orbiting at $\\approx$330 AU (2.2"). Previous photometry and spectroscopy spanning 0.3-5 $\\mu$m revealed optical and thermal excess as well as strong H$\\alpha$ and Pa~$\\beta$ emission originating from a circum-substellar accretion disk around GSC 6214-210 B, making it the lowest mass companion with unambiguous evidence of a subdisk. Despite ALMA's unprecedented sensitivity and angular resolution, neither component was detected in our 880 $\\mu$m (341 GHz) continuum observations down to a 3-$\\sigma$ limit of 0.22 mJy/beam. The corresponding constraints on the dust mass and total mass are <0.15 Mearth and <0.05 Mjup, respectively, or <0.003% and <0.3% of the mass of GSC 6214-210 B itself assuming a 100:1 gas-to-dust ratio and characteristic dust temperature of 10-20 K. If the host star possesses a putative c...

  2. IRAS 16293-2422: Evidence for Infall onto a Counter-Rotating Protostellar Accretion Disk

    CERN Document Server

    Remijan, A J; Remijan, Anthony J.

    2006-01-01

    We report high spatial resolution VLA observations of the low-mass star-forming region IRAS 16293-2422 using four molecular probes: ethyl cyanide (CH$_3$CH$_2$CN), methyl formate (CH$_3$OCHO), formic acid (HCOOH), and the ground vibrational state of silicon monoxide (SiO). Ethyl cyanide emiss ion has a spatial scale of $\\sim20''$ and encompasses binary cores A and B as determined by continuum emission peaks. Surrounded by formic acid emission, methyl formate emission has a spatial scale of $\\sim6''$and is confined to core B. SiO emission shows two velocity components with spatial scales less than 2$''$ that map $\\sim2''$ northeast of the A and B symmetry axis. The redshifted SiO is $\\sim2''$ northwest of blueshifted SiO along a position angle of $\\sim135^o$ which is approximately parallel to the A and B symmetry axis. We interpret the spatial position offset in red and blueshifted SiO emission as due to rotation of a protostellar accretion disk and we derive $\\sim$1.4 M$_{\\odot}$ interior to the SiO emission....

  3. Broad K$\\alpha$ iron line from accretion disks around traversable wormholes

    CERN Document Server

    Bambi, Cosimo

    2013-01-01

    It has been proposed that the supermassive black hole candidates at the centers of galaxies might be wormholes formed in the early Universe and connecting our Universe with other sister Universes. The analysis of the profile of the relativistic K$\\alpha$ iron line is currently the only available approach to probe the spacetime geometry around these objects. In this paper, I compute the expected K$\\alpha$ iron line in some wormhole spacetimes and I compare the results with the line produced around Kerr black holes. The line produced in accretion disks around non-rotating or very slow-rotating wormholes is relatively similar to the one expected around Kerr black holes with mid or high value of spin parameter and current observations are still marginally compatible with the possibility that the supermassive black hole candidates in galactic nuclei are these objects. For wormholes with spin parameter $a_* \\gtrsim 0.02$, the associated K$\\alpha$ iron line is instead quite different from the one produced around Ker...

  4. K$\\alpha$ iron line profile from accretion disks around regular and singular exotic compact objects

    CERN Document Server

    Bambi, Cosimo

    2013-01-01

    The nature of the super-massive black hole candidates in galactic nuclei can be tested by analyzing the profile of the K$\\alpha$ iron line observed in their X-ray spectrum. In this paper, we consider the possibility that the spacetime in the immediate vicinity of these objects may be described by some non vacuum exact solutions of Einstein's equations resulting as the end-state of gravitational collapse. The vacuum far away portion of the spacetime is described by the Schwarzschild metric, while the interior part may be either regular or have a naked singularity at the center. The iron line generated around this class of objects has specific features, which can be used to distinguish such objects from Kerr black holes. In particular, their iron line cannot have the characteristic low-energy tail of the line generated from accretion disks around fast-rotating Kerr black holes. We can thus conclude that the super-massive black hole candidates whose spin parameter has been estimated to be close to 1 assuming the...

  5. Spread of Matter over a Neutron-Star Surface During Disk Accretion: Deceleration of Rapid Rotation

    CERN Document Server

    Sunyaev, R A

    2011-01-01

    The problem of disk accretion onto the surface of a neutron star with a weak magnetic field at a luminosity exceeding several percent of Eddington is reduced to the problem of the braking of a hypersonic flow with a velocity that is 0.4-0.5 of the speed of light above the base of the spreading layer -- a dense atmosphere made up of previously fallen matter. We show that turbulent braking in the Prandtl-Karman model with universally accepted coefficients for terrestrial conditions and laboratory experiments and a ladder of interacting gravity waves in a stratified quasi-exponential atmosphere at standard Richardson numbers lead to a spin-up of the massive zone that extends to the ocean made up of a plasma with degenerate electrons. Turbulent braking in the ocean at the boundary with the outer solid crust reduces the rotation velocity to the solid-body rotation velocity of the star. This situation should lead to strong heating of deep atmospheric layers and to the switch-off of the explosive helium burning mech...

  6. Effects of anisotropic thermal conduction on wind properties in hot accretion flow

    CERN Document Server

    Bu, De-Fu; Yuan, Ye-Fei

    2016-01-01

    Previous works have clearly shown the existence of winds from black hole hot accretion flow and investigated their detailed properties. In extremely low accretion rate systems, the collisional mean-free path of electrons is large compared with the length-scale of the system, thus thermal conduction is dynamically important. When the magnetic field is present, the thermal conduction is anisotropic and energy transport is along magnetic field lines. In this paper, we study the effects of anisotropic thermal conduction on the wind production in hot accretion flows by performing two-dimensional magnetohydrodynamic simulations. We find that thermal conduction has only moderate effects on the mass flux of wind. But the energy flux of wind can be increased by a factor of $\\sim 10$ due to the increase of wind velocity when thermal conduction is included. The increase of wind velocity is because of the increase of driving forces (e.g. gas pressure gradient force and centrifugal force) when thermal conduction is includ...

  7. Clumpy wind accretion in supergiant neutron star high mass X-ray binaries

    CERN Document Server

    Bozzo, E; Feldmeier, A; Falanga, M

    2016-01-01

    The accretion of the stellar wind material by a compact object represents the main mechanism powering the X-ray emission in classical supergiant high mass X-ray binaries and supergiant fast X-ray transients. In this work we present the first attempt to simulate the accretion process of a fast and dense massive star wind onto a neutron star, taking into account the effects of the centrifugal and magnetic inhibition of accretion ("gating") due to the spin and magnetic field of the compact object. We made use of a radiative hydrodynamical code to model the non-stationary radiatively driven wind of an O-B supergiant star and then place a neutron star characterized by a fixed magnetic field and spin period at a certain distance from the massive companion. Our calculations follow, as a function of time (on a total time scale of several hours), the transition of the system through all different accretion regimes that are triggered by the intrinsic variations in the density and velocity of the non-stationary wind. Th...

  8. Anti-correlated time lags in the Z source GX 5-1: Possible evidence for a truncated accretion disk

    CERN Document Server

    Sriram, K; Rao, A R

    2012-01-01

    We investigate the nature of the inner accretion disk in the neutron star source GX 5-1 by making a detailed study of time lags between X-rays of different energies. Using the cross-correlation analysis, we found anti-correlated hard and soft time lags of the order of a few tens to a few hundred seconds and the corresponding intensity states were mostly the horizontal branch (HB) and upper normal branch (NB). The model independent and dependent spectral analysis showed that during these time lags the structure of accretion disk significantly varied. Both eastern and western approaches were used to unfold the X-ray continuum and systematic changes were observed in soft and hard spectral components. These changes along with a systematic shift in the frequency of quasi-periodic oscillations (QPOs) made it substantially evident that the geometry of the accretion disk is truncated. Simultaneous energy spectral and power density spectral study shows that the production of the horizontal branch oscillations (HBOs) a...

  9. NuSTAR and Suzaku X-ray Spectroscopy of NGC 4151: Evidence for Reflection from the Inner Accretion Disk

    CERN Document Server

    Keck, M L; Ballantyne, D R; Bauer, F; Boggs, S E; Christensen, F E; Craig, W W; Dauser, T; Elvis, M; Fabian, A C; Fuerst, F; García, J; Grefenstette, B W; Hailey, C J; Harrison, F A; Madejski, G; Marinucci, A; Matt, G; Reynolds, C S; Stern, D; Walton, D J; Zoghbi, A

    2015-01-01

    We present X-ray timing and spectral analyses of simultaneous 150 ks Nuclear Spectroscopic Telescope Array (NuSTAR) and Suzaku X-ray observations of the Seyfert 1.5 galaxy NGC 4151. We disentangle the continuum emission, absorption, and reflection properties of the active galactic nucleus (AGN) by applying inner accretion disk reflection and absorption-dominated models. With a time-averaged spectral analysis, we find strong evidence for relativistic reflection from the inner accretion disk. We find that relativistic emission arises from a highly ionized inner accretion disk with a steep emissivity profile, which suggests an intense, compact illuminating source. We find a preliminary, near-maximal black hole spin a>0.9 accounting for statistical and systematic modeling errors. We find a relatively moderate reflection fraction with respect to predictions for the lamp post geometry, in which the illuminating corona is modeled as a point source. Through a time-resolved spectral analysis, we find that modest coron...

  10. Disk reflection and a possible disk wind during a soft X-ray state in the neutron star low-mass X-ray binary 1RXS J180408.9-342058

    CERN Document Server

    Degenaar, N; Parker, M; Miller-Jones, J C A; Miller, J M; Heinke, C O; Wijnands, R; Ludlam, R; Parikh, A; Hessels, J W T; Gusinskaia, N; Deller, A T; Fabian, A C

    2016-01-01

    1RXS J180408.9-342058 is a transient neutron star low-mass X-ray binary that exhibited a bright accretion outburst in 2015. We present Nustar, Swift, and Chandra observations obtained around the peak of this outburst. The source was in a soft X-ray spectral state and displayed an X-ray luminosity of Lx~(2-3)E37 (D/5.8 kpc)^2 erg cm-2 (0.5-10 keV). The Nustar data reveal a broad Fe-K emission line that we model as relativistically broadened reflection to constrain the accretion geometry. We found that the accretion disk is viewed at an inclination of i~27-35 degrees and extended close to the neutron star, down to Rin~5-7.5 gravitational radii (~11-17 km). This inner disk radius suggests that the neutron star magnetic field strength is B<2E8 G. We find a narrow absorption line in the Chandra/HEG data at an energy of ~7.64 keV with a significance of ~4.8 sigma. This feature could correspond to blue-shifted Fe xxvi and arise from an accretion disk wind, which would imply an outflow velocity of v~0.086c (~25800...

  11. Reverberation Mapping of the Broad Line Region: Application to a Hydrodynamical Line-driven Disk Wind Solution

    Science.gov (United States)

    Waters, Tim; Kashi, Amit; Proga, Daniel; Eracleous, Michael; Barth, Aaron J.; Greene, Jenny

    2016-08-01

    The latest analysis efforts in reverberation mapping are beginning to allow reconstruction of echo images (or velocity-delay maps) that encode information about the structure and kinematics of the broad line region (BLR) in active galactic nuclei (AGNs). Such maps can constrain sophisticated physical models for the BLR. The physical picture of the BLR is often theorized to be a photoionized wind launched from the AGN accretion disk. Previously we showed that the line-driven disk wind solution found in an earlier simulation by Proga and Kallman is virialized over a large distance from the disk. This finding implies that, according to this model, black hole masses can be reliably estimated through reverberation mapping techniques. However, predictions of echo images expected from line-driven disk winds are not available. Here, after presenting the necessary radiative transfer methodology, we carry out the first calculations of such predictions. We find that the echo images are quite similar to other virialized BLR models such as randomly orbiting clouds and thin Keplerian disks. We conduct a parameter survey exploring how echo images, line profiles, and transfer functions depend on both the inclination angle and the line opacity. We find that the line profiles are almost always single peaked, while transfer functions tend to have tails extending to large time delays. The outflow, despite being primarily equatorially directed, causes an appreciable blueshifted excess on both the echo image and line profile when seen from lower inclinations (i≲ 45^\\circ ). This effect may be observable in low ionization lines such as {{H}}β .

  12. Stochastic Resonance of Accretion Disk and the Persistent Low-Frequency Quasi-Periodic Oscillations in Black Hole X-ray Binaries

    Indian Academy of Sciences (India)

    Z. Y. Wang; P. J. Chen; D. X. Wang; L. Y. Zhang

    2013-03-01

    In this paper, we use a Langevin type equation with a damping term and stochastic force to describe the stochastic oscillations on the vertical direction of the accretion disk around a black hole, and calculate the luminosity and power spectral density (PSD) for an oscillating disk. Then we discuss the stochastic resonance (SR) phenomenon in PSD curves for different parameter values of viscosity coefficient, accretion rate, mass of black hole and outer radius of the disk. The results show that our simulated PSD curves of luminosity for disk oscillation have the same profile as the observed PSD of black hole X-ray binaries (BHXBs) in the lowhard state, and the SR of accretion disk oscillation may be an alternative interpretation of the persistent low-frequency quasi-periodic oscillations (LFQPOs).

  13. Numerical studies of gravitational accretion from x-ray heated stellar winds. Doctoral thesis

    Energy Technology Data Exchange (ETDEWEB)

    Lupo, J.A.

    1981-12-01

    We present three numerical models of accretion from radiation driven stellar winds onto compact objects in massive X-ray binary systems. The wind is given a velocity profile consistent with a radiatively driven wind, and a 'negative mass' gravitational potential is derived from this profile to represent the wind driving force in the hydrodynamic equations. An X-ray heating model is used which determines the X-ray heating time from the Compton heating time and the known steady state energies for optically thin gas illuminated by X-rays. This allows X-ray heating to be included in the hydrodynamic equations. The X-ray luminosity is held proportional to the accretion rate, assuming that the gravitational potential energy released is equivalent to 10% of the infalling rest-mass energy. A two-dimensional Eulerian computer code is used to solve the equations of motion. Model estimates of the ionization structure, accretion rates and flow characteristics, and the effects of thermal instabilities are discussed. The impact of the X-ray radiation on the wind driving force is demonstrated. Results indicate a possible mechanism for slow X-ray flares, such as observed in 4U1700-37.

  14. Numerical studies of gravitational accretion from x-ray heated stellar winds

    Energy Technology Data Exchange (ETDEWEB)

    Lupo, J.A.

    1981-01-01

    Three numerical models of accretion from radiation driven stellar winds onto compact objects in massive x-ray binary systems are presented. The wind is given a velocity profile consistent with a radiatively driven wind, and a ''negative mass'' gravitational potential is derived from this profile to represent the wind driving force in the hydrodynamic equations. An x-ray heating model is used which determines the x-ray heating time from the Compton heating time and the known steady state energies for optically thin gas illuminated by x-rays. This allows x-ray heating to be included in the hydrodynamic equations. The x-ray luminosity is held proportional to the accretion rate, assuming that the gravitational potential energy released is equivalent to 10% of the infalling rest-mass energy. A two-dimensional Eulerian computer code is used to solve the equations of motion. Model estimates of the ionization structure, accretion rates and flow characteristics, and the effects of thermal instabilities are discussed. The impact of the x-ray radiation on the wind driving force is demonstrated. Results indicate a possible mechanism for slow x-ray flares, such as observed in 4U1700-37.

  15. Density, Velocity and Ionization Structure in Accretion-Disc Winds

    Science.gov (United States)

    Sonneborn, George (Technical Monitor); Long, Knox

    2004-01-01

    This was a project to exploit the unique capabilities of FUSE to monitor variations in the wind- formed spectral lines of the luminous, low-inclination, cataclysmic variables(CV) -- RW Sex. (The original proposal contained two additional objects but these were not approved.) These observations were intended to allow us to determine the relative roles of density and ionization state changes in the outflow and to search for spectroscopic signatures of stochastic small-scale structure and shocked gas. By monitoring the temporal behavior of blue-ward extended absorption lines with a wide range of ionization potentials and excitation energies, we proposed to track the changing physical conditions in the outflow. We planned to use a new Monte Carlo code to calculate the ionization structure of and radiative transfer through the CV wind. The analysis therefore was intended to establish the wind geometry, kinematics and ionization state, both in a time-averaged sense and as a function of time.

  16. A possible origin of viscosity in Keplerian accretion disks due to secondary perturbation: Turbulent transport without magnetic fields

    Institute of Scientific and Technical Information of China (English)

    Banibrata Mukhopadhyay; Kanak Saha

    2011-01-01

    The origin of hydrodynamic turbulence in rotating shear flow is a long standing puzzle.Resolving it is especially important in astrophysics when the flow's angular momentum profile is Keplerian which forms an accretion disk having negligible molecular viscosity.Hence, any viscosity in such systems must be due to turbulence, arguably governed by magnetorotational instability, especially when temperature T (≥)105.However, such disks around quiescent cataclysmic variables, protoplanetary and star-forming disks, and the outer regions of disks in active galactic nuclei are practically neutral in charge because of their low temperature, and thus are not expected to be coupled with magnetic fields enough to generate any transport due to the magnetorotational instability.This flow is similar to plane Couette flow including the Coriolis force, at least locally.What drives their turbulence and then transport,when such flows do not exhibit any unstable mode under linear hydrodynamic perturbation? We demonstrate that the three-dimensional secondary disturbance to the primarily perturbed flow that triggers elliptical instability may generate significant turbulent viscosity in the range 0.0001 (≤) vt (≤) 0.1, which can explain transport in accretion flows.

  17. NuSTAR and XMM-Newton Observations of NGC 1365: Extreme Absorption Variability and a Constant Inner Accretion Disk

    CERN Document Server

    Walton, D J; Harrison, F A; Fabian, A C; Miller, J M; Arevalo, P; Ballantyne, D R; Boggs, S E; Brenneman, L W; Christensen, F E; Craig, W W; Elvis, M; Fuerst, F; Gandhi, P; Grefenstette, B W; Hailey, C J; Kara, E; Luo, B; Madsen, K K; Marinucci, A; Matt, G; Parker, M L; Reynolds, C S; Rivers, E; Ross, R R; Stern, D; Zhang, W W

    2014-01-01

    We present a spectral analysis of four coordinated NuSTAR+XMM-Newton observations of the Seyfert galaxy NGC 1365. These exhibit an extreme level of spectral variability, which is primarily due to variable line-of-sight absorption, revealing relatively unobscured states in this source for the first time. Despite the diverse range of absorption states, each of the observations displays the same characteristic signatures of relativistic reflection from the inner accretion disk. Through time-resolved spectroscopy we find that the strength of the relativistic iron line and the Compton reflection hump relative to the intrinsic continuum are well correlated, as expected if they are two aspects of the same broadband reflection spectrum. We apply self-consistent disk reflection models to these time-resolved spectra in order to constrain the inner disk parameters, allowing for variable, partially covering absorption to account for the vastly different absorption states observed. Each of the four observations is treated...

  18. Production of all $r$-process nuclides by black hole accretion disk outflows from neutron star mergers

    CERN Document Server

    Wu, Meng-Ru; Martínez-Pinedo, Gabriel; Metzger, Brian D

    2016-01-01

    We consider $r$-process nucleosynthesis in outflows from black hole accretion disks formed in double neutron star and neutron star - black hole mergers. These outflows, powered by angular momentum transport processes and nuclear recombination, represent an important -- and in some cases dominant -- contribution to the total mass ejected by the merger. Here we calculate the nucleosynthesis yields from disk outflows using thermodynamic trajectories from hydrodynamic simulations, coupled to a nuclear reaction network. We find that outflows produce a robust abundance pattern around the second $r$-process peak (mass number $A \\sim 130$), independent of model parameters, with significant production of $A < 130$ nuclei. This implies that dynamical ejecta with high electron fraction may not be required to explain the observed abundances of $r$-process elements in metal poor stars. Disk outflows reach the third peak ($ A \\sim 195$) in most of our simulations, although the amounts produced depend sensitively on the ...

  19. TOWARD A GLOBAL EVOLUTIONARY MODEL OF PROTOPLANETARY DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Bai, Xue-Ning, E-mail: xbai@cfa.harvard.edu [Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS-51, Cambridge, MA 02138 (United States)

    2016-04-20

    A global picture of the evolution  of protoplanetary disks (PPDs) is key to understanding almost every aspect of planet formation, where standard α-disk models have been continually employed for their simplicity. In the meantime, disk mass loss has been conventionally attributed to photoevaporation, which controls disk dispersal. However, a paradigm shift toward accretion driven by magnetized disk winds has taken place in recent years, thanks to studies of non-ideal magnetohydrodynamic effects in PPDs. I present a framework of global PPD evolution aiming to incorporate these advances, highlighting the role of wind-driven accretion and wind mass loss. Disk evolution is found to be largely dominated by wind-driven processes, and viscous spreading is suppressed. The timescale of disk evolution is controlled primarily by the amount of external magnetic flux threading the disks, and how rapidly the disk loses the flux. Rapid disk dispersal can be achieved if the disk is able to hold most of its magnetic flux during the evolution. In addition, because wind launching requires a sufficient level of ionization at the disk surface (mainly via external far-UV (FUV) radiation), wind kinematics is also affected by the FUV penetration depth and disk geometry. For a typical disk lifetime of a few million years, the disk loses approximately the same amount of mass through the wind as through accretion onto the protostar, and most of the wind mass loss proceeds from the outer disk via a slow wind. Fractional wind mass loss increases with increasing disk lifetime. Significant wind mass loss likely substantially enhances the dust-to-gas mass ratio and promotes planet formation.

  20. Disk and wind interaction in the young stellar object MWC 297 spatially resolved with VLTI/AMBER

    CERN Document Server

    Malbet, F; De Wit, W J; Kraus, S; Meilland, A; Millour, F; Tatulli, E; Berger, J P; Chesneau, O; Hofmann, Karl Heinrich; Isella, A; Natta, A; Petrov, R; Preibisch, T; Stee, P; Testi, L; Weigelt, G; Antonelli, P; Beckmann, U; Bresson, Y; Chelli, A; Duvert, G; Gluck, L; Kern, P; Lagarde, S; Le Coarer, E; Lisi, F; Perraut, K; Robbe-Dubois, S; Roussel, A; Zins, G; Accardo, M; Acke, B; Agabi, K; Arezki, B; Aristidi, E; Baffa, C; Behrend, J; Blöcker, T; Bonhomme, S; Busoni, S; Cassaing, F; Clausse, J M; Colin, J; Connot, C; Delboulbé, A; Driebe, T; Dugué, M; Feautrier, P; Ferruzzi, D; Forveille, T; Fossat, E; Foy, R; Fraix-Burnet, D; Gallardo, A; Gennari, S; Glentzlin, A; Giani, E; Gil, C; Heiden, M; Heininger, M; Kamm, D; Le Contel, D; Le Contel, J M; López, B; Magnard, Y; Marconi, A; Mars, G; Martinot-Lagarde, G; Mathias, P; Monin, J L; Mouillet, D; Mourard, D; Mege, P; Nussbaum, E; Ohnaka, K; Pacheco, J; Pacini, F; Perrier, C; Puget, P; Rabbia, Y; Rebattu, S; Reynaud, F; Richichi, A; Sacchettini, M; Salinari, P; Schertl, D; Solscheid, W; Stefanini, P; Tallon, M; Tallon-Bosc, I; Tasso, D; Valtier, J C; Vannier, M; Ventura, N; Kiekebusch, M; Rantakyro, F; Schöller, M

    2005-01-01

    The young stellar object MWC 297 has been observed with the VLT interferometer equipped with the AMBER instrument. MWC 297 has been spatially resolved in the continuum with a visibility of 0.50 as well as in the Br gamma emission line where the visibility decrease to a lower value of 0.33. This change in the visibility with the wavelength can be interpreted by the presence of an optically thick disk responsible for the visibility in the continuum and of a stellar wind traced by Br gamma and whose apparent size is 40% larger. We validate this interpretation by building a model of the stellar environment that combines a geometrically thin, optically thick accretion disk model consisting of gas and dust, and a latitude-dependent stellar wind outflowing above the disk surface. The continuum emission and visibilities obtained from this model are fully consistent with the interferometric AMBER data. They agree also with existing optical, near-infrared spectra and other broad-band near-infrared interferometric visib...

  1. Do Stellar Winds Prevent the Formation of Supermassive Stars by Accretion?

    CERN Document Server

    Nakauchi, Daisuke; Omukai, Kazuyuki; Saio, Hideyuki; Nomoto, Ken'ichi

    2016-01-01

    Supermassive stars (SMS; ~ 10^5 M_sun) formed from metal-free gas in the early Universe attract attention as progenitors of supermassive black holes observed at high redshifts. To form SMSs by accretion, central protostars must accrete at as high rates as ~ 0.1-1 M_sun/yr. Such protostars have very extended structures with bloated envelopes, like super-giant stars, and are called super-giant protostars (SGPSs). Under the assumption of hydrostatic equilibrium, SGPSs have density inverted layers, where the luminosity becomes locally super-Eddington, near the surface. If the envelope matter is allowed to flow out, however, a stellar wind could be launched and hinder the accretion growth of SGPSs before reaching the supermassive regime. We examine whether radiation-driven winds are launched from SGPSs by constructing steady and spherically symmetric wind solutions. We find that the wind velocity does not reach the escape velocity in any case considered. This is because once the temperature falls below ~ 10^4 K, t...

  2. X-RAYING AN ACCRETION DISK IN REALTIME: THE EVOLUTION OF IONIZED REFLECTION DURING A SUPERBURST FROM 4U 1636-536

    Energy Technology Data Exchange (ETDEWEB)

    Keek, L.; Ballantyne, D. R. [Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, 837 State Street, Atlanta, GA 30332-0430 (United States); Kuulkers, E. [European Space Astronomy Centre (ESA/ESAC), Science Operations Department, E-28691 Villanueva de la Cañada, Madrid (Spain); Strohmayer, T. E., E-mail: l.keek@gatech.edu [X-Ray Astrophysics Lab, Astrophysics Science Division, NASA' s Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

    2014-12-20

    When a thermonuclear X-ray burst ignites on an accreting neutron star, the accretion disk undergoes sudden strong X-ray illumination, which can drive a range of processes in the disk. Observations of superbursts, with durations of several hours, provide the best opportunity to study these processes and to probe accretion physics. Using detailed models of X-ray reflection, we perform time resolved spectroscopy of the superburst observed from 4U 1636-536 in 2001 with the Rossi X-Ray Timing Explorer. The spectra are consistent with a blackbody reflecting off a photoionized accretion disk, with the ionization state dropping with time. The evolution of the reflection fraction indicates that the initial reflection occurs from a part of the disk at larger radius, subsequently transitioning to reflection from an inner region of the disk. Even though this superburst did not reach the Eddington limit, we find that a strong local absorber develops during the superburst. Including this event, only two superbursts have been observed by an instrument with sufficient collecting area to allow for this analysis. It highlights the exciting opportunity for future X-ray observatories to investigate the processes in accretion disks when illuminated by superbursts.

  3. Composite Accretion Disk and White Dwarf Photosphere Analyses of the FUSE and HST Observations of EY Cygni

    CERN Document Server

    Sion, E M; Urban, J A; Tovmassian, G H; Zharikov, S; Gänsicke, B T; Orio, M

    2004-01-01

    We explore the origin of FUSE and HST STIS far UV spectra of the dwarf nova, EY Cyg, during its quiescence using \\emph{combined} high gravity photosphere and accretion disk models as well as model accretion belts. The best-fitting single temperature white dwarf model to the FUSE plus HST STIS spectrum of EY Cygni has T$_{eff} = 24,000$K, log $g = 9.0$, with an Si abundance of 0.1 x solar and C abundance of 0.2 x solar but the distance is only 301 pc. The best-fitting composite model consists of white dwarf with T$_{eff} = 22,000$K, log $g = 9$, plus an accretion belt with T$_{belt} = 36,000$K covering 27% of the white dwarf surface with V$_{belt} sin i = 2000$ km/s. The accretion belt contributes 63% of the FUV light and the cooler white dwarf latitudes contribute 37%. This fit yields a distance of 351 pc which is within 100 pc of our adopted distance of 450 pc. EY Cyg has very weak C {\\sc iv} emission and very strong N {\\sc v} emission, which is atypical of the majority of dwarf novae in quiescence. We also ...

  4. Modelling accretion disc and stellar wind interactions: the case of Sgr A*

    Science.gov (United States)

    Christie, I. M.; Petropoulou, M.; Mimica, P.; Giannios, D.

    2016-07-01

    Sgr A* is an ideal target to study low-luminosity accreting systems. It has been recently proposed that properties of the accretion flow around Sgr A* can be probed through its interactions with the stellar wind of nearby massive stars belonging to the S-cluster. When a star intercepts the accretion disc, the ram and thermal pressures of the disc terminate the stellar wind leading to the formation of a bow shock structure. Here, a semi-analytical model is constructed which describes the geometry of the termination shock formed in the wind. With the employment of numerical hydrodynamic simulations, this model is both verified and extended to a region prone to Kelvin-Helmholtz instabilities. Because the characteristic wind and stellar velocities are in ˜108 cm s-1 range, the shocked wind may produce detectable X-rays via thermal bremsstrahlung emission. The application of this model to the pericentre passage of S2, the brightest member of the S-cluster, shows that the shocked wind produces roughly a month long X-ray flare with a peak luminosity of L ≈ 4 × 1033 erg s-1 for a stellar mass-loss rate, disc number density, and thermal pressure strength of dot{M}_w= 10^{-7} M_{⊙} yr^{-1}, nd = 105 cm-3, and α = 0.1, respectively. This peak luminosity is comparable to the quiescent X-ray emission detected from Sgr A* and is within the detection capabilities of current X-ray observatories. Its detection could constrain the density and thickness of the disc at a distance of ˜3000 gravitational radii from the supermassive black hole.

  5. On the nature of the first transient Z-source XTE J1701-462: its accretion disk structure, neutron star magnetic field strength, and hard tail

    CERN Document Server

    Ding, G Q; Wang, N; Qu, J L; Yan, S P

    2011-01-01

    Using the data from the Rossi X-Ray Timing Explorer satellite, we investigate the spectral evolution along a "Z" track and a "v" 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 ((dM/dt)_disk)^{2/7}, for a radiation pressure dominated accretion disk interacting with the magnetosphere of a neutron star (NS). The changes in the disk mass accretion rate (dM/dt)_disk are responsible for the evolution of the "Z" or "v" track. The radiation pressure thickens the disk considerably, and also produces significant outflows. The NS surface magnetic field strength, derived from the interaction between the magnetosphere and the radiation pressure dominated accretion disk, is ~(1--3)X10^9 G, which is possibly between normal atoll and Z sources. A significant hard tail is detected in the horizontal branches and we discuss several possible ori...

  6. Advective Accretion Disks around Black Holes with Account of Magnetic Fields

    Science.gov (United States)

    Bisnovatyi-Kogan, G. S.

    2002-09-01

    Accretion disc theory was first developed as a theory with the local heat balance, where the whole energy produced by a viscous heating was emitted to the sides of the disc. One of the most important new invention of this theory was a phenomenological treatment of the turbulent viscosity, known as "alpha" prescription, when the (rφ) component of the stress tensor was approximated by (αP) with a unknown constant α. This prescription played the role in the accretion disc theory as well important as the mixing-length theory of convection for stellar evolution. Sources of turbulence in the accretion disc are discussed, including nonlinear hydrodynamic turbulence, convection and magnetic field role. In parallel to the optically thick geometrically thin accretion disc models, a new branch of the optically thin accretion disc models was discovered, with a larger thickness for the same total luminosity. The choice between these solutions should be done of the base of a stability analysis. The ideas underlying the necessity to include advec-tion into the accretion disc theory are presented and first models with advection are reviewed. The present status of the solution for a low-luminous optically thin accretion disc model with advection is discussed and the limits for an advection dominated accretion flows (ADAF) imposed by the presence of magnetic field are analyzed.

  7. The power of relativistic jets is larger than the luminosity of their accretion disks

    CERN Document Server

    Ghisellini, G; Maraschi, L; Celotti, A; Sbarrato, T

    2014-01-01

    Theoretical models for the production of relativistic jets from active galactic nuclei predict that jet power arises from the spin and mass of the central black hole, as well as the magnetic field near the event horizon. The physical mechanism mechanism underlying the contribution from the magnetic field is the torque exerted on the rotating black hole by the field amplified by the accreting material. If the squared magnetic field is proportional to the accretion rate, then there will be a correlation between jet power and accretion luminosity. There is evidence for such a correlation, but inadequate knowledge of the accretion luminosity of the limited and inhomogeneous used samples prevented a firm conclusion. Here we report an analysis of archival observations of a sample of blazars (quasars whose jets point towards Earth) that overcomes previous limitations. We find a clear correlation between jet power as measured through the gamma-ray luminosity, and accretion luminosity as measured by the broad emission...

  8. 3D Dynamical Modeling of Wind Accretion in Cyg X-3

    CERN Document Server

    Okazaki, Atsuo T

    2014-01-01

    Cyg X-3 is a high mass X-ray binary consisting of a Wolf-Rayet star and a compact object in a very short orbital period of 4.8h. The only confirmed microquasar with high energy gamma-ray emission, Cyg X-3 provides a unique opportunity to study the relationship between the accretion power and the power in high energy emission. Because of a compact orbit and a slow Wolf-Rayet wind, the flow structure around the compact object is thought to be strongly affected by the orbital motion, details of which can be obtained only by numerical simulations. In this paper, we report on the results from 3D hydrodynamic simulations of the wind accretion in Cyg X-3. For simplicity we adopt an anti-gravity-like force that emulates the radiative acceleration consistent with the beta-velocity wind. Due to the rapid orbital motion, the flow around the compact object has large density gradients. As a result, the accretion rate onto the compact object is significantly lower than that of the Bondi-Hoyle-Lyttleton rate. We also calcul...

  9. Exploring non-normality in magnetohydrodynamic rotating shear flows: Application to astrophysical accretion disks

    Science.gov (United States)

    Singh Bhatia, Tanayveer; Mukhopadhyay, Banibrata

    2016-10-01

    shear flows are ubiquitous in astrophysics, especially accretion disks, where molecular viscosity is too low to account for observed data. The primary accepted cause of energy-momentum transport therein is turbulent viscosity. Hence, these results would have important implications in astrophysics.

  10. The Disk-Wind-Jet Connection in the Black Hole H 1743-322

    CERN Document Server

    Miller, J M; Fabian, A C; Reynolds, C S; King, A L; Kallman, T R; Cackett, E M; van der Klis, M; Steeghs, D T H

    2012-01-01

    X-ray disk winds are detected in spectrally soft, disk-dominated phases of stellar-mass black hole outbursts. In contrast, compact, steady, relativistic jets are detected in spectrally hard states that are dominated by non-thermal X-ray emission. Although these distinctive outflows appear to be almost mutually exclusive, it is possible that a disk wind persists in hard states but cannot be detected via X-ray absorption lines owing to very high ionization. Here, we present an analysis of a deep, 60 ksec Chandra/HETGS observation of the black hole candidate H 1743-322 in the low/hard state. The spectrum shows no evidence of a disk wind, with tight limits, and within the range of ionizing flux levels that were measured in prior Chandra observations wherein a wind was clearly detected. In H 1743-322, at least, disk winds are actually diminished in the low/hard state, and disk winds and jets are likely state-dependent and anti-correlated. These results suggest that although the launching radii of winds and jets ma...

  11. Computations of Photon Orbits Emitted by Flares at the ISCO of Accretion Disks Around Rotating Black Holes

    Science.gov (United States)

    Kazanas, Demosthenes; Fukumura, K.

    2009-01-01

    We present detailed computations of photon orbits emitted by flares at the ISCO of accretion disks around rotating black holes. We show that for sufficiently large spin parameter, i.e. $a > 0.94 M$, following a flare at ISCO, a sufficient number of photons arrive at an observer after multiple orbits around the black hole, to produce an "photon echo" of constant lag, i.e. independent of the relative phase between the black hole and the observer, of $\\Delta T \\simeq 14 M$. This constant time delay, then, leads to the presence of a QPO in the source power spectrum at a frequency $\

  12. A UV-to-MIR monitoring of DR Tau: exploring how water vapor in the planet formation region of the disk is affected by stellar accretion variability

    CERN Document Server

    Banzatti, Andrea; Manara, Carlo F; Pontoppidan, Klaus M; Testi, Leonardo

    2013-01-01

    Young stars are known to show variability due to non-steady mass accretion rate from their circumstellar disks. Accretion flares can produce strong energetic irradiation and heating that may affect the disk in the planet formation region, close to the central star. During an extreme accretion outburst in the young star EX Lupi, the prototype of EXor variables, remarkable changes in molecular gas emission from $\\sim1$ AU in the disk have recently been observed (Banzatti et al. 2012). Here, we focus on water vapor and explore how it is affected by variable accretion luminosity in T Tauri stars. We monitored a young highly variable solar-mass star, DR Tau, using simultaneously two high/medium-resolution ESO-VLT spectrographs: VISIR at 12.4 $\\mu$m to observe water lines from the disk, and X-shooter covering from 0.3 to 2.5 $\\mu$m to constrain the stellar accretion. Three epochs spanning timescales from several days to several weeks were obtained. Accretion luminosity was estimated to change within a factor $\\sim2...

  13. LES of wind farm response to transient scenarios using a high fidelity actuator disk model

    Science.gov (United States)

    Moens, M.; Duponcheel, M.; Winckelmans, G.; Chatelain, P.

    2016-09-01

    Large eddy simulations coupled to Actuator Disks are used to investigate wake effects in wind farms. An effort is made on the wind turbine model: it uses the prevailing velocities at each point of the disk to estimate the aerodynamic loads and is improved using a tip-loss correction and realistic control schemes. This accurate and efficient tool is used to study the wind farm response in terms of flow and power production during an unsteady scenario: this work focuses on an emergency shutdown of one rotor inside a wind farm.

  14. The Central Engine Structure of 3C120: Evidence for a Retrograde Black Hole or a Refilling Accretion Disk

    Science.gov (United States)

    Cowperthwaite, Philip S.; Reynolds, Christopher S.

    2012-06-01

    The broad-line radio galaxy 3C120 is a powerful source of both X-ray and radio emission including superluminal jet outflows. We report on our reanalysis of 160 ks of Suzaku data taken in 2006, previously examined by Kataoka et al. Spectral fits to the X-ray Imaging Spectrometer and Hard X-ray Detector/positive intrinsic negative data over a range of 0.7-45 keV reveal a well-defined iron K line complex with a narrow Kα core and relativistically broadened features consistent with emission from the inner regions of the accretion disk. Furthermore, the inner region of the disk appears to be truncated, with an inner radius of r in = 11.7+3.5 - 5.2 rg . If we assume that fluorescent iron line features terminate at the inner-most stable circular orbit (ISCO), then we measure a black hole spin of \\hat{a} black hole (\\hat{a} > 0.8) can be ruled out at the 99% confidence level. Alternatively, the disk may be truncated well outside of the ISCO of a rapid prograde hole. The most compelling scenario is the possibility that the inner regions of the disk were destroyed/ejected by catastrophic instabilities just prior to the time these observations were made.

  15. Magnetized accretion

    Science.gov (United States)

    Heyvaerts, J.

    This lecture reviews in simple terms the general subject of large scale magnetic field coupling to plasma flows in the vicinity of accreting compact stars. The relevant astrophysical phenomenology is summarized. Disk interaction with the magnetosphere of accreting stars is first discussed, in particular the structure of the magnetopause, its stability and plasma ejection in so-called propeller systems. The physics of accretion/ejection is then considered. Acceleration and focusing mechanisms of jets from accretion disks around compact stars or black holes and the question of the self-consistency of accretion and ejection are described. By contrast, small scale MHD turbulence in disks is not discussed, neither are accretion columns near the polar caps of neutron stars or white dwarfs. The reader is only assumed to have some basic knowledge of astrophysics and of fluid mechanics and electromagnetism.

  16. Quasi Periodic Oscillations (QPOs) and frequencies in an accretion disk and comparison with the numerical results from non-rotating black hole computed by the GRH code

    CERN Document Server

    Donmez, O

    2006-01-01

    The shocked wave created on the accretion disk after different physical phenomena (accretion flows with pressure gradients, star-disk interaction etc.) may be responsible observed Quasi Periodic Oscillations (QPOs) in $X-$ray binaries. We present the set of characteristics frequencies associated with accretion disk around the rotating and non-rotating black holes for one particle case. These persistent frequencies are results of the rotating pattern in an accretion disk. We compare the frequency's from two different numerical results for fluid flow around the non-rotating black hole with one particle case. The numerical results are taken from our papers Refs.\\refcite{Donmez2} and \\refcite{Donmez3} using fully general relativistic hydrodynamical code with non-selfgravitating disk. While the first numerical result has a relativistic tori around the black hole, the second one includes one-armed spiral shock wave produced from star-disk interaction. Some physical modes presented in the QPOs can be excited in nume...

  17. Time dependent models of accretion disks with nuclear burning following the tidal disruption of a white dwarf by a neutron star

    CERN Document Server

    Margalit, Ben

    2016-01-01

    We construct time-dependent one-dimensional (vertically averaged) models of accretion disks produced by the tidal disruption of a white dwarf (WD) by a binary neutron star (NS) companion. Nuclear reactions in the disk midplane burn the WD matter to increasingly heavier elements at sequentially smaller radii, releasing substantial energy which can impact the disk dynamics. A model for disk outflows is employed, by which cooling from the outflow balances other sources of heating (viscous, nuclear) in regulating the Bernoulli parameter of the midplane to a fixed value $\\lesssim 0$. We perform a comprehensive parameter study of the compositional yields and velocity distributions of the disk outflows for WDs of different initial compositions. For C/O WDs, the radial composition profile of the disk evolves self-similarly in a quasi-steady-state manner, and is remarkably robust to model parameters. The nucleosynthesis in helium WD disks does not exhibit this behavior, which instead depends sensitively on factors con...

  18. Long-term Properties of Accretion Disks in X-ray Binaries II. Stability of Radiation-Driven Warping

    CERN Document Server

    Clarkson, W I; Coe, M J; Laycock, S

    2003-01-01

    A significant number of X-ray binaries are now known to exhibit long-term ``superorbital'' periodicities on timescales of $\\sim$ 10 - 100 days. Several physical mechanisms have been proposed that give rise to such periodicities, in particular warping and/or precession of the accretion disk. Recent theoretical work predicts the stability to disk warping of X-ray binaries as a function of the mass ratio, binary radius, viscosity and accretion efficiency, and here we examine the constraints that can be placed on such models by current observations. In paper I we used a dynamic power spectrum (DPS) analysis of long-term X-ray datasets (CGRO, RXTE), focusing on the remarkable, smooth variations in the superorbital period exhibited by SMC X-1. Here we use a similar DPS analysis to investigate the stability of the superorbital periodicities in the neutron star X-ray binaries Cyg X-2, LMC X-4 and Her X-1, and thereby confront stability predictions with observation. We find that the period and nature of superorbital v...

  19. THE ROLE OF THE ACCRETION DISK, DUST, AND JETS IN THE IR EMISSION OF LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI

    Energy Technology Data Exchange (ETDEWEB)

    Mason, R. E. [Gemini Observatory, Northern Operations Center, 670 N. A' ohoku Place, Hilo, HI 96720 (United States); Ramos Almeida, C. [Instituto de Astrofísica de Canarias, C/Vía Láctea, s/n, E-38205 La Laguna, Tenerife (Spain); Levenson, N. A. [Gemini Observatory, Southern Operations Center, c/o AURA, Casilla 603, La Serena (Chile); Nemmen, R. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Alonso-Herrero, A., E-mail: rmason@gemini.edu [Instituto de Física de Cantabria, CSIC-UC, Avenida de los Castros s/n, E-39005 Santander (Spain)

    2013-11-10

    We use recent high-resolution infrared (IR; 1-20 μm) photometry to examine the origin of the IR emission in low-luminosity active galactic nuclei (LLAGN). The data are compared with published model fits that describe the spectral energy distribution (SED) of LLAGN in terms of an advection-dominated accretion flow, truncated thin accretion disk, and jet. The truncated disk in these models is usually not luminous enough to explain the observed IR emission, and in all cases its spectral shape is much narrower than the broad IR peaks in the data. Synchrotron radiation from the jet appears to be important in very radio-loud nuclei, but the detection of strong silicate emission features in many objects indicates that dust must also contribute. We investigate this point by fitting the IR SED of NGC 3998 using dusty torus and optically thin (τ{sub mid-IR} ∼ 1) dust shell models. While more detailed modeling is necessary, these initial results suggest that dust may account for the nuclear mid-IR emission of many LLAGN.

  20. Free-fall accretion and emitting caustics in wind-fed X-ray sources

    CERN Document Server

    Illarionov, A F; Illarionov, Andrei F.; Beloborodov, Andrei M.

    2000-01-01

    In wind-fed X-ray binaries, the accreting matter is Compton cooled and falls freely onto the compact object. The matter has a modest angular momentum, $l$, and accretion is quasi-spherical at large distances from the compact object. Initially small non-radial velocities grow in the converging supersonic flow and become substantial in the vicinity of the accretor. The streamlines with $l>(GMR_*)^{1/2}$ (where $M$ and $R_*$ are the mass and radius of the compact object) intersect outside $R_*$ and form a two-dimensional caustic which emits X-rays. The streamlines with low angular momentum, $l<(GMR_*)^{1/2}$, run into the accretor. If the accretor is a neutron star, a large X-ray luminosity results. We show that the distribution of accretion rate/luminosity over the star surface is sensitive to the angular momentum distribution of the accreting matter. The apparent luminosity depends on the side from which the star is observed and can change periodically with the orbital phase of the binary. The accretor then...

  1. A sub-AU outwardly truncated accretion disk around a classical T Tauri star

    CERN Document Server

    McClure, M K; Sargent, B A; Watson, Dan M; Furlan, E; Manoj, P; Tayrien, C; Harrold, S T; Calvet, N; Hartmann, L W

    2008-01-01

    We present the Spitzer Infrared Spectrograph (IRS) spectrum of SR20, a 5--10 AU binary T Tauri system in the rho Ophiuchi star forming region. The spectrum has features consistent with the presence of a disk; however, the continuum slope is steeper than the lambda^{-4/3} slope of an infinite geometrically thin, optically thick disk, indicating that the disk is outwardly truncated. Comparison with photometry from the literature shows large variability from 1993 to 1996. We model the spectral energy distribution and IRS spectrum with a geometrically thin, optically thick irradiated disk, yielding an outer radius of 0.15 AU, much smaller than predicted by models of binary orbits. Using a two temperature chi-squared minimization model to fit the dust composition of the IRS spectrum, we find the disk is comprised of large (5 micron) amorphous olivine grains. These results lead us to conclude that there is likely an unseen companion orbiting close to the primary.

  2. Free-fall accretion and emitting caustics in wind-fed X-ray sources

    Science.gov (United States)

    Illarionov, Andrei F.; Beloborodov, Andrei M.

    2001-05-01

    In wind-fed X-ray binaries the accreting matter is Compton-cooled and falls freely on to the compact object. The matter has a modest angular momentum l and accretion is quasi-spherical at large distances from the compact object. Initially small non-radial velocities grow in the converging supersonic flow and become substantial in the vicinity of the accretor. The streamlines with l>(GMR*)1/2 (where M and R* are the mass and radius of the compact object) intersect outside R* and form a two-dimensional caustic which emits X-rays. The streamlines with low angular momentum, lorbital phase of the binary. The accretor then appears as a `Moon-like' X-ray source.

  3. CSI 2264: Investigating rotation and its connection with disk accretion in the young open cluster NGC 2264

    Science.gov (United States)

    Venuti, L.; Bouvier, J.; Cody, A. M.; Stauffer, J. R.; Micela, G.; Rebull, L. M.; Alencar, S. H. P.; Sousa, A. P.; Hillenbrand, L. A.; Flaccomio, E.

    2017-02-01

    Context. The low spin rates measured for solar-type stars at an age of a few Myr ( 10% of the break-up velocity) indicate that some mechanism of angular momentum regulation must be at play in the early pre-main sequence. This may be associated with magnetospheric accretion and star-disk interaction, as suggested by observations that disk-bearing objects (CTTS) are slower rotators than diskless sources (WTTS) in young star clusters. Aims: We characterize the rotation properties for members of the star-forming region NGC 2264 ( 3 Myr) as a function of mass, and investigate the accretion-rotation connection at an age where about 50% of the stars have already lost their disks. Methods: We examined a sample of 500 cluster members (40% with disks, 60% without disks), distributed in mass between 0.15 and 2 M⊙, whose photometric variations were monitored in the optical for 38 consecutive days with the CoRoT space observatory. Light curves were analyzed for periodicity using three different techniques: the Lomb-Scargle periodogram, the autocorrelation function and the string-length method. Periods were searched in the range between 0.17 days (i.e., 4 h, twice the data sampling adopted) and 19 days (half the total time span). Period detections were confirmed using a variety of statistical tools (false alarm probability, Q-statistics), as well as visual inspection of the direct and phase-folded light curves. Results: About 62% of sources in our sample were found to be periodic; the period detection rate is 70% among WTTS and 58% among CTTS. The vast majority of periodic sources exhibit rotational periods shorter than 13 d. The period distribution obtained for the cluster consists of a smooth distribution centered around P = 5.2 d with two peaks, located respectively at P = 1-2 d and at P = 3-4 d. A separate analysis of the rotation properties for CTTS and WTTS indicates that the P = 1-2 d peak is associated with the latter, while both groups contribute to the P = 3-4 d peak

  4. Disk-Wind Connection During the Heartbeats of GRS 1915+105

    DEFF Research Database (Denmark)

    Zoghbi, Abderahmen; Miller, M. C.; King, A. L.;

    2016-01-01

    Disk and wind signatures are seen in the soft state of Galactic black holes, while the jet is seen in the hard state. Here we study the disk–wind connection in the ρ class of variability in GRS 1915+105 using a joint NuSTAR–Chandra observation. The source shows 50 s limit cycle oscillations...

  5. X-Raying an Accretion Disk in Realtime: the Evolution of Ionized Reflection during a Superburst from 4U 1636-536

    CERN Document Server

    Keek, L; Kuulkers, E; Strohmayer, T E

    2014-01-01

    When a thermonuclear X-ray burst ignites on an accreting neutron star, the accretion disk undergoes sudden strong X-ray illumination, which can drive a range of processes in the disk. Observations of superbursts, with durations of several hours, provide the best opportunity to study these processes and to probe accretion physics. Using detailed models of ionized reflection, we perform time resolved spectroscopy of the superburst observed from 4U 1636-536 in 2001 with RXTE. The spectra are consistent with a blackbody reflecting off a photoionized accretion disk, with the ionization state dropping with time. The evolution of the reflection fraction indicates that the initial reflection occurs from a part of the disk at larger radius, subsequently transitioning to reflection from an inner region of the disk. Even though this superburst did not reach the Eddington limit, we find that a strong local absorber develops during the superburst. Including this event, only two superbursts have been observed by an instrum...

  6. Super-Eddington wind scenario for the progenitors of type Ia supernovae: Accreting He-rich matter onto white dwarfs

    CERN Document Server

    Wang, Bo; Ma, Xin; Liu, Dongdong; Cui, Xiao; Han, Zhanwen

    2015-01-01

    Supernovae of type Ia (SNe Ia) are believed to be thermonuclear explosions of carbon-oxygen white dwarfs (CO WDs). However, the mass accretion process onto CO WDs is still not completely understood. In this paper, we study the accretion of He-rich matter onto CO WDs and explore a scenario in which a strong wind forms on the surface of the WD if the total luminosity exceeds the Eddington limit. Using a stellar evolution code called modules for experiments in stellar astrophysics (MESA), we simulated the He accretion process onto CO WDs for WDs with masses of 0.6-1.35Msun and various accretion rates of 10^{-8}-10^{-5}Msun/yr. If the contribution of the total luminosity is included when determining the Eddington accretion rate, then a super-Eddington wind could be triggered at relatively lower accretion rates than those of previous studies based on steady-state models. The super-Eddington wind can prevent the WDs with high accretion rates from evolving into red-giant-like He stars. We found that the contribution...

  7. CONTRIBUTION OF THE ACCRETION DISK, HOT CORONA, AND OBSCURING TORUS TO THE LUMINOSITY OF SEYFERT GALAXIES: INTEGRAL AND SPITZER OBSERVATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Sazonov, S.; Churazov, E.; Krivonos, R.; Revnivtsev, M.; Sunyaev, R.; Vikhlinin, A. [Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, Moscow 117997 (Russian Federation); Willner, S. P.; Goulding, A. D.; Jones, C.; Murray, S. S. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Hickox, R. C. [Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755 (United States); Gorjian, V.; Werner, M. W. [Jet Propulsion Laboratory, California Institute of Technology, MS 169-327, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Fabian, A. C. [Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom); Forman, W. R. [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, D-85741 Garching (Germany)

    2012-10-01

    We estimate the relative contributions of the supermassive black hole (SMBH) accretion disk, corona, and obscuring torus to the bolometric luminosity of Seyfert galaxies, using Spitzer mid-infrared (MIR) observations of a complete sample of 68 nearby active galactic nuclei (AGNs) from the INTEGRAL all-sky hard X-ray (HX) survey. This is the first HX-selected (above 15 keV) sample of AGNs with complementary high angular resolution, high signal-to-noise, MIR data. Correcting for the host galaxy contribution, we find a correlation between HX and MIR luminosities: L{sub 15{mu}m}{proportional_to}L{sup 0.74{+-}0.06}{sub HX}. Assuming that the observed MIR emission is radiation from an accretion disk reprocessed in a surrounding dusty torus that subtends a solid angle decreasing with increasing luminosity (as inferred from the declining fraction of obscured AGNs), the intrinsic disk luminosity, L{sub Disk}, is approximately proportional to the luminosity of the corona in the 2-300 keV energy band, L{sub Corona}, with the L{sub Disk}/L{sub Corona} ratio varying by a factor of 2.1 around a mean value of 1.6. This ratio is a factor of {approx}2 smaller than for typical quasars producing the cosmic X-ray background. Therefore, over three orders of magnitude in luminosity, HX radiation carries a large, and roughly comparable, fraction of the bolometric output of AGNs. We estimate the cumulative bolometric luminosity density of local AGNs at {approx}(1-3) Multiplication-Sign 10{sup 40} erg s{sup -1} Mpc{sup -3}. Finally, the Compton temperature ranges between kT{sub c} Almost-Equal-To 2 and Almost-Equal-To 6 keV for nearby AGNs, compared to kT{sub c} Almost-Equal-To 2 keV for typical quasars, confirming that radiative heating of interstellar gas can play an important role in regulating SMBH growth.

  8. Plasma physics of accreting neutron stars

    Science.gov (United States)

    Ghosh, Pranab; Lamb, Frederick K.

    1991-01-01

    Plasma concepts and phenomena that are needed to understand X- and gamma-ray sources are discussed. The capture of material from the wind or from the atmosphere or envelope of a binary companion star is described and the resulting types of accretion flows discussed. The reasons for the formation of a magnetosphere around the neutron star are explained. The qualitative features of the magnetospheres of accreting neutron stars are then described and compared with the qualitative features of the geomagnetosphere. The conditions for stable flow and for angular and linear momentum conservation are explained in the context of accretion by magnetic neutron stars and applied to obtain rough estimates of the scale of the magnetosphere. Accretion from Keplerian disks is then considered in some detail. The radial structure of geometrically thin disk flows, the interaction of disk flows with the neutron star magnetosphere, and models of steady accretion from Keplerian disks are described. Accretion torques and the resulting changes in the spin frequencies of rotating neutron stars are considered. The predicted behavior is then compared with observations of accretion-powered pulsars. Magnetospheric processes that may accelerate particles to very high energies, producing GeV and, perhaps, TeV gamma-rays are discussed. Finally, the mechanisms that decelerate and eventually stop accreting plasma at the surfaces of strongly magnetic neutron stars are described.

  9. Photo-reverberation Mapping of a Protoplanetary Accretion Disk around a T Tauri Star

    CERN Document Server

    Meng, Huan Y A; Rieke, George H; Cody, Ann Marie; Güth, Tina; Stauffer, John; Covey, Kevin; Carey, Sean; Ciardi, David; Duran-Rojas, Maria C; Gutermuth, Robert A; Morales-Calderón, María; Rebull, Luisa M; Watson, Alan M

    2016-01-01

    Theoretical models and spectroscopic observations of newborn stars suggest that protoplantary disks have an inner "wall" at a distance set by the disk interaction with the star. Around T Tauri stars, the size of this disk hole is expected to be on a 0.1-AU scale that is unresolved by current adaptive optics imaging, though some model-dependent constraints have been obtained by near-infrared interferometry. Here we report the first measurement of the inner disk wall around a solar-mass young stellar object, YLW 16B in the {\\rho} Ophiuchi star-forming region, by detecting the light travel time of the variable radiation from the stellar surface to the disk. Consistent time lags were detected on two nights, when the time series in H (1.6 {\\mu}m) and K (2.2 {\\mu}m) bands were synchronized while the 4.5 {\\mu}m emission lagged by 74.5 +/- 3.2 seconds. Considering the nearly edge-on geometry of the disk, the inner rim should be 0.084 AU from the protostar on average, with an error of order 0.01 AU. This size is likel...

  10. Wind turbine rotor simulation using the actuator disk and actuator line methods

    Science.gov (United States)

    Tzimas, M.; Prospathopoulos, J.

    2016-09-01

    The present paper focuses on wind turbine rotor modeling for loads and wake flow prediction. Two steady-state models based on the actuator disk approach are considered, using either a uniform thrust or a blade element momentum calculation of the wind turbine loads. A third model is based on the unsteady-state actuator line approach. Predictions are compared with measurements in wind tunnel experiments and in atmospheric environment and the capabilities and weaknesses of the different models are addressed.

  11. Baryonic pollution in gamma-ray bursts the case of a magnetically driven wind emitted from a disk orbiting a stellar mass black hole

    CERN Document Server

    Daigne, F; Daigne, Frederic; Mochkovitch, Robert

    2002-01-01

    Most models for the central engine of gamma-ray bursts involve a stellar mass black hole surrounded by a thick disk formed after the merging of a system of compact objects or the collapse of a massive star. Energy released from the accretion of disk material by the black hole or from the rotation of the hole itself extracted by the Blandford-Znajek mechanism powers a relativistic wind along the system axis. Lorentz factors of several hundreds are needed to solve the compactness problem in the wind which implies the injection of a tremendous power into a very small amount of matter. The Blandford-Znajek mechanism, where the outflow follows magnetic field lines anchored to the black hole is probably the best way to prevent baryonic pollution and can even initially produce a purely leptonic wind. In this paper we rather study the wind emitted from the inner part of the disk where the risk of baryonic pollution is much larger since the outflow originates from high density regions. We show that the baryonic load o...

  12. Structure and Dynamics of the Accretion Process and Wind in TW Hya

    Science.gov (United States)

    Dupree, A. K.; Brickhouse, N. S.; Cranmer, S. R.; Berlind, P.; Strader, Jay; Smith, Graeme H.

    2014-07-01

    Time-domain spectroscopy of the classical accreting T Tauri star, TW Hya, covering a decade and spanning the far UV to the near-infrared spectral regions can identify the radiation sources, the atmospheric structure produced by accretion, and properties of the stellar wind. On timescales from days to years, substantial changes occur in emission line profiles and line strengths. Our extensive time-domain spectroscopy suggests that the broad near-IR, optical, and far-uv emission lines, centered on the star, originate in a turbulent post-shock region and can undergo scattering by the overlying stellar wind as well as some absorption from infalling material. Stable absorption features appear in Hα, apparently caused by an accreting column silhouetted in the stellar wind. Inflow of material onto the star is revealed by the near-IR He I 10830 Å line, and its free-fall velocity correlates inversely with the strength of the post-shock emission, consistent with a dipole accretion model. However, the predictions of hydrogen line profiles based on accretion stream models are not well-matched by these observations. Evidence of an accelerating warm to hot stellar wind is shown by the near-IR He I line, and emission profiles of C II, C III, C IV, N V, and O VI. The outflow of material changes substantially in both speed and opacity in the yearly sampling of the near-IR He I line over a decade. Terminal outflow velocities that range from 200 km s-1 to almost 400 km s-1 in He I appear to be directly related to the amount of post-shock emission, giving evidence for an accretion-driven stellar wind. Calculations of the emission from realistic post-shock regions are needed. Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support

  13. Formation of terrestrial planets in disks evolving via disk winds and implications for the origin of the solar system's terrestrial planets

    CERN Document Server

    Ogihara, Masahiro; Inutsuka, Shu-ichiro; Suzuki, Takeru K

    2015-01-01

    Recent three-dimensional magnetohydrodynamical simulations have identified a disk wind by which gas materials are lost from the surface of a protoplanetary disk, which can significantly alter the evolution of the inner disk and the formation of terrestrial planets. A simultaneous description of the realistic evolution of the gaseous and solid components in a disk may provide a clue for solving the problem of the mass concentration of the terrestrial planets in the solar system. We simulate the formation of terrestrial planets from planetary embryos in a disk that evolves via magnetorotational instability and a disk wind. The aim is to examine the effects of a disk wind on the orbital evolution and final configuration of planetary systems. We perform N-body simulations of sixty 0.1 Earth-mass embryos in an evolving disk. The evolution of the gas surface density of the disk is tracked by solving a one-dimensional diffusion equation with a sink term that accounts for the disk wind. We find that even in the case ...

  14. Accretion Disks Around Binary Black Holes: A Simple GR-Hybrid Evolution Model

    CERN Document Server

    Shapiro, Stuart L

    2013-01-01

    We consider a geometrically thin, Keplerian disk in the orbital plane of a binary black hole (BHBH) consisting of a spinning primary and low-mass secondary (mass ratio q < 1). To account for the principle effects of general relativity (GR), we propose a modification of the standard Newtonian evolution equation for the (orbit-averaged) time-varying disk surface density. In our modified equation the viscous torque in the disk is treated in full GR, while the tidal torque is handled in the Newtonian limit. Our GR-hybrid treatment is reasonable because the tidal torque is concentrated near the orbital radius of the secondary and is most important prior to binary-disk decoupling, when the orbital separation is large and resides in the weak-field regime. The tidal torque on the disk diminishes during late merger and vanishes altogether following merger. By contrast, the viscous torque drives the flow into the strong-field region and onto the primary during all epochs. Following binary coalescence, the viscous to...

  15. Probing the Accretion Disk and Central Engine Structure of the NGC 4258 with Suzaku and XMM-Newton Observations

    Science.gov (United States)

    Reynolds, Christopher S.; Nowak, Michael A.; Markoff, Sera; Tueller, Jack; Wilms, Joern; Young, Andrew

    2009-01-01

    We present an X-ray study of the low-luminosity active galactic nucleus (AGN) in NGC 4258 using data from Suzaku, XMM-Newton, and the Swift/Burst Alert Telescope survey. We find that signatures of X-ray reprocessing by cold gas are very weak in the spectrum of this Seyfert-2 galaxy; a weak, narrow fluorescent K(alpha) emission line of cod iron is robustly detected in both the Suzaku and XMM-Newton spectra but at a level much below that of most other Seyfert-2 galaxies. We conclude that the circumnuclear environment of this AGN is very "clean" and lacks the Compton-thick obscuring torus of unified Seyfert schemes. From the narrowness of the iron line, together with evidence of line flux variability between the Suzaku and XMM-Newton observations, we constrain the line emitting region to be between 3 x 10(exp 3)r(sub g) and 4 x 10(exp 4)r(sub g), from the black hole. We show that the observed properties of the iron line can be explained if the line originates from the surface layers of a warped accretion disk. In particular, we present explicit calculations of the expected iron line from a disk warped by Lens-Thirring precession from a misaligned central black hole. Finally, the Suzaku data reveal clear evidence of large amplitude 2-10 keV variability on timescales of 50 ksec and smaller amplitude flares on timescales as short as 5-10 ksec. If associated with accretion disk processes, such rapid variability requires an origin in the innermost regions of the disk (r approx. equals 10(r(sub g) or less). Analysis of the difference spectrum between a high- and low-flux states suggests that the variable component of the X-ray emission is steeper and more absorbed than the average AGN emission, suggesting that the primary X-ray source and absorbing screen have a spatial structure on comparable scales. We note the remarkable similarity between the circumnuclear environment of NGC 4258 and another well studied low-luminosity AGN, M81*.

  16. Self-destructing Spiral Waves: Global Simulations of a Spiral-wave Instability in Accretion Disks

    Science.gov (United States)

    Bae, Jaehan; Nelson, Richard P.; Hartmann, Lee; Richard, Samuel

    2016-09-01

    We present results from a suite of three-dimensional global hydrodynamic simulations that shows that spiral density waves propagating in circumstellar disks are unstable to the growth of a parametric instability that leads to break down of the flow into turbulence. This spiral wave instability (SWI) arises from a resonant interaction between pairs of inertial waves, or inertial-gravity waves, and the background spiral wave. The development of the instability in the linear regime involves the growth of a broad spectrum of inertial modes, with growth rates on the order of the orbital time, and results in a nonlinear saturated state in which turbulent velocity perturbations are of a similar magnitude to those induced by the spiral wave. The turbulence induces angular momentum transport and vertical mixing at a rate that depends locally on the amplitude of the spiral wave (we obtain a stress parameter α ˜ 5 × 10-4 in our reference model). The instability is found to operate in a wide range of disk models, including those with isothermal or adiabatic equations of state, and in viscous disks where the dimensionless kinematic viscosity ν ≤ 10-5. This robustness suggests that the instability will have applications to a broad range of astrophysical disk-related phenomena, including those in close binary systems, planets embedded in protoplanetary disks (including Jupiter in our own solar system) and FU Orionis outburst models. Further work is required to determine the nature of the instability and to evaluate its observational consequences in physically more complete disk models than we have considered in this paper.

  17. Disk-Magnetosphere Interaction and Outflows: Conical Winds and Axial Jets

    CERN Document Server

    Romanova, M M; Koldoba, A V; Lovelace, R V E

    2009-01-01

    We investigate outflows from the disk-magnetosphere boundary of rotating magnetized stars in cases where the magnetic field of a star is bunched into an X-type configuration using axisymmetric and full 3D MHD simulations. Such configuration appears if viscosity in the disk is larger than diffusivity, or if the accretion rate in the disk is enhanced. Conical outflows flow from the inner edge of the disk to a narrow shell with an opening angle 30-45 degrees. Outflows carry 0.1-0.3 of the disk mass and part of the disk's angular momentum outward. Conical outflows appear around stars of different periods, however in case of stars in the "propeller" regime, an additional - much faster component appears: an axial jet, where matter is accelerated up to very high velocities at small distances from the star by magnetic pressure force above the surface of the star. Exploratory 3D simulations show that conical outflows are symmetric about rotational axis of the disk even if magnetic dipole is significantly misaligned. C...

  18. Hydrodynamical numerical simulation of wind production from black hole hot accretion flows at very large radii

    CERN Document Server

    Bu, De-Fu; Gan, Zhao-Ming; Yang, Xiao-hong

    2015-01-01

    In previous works, it has been shown that strong winds exist in hot accretion flows around black holes. Those works focus only on the region close to the black hole thus it is unknown whether or where the wind production stops at large radii. In this paper, we investigate this problem based on hydrodynamical numerical simulations. For this aim, we have taken into account the gravity of both the central black hole and the nuclear star clusters. When calculating the latter, we assume that the velocity dispersion of stars is a constant and the gravitational potential of the nuclear star cluster $\\propto \\sigma^2 \\ln (r)$, where $\\sigma$ is the velocity dispersion of stars and $r$ is the distance from the center of the galaxy. Different from previous works, we focus on the region where the gravitational potential is dominated by the star cluster. We find that, same as the accretion flow at small radii, the mass inflow rate decreases inward and the flow is convectively unstable. However, trajectory analysis has sh...

  19. Wind Tunnel Test and Numerical Computation on Ice Accretion on Blade Airfoil for Straight-bladed VAWT

    Institute of Scientific and Technical Information of China (English)

    LI Shengmao; LI Yan; FENG Fang; WANG Lijun; CHI Yuan

    2010-01-01

    To invest the condition of ice accretion on the blade used for straight-bladed vertical axis wind turbine(SB-VAWT),wind tunnel tests were carded out on a blade with NACA0015 airfoil by using a small simple icing wind tunnel.Tests were carried out at some typical attack angles under different wind speeds and flow discharges of a water spray with wind.The icing shape and area on blade surface were recorded and measured.Then the numerical computation was carried out to calculate the lift and drag coefficients of the blade before and after ice accretion according to the experiment result,the effect of icing on the aerodynamic characteristics of blade were discussed.

  20. Global Time Dependent Solutions of Stochastically Driven Standard Accretion Disks: Development of Hydrodynamical Code

    Science.gov (United States)

    Wani, Naveel; Maqbool, Bari; Iqbal, Naseer; Misra, Ranjeev

    2016-07-01

    X-ray binaries and AGNs are powered by accretion discs around compact objects, where the x-rays are emitted from the inner regions and uv emission arise from the relatively cooler outer parts. There has been an increasing evidence that the variability of the x-rays in different timescales is caused by stochastic fluctuations in the accretion disc at different radii. These fluctuations although arise in the outer parts of the disc but propagate inwards to give rise to x-ray variability and hence provides a natural connection between the x-ray and uv variability. There are analytical expressions to qualitatively understand the effect of these stochastic variabilities, but quantitative predictions are only possible by a detailed hydrodynamical study of the global time dependent solution of standard accretion disc. We have developed numerical efficient code (to incorporate all these effects), which considers gas pressure dominated solutions and stochastic fluctuations with the inclusion of boundary effect of the last stable orbit.