Bibliografías temáticas / Shakura-Sunyaev disk

Literatura académica sobre el tema "Shakura-Sunyaev disk"

Autor: Grafiati

Publicado: 6 de septiembre de 2023

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Artículos de revistas sobre el tema "Shakura-Sunyaev disk"

Berdina, L. A., V. S. Tsvetkova y V. M. Shulga. "Super-Eddington accretion in the Q2237+0305 quasar?" Astronomy & Astrophysics 645 (enero de 2021): A78. http://dx.doi.org/10.1051/0004-6361/202039379.

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The interband time lags between the flux variations of the Q2237+0305 quasar have been determined from light curves in the Johnson-Cousins V, R, and I spectral bands. The values of the time lags for filter pairs R − V, I − R, and I − V are significantly higher than those predicted by the standard accretion disk model by Shakura and Sunyaev. To explain the discrepancy, the idea of a supercritical accretion regime in quasars considered in 1973 by Shakura and Sunyaev is applied. This regime has been shown by them to cause an extended scattering envelope around the accretion disk. The envelope efficiently scatters and re-emits the radiation from the accretion disk and thus increases the apparent disk size. We made use of analytical expressions for the envelope radius and temperature derived by Shakura and Sunyaev in their analysis of super-Eddington accretion and show that our results are consistent with the existence of such an envelope. The corresponding parameters of the accretion regime were calculated. They provide the radii of the envelope in the V, R, and I spectral bands consistent with the inter-band time lags determined in our work.

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Gu, Wei-Min y Ju-Fu Lu. "Bimodal Accretion Disks: Shakura-Sunyaev Disk–Advection-dominated Accretion Flow Transitions". Astrophysical Journal 540, n.º 1 (1 de septiembre de 2000): L33—L36. http://dx.doi.org/10.1086/312864.

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Lominadze, J. G. "Nature of Turbulence: Governing Factor of Accretion Disk Dynamics". Highlights of Astronomy 11, n.º 2 (1998): 786–89. http://dx.doi.org/10.1017/s1539299600018785.

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It has long been suggested that turbulence provide viscous torques to transport angular momentum outward and flow mass inward in accretion disks (von Weizsäcker 1948, Shakura & Sunyaev 1973). Recent advances in subject of understanding of accretion disk turbulence are mach linked with magnetised disks (cf. Vishniac & Diamond 1992, Balbus, Gammie & Hawley 1994, Brandenburg et al. 1995, Stone et al 1996). However, not all the disks are magnetically coupled (see Balbus, Hawley & Stone 1996). Two different sources that are able to sustain turbulence in not magnetised accretion disk are the following:

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Piotrovich, Mikhail, Stanislava Buliga y Tinatin Natsvlishvili. "Determination of the Magnetic Field Strength and Geometry in the Accretion Disks of AGNs by Optical Spectropolarimetry". Universe 7, n.º 6 (18 de junio de 2021): 202. http://dx.doi.org/10.3390/universe7060202.

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Based on the spectropolarimetric data of 33 Seyfert type 1 galaxies observed with the BTA-6m telescope of the Special Astrophysical Observatory, we estimated the magnetic field values at the event horizon of the supermassive black hole BH and the exponents of the power-law dependence s of the magnetic field on the radius. We used the model of optically thick geometrically thin Shakura–Sunyaev accretion disk. The average value of logBH[G] was found to be ∼4, which is in good agreement with the results obtained by other methods. The average value of s is s≈1.7, and its distribution maximum span is in the range od 1.85<s<2.0. This is a rather interesting result, since s=5/4 is usually adopted in calculations for Shakura–Sunyaev accretion disks. In addition, for two objects PG 1545+210 and 2MASX J06021107+2828382, the measured degree of polarization is greater than the maximum possible value at the angle between the line of sight and the axis of the accretion disk i=45°. It was concluded that for these objects the angle should be closer to i=60°.

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Huré, Jean Marc, Suzy Collin y Guillaume Pineau Des Forêts. "Structure of Outer Regions of Accretion Disks in AGN: Non Irradiated, Vertically Averaged Accretion Disks". Symposium - International Astronomical Union 159 (1994): 483. http://dx.doi.org/10.1017/s0074180900176594.

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Radial structure of outer regions of α-disks (Shakura & Sunyaev 1973) is investigated in a more sophisticated way than in Collin-Souffrin & Dumont (1990). The vertically averaged equations for the disk structure hold but some of them are reconsidered : the equation of state (atoms, ions and molecules) with a the rigourous treatment of opacities is introduced. The radiative flux is treated as in Hubeny (1990), and finally a rigourous treatment of the self-gravitaty is included.

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Dudorov, A. E. y R. E. Pudritz. "An MHD Model of Be Stars with Disks". International Astronomical Union Colloquium 175 (2000): 611–16. http://dx.doi.org/10.1017/s0252921100056633.

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AbstractAn investigation of the formation and evolution of Be stars show that these stars could have dipolar fossil magnetic fields. This magnetic field should constrain the circumstellar magnetic disk and influence its dynamical features. For studying these effects we refine the alphamodel of accretion disks of Shakura and Sunyaev by incorporating into this model the evolution of large-scale magnetic fields. In the frame of our model we can investigate the rotational history of the star with the disk and the ionization and thermal properties of disks. We show in particular that in the magnetopause region a current sheet can form that can generate X-ray radiation.

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Kadam, Kundan, E. Vorobyov, Zs Regály, Á. Kóspál y P. Ábráham. "Global Protoplanetary Disk Simulations: Dead Zone Formation and FUor Outbursts". Proceedings of the International Astronomical Union 14, S345 (agosto de 2018): 324–25. http://dx.doi.org/10.1017/s1743921319001650.

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AbstractWe conducted global hydrodynamic simulations of protoplanetary disk evolution with an adaptive Shakura-Sunyaev α prescription to represent the layered disk structure, and starting with the collapse phase of the molecular cloud. With the canonical values of model parameters, self-consistent dead zones formed at the scale of a few au. The instabilities associated with the dead zone and corresponding outbursts, similar to FUor eruptions, were also observed in the simulations.

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Mao, Shunyuan, Ruobing Dong, Lu Lu, Kwang Moo Yi, Sifan Wang y Paris Perdikaris. "PPDONet: Deep Operator Networks for Fast Prediction of Steady-state Solutions in Disk–Planet Systems". Astrophysical Journal Letters 950, n.º 2 (1 de junio de 2023): L12. http://dx.doi.org/10.3847/2041-8213/acd77f.

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Abstract We develop a tool, which we name Protoplanetary Disk Operator Network (PPDONet), that can predict the solution of disk–planet interactions in protoplanetary disks in real time. We base our tool on Deep Operator Networks, a class of neural networks capable of learning nonlinear operators to represent deterministic and stochastic differential equations. With PPDONet we map three scalar parameters in a disk–planet system—the Shakura–Sunyaev viscosity α, the disk aspect ratio h 0, and the planet–star mass ratio q—to steady-state solutions of the disk surface density, radial velocity, and azimuthal velocity. We demonstrate the accuracy of the PPDONet solutions using a comprehensive set of tests. Our tool is able to predict the outcome of disk–planet interaction for one system in less than a second on a laptop. A public implementation of PPDONet is available at https://github.com/smao-astro/PPDONet.

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Mineshige, S. "Accretion Disk Instabilities". International Astronomical Union Colloquium 134 (1993): 83–103. http://dx.doi.org/10.1017/s0252921100013968.

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AbstractBasic properties of accretion disk instabilities are summarized. We first explain the standard disk model by Shakura and Sunyaev. In this model, the dominant sources of viscosity are assumed to be chaotic magnetic fields and turbulence in gas flow, and the magnitude of viscosity is prescribed by so-called a model. It is then possible to build a particular disk model. In the framework of the standard model, accretion disks are stationary, but when some of the basic assumptions are relaxed, various kinds of instabilities appear. In particular, we focus on the thermal limit-cycle instability caused by partial ionization of hydrogen (and helium). We demonstrate that the disk instability model well accounts for the basic observed features of outbursts of dwarf novae and X-ray nova. We then introduce other kinds of instabilities based on the α viscosity model. They are suspected to produce time variabilities observed on a wide range of timescales in close binaries and active galactic nuclei.

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Olson, Edward C. "Photometric Effects of Accretion Disks in Long-Period Eclipsing Binaries". International Astronomical Union Colloquium 107 (1989): 23–34. http://dx.doi.org/10.1017/s0252921100087649.

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Accretion disks are invoked in a variety of astrophysical settings, ranging from stellar-mass black holes to active galactic nuclei. There is now little doubt that true accretion disks can also occur in binaries containing non-degenerate stars (Peters 1980; Plavec et al. 1984; Polidan 1987). In this paper, I will discuss some of the properties of disks observed photometrically in the long-period systems KU Cyg and RZ Oph.The most intensively-studied disks are of course those in cataclysmic binaries. Accretion disks in such binaries are thought to have the classical ′alpha′ structure of Shakura and Sunyaev (1973), in which viscous dissipation arising from differential rotation converts gravitational potential energy to thermal energy in supplying the disk luminosity. This physical process requires that the viscous time scale be comparable to the radiative decay time of the disk (Pringle 1981). Most of the disk′s volume is optically thick, so disk luminosity is estimated by integrating black-body or stellar atmospheric fluxes over the disk (see Kriz and Hubeny 1986 for qualifications).

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Actas de conferencias sobre el tema "Shakura-Sunyaev disk"

Piotrovich, M., S. Buliga y T. Natsvlishvili. "Determination of the magnetic field strength and geometry in the accretion disks of AGNs". En ASTRONOMY AT THE EPOCH OF MULTIMESSENGER STUDIES. Proceedings of the VAK-2021 conference, Aug 23–28, 2021. Crossref, 2022. http://dx.doi.org/10.51194/vak2021.2022.1.1.158.

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Based on the spectropolarimetric data of 33 Seyfert type 1 galaxies observed with the BTA-6m telescope of the SpecialAstrophysical Observatory, we estimated the magnetic ﬁeld values at the event horizon of the supermassive black hole B Hand the exponents of the power-law dependence s of the magnetic ﬁeld on the radius. We used the model of Shakura-Sunyaevaccretion disk. The average value of log B H [G] was found to be ∼ 4. The average value of s is ≈ 1.7, and its distributionmaximum span is in the range of 1.85 < s < 2.0. This is a rather interesting result, since s = 5/4 is usually adoptedin calculations for Shakura-Sunyaev accretion disks. For two objects PG 1545+210 and 2MASX J06021107+2828382, themeasured degree of polarization is greater than the maximum possible value at the angle between the line of sight and theaxis of the accretion disk i = 45 ◦ . It was concluded that for these objects the angle should be closer to i = 60 ◦ .

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