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1
Gárate, Matías, Timmy N. Delage, Jochen Stadler, Paola Pinilla, Til Birnstiel, Sebastian Markus Stammler, Giovanni Picogna, Barbara Ercolano, Raphael Franz, and Christian Lenz. "Large gaps and high accretion rates in photoevaporative transition disks with a dead zone." Astronomy & Astrophysics 655 (November 2021): A18. http://dx.doi.org/10.1051/0004-6361/202141444.
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Context. Observations of young stars hosting transition disks show that several of them have high accretion rates, despite their disks presenting extended cavities in their dust component. This represents a challenge for theoretical models, which struggle to reproduce both features simultaneously. Aims. We aim to explore if a disk evolution model, including a dead zone and disk dispersal by X-ray photoevaporation, can explain the high accretion rates and large gaps (or cavities) measured in transition disks. Methods. We implemented a dead zone turbulence profile and a photoevaporative mass-loss profile into numerical simulations of gas and dust. We performed a population synthesis study of the gas component and obtained synthetic images and SEDs of the dust component through radiative transfer calculations. Results. This model results in long-lived inner disks and fast dispersing outer disks that can reproduce both the accretion rates and gap sizes observed in transition disks. For a dead zone of turbulence αdz = 10−4 and an extent rdz = 10 AU, our population synthesis study shows that 63% of our transition disks are still accreting with Ṁg ≥ 10−11 M⊙ yr−1 after opening a gap. Among those accreting transition disks, half display accretion rates higher than 5.0 × 10−10 M⊙ yr−1. The dust component in these disks is distributed in two regions: in a compact inner disk inside the dead zone, and in a ring at the outer edge of the photoevaporative gap, which can be located between 20 and 100 AU. Our radiative transfer calculations show that the disk displays an inner disk and an outer ring in the millimeter continuum, a feature that resembles some of the observed transition disks. Conclusions. A disk model considering X-ray photoevaporative dispersal in combination with dead zones can explain several of the observed properties in transition disks, including the high accretion rates, the large gaps, and a long-lived inner disk at millimeter emission.
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Daemgen, Sebastian, Monika G. Petr-Gotzens, and Serge Correia. "T Tauri Binaries in Orion: Evidence for Accelerated and Synchronized Disk Evolution." Proceedings of the International Astronomical Union 7, S282 (July 2011): 452–53. http://dx.doi.org/10.1017/s1743921311028043.
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AbstractIn order to trace the role of binarity for disk evolution and hence planet formation, we started the currently largest spatially resolved near-infrared photometric and spectroscopic study of the inner dust and accretion disks of the individual components of 27 visual, 100–400 AU binaries in the Orion Nebula Cluster (ONC). We study the frequency of Brackett-γ (2.165μm) emitters to assess the frequency of accretion disk-bearing stars among the binaries of the ONC: only 34±9% of the binary components show signs of accretion and, hence, the presence of gaseous inner disks—less than the fraction of gas accretion disks among single stars of the ONC of ~50%. Additionally, we find a significant difference between binaries above and below 200 AU separation: no close systems with only one accreting component are found. The results suggest shortened disk lifetimes as well as synchronized disk evolution.
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Khaibrakhmanov, Sergey A., Alexander E. Dudorov, and Andrey M. Sobolev. "Rising magnetic flux tubes as a source of IR-variability of the accretion disks of young stars." Proceedings of the International Astronomical Union 14, S345 (August 2018): 295–96. http://dx.doi.org/10.1017/s1743921319001431.
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AbstractWe investigate dynamics of slender magnetic flux tubes (MFT) in the accretion disks of young stars. Simulations show that MFT rise from the disk and can accelerate to 20-30 km/s causing periodic outflows. Magnetic field of the disk counteracts the buoyancy, and the MFT oscillate near the disk’s surface with periods of 10-100 days. We demonstrate that rising and oscillating MFT can cause the IR-variability of the accretion disks of young stars.
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Manara, C. F., C. Mordasini, L. Testi, J. P. Williams, A. Miotello, G. Lodato, and A. Emsenhuber. "Constraining disk evolution prescriptions of planet population synthesis models with observed disk masses and accretion rates." Astronomy & Astrophysics 631 (October 11, 2019): L2. http://dx.doi.org/10.1051/0004-6361/201936488.
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While planets are commonly discovered around main-sequence stars, the processes leading to their formation are still far from being understood. Current planet population synthesis models, which aim to describe the planet formation process from the protoplanetary disk phase to the time exoplanets are observed, rely on prescriptions for the underlying properties of protoplanetary disks where planets form and evolve. The recent development in measuring disk masses and disk-star interaction properties, i.e., mass accretion rates, in large samples of young stellar objects demand a more careful comparison between the models and the data. We performed an initial critical assessment of the assumptions made by planet synthesis population models by looking at the relation between mass accretion rates and disk masses in the models and in the currently available data. We find that the currently used disk models predict mass accretion rate in line with what is measured, but with a much lower spread of values than observed. This difference is mainly because the models have a smaller spread of viscous timescales than what is needed to reproduce the observations. We also find an overabundance of weakly accreting disks in the models where giant planets have formed with respect to observations of typical disks. We suggest that either fewer giant planets have formed in reality or that the prescription for planet accretion predicts accretion on the planets that is too high. Finally, the comparison of the properties of transition disks with large cavities confirms that in many of these objects the observed accretion rates are higher than those predicted by the models. On the other hand, PDS70, a transition disk with two detected giant planets in the cavity, shows mass accretion rates well in line with model predictions.
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Pudritz, Ralph E., and Colin A. Norman. "Hydromagnetic winds from accretion disks." Canadian Journal of Physics 64, no. 4 (April 1, 1986): 501–6. http://dx.doi.org/10.1139/p86-094.
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We present a hydromagnetic wind model for molecular and ionized gas outflows associated with protostars. If the luminosity of protostars is due to accretion, then centrifugally driven winds that arise from the envelopes of molecular disks explain the observed rates of momentum and energy transport. Ionized outflow originates from disk radii r ≤ 1015 cm inside of which Ly-continuum photons from the protostellar accretion shock are intercepted. Observed molecular outflows arise from the cool disk envelope at radii 1015 ≤ r ≤ 1017 cm. The mass-loss rates of these two component outflows are [Formula: see text] and [Formula: see text]. These winds solve the angular-momentum problem of star formation. We propose that the collimation of such outflows is due to "hoop" stresses generated by the increasingly toroidal magnetic field in the wind and suggest that the structure of the underlying disks makes self-similar solutions for these outflows likely. Finally, we apply this analysis to other accreting systems such as cataclysmic variables.
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Coroniti, F. V. "Accretion Disk Electrodynamics." Symposium - International Astronomical Union 107 (1985): 453–69. http://dx.doi.org/10.1017/s007418090007594x.
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Accretion disk electrodynamic phenomenae are separable into two classes: 1) disks and coronae with turbulent magnetic fields; 2) disks and black holes which are connected to a large-scale external magnetic field. Turbulent fields may originate in an α - ω dynamo, provide anomalous viscous transport, and sustain an active corona by magnetic buoyancy. The large-scale field can extract energy and angular momentum from the disk and black hole, and be dynamically configured into a collimated relativistic jet.
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Maeda, Natsuho, Keiji Ohtsuki, Takayuki Tanigawa, Masahiro N. Machida, and Ryo Suetsugu. "Delivery of Gas onto the Circumplanetary Disk of Giant Planets: Planetary-mass Dependence of the Source Region of Accreting Gas and Mass Accretion Rate." Astrophysical Journal 935, no. 1 (August 1, 2022): 56. http://dx.doi.org/10.3847/1538-4357/ac7ddf.
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Abstract Gas accretion onto the circumplanetary disks and the source region of accreting gas are important to reveal dust accretion that leads to satellite formation around giant planets. We performed local three-dimensional high-resolution hydrodynamic simulations of an isothermal and inviscid gas flow around a planet to investigate the planetary-mass dependence of the gas accretion bandwidth and gas accretion rate onto circumplanetary disks. We examined cases with various planetary masses corresponding to M p = 0.05–1M Jup at 5.2 au, where M Jup is the current Jovian mass. We found that the radial width of the gas accretion band is proportional to M p 1 / 6 for the low-mass regime with M p ≲ 0.2M Jup while it is proportional to M p for the high-mass regime with M p ≳ 0.2M Jup. We found that the ratio of the mass accretion rate onto the circumplanetary disk to that into the Hill sphere is about 0.4 regardless of the planetary mass for the cases we examined. Combining our results with the gap model obtained from global hydrodynamic simulations, we derive a semi-analytical formula of mass accretion rate onto circumplanetary disks. We found that the mass dependence of our three-dimensional accretion rates is the same as the previously obtained two-dimensional case, although the qualitative behavior of accretion flow onto the circumplanetary disk is quite different between the two cases.
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Burke, Colin J., Yue Shen, Omer Blaes, Charles F. Gammie, Keith Horne, Yan-Fei Jiang, Xin Liu, et al. "A characteristic optical variability time scale in astrophysical accretion disks." Science 373, no. 6556 (August 12, 2021): 789–92. http://dx.doi.org/10.1126/science.abg9933.
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Accretion disks around supermassive black holes in active galactic nuclei produce continuum radiation at ultraviolet and optical wavelengths. Physical processes in the accretion flow lead to stochastic variability of this emission on a wide range of time scales. We measured the optical continuum variability observed in 67 active galactic nuclei and the characteristic time scale at which the variability power spectrum flattens. We found a correlation between this time scale and the black hole mass extending over the entire mass range of supermassive black holes. This time scale is consistent with the expected thermal time scale at the ultraviolet-emitting radius in standard accretion disk theory. Accreting white dwarfs lie close to this correlation, suggesting a common process for all accretion disks.
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Narayan, R. "Advective Disks." International Astronomical Union Colloquium 163 (1997): 75–89. http://dx.doi.org/10.1017/s0252921100042524.
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AbstractRecent work on advection-dominated accretion flows (ADAFs) is reviewed. The article concentrates on an optically thin branch of ADAFs which is present at mass accretion rates below a critical value ~ (10−2– 10−1) the Eddington rate. Models based on this branch have been quite successful at explaining a number of low-luminosity X-ray binaries and galactic nuclei, and some brighter systems. Some progress has also been made toward understanding the various spectral states of accreting black holes. It is argued that ADAFs may provide one of the best techniques for demonstrating the reality of event horizons in black holes.
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Kuperus, Max. "Accretion Disk Coronae." Highlights of Astronomy 8 (1989): 535–38. http://dx.doi.org/10.1017/s1539299600008248.
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SummaryAccretion disk coronae around compact objects are the result of strong magnetic activity in the inner regions of accretion disks. Part of the accreting energy is dissipated in te corona and can be observed as hard X-ray emission with a time variability caused by the coronal structures. The interaction of disk coronae with neutron stars and black holes may cause quaslperiodlc oscillations respectively flare type emission.
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Czerny, B. "Emission of Accretion Disks." Symposium - International Astronomical Union 159 (1994): 261–70. http://dx.doi.org/10.1017/s0074180900175138.
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Accretion disks surrounding massive black hole is an attractive scenario of nuclear activity. A number of arguments support it although there is no unquestionable proof of the existence of accretion disks in active galactic nuclei. Meaningful comparison of the disk model prediction with the data can only be made if emission of accretion disks is calculated taking into account the existence of optically thin parts responsible for the emission of x-ray radiation. Nonlocal reprocessing phenomena have to be also included. Since we have no real understanding of the viscous processes operating in accretion disks some ad hoc parameterization of these processes has to be used and its applicability should be checked by broad band comparison of predictions for continuum emission and spectral features with available data.
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Bisnovatyi-Kogan, Gennady, Alexandr S. Klepnev, and Richard V. E. Lovelace. "ACCRETION DISKS WITH A LARGE SCALE MAGNETIC FIELD AROUND BLACK HOLES." Acta Polytechnica 53, A (December 18, 2013): 677–82. http://dx.doi.org/10.14311/ap.2013.53.0677.
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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.
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Manara, C. F., A. Natta, G. P. Rosotti, J. M. Alcalá, B. Nisini, G. Lodato, L. Testi, et al. "X-shooter survey of disk accretion in Upper Scorpius." Astronomy & Astrophysics 639 (July 2020): A58. http://dx.doi.org/10.1051/0004-6361/202037949.
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Determining the mechanisms that drive the evolution of protoplanetary disks is a necessary step toward understanding how planets form. For this work, we measured the mass accretion rate for young stellar objects with disks at age > 5 Myr, a critical test for the current models of disk evolution. We present the analysis of the spectra of 36 targets in the ∼5–10 Myr old Upper Scorpius star-forming region for which disk masses were measured with ALMA. We find that the mass accretion rates in this sample of old but still surviving disks are similarly high as those of the younger (∼1−3 Myr old) star-forming regions of Lupus and Chamaeleon I, when considering the dependence on stellar and disk mass. In particular, several disks show high mass accretion rates ≳10−9 M⊙ yr−1 while having low disk masses. Furthermore, the median values of the measured mass accretion rates in the disk mass ranges where our sample is complete at a level ∼60−80% are compatible in these three regions. At the same time, the spread of mass accretion rates at any given disk mass is still > 0.9 dex, even at age > 5 Myr. These results are in contrast with simple models of viscous evolution, which would predict that the values of the mass accretion rate diminish with time, and a tighter correlation with disk mass at age > 5 Myr. Similarly, simple models of internal photoevaporation cannot reproduce the observed mass accretion rates, while external photoevaporation might explain the low disk masses and high accretion rates. A possible partial solution to the discrepancy with the viscous models is that the gas-to-dust ratio of the disks at ∼5–10 Myr is significantly different and higher than the canonical 100, as suggested by some dust and gas disk evolution models. The results shown here require the presence of several interplaying processes, such as detailed dust evolution, external photoevaporation, and possibly MHD winds, to explain the secular evolution of protoplanetary disks.
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Kumar, Shrabani, G. C. Dewangan, K. P. Singh, P. Gandhi, I. E. Papadakis, P. Tripathi, and L. Mallick. "Far-ultraviolet Spectroscopy of Active Galactic Nuclei with ASTROSAT/UVIT." Astrophysical Journal 950, no. 2 (June 1, 2023): 90. http://dx.doi.org/10.3847/1538-4357/acc941.
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Abstract We study accretion disk emission from eight Seyfert 1–1.5 active galactic nuclei (AGN) using far-ultraviolet (FUV) (1300–1800 Å) slitless grating spectra acquired with AstroSat/UVIT. We correct for the Galactic and intrinsic extinction, contamination from the host galaxies, narrow and broad-line regions, Fe ii emission, and Balmer continuum, and derive the intrinsic continua. We use Hubble Space Telescope COS/FOS spectra to account for the emission/absorption lines in the low-resolution UVIT spectra. We find generally redder power-law (f ν ∝ ν α ) slopes (α ∼ −1.1 to 0.3) in the FUV band than predicted by the standard accretion disk model in the optical/UV band. We fit accretion disk models such as the multitemperature disk blackbody (DISKBB) and relativistic disk (ZKERRBB, OPTXAGNF) models to the observed intrinsic continuum emission. We measure the inner disk temperatures using the DISKBB model for seven AGN. These temperatures in the range ∼3.6–5.8 eV are lower than the peak temperatures predicted for standard disks around maximally spinning supermassive black holes accreting at Eddington rates. The inner disks in two AGN, NGC 7469, and Mrk 352, appear to be truncated at ∼35–125 and 50–135 r g , respectively. While our results show that the intrinsic FUV emission from the AGN is consistent with the standard disks, it is possible that UV continua may be affected by the presence of soft X-ray excess emission, X-ray reprocessing, and thermal Comptonization in the hot corona. Joint spectral modeling of simultaneously acquired UV/X-ray data may be necessary to further investigate the nature of accretion disks in AGN.
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Kamali, F., C. Henkel, S. Koyama, C. Y. Kuo, J. J. Condon, A. Brunthaler, M. J. Reid, et al. "Accretion disk versus jet orientation in H2O megamaser galaxies." Astronomy & Astrophysics 624 (April 2019): A42. http://dx.doi.org/10.1051/0004-6361/201834600.
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Context. An essential part of the paradigm describing active galactic nuclei is the alignment between the radio jet and the associated rotation axis of the sub-pc accretion disks. Because of the small linear and angular scales involved, this alignment has not yet been checked in a sufficient number of low luminosity active galactic nuclei (LLAGNs). Aims. The project examines the validity of this paradigm by measuring the radio continuum on the same physical scale as the accretion disks to investigate any possible connection between these disks and the radio continuum. Methods. We observed a sample of 18 LLAGNs in the 4.8 GHz (6 cm) radio continuum using the Very Long Baseline Array (VLBA) with 3.3–6.5 ms resolution. The sources were selected to show both an edge-on accretion disk revealed by 22 GHz H2O megamaser emission and signatures of a radio jet. Furthermore, the sources were previously detected in 33 GHz radio continuum observations made with the Very Large Array. Results. Five out of 18 galaxies observed were detected at 8σ or higher levels (Mrk 0001, Mrk 1210, Mrk 1419, NGC 2273, and UGC 3193). While these five sources are known to have maser disks, four of them exhibit a maser disk with known orientation. For all four of these sources, the radio continuum is misaligned relative to the rotation axis of the maser disk, but with a 99.1% confidence level, the orientations are not random and are confined to a cone within 32° of the maser disk’s normal. Among the four sources the misalignment of the radio continuum with respect to the normal vector to the maser disk is smaller when the inner radius of the maser disk is larger. Furthermore, a correlation is observed between the 5 GHz VLBA radio continuum and the [OIII] luminosity and also with the H2O maser disk’s inner radius.
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Lominadze, J. G. "Nature of Turbulence: Governing Factor of Accretion Disk Dynamics." Highlights of Astronomy 11, no. 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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Nowak, Michael A., and Robert V. Wagoner. "Variability of Black Hole Accretion Disks." Symposium - International Astronomical Union 159 (1994): 487. http://dx.doi.org/10.1017/s0074180900176636.
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We consider two forms of variability in black hole accretion disks: harmonically oscillating modes trapped near the disk inner edge, and noisy fluctuations throughout the entire disk. We apply the former to AGN disks, and the latter to the X-ray power spectra of GX339-4.
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Liu, Hanpu, Gregory J. Herczeg, Doug Johnstone, Carlos Contreras-Peña, Jeong-Eun Lee, Haifeng Yang, Xingyu Zhou, et al. "Diagnosing FU Ori-like Sources: The Parameter Space of Viscously Heated Disks in the Optical and Near-infrared." Astrophysical Journal 936, no. 2 (September 1, 2022): 152. http://dx.doi.org/10.3847/1538-4357/ac84d2.
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Abstract FU Ori-type objects (FUors) are decades-long outbursts of accretion onto young stars that are strong enough to viscously heat disks so that the disk outshines the central star. We construct models for FUor objects by calculating emission components from a steady-state viscous accretion disk, a passively-heated dusty disk, magnetospheric accretion columns, and the stellar photosphere. We explore the parameter space of the accretion rate M ̇ and stellar mass M * to investigate implications on the optical and near-infrared spectral energy distribution and spectral lines. The models are validated by fitting to multiwavelength photometry of three confirmed FUor objects, FU Ori, V883 Ori, and HBC 722, and then comparing the predicted spectra to the observed optical and infrared spectra. The brightness ratio between the viscous disk and the stellar photosphere, η, provides an important guide for identifying viscous accretion disks, with η = 1 (“transition line”) and η = 5 (“sufficient dominance line”) marking turning points in diagnostics, evaluated here in the near-infrared. These turning points indicate the emergence and complete development of FUor-characteristic strong CO absorption, weak metallic absorption, the triangular spectral continuum shape in the H band, and location in color–magnitude diagrams. Lower M * and higher M ̇ imply larger η; for M * = 0.3 M ⊙, η = 1 corresponds to M ̇ = 2 × 10 − 7 M ⊙ yr−1 and η = 5 to M ̇ = 6 × 10 − 7 M ⊙ yr−1. The “sufficient dominance line” also coincides with the expected accretion rate where accreting material directly reaches the star. We discuss implications of the models on extinction diagnostics, FUor brightening timescales, viscous disks during initial protostellar growth, and eruptive young stellar objects associated with FUors.
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Miller, M. Coleman, Frederick K. Lamb, and Russell J. Hamilton. "Electrodynamics of Disk-Accreting Magnetic Neutron Stars." International Astronomical Union Colloquium 142 (1994): 833–35. http://dx.doi.org/10.1017/s0252921100078179.
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AbstractWe have investigated the electrodynamics of magnetic neutron stars accreting from Keplerian disks and the implications for particle acceleration and γ-ray emission by such systems. We argue that the particle density in the magnetospheres of such stars is larger by orders of magnitude than the Goldreich-Julian density, so that the formation of vacuum gaps is unlikely. We show that even if the star rotates slowly, electromotive forces ( EMFs ) of order 1015 V are produced by the interaction of plasma in the accretion disk with the magnetic field of the neutron star. The resistance of the disk-magnetosphere-star circuit is small, and hence these EMFs drive very large conduction currents. Such large currents are likely to produce magnetospheric instabilities, such as relativistic double layers and reconnection events, that can accelerate electrons or ions to very high energies.Subject headings: acceleration of particles — accretion, accretion disks — MHD — stars: neutron
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Khaibrakhmanov, Sergey, and Alexander Dudorov. "Outflows and particle acceleration in the accretion disks of young stars." EPJ Web of Conferences 201 (2019): 09004. http://dx.doi.org/10.1051/epjconf/201920109004.
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Magneto-gas-dynamic (MGD) outflows from the accretion disks of T Tauri stars with fossil large-scale magnetic fileld are investigated. We consider two mechanisms of the outflows: rise of the magnetic flux tubes (MFT) formed in the regions of efficient generation of the toroidal magnetic fileld in the disk due to Parker instability, and acceleration of particles in the current layer formed near the boundary between stellar magnetosphere and the accretion disk. Structure of the disk is calculated using our MGD model of the accretion disks. We simulate dynamics of the MFT in frame of slender flux tube approximation taking into account aerodynamic and turbulent drags, and radiative heat exchange with external gas. Particle acceleration in the current layer is investigated on the basis of Sweet-Parker model of magnetic reconnection. Our calculations show that the MFT can accelerate to velocities up to 50 km s-1 causing periodic outflows from the accretion disks. Estimations of the particle acceleration in the current layer are applied to interpret high-speed jets and X-rays observed in T Tauri stars with the accretion disks.
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Stepinski, T. "Kinematic Dynamo in Turbulent Circumstellar Disks." Symposium - International Astronomical Union 157 (1993): 203–7. http://dx.doi.org/10.1017/s0074180900174121.
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Many circumstellar disks associated with objects ranging from protoplanetary nebulae to accretion disks around compact stars allow for the generation of magnetic fields by an αω dynamo. We have applied kinematic dynamo formalism to geometrically thin accretion disks. We calculate, in the framework of an adiabatic approximation, the normal mode solutions for dynamos operating in disks around compact stars. We then describe the criteria for a viable dynamo in protoplanetary nebulae, and discuss the particular features that make accretion disk dynamos different from planetary, stellar, and galactic dynamos.
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Hure, J. M., and D. Richard. "Accretion Discs in AGN, Viscosity and Structure of Accretion Disks." EAS Publications Series 1 (2001): 53–61. http://dx.doi.org/10.1051/eas:2001008.
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Jacquemin-Ide, J., G. Lesur, and J. Ferreira. "Magnetic outflows from turbulent accretion disks." Astronomy & Astrophysics 647 (March 2021): A192. http://dx.doi.org/10.1051/0004-6361/202039322.
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Context. Astrophysical disks are likely embedded in an ambient vertical magnetic field generated by its environment. This ambient field is known to drive magneto-rotational turbulence in the disk bulk, but it is also responsible for launching magnetised outflows at the origin of astrophysical jets. Yet, the interplay between turbulence and outflows is not understood. In particular, the vertical structure and long-term (secular) evolution of such a system lack quantitative predictions. It is, nevertheless, this secular evolution which is proposed to explain time variability in many accreting systems such as FuOr, X-ray binaries, and novae like systems. Aims. We seek to constraint the structure and long-term evolution of turbulent astrophysical disks subject to magnetised outflows in the non-relativistic regime. More specifically we aim to characterise the mechanism driving accretion, the dynamics of the disk atmosphere, the role played by the outflow, and the long-term evolution of mass and magnetic flux distributions. Methods. We computed and analysed global 3D ideal magnetohydrynamic (MHD) simulations of an accretion disk threaded by a large-scale magnetic field. We measured the turbulent state of the system by Reynolds averaging the ideal MHD equations and evaluate the role of the turbulent terms in the equilibrium of the system. We then computed the transport of mass, angular momentum, and magnetic fields in the disk to characterise its secular evolution. Finally, we performed a parameter exploration survey in order to characterise how the transport properties depend on the disk properties. Results. We find that weakly magnetised disks drive jets that carry a small fraction of the disk angular momentum away. The mass-weighted accretion speed remains subsonic, although there is always an upper turbulent atmospheric region where transsonic accretion takes place. We show that this turbulence is driven by a strongly magnetised version of the magneto-rotational instability. The internal disk structure therefore appears drastically different from the conventional hydrostatic picture. We expect that the turbulent atmosphere region will lead to non-thermal features in the emission spectra from compact objects. In addition, we show that the disk is subject to a secular viscous-type instability, which leads to the formation of long-lived ring-like structures in the disk surface density distribution. This instability is likely connected to the magnetic field transport. Finally, we show that for all of the parameters explored, the ambient magnetic field is always dragged inward in the disk at a velocity which increases with the disk magnetisation. Beyond a threshold on the latter, the disk undergoes a profound radial readjustment. It leads to the formation of an inner accretion-ejection region with a supersonic mass-weighted accretion speed and where the magnetic field distribution becomes steady and reaches a magnitude near equipartition with the thermal pressure. This inner structure shares many properties with the jet emitting disk model. Overall, these results pave the way for quantitative self-consistent secular disk models.
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Klahr, Hubert. "Thermal convection in accretion disks." Proceedings of the International Astronomical Union 2, S239 (August 2006): 405–16. http://dx.doi.org/10.1017/s1743921307000828.
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AbstractFor a long time it was believed that thermal convection could serve as the driving mechanism for turbulence and angular momentum transport in accretion disks. Even it is meanwhile accepted that convection had to leave that role to the magneto rotational instability, it is still an important effect arising in a realistic treatment of accretion disks, i.e. with proper thermodynamics and radiation transport. We review the history of thermal convection in astrophysical disks and show the relevant analytic and numerical work, including energy transport by convection and the effect of “negative” Reynolds stresses. We will also place the convective instability into the context of the magnetorotational instability and planet–disk interaction.
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Thanathibodee, Thanawuth, Nuria Calvet, Jesús Hernández, Karina Maucó, and César Briceño. "A Census of the Low Accretors. I. The Catalog." Astronomical Journal 163, no. 2 (January 19, 2022): 74. http://dx.doi.org/10.3847/1538-3881/ac3ee6.
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Abstract Observations have shown that the disk frequency and the fraction of accreting pre-main-sequence stars decrease with the age of the population and that some stars appear to have disks while their accretion has stopped. Still, it is unclear how disk-bearing stars stop their accretion. To provide insight into the last stages of accretion in low-mass young stars, we conducted a survey of disk-bearing stars that are thought to be non-accretors to identify stars still accreting at very low rates. Here we present the first catalog of the survey of 170 disk-bearing non-accreting stars in Chamaeleon I, Orion OB1, Upper Scorpius, γ Velorum, and Upper Centaurus–Lupus, using He i λ10830 as a sensitive probe of accretion. We classify the line profiles into six types and argue that those showing redshifted and/or blueshifted absorption are still accreting. Using these classifications, we found that, among disk-bearing stars previously classified as non-accretors, at least 20%–30% are still accreting, with a larger fraction of those at younger population ages. While the difference between the outer disk signature and accretion status is unclear, we found a difference between the inner disk excess and accretion status. There is no preference in the mass of the newly identified accretors, suggesting that the processes inhibiting accretion do not directly depend on mass in the typical mass range of T Tauri stars. Lastly, we found that at a low accretion level, the “Hα width at the 10% height” criterion mischaracterizes a larger fraction of accretors than the line’s equivalent width.
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Kitabatake, Etsuko, and Jun Fukue. "Cloudy Accretion Disks." Publications of the Astronomical Society of Japan 55, no. 6 (December 25, 2003): 1115–20. http://dx.doi.org/10.1093/pasj/55.6.1115.
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Lovelace, R. V. E., and Tom Chou. "Counterrotating Accretion Disks." Astrophysical Journal 468, no. 1 (September 1, 1996): L25—L28. http://dx.doi.org/10.1086/310232.
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Abramowicz, M. A., B. Czerny, J. P. Lasota, and E. Szuszkiewicz. "Slim accretion disks." Astrophysical Journal 332 (September 1988): 646. http://dx.doi.org/10.1086/166683.
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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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Wallinder, F. H. "Variability and Slim Accretion Disks." Symposium - International Astronomical Union 159 (1994): 253–56. http://dx.doi.org/10.1017/s0074180900175114.
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Many compact galactic and extra-galactic sources have a luminosity in the slim accretion disk regime, i.e. L/LE ∼ 1, where LE is the Eddington luminosity. The correspondingly large accretion rates diminish the relevance of variability interpretations based on the thin disk model. This paper explores the possible connection between variability in AGN and local instabilities in slim disks, and points out some relevant areas of future research.
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de Kool, Marthijn, Geoffrey V. Bicknell, and Zdenka Kuncic. "Magnetic Fields in Accretion Disks." Publications of the Astronomical Society of Australia 16, no. 3 (1999): 225–33. http://dx.doi.org/10.1071/as99225.
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AbstractThis paper summarises our work on the role of magnetic fields in accretion disks presented in two papers elsewhere. In the first part (a summary of part of Kuncic & Bicknell 1999), we present a formal development of the equations governing the structure of an accretion disk containing magnetohydrodynamic turbulence. The importance of the different terms in the energy and momentum equations is discussed, and a parametrisation of the unresolved processes is suggested that could be used to make further progress. We briefly explore whether an MHD accretion disk can transport a significant part of the gravitational power into a corona by buoyancy. In the second part, we present some exploratory calculations of the vertical structure of accretion disks, in which non-local dissipation of energy due to the buoyant transport of magnetic field energy is taken into account. It is argued that the efficiency of buoyant magnetic transport depends very strongly on the size of the coherent magnetic regions. If the size of the buoyant cells is not very close to the disk thickness, magnetic energy generated by dynamo action inside the disk will be dissipated locally, and will not be available to transport a significant part of the accretion luminosity into a corona.
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Koratkar, Anuradha. "11.7. Signature of accretion disks in active galactic nuclei." Symposium - International Astronomical Union 184 (1998): 469–70. http://dx.doi.org/10.1017/s0074180900085612.
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One of the fundamental components of any theory of Active Galactic Nuclei (AGNs) is an accretion disk surrounding a supermassive blackhole. While most theories predict the formation of such a disk, fewer say anything about the observational consequences of the disk. Those studies which have addressed the observational signatures of accretion disks have found that the Lyman edge at 912Å is a powerful diagnostic feature for the physical characteristics of the disk. One of the important consequences of such disks is a feature at the Lyman edge (912Å). Spectroscopic investigations have found scant evidence for Lyman edge features arising in an accretion disk (Koratkar, Kinney and Bohlin 1992). Proving the existence of radiating disks in even a few AGNs would be a major step in our understanding of the phenomenon.
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Sousa, Alana P., Silvia H. P. Alencar, Luisa M. Rebull, Catherine C. Espaillat, Nuria Calvet, and Paula S. Teixeira. "A study of accretion and disk diagnostics in the NGC 2264 cluster." Astronomy & Astrophysics 629 (September 2019): A67. http://dx.doi.org/10.1051/0004-6361/201935563.
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Context. Understanding disk dissipation is essential for studying how planets form. Disk gaps and holes, which almost correspond to dust-free regions, are inferred from infrared observations of T Tauri stars (TTS), indicating the existence of a transitional phase between thick accreting disks and debris disks. Transition disks are usually referred to as candidates for newly formed planets. Aims. We searched for transition disk candidates belonging to NGC 2264. Using stellar and disk parameters obtained in the observational multiwavelength campaign CSI 2264, we characterized accretion, disk, and stellar properties of transition disk candidates and compared them to systems with a full disk and diskless stars. Methods. We modeled the spectral energy distribution (SED) of a sample of 401 TTS, observed with both CFHT equipped with MegaCam and IRAC instrument on the Spitzer, with Hyperion SED fitting code using photometric data from the U band (0.3 μm) to the Spitzer/MIPS 24 μm band. We used the SED modeling to distinguish transition disk candidates, full disk systems, and diskless stars. Results. We classified ∼52% of the sample as full disk systems, ∼41% as diskless stars, and ∼7% of the systems as transition disk candidates, among which seven systems are new transition disk candidates belonging to the NGC 2264 cluster. The sample of transition disk candidates present dust in the inner disk similar to anemic disks, according to the αIRAC classification, which shows that anemic disk systems can be candidate transition disks. We show that the presence of a dust hole in the inner disk does not stop the accretion process since 82% of transition disk candidates accrete and show Hα, UV excess, and mass accretion rates at the same level as full disk systems. We estimate the inner hole sizes, ranging from 0.1 to 78 AU, for the sample of transition disk candidates. In only ∼18% of the transition disk candidates, the hole size could be explained by X-ray photoevaporation from stellar radiation.
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McCray, Richard. "Compact Binary X-Ray Sources." International Astronomical Union Colloquium 89 (1986): 184–97. http://dx.doi.org/10.1017/s0252921100086085.
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AbstractCompact binary X-ray sources include white dwarfs, neutron stars, and black holes that are accreting matter from a companion star. The X-ray emission from these systems is produced by the accreting matter as it flows through an accretion disk and strikes the surface of the compact object. The emitting regions have opacities dominated by electron scattering, and radiation pressure is likely to play an important role in the hydrodynamics. Strong magnetic fields greatly modify the hydrodynamics and radiation transfer in the pulsating neutron star sources. Accretion disks have complex structure, including an electron scattering corona, a cool outer region, and possibly a thick torus in their inner region. The structure and stability properties of accretion disks are only partially understood. Major problems exist with the interpretation of the spectra and luminosities of the X-ray burst sources. The pulsed X-ray emission from the pulsating binary X-ray sources probably comes from “mounds” of accreting gas at the magnetic poles of neutron stars, in which the accreting matter is decelerated by radiation pressure. The physics of these systems is reviewed, with an emphasis on problems for which hydrodynamical simulations may be especially useful.
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Hasegawa, Yasuhiro, Thomas J. Haworth, Keri Hoadley, Jinyoung Serena Kim, Hina Goto, Aine Juzikenaite, Neal J. Turner, Ilaria Pascucci, and Erika T. Hamden. "Determining Dispersal Mechanisms of Protoplanetary Disks Using Accretion and Wind Mass Loss Rates." Astrophysical Journal Letters 926, no. 2 (February 1, 2022): L23. http://dx.doi.org/10.3847/2041-8213/ac50aa.
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Abstract Understanding the origin of accretion and dispersal of protoplanetary disks is fundamental for investigating planet formation. Recent numerical simulations show that launching winds are unavoidable when disks undergo magnetically driven accretion and/or are exposed to external UV radiation. Observations also hint that disk winds are common. We explore how the resulting wind mass loss rate can be used as a probe of both disk accretion and dispersal. As a proof-of-concept study, we focus on magnetocentrifugal winds, magnetorotational instability turbulence, and external photoevapotaion. By developing a simple yet physically motivated disk model and coupling it with simulation results available in the literature, we compute the wind mass loss rate as a function of external UV flux for each mechanism. We find that different mechanisms lead to different levels of mass loss rate, indicating that the origin of disk accretion and dispersal can be determined, by observing the wind mass loss rate resulting from each mechanism. This determination provides important implications for planet formation. This work thus shows that the ongoing and future observations of the wind mass loss rate for protoplanetary disks are paramount to reliably constrain how protoplanetary disks evolve with time and how planet formation takes place in the disks.
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Bisikalo, Dmitry V., and Andrey G. Zhilkin. "Flow Structure in Magnetic CVs." Proceedings of the International Astronomical Union 7, S282 (July 2011): 509–16. http://dx.doi.org/10.1017/s1743921311028286.
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AbstractWe present a review of the modern concept of physical processes which go on in magnetic CVs with the mass transfer between the components. Using results of 3D MHD simulations, we investigated variations of the main characteristics of accretion disks depending on the value of the magnetic induction on the surface of the accreting star. In the frame of a self-consistent description of the MHD flow structure in close binaries, we formulate conditions of the disk formation and find a criterion that separates two types of flows corresponding to intermediate polars (intermediate magnetic field) and polars (strong field).The influence of asynchronous rotation of the accretor on the flow structure in magnetic close binaries is also discussed. Simulations show that the accretion instability arising in binaries with rapid rotation of accretor (“propeller” regime) can explain the mechanism of quasi-periodic dwarf nova outbursts observed in DQ Her systems.
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Fukue, Jun, and Masayuki Ioroi. "Hoyle-Lyttleton Accretion onto Accretion Disks." Publications of the Astronomical Society of Japan 51, no. 1 (February 1, 1999): 151–59. http://dx.doi.org/10.1093/pasj/51.1.151.
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Kazanas, Demosthenes. "MHD Accretion Disk Winds: The Key to AGN Phenomenology?" Galaxies 7, no. 1 (January 10, 2019): 13. http://dx.doi.org/10.3390/galaxies7010013.
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Accretion disks are the structures which mediate the conversion of the kinetic energy of plasma accreting onto a compact object (assumed here to be a black hole) into the observed radiation, in the process of removing the plasma’s angular momentum so that it can accrete onto the black hole. There has been mounting evidence that these structures are accompanied by winds whose extent spans a large number of decades in radius. Most importantly, it was found that in order to satisfy the winds’ observational constraints, their mass flux must increase with the distance from the accreting object; therefore, the mass accretion rate on the disk must decrease with the distance from the gravitating object, with most mass available for accretion expelled before reaching the gravitating object’s vicinity. This reduction in mass flux with radius leads to accretion disk properties that can account naturally for the AGN relative luminosities of their Optical-UV and X-ray components in terms of a single parameter, the dimensionless mass accretion rate. Because this critical parameter is the dimensionless mass accretion rate, it is argued that these models are applicable to accreting black holes across the mass scale, from galactic to extragalactic.
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Torkelsson, Ulf. "Dynamo Action in Accretion Disks." Symposium - International Astronomical Union 157 (1993): 209–10. http://dx.doi.org/10.1017/s0074180900174133.
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Employing the standard theory for thin accretion disks I estimate the relevant parameters for a dynamo in an accretion disk. These estimates could then be compared to the results of numerical simulations. Some preliminary results of such simulations (Torkelsson & Brandenburg 1992) are presented too.
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Murray, James Rhys. "Spiral Shocks in Accretion Disks with SPH." International Astronomical Union Colloquium 163 (1997): 770. http://dx.doi.org/10.1017/s025292110004389x.
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AbstractSmoothed Particle Hydrodynamics (SPH) is now seen as a numerical scheme well suited to the study of accretion disks. SPH simulations have been conducted of cataclysmic variable disks (Lubow 1991, Murray 1996, Armitage and Livio 1996), galactic disks (Artymowicz and Lubow 1989), and protostellar disks (Artymowicz and Lubow 1994). It is therefore important to test the technique against theory and other numerical results to obtain an estimate of the accuracy and reliability of SPH in this context. Previously SPH has been tested against standard stationary and time-dependent results of viscous thin disk theory (Murray 1996). Strictly these tests relate to disks where ‘viscous’ terms dominate pressure terms in the equations of motion.In this paper we describe tests of the code more appropriate for hot disks where pressure forces are relatively more important than viscosity. Specifically we consider the form of the spiral density waves that can be excited in a disk by a perturbing gravitational potential. Very low mass perturbing bodies excite linear spiral waves which redistribute angular momentum in the disk. For increasingly massive perturbers, the disk response becomes nonlinear and eventually shocks form. In the standard formulation of SPH, an artificial viscosity term is added to the SPH equations to improve shock capture. This is equivalent to introducing a fixed ratio of shear to bulk viscosity into the equations of motion. In Eulerian schemes, artificial viscosity has been discarded in favour of other more accurate, less dissipative schemes for resolving shocks. The continued use of artificial viscosity in SPH has become a source of ‘friction’ between numericists. The simulations described here demonstrate the scheme’s ability to resolve spiral shocks, and show that SPH is a valuable tool for probing the structure of tidally perturbed accretion disks.
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Kondo, Katsushi, Satoshi Okuzumi, and Shoji Mori. "The Roles of Dust Growth in the Temperature Evolution and Snow Line Migration in Magnetically Accreting Protoplanetary Disks." Astrophysical Journal 949, no. 2 (June 1, 2023): 119. http://dx.doi.org/10.3847/1538-4357/acc840.
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Abstract The temperature structure of protoplanetary disks provides an important constraint on where in the disks rocky planets like our own form. Recent nonideal magnetohydrodynamical (MHD) simulations have shown that the internal Joule heating associated with magnetically driven disk accretion is inefficient at heating the disk midplane. A disk temperature model based on the MHD simulations predicts that in a disk around a solar-mass young star, the water snow line can move inside the current Earth’s orbit within 1 Myr after disk formation. However, the efficiency of the internal Joule heating depends on the disk’s ionization and opacity structures, both of which are governed by dust grains. In this study, we investigate these effects by combining the previous temperature model for magnetically accreting disks with a parameterized model for the grain size and vertical distribution. Grain growth enhances the gas ionization fraction and thereby allows Joule heating to occur closer to the midplane. However, growth beyond 10 μm causes a decrease in the disk opacity, leading to a lower midplane temperature. The combination of these two effects results in the midplane temperature being maximized when the grain size is in the range 10–100 μm. Grain growth to millimeter sizes can also delay the snow line’s migration to the 1 au orbit by up to a few million years. We conclude that accounting for dust growth is essential for accurately modeling the snow line evolution and terrestrial planet formation in magnetically accreting protoplanetary disks.
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Yusupova, R. М., G. R. Muchtarova, and R. N. Izmailov. "EDDINGTON LUMINOSITY LIMIT FOR MASSLESS WORMHOLES WITH SCALAR FIELD." Izvestia Ufimskogo Nauchnogo Tsentra RAN, no. 1 (March 28, 2022): 21–24. http://dx.doi.org/10.31040/2222-8349-2022-0-1-21-24.
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Most astrophysical objects growth by mass accretion. The almost universal presence of interstellar matter generally leads to the formation around compact objects of accretion disks. The emission of the radiation from the disk is determined by the external gravitational potentials of the central massive object, which in turn are essentially determined by its nature – neutron star, black hole, wormhole or naked singularity. Hence the astrophysical observations of the emission spectra from accretion disks may lead to the possibility of directly testing the physical and astrophysical properties of the compact general relativistic objects that have generated the disk via their gravitational field. The accretion process proceeds due to the viscosity caused by the turbulent motions of matter in the accretion disks. In turn, disks have an important property – luminosity, which today allows indirect observation of astrophysical compact objects. In this work, calculations are performed to determine the Eddington luminosity limit of an accretion disk formed around a massless wormhole. The dependence of the limiting luminosity in the throat region and at infinity on the dilatonic, electric and magnetic charges for the Goulart wormhole was established. An upper limit was also obtained for the dilatonic charge, at which the maximum value of Eddington's luminosity is reached. As a result, it was found that with an increase in the dilatonic charge, the value of the Eddington luminosity limit increases.
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Nishikori, H., M. Machida, and R. Matsumoto. "Magnetic Activity Following Re-Accretion on to Galaxies." Symposium - International Astronomical Union 217 (2004): 174–76. http://dx.doi.org/10.1017/s0074180900197396.
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We carried out global three-dimensional magnetohydrody-namical (MHD) simulations of galactic gaseous disks re-accreting intergalactic plasma. As the initial condition, we assume that a rotating slender torus is formed at 10kpc from the galactic center. We assume a gravitational potential generated by bulge stars, disk stars and dark matters. Numerical results indicate that magnetorotational instability (MRI) growing in the torus amplifies magnetic fields and generates turbulence. The Maxwell stress enhanced by turbulent magnetic fields drives mass accretion of the disk gas. The amplification of magnetic fields in the accreting gas disk drives magnetic activities such as flares and plasma heating due to magnetic reconnection. The magnetic activity is maintained for time scales longer than the accretion time scale, typically 5Gyr.
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Maloney, Philip R., and Mitchell C. Begelman. "Radiation-Driven Warping: The Origin of Warps and Precession in Accretion Disks." International Astronomical Union Colloquium 163 (1997): 311–20. http://dx.doi.org/10.1017/s0252921100042780.
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AbstractA geometrically thin, optically thick, warped accretion disk with a central source of luminosity is subject to non-axisymmetric forces due to radiation pressure; the resulting torque acts to modify the warp. Initially planar accretion disks are unstable to warping driven by radiation torque, as shown in a local analysis by Pringle (1996) and a global analysis of the stable and unstable modes by Maloney, Begelman, & Pringle (1996). In general, the warp also precesses.We discuss the nature of this instability, and its possible implications for accretion disks in X-ray binaries and active galactic nuclei. Specifically, we argue that this effect provides a plausible explanation for the misalignment and precession of the accretion disks in X-ray binaries such as SS 433 and Her X–l; the same mechanism explains why the maser disk in NGC 4258 is warped.
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Noguchi, Masafumi. "Diverse Star Formation History in Presence of Cold-Mode Gas Accretion: From Solar Neighborhood to Distant Galaxies." Proceedings of the International Astronomical Union 17, S373 (August 2021): 322–24. http://dx.doi.org/10.1017/s1743921322004811.
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AbstractExistence of cold-mode gas accretion along with the hot-mode accretion of the shock-heated gas can explain the bimodality in the elemental abundance of the Milky Way disk stars as well as the mass-dependence of galaxy morphology represented by mass ratios of thin disks, thick disks, and bulges.
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Tovmassian, Gagik, and Sergey Zharikov. "Accretion Disks of Bounce-Back CVs." Proceedings of the International Astronomical Union 8, S290 (August 2012): 149–52. http://dx.doi.org/10.1017/s1743921312019412.
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AbstractWe explore conditions and structure of accretion disks in the short-period Cataclysmic Variables, which have evolved beyond the period minimum. We show that the accretion disk in a system with extreme mass ratio grows in the size reaching 2:1 resonance radius and are relatively cool. They also become largely optically thin in the continuum, contributing to the total flux less than the stellar components of the system. In contrast, the viscosity and the temperature in spiral arms formed at the outer edge of the disk are higher and their contribution in continuum plays an increasingly important role. We model such disks and generate light curves which successfully simulate the observed double-humped light curves in the quiescence.
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Rutten, René G. M. "Eclipse mapping and related techniques." Symposium - International Astronomical Union 176 (1996): 69–84. http://dx.doi.org/10.1017/s007418090008311x.
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Eclipse mapping is a technique to deduce spatial structure on very small angular scales in eclipsing cataclysmic variable stars (CVs). By analysing the eclipse light curve, information is obtained on the brightness structure of the accretion disk and of the compact mass-accreting object in these systems. This information would otherwise be well beyond the resolving power of any optical telescope. Since the development of the eclipse mapping technique by K. Horne, about one decade ago, it has now become an important tool in the study of CVs. Originally eclipse mapping was employed to construct brightness maps of accretion disks in broad spectral bands. Recently, maps of much higher spectral resolution have become available from which optical and UV spectra have been reconstructed in spatial detail across accretion disks. Such information is very important for our understanding of the physics of the accretion process.In this paper I will describe the eclipse mapping technique and review recent results. In conjunction, I will briefly highlight other techniques related to the mapping of surface structure in CVs.
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Balbus, Steven A., and John F. Hawley. "Instability, Turbulence, and Enhanced Transport in Accretion Disks." International Astronomical Union Colloquium 163 (1997): 90–100. http://dx.doi.org/10.1017/s0252921100042536.
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AbstractThe nature of MHD and hydrodynamical turbulence in accretion disks is discussed. Comparison is made with planar Couette flow, a classical system prone to nonlinear shear instability resulting in enhanced turbulent transport. Both Keplerian and non-Keplerian hydrodynamical disks are studied, and it is found that only constant angular momentum disks are unstable to nonlinear disturbances and develop enhanced turbulent transport. Convective instabilities do not lead to enhanced turbulent transport. Hydrodynamical Keplerian disks are quite stable to nonlinear disturbances. Several lines of argument are presented which all lead to this conclusion, but the key to disk turbulence is the interaction between the stress tensor and the mean flow gradients. The nature of this coupling is found to determine completely the stability properties of disks (hydrodynamics and magnetic), and the nature of turbulent transport. The weak field MHD instability, which is of great astrophysical importance, displays the same type of stress tensor – mean flow coupling that all classical local shear instabilities exhibit. Hydrodynamical Keplerian disks, on the other hand, do not. Accretion disk turbulence is MHD turbulence.
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Maksimova, Lomara, and Yaroslav Pavlyuchenkov. "Long-Term Evolution of Convectively Unstable Disk." Proceedings of the International Astronomical Union 16, S362 (June 2020): 306–8. http://dx.doi.org/10.1017/s1743921322001478.
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AbstractWe continue studying convection as a possible factor of episodic accretion in protoplanetary disks. Within the model of a viscous disk, the accretion history is analyzed at different rates and regions of matter inflow from the envelope onto the disk. It is shown that the burst-like regime occurs in a wide range of parameters. The long-term evolution of the disk is modeled, including the decreasing-with-time matter inflow from the envelope. It is demonstrated that the disk becomes convectively unstable and maintains burst-like accretion onto the star for several million years. The general conclusion of the study is that convection can serve as one of the mechanisms of episodic accretion in protostellar disks, but this conclusion needs to be verified using more consistent hydrodynamic models.
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Liu, Xiang, Ning Chang, Xin Wang, and Qi Yuan. "The Origin of Radio Emission in Black Hole X-ray Binaries." Galaxies 9, no. 4 (October 17, 2021): 78. http://dx.doi.org/10.3390/galaxies9040078.
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We studied the relation of accretion-jet power and disk luminosity, especially the jet efficiencies and disk radiative efficiencies for different accretion disks as well as black hole (BH) spin, in order to explore the origin of radio emission in black hole X-ray binaries (BHXBs). We found that jet efficiency increases more rapidly (efficient) than the nearly constant disk radiative efficiency for thin disk component in high accretion regime, which could account for the steep track (μ>1) in the observed radio and X-ray luminosity relations (LR∝LXμ), but the thin disk component may not be able to explain the standard track (μ≈0.6) in the BHXBs. For hot accretion flows (HAF), the resulting jet efficiency changes along with the large range of accretions from quiescent state to nearly Eddington state, which could account for the standard track in the BHXBs. The BH spin-jet is discussed for the magnetic arrested disk (MAD) state; in this state, the spin-jet power might contribute to a linear correlation between jet power and mass accretion rate for a given source. More accurate observations are required to test the results.