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Bjorkman, J. E. "The Formation and Structure of Circumstellar Disks". International Astronomical Union Colloquium 175 (2000): 422–47. http://dx.doi.org/10.1017/s0252921100056220.
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AbstractSeveral theories have been proposed to explain the origin of Be star disks. Among them are Wind-Compressed Disks, accretion disks, decretion disks, and “explosive” ejections. In reviewing these mechanisms, I first concentrate on the current status of the Wind-Compressed Disk model. In particular, I discuss how non-radial forces may prevent disk formation and then discuss various physical effects that may restore the disk. Second, I examine the observational evidence and what it tells us about the structure of the disk. Of particular interest is evidence in favor of Keplerian disks. Finally, I discuss theories for Keplerian disk formation and some of the constraints such theories must satisfy.
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Wardle, Mark, i Farhad Yusef-Zadeh. "The origin of Keplerian megamaser disks". Proceedings of the International Astronomical Union 8, S287 (styczeń 2012): 354–55. http://dx.doi.org/10.1017/s1743921312007302.
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AbstractSeveral examples of thin, Keplerian, sub-parsec megamaser disks have been discovered in the nuclei of active galaxies and used to precisely determine the mass of their host black holes. We show that there is an empirical linear correlation between the disk radius and black hole mass and that such disks are naturally formed as molecular clouds pass through the galactic nucleus and temporarily engulf the central supermassive black hole. For initial cloud column densities below about 1023.5 cm−2 the disk is non-self gravitating, but for higher cloud columns the disk would fragment and produce a compact stellar disk similar to that observed around Sgr A* at the galactic centre.
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T. Okazaki, Atsuo. "Global Oscillations of Masing Disks in Megamasers". Symposium - International Astronomical Union 194 (1999): 90–91. http://dx.doi.org/10.1017/s0074180900161819.
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We study the characteristics of global oscillation modes of masing disks in megamasers and the effect of the modes on the disk kinematics. We find that the eccentric mode is responsible for the observed sub-Keplerian velocity distribution of the maser source of NGC 1068, whereas in the masing disk of NGC 4258 the warping mode is dominant so that the angular rotation velocity remains near Keplerian.
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Balbus, Steven A., i 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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Terry, J. P., C. Hall, S. Abreau i S. Gleyzer. "Kinematic Evidence of an Embedded Protoplanet in HD 142666 Identified by Machine Learning". Astrophysical Journal 947, nr 2 (1.04.2023): 60. http://dx.doi.org/10.3847/1538-4357/acc737.
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Abstract Observations of protoplanetary disks have shown that forming exoplanets leave characteristic imprints on the gas and dust of the disk. In the gas, these forming exoplanets cause deviations from Keplerian motion, which can be detected through molecular line observations. Our previous work has shown that machine learning can correctly determine if a planet is present in these disks. Using our machine-learning models, we identify strong, localized non-Keplerian motion within the disk HD 142666. Subsequent hydrodynamics simulations of a system with a 5 M J planet at 75 au recreate the kinematic structure. By currently established standards in the field, we conclude that HD 142666 hosts a planet. This work represents a first step toward using machine learning to identify previously overlooked non-Keplerian features in protoplanetary disks.
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Oudmaijer, René D., Hugh E. Wheelwright, Alex C. Carciofi, Jon E. Bjorkman i Karen S. Bjorkman. "Spectrally and spatially resolved Hα emission from Be stars: their disks rotate Keplerian". Proceedings of the International Astronomical Union 6, S272 (lipiec 2010): 418–19. http://dx.doi.org/10.1017/s1743921311011008.
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AbstractWe test whether Be star disks rotate in a Keplerian or an Angular Momentum Conserving fashion. This is done by employing sub-milli arcsecond spectroastrometry around Hα. We spatially resolve the disks, and are the first to do so at such a high spectral resolution. We fit the emission line profiles with parametric models. The Keplerian models reproduce the spectro-astrometry, whereas the AMC models do not, thereby supporting the viscous disk model for Be stars.
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Abdulmyanov, Tagir. "On the forms of accretion of interstellar gas and dust during the formation of single stars and their planetary systems". Open Astronomy 30, nr 1 (1.01.2021): 83–90. http://dx.doi.org/10.1515/astro-2021-0010.
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Abstract In this paper, the mechanisms of star formation and the formation of the equatorial gas and dust disk of protostars are considered. The viscous dynamics of the interstellar matter of gas and dust disks is mainly determined by perturbations of the matter density during gas accretion onto the equilibrium core of the protostar. Using the model of pulsating perturbations of the density of the gas-dust envelope of the protostar and the Navier-Stokes equations, the formulas for the dynamic viscosity of Keplerian and almost Keplerian disks are obtained. It is shown that in the regime of unstable equilibrium of the envelope, accretion of gas onto the core of the protostar begins. In the regime of stable equilibrium, the fragmentation of the gas-dust envelope and the equatorial disk of the protostar occurs. In the ring-shaped fragments of the disk, the process of formation of “embryos” of planets begins and accretion on the “embryos” of the planet also begins.
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Pesce, Dominic, James Braatz, James Condon, Feng Gao, Christian Henkel, Violette Impellizzeri, Eugenia Litzinger, K. Y. Lo i Mark Reid. "AGN accretion disk physics using H2O megamasers". Proceedings of the International Astronomical Union 13, S336 (wrzesień 2017): 125–28. http://dx.doi.org/10.1017/s1743921317009966.
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AbstractMany accretion disks surrounding supermassive black holes in nearby AGN are observed to host 22 GHz water maser activity. We have analyzed single-dish 22 GHz spectra taken with the GBT to identify 32 such “Keplerian disk systems,” which we used to investigate maser excitation and explore the possibility of disk reverberation. Our results do not support a spiral shock model for population inversion in these disks, and we find that any reverberating signal propagating radially outwards from the AGN must constitute <10% of the total observed maser variability. Additionally, we have used ALMA to begin exploring the variety of sub-mm water megamasers that are also predicted, and in the case of the 321 GHz transition found, to be present in these accretion disks. By observing multiple masing transitions within a single system, we can better constrain the physical conditions (e.g., gas temperature and density) in the accretion disk.
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Watson, W. D., i H. W. Wyld. "Maser Radiation in a Keplerian Disk". Astrophysical Journal 530, nr 1 (10.02.2000): 207–12. http://dx.doi.org/10.1086/308352.
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Tanga, P., P. Michel i D. C. Richardson. "Planetesimal clusters in a Keplerian disk". Astronomy & Astrophysics 395, nr 2 (listopad 2002): 613–23. http://dx.doi.org/10.1051/0004-6361:20021274.
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Rüdiger, Günther, i Udo Ziegler. "Angular Momentum Transport and Dynamo Effect in Kepler Disks". Symposium - International Astronomical Union 200 (2001): 410–14. http://dx.doi.org/10.1017/s0074180900225473.
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Properties have been demonstrated of the magneto-rotational instability for two different applications, i.e. for a global spherical model and a box simulation with Keplerian background shear flow. In both nonlinear cases a dynamo operates with a negative (positive) α-effect in the northern (southern) disk hemisphere and in both cases the angular momentum transport is outwards. Keplerian accretion disks should therefore exhibit large-scale magnetic fields with a dipolar geometry of the poloidal components favoring jet formation.
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GHOSH, HIMADRI, SANDIP K. CHAKRABARTI i PHILIPPE LAURENT. "MONTE CARLO SIMULATIONS OF THE THERMAL COMPTONIZATION PROCESS IN A TWO-COMPONENT ACCRETION FLOW AROUND A BLACK HOLE". International Journal of Modern Physics D 18, nr 11 (15.11.2009): 1693–706. http://dx.doi.org/10.1142/s0218271809015242.
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We compute the effects of thermal Comptonization of soft photons emitted from a Keplerian disk around a black hole by the postshock region of a sub-Keplerian flow, known as the CENtrifugal-pressure-dominated BOundary Layer (CENBOL). We show that the spectral state transitions of black hole candidates could be explained either by varying the outer boundary of the CENBOL, which also happens to be the inner edge of the Keplerian disk, or by changing the central density of the CENBOL, which is governed by the rate of the sub-Keplerian flow. We confirm the conclusions of the previous theoretical studies that the interplay between the intensity of the soft photons emitted by the Keplerian flow, the optical depth and electron temperature of the Comptonizing cloud is responsible for the state transitions in a black hole.
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Okazaki, Atsuo T. "Theory of Global Disk Oscillations". International Astronomical Union Colloquium 175 (2000): 409–21. http://dx.doi.org/10.1017/s0252921100056207.
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AbstractWe discuss the characteristics of global oscillation modes in Be disks and review recent studies related to the disk oscillation model. Since the m = 1 modes are present only in near Keplerian disks and the mode confinement occurs only in the region in which the radial flow is subsonic, the model of global disk oscillation strongly prefers the viscous decretion disk scenario proposed by Lee et al. (1991), whereas it is incompatible with the wind-compressed disk scenario of Bjorkman & Cassinelli (1993), which predicts angular-momentum conserving disks with supersonic radial flow. Based on the viscous decretion disk scenario, we discuss transonic solutions of decretion and examine the effect of viscosity on the global one-armed modes.
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Gallardo Cava, I., V. Bujarrabal, J. Alcolea, M. Gómez-Garrido i M. Santander-García. "Chemistry of nebulae around binary post-AGB stars: A molecular survey of mm-wave lines",. Astronomy & Astrophysics 659 (marzec 2022): A134. http://dx.doi.org/10.1051/0004-6361/202142339.
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Context. There is a class of binary post-asymptotic giant branch (post-AGB) stars that exhibit remarkable near-infrared excess. Such stars are surrounded by Keplerian or quasi-Keplerian disks, as well as extended outflows composed of gas escaping from the disk. This class can be subdivided into disk- and outflow-dominated sources, depending on whether it is the disk or the outflow that represents most of the nebular mass, respectively. The chemistry of this type of source has been practically unknown thus far. Aims. Our objective is to study the molecular content of nebulae around binary post-AGB stars that show disks with Keplerian dynamics, including molecular line intensities, chemistry, and abundances. Methods. We focused our observations on the 1.3, 2, 3 mm bands of the 30mIRAM telescope and on the 7 and 13 mm bands of the 40 m Yebes telescope. Our observations add up ~600 h of telescope time. We investigated the integrated intensities of pairs of molecular transitions for CO, other molecular species, and IRAS fluxes at 12, 25, and 60 μm. Additionally, we studied isotopic ratios, in particular 17O/18O, to analyze the initial stellar mass, as well as 12CO/13CO, to study the line and abundance ratios. Results. We present the first single-dish molecular survey of mm-wave lines in nebulae around binary post-AGB stars. We conclude that the molecular content is relatively low in nebulae around binary post-AGB stars, as their molecular lines and abundances are especially weaker compared with AGB stars. This fact is very significant in those sources where the Keplerian disk is the dominant component of the nebula. The study of their chemistry allows us to classify nebulae around AC Her, the Red Rectangle, AI CMi, R Sct, and IRAS 20056+1834 as O-rich, while that of 89 Her is probably C-rich. The calculated abundances of the detected species other than CO are particularly low compared with AGB stars. The initial stellar mass derived from the 17O/18O ratio for the Red Rectangle and 89 Her is compatible with the central total stellar mass derived from previous mm-wave interferometric maps. The very low 12CO/13CO ratios found in binary post-AGB stars reveal a high 13CO abundance compared to AGB and other post-AGB stars.
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Kaitchuck, Ronald H. "Time-Resolved Spectroscopy of Accretion Disks in Algols". International Astronomical Union Colloquium 107 (1989): 51–61. http://dx.doi.org/10.1017/s0252921100087662.
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AbstractTime-resolved spectroscopy during the eclipse of short-period Algol systems, has shown their accretion disks to be small, turbulent structures with non-Keplerian velocity fields and asymmetries between the leading and trailing sides of the disk. These transient disks are produced by the impact of the gas stream on the mass-gaining star, and occur in systems where the star is just large enough to ensure the stream collision is complete. These emission line disks and the excess continuum emission do not always occur together. The permanent accretion disks in at least a few of the long-period Algol systems have features in common with the transient disks including non-Keplerian velocity fields.
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Okazaki, A. T. "Structure and Time-Dependent Behavior of Be Star Disks in Be/X-Ray Binaries". Symposium - International Astronomical Union 188 (1998): 362–63. http://dx.doi.org/10.1017/s0074180900115542.
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We consider the structure and time dependent behavior of the outflow in disks of Be stars in Be/X-ray binaries, based on the viscous decretion disk scenario (Lee et al. 1991). In this scenario, the matter ejected from the star with the Keplerian velocity at the equatorial surface of the star drifts outward because of the effects of viscosity, and forms the disk.
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Kudoh, T., R. Matsumoto i K. Shibata. "Magnetically Driven Jets from Accretion Disks: Comparison Between 2.5D Nonsteady Simulations and 1.5D Nonsteady/Steady Solutions". International Astronomical Union Colloquium 163 (1997): 753. http://dx.doi.org/10.1017/s0252921100043797.
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We have performed 1D(1.5D) and 2D(2.5D) nonsteady MHD numerical simulations of astrophysical jets which are magnetically driven from Keplerian disks, in order to clarify the origin and structure of jets ejected from protostars and active galactic nuclei. The initial and boundary conditions are similar to those of 2D(2.5D) nonsteady MHD simulations of Shibata and Uchida (1986) and Matsumoto et al. (1996); there is initially a Keplerian disk with a nonrotating corona outside, both of which are penetrated by vertical magnetic fields. The subsequent interaction between the disk/corona and the vertical fields are studied as an initial value problem. Against the current belief that this kind of simulations show simply a transient jet caused by nonsteady interaction between the disk/corona and the magnetic field, we have found that the jets ejected from the disk in this way have the same properties of the steady magnetically driven jets that were investigated by using ID steady wind solution (Kudoh & Shibata 1995), even if the jets are not exactly in steady state.
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Aso, Yusuke, Woojin Kwon, Nagayoshi Ohashi, Jes K. Jørgensen, John J. Tobin, Yuri Aikawa, Itziar de Gregorio-Monsalvo i in. "Early Planet Formation in Embedded Disks (eDisk). VI. Kinematic Structures around the Very-low-mass Protostar IRAS 16253-2429". Astrophysical Journal 954, nr 1 (25.08.2023): 101. http://dx.doi.org/10.3847/1538-4357/ace624.
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Abstract Precise estimates of protostellar masses are crucial to characterize the formation of stars of low masses down to brown dwarfs (BDs; M * < 0.08 M ☉). The most accurate estimation of protostellar mass uses the Keplerian rotation in the circumstellar disk around the protostar. To apply the Keplerian rotation method to a protostar at the low-mass end, we have observed the Class 0 protostar IRAS 16253-2429 using the Atacama Large Millimeter/submillimeter Array (ALMA) in the 1.3 mm continuum at an angular resolution of 0.″07 (10 au), and in the 12CO, C18O, 13CO (J = 2–1), and SO (J N = 65−54) molecular lines, as part of the ALMA Large Program Early Planet Formation in Embedded Disks project. The continuum emission traces a nonaxisymmetric, disk-like structure perpendicular to the associated 12CO outflow. The position–velocity (PV) diagrams in the C18O and 13CO lines can be interpreted as infalling and rotating motions. In contrast, the PV diagram along the major axis of the disk-like structure in the 12CO line allows us to identify Keplerian rotation. The central stellar mass and the disk radius are estimated to be ∼0.12–0.17 M ☉ and ∼13–19 au, respectively. The SO line suggests the existence of an accretion shock at a ring (r ∼ 28 au) surrounding the disk and a streamer from the eastern side of the envelope. IRAS 16253-2429 is not a proto-BD but has a central stellar mass close to the BD mass regime, and our results provide a typical picture of such very-low-mass protostars.
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Kuo, I.-Hsuan Genevieve, Hsi-Wei Yen, Pin-Gao Gu i Tze-En Chang. "Kinematical Constraint on Eccentricity in the Protoplanetary Disk MWC 758 with ALMA". Astrophysical Journal 938, nr 1 (1.10.2022): 50. http://dx.doi.org/10.3847/1538-4357/ac9228.
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Abstract We analyzed the archival data of the 13CO and C18O J = 3 − 2 emission lines in the protoplanetary disk around MWC 758 obtained with the Atacama Large Millimeter/submillimeter Array to discuss possible planet–disk interaction and non-Keplerian motion in the disk. We performed fitting of a Keplerian disk model to the observational data and measured the velocity deviations from the Keplerian rotation. We found significant velocity deviations around the inner cavity in the MWC 758 disk. We examined several possibilities that may cause the velocity deviations, such as pressure gradient, height of the emitting layer, infall motion, inner warp, and eccentricity in the disk. We found that the combination of an eccentric orbital motion with eccentricity of 0.1 ± 0.04 at the radius of the inner cavity and an infalling flow best explains the observed velocity deviations. Our kinematically constrained eccentricity of the gas orbital motion close to the inner cavity is consistent with the eccentricity of the dust ring around the inner cavity measured in the submillimeter continuum emission. Our results hint at strong dust–gas coupling around the inner cavity and presence of a gas giant planet inside the inner cavity in the MWC 758 disk.
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GHOSH, HIMADRI, SUDIP K. GARAIN, SANDIP K. CHAKRABARTI i PHILIPPE LAURENT. "MONTE CARLO SIMULATIONS OF THE THERMAL COMPTONIZATION PROCESS IN A TWO-COMPONENT ACCRETION FLOW AROUND A BLACK HOLE IN THE PRESENCE OF AN OUTFLOW". International Journal of Modern Physics D 19, nr 05 (maj 2010): 607–20. http://dx.doi.org/10.1142/s0218271810016555.
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A black hole accretion may have both the Keplerian and the sub-Keplerian component. In the so-called Chakrabarti–Titarchuk scenario, the Keplerian component supplies low-energy (soft) photons while the sub-Keplerian component supplies hot electrons which exchange their energy with the soft photons through Comptonization or inverse Comptonization processes. In the sub-Keplerian component, a shock is generally produced due to the centrifugal force. The postshock region is known as the CENtrifugal pressure–supported BOundary Layer (CENBOL). In this paper, we compute the effects of the thermal and the bulk motion Comptonization on the soft photons emitted from a Keplerian disk by the CENBOL, the preshock sub-Keplerian disk and the outflowing jet. We study the emerging spectrum when the converging inflow and the diverging outflow (generated from the CENBOL) are simultaneously present. From the strength of the shock, we calculate the percentage of matter being carried away by the outflow and determine how the emerging spectrum depends on the outflow rate. The preshock sub-Keplerian flow is also found to Comptonize the soft photons significantly. The interplay between the up-scattering and down-scattering effects determines the effective shape of the emerging spectrum. By simulating several cases with various inflow parameters, we conclude that whether the preshock flow, or the postshock CENBOL or the emerging jet is dominant in shaping the emerging spectrum depends strongly on the geometry of the flow and the strength of the shock in the sub-Keplerian flow.
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Shu, Frank H., Daniele Galli, Susana Lizano i Mike J. Cai. "Magnetization, accretion, and outflows in young stellar objects". Proceedings of the International Astronomical Union 3, S243 (maj 2007): 249–64. http://dx.doi.org/10.1017/s1743921307009611.
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AbstractWe review the theory of the formation and gravitational collapse of magnetized molecular cloud cores, leading to the birth of T Tauri stars surrounded by quasi-Keplerian disks whose accretion is driven by the magnetorotational instability (MRI). Some loss of magnetic flux during the collapse results typically in a dimensionless mass-to-flux ratio for the star plus disk of λ0≈ 4. Most of the mass ends up in the star, while almost all of the flux and the angular momentum ends up in the disk; therefore, a known mass for the central star implies a computable flux in the surrounding disk. A self-contained theory of the MRI that drives the viscous/resistive spreading in such circumstances then yields the disk radius needed to contain the flux trapped in the disk as a function of the aget. This theory yields analytic predictions of the distributions with distance ϖ from the central star of the surface density Σ(ϖ), the vertical magnetic fieldBz(ϖ), and the (sub-Keplerian) angular rotation rate Ω (ϖ). We discuss the implications of this picture for disk-winds, X-winds, and funnel flows, and we summarize the global situation by giving the energy and angular-momentum budget for the overall problem.
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Rivinius, Thomas. "Be stars in the X-ray binary context". Proceedings of the International Astronomical Union 14, S346 (sierpień 2018): 105–13. http://dx.doi.org/10.1017/s1743921318008207.
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AbstractRapidly rotating B-type stars with gaseous mass-loss disks in Keplerian rotation are common central objects in X-Ray binaries. These disks are physically well understood in the framework of the viscous decretion disk, and their typical parameters have been established for a large number of single Be stars in the recent years. According to the current observational evidence, the Be stars and disks found in BeXRBs are well within the boundaries known from single Be stars, i.e., they are normal Be stars. New results have also been obtained on the orbital disk truncation and other tidal effects of the companion objects on the disk.
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Hone, Edward, Stefan Kraus, Claire L. Davies, Alexander Kreplin, John D. Monnier, Fabien Baron, Rafael Millan-Gabet i in. "Compact gaseous accretion disk in Keplerian rotation around MWC 147". Astronomy & Astrophysics 623 (28.02.2019): A38. http://dx.doi.org/10.1051/0004-6361/201834626.
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Context. The disks around some Herbig Be stars have been observed to be more compact than the expected dust sublimation radius for such objects. Highly refractory dust grains and optically thick gas emission have been proposed as possible explanations for this phenomenon. Aims. Previously, the “undersized” Herbig Be star MWC 147 was observed with interferometry, and the results indicated a presence of a compact gaseous disk based on the measured wavelength-dependence of near-infrared or mid-infrared visibilities. Our aim is to search for direct evidence for the presence of hot gas inside of the expected dust sublimation radius of MWC 147. Methods. By combining VLTI/AMBER spectro-interferometry (R = 12 000) with CRIRES spectroscopy (R = 100 000) we can both spectrally and spatially resolve the Brγ line-emitting gas around MWC 147. Additionally, using CHARA/CLIMB enables us to achieve baseline lengths up to 330 m, offering ~2 times higher angular resolution (and a better position angle coverage) than has previously been achieved with interferometry for MWC 147. To model the continuum we fit our AMBER and CLIMB measurements with a geometric model of an inclined Gaussian distribution as well as a ring model. We fit our high-resolution spectra and spectro-interferometric data with a kinematic model of a disk in Keplerian rotation. Results. Our interferometric visibility modelling of MWC 147 indicates the presence of a compact continuum disk with a close to face-on orientation. We model the continuum with an inclined Gaussian and a ring with a radius of 0.60 mas (0.39 au), which is well within the expected dust sublimation radius of 1.52 au. We detect no significant change in the measured visibilities across the Brγ line, indicating that the line-emitting gas is located in the same region as the continuum-emitting disk. Using our differential phase data we construct photocentre displacement vectors across the Brγ line, revealing a velocity profile consistent with a rotating disk. We fit our AMBER spectro-interferometry data with a kinematic model of a disk in Keplerian rotation, where both the line-emitting and continuum-emitting components of the disk originate from the same compact region close to the central star. The presence of line-emitting gas in the same region as the K-band continuum supports the interpretation that the K-band continuum traces an optically thick gas disk. Conclusions. Our spatially and spectrally resolved observations of MWC 147 reveal that the K-band continuum and Brγ emission both originate from a similar region which is 3.9 times more compact than the expected dust sublimation radius for the star; Brγ is emitted from the accretion disk or disk wind region and exhibits a rotational velocity profile. We conclude that we detect the presence of a compact, gaseous accretion disk in Keplerian rotation around MWC 147.
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Waisberg, Idel, Jason Dexter, Pierre-Olivier Petrucci, Guillaume Dubus i Karine Perraut. "Super-Keplerian equatorial outflows in SS 433". Astronomy & Astrophysics 623 (marzec 2019): A47. http://dx.doi.org/10.1051/0004-6361/201834746.
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Context. The microquasar SS 433 is the only known steady supercritical accretor in the Galaxy. It is well-known for its relativistic baryonic jets, but the system also drives equatorial outflows. These have been routinely detected in radio images, and components associated with a circumbinary disk have also been suggested in optical emission lines. Aims. We aim to spatially resolve the regions producing the stationary emission lines of SS 433 to shed light on its circumbinary structure and outflows. With an estimated binary orbit size of ≲0.1 mas, this requires optical interferometry. Methods. We use the optical interferometer VLTI+GRAVITY to spatially resolve SS 433 in the near-infrared K band at high spectral resolution (R ≈ 4000) on three nights in July 2017. This is the second such observation, after the first one in July 2016. Results. The stationary Brγ line in the 2017 observation is clearly dominated by an extended ∼1 mas ∼ 5 AU circumbinary structure perpendicular to the jets with a strong rotation component. The rotation direction is retrograde relative to the jet precession, in accordance with the slaved disk precession model. The structure has a very high specific angular momentum and is too extended to be a stable circumbinary disk in Keplerian rotation; interpreting it as such leads to a very high enclosed mass M ≳ 400 M⊙. We instead interpret it as the centrifugal ejection of the circumbinary disk, with the implication that there must be an efficient transfer of specific angular momentum from the binary to the disk. We suggest that the equatorial outflows sometimes seen in radio images result from similar episodes of circumbinary disk centrifugal ejection. In addition to the equatorial structure, we find a very extended ∼6 mas ∼ 30 AU spherical wind component to the Brγ line: the entire binary is engulfed in an optically thin spherical line emission envelope.
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Gallardo Cava, Iván, Valentín Bujarrabal, Javier Alcolea, Miguel Gómez-Garrido, Arancha Castro-Carrizo, Hans Van Winckel i Miguel Santander-García. "Rotating and Expanding Gas in Binary Post-AGB Stars". Astronomy 1, nr 2 (2.08.2022): 84–92. http://dx.doi.org/10.3390/astronomy1020008.
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There is a class of binary post-AGB stars (binary system including a post-AGB star) that are surrounded by Keplerian disks and outflows resulting from gas escaping from the disk. To date, there are seven sources that have been studied in detail through interferometric millimeter-wave maps of CO lines (ALMA/NOEMA). For the cases of the Red Rectangle, IW Carinae, IRAS 08544-4431, and AC Herculis, it is found that around ≥85% of the total nebular mass is located in the disk with Keplerian dynamics. The remainder of the nebular mass is located in an expanding component. This outflow is probably a disk wind consisting of material escaping from the rotating disk. These sources are the disk-dominated nebulae. On the contrary, our maps and modeling of 89 Herculis, IRAS 19125+0343, and R Scuti, which allowed us to study their morphology, kinematics, and mass distribution, suggest that, in these sources, the outflow clearly is the dominant component of the nebula (∼75% of the total nebular mass), resulting in a new subclass of nebulae around binary post-AGB stars: the outflow-dominated sources.Besides CO, the chemistry of this type of source has been practically unknown thus far. We also present a very deep single-dish radio molecular survey in the 1.3, 2, 3, 7, and 13 mm bands (∼600 h of telescope time). Our results and detections allow us to classify our sources as O- or /C-rich. We also conclude that the calculated abundances of the detected molecular species other than CO are particularly low, compared with AGB stars. This fact is very significant in those sources where the rotating disk is the dominant component of the nebula.
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Pudritz, Ralph E., i Rachid Ouyed. "Numerical Simulations of Jets from Accretion Disks". Symposium - International Astronomical Union 182 (1997): 259–74. http://dx.doi.org/10.1017/s0074180900061696.
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Hydromagnetic disk winds have great potential as a general theory for the production and collimation of astrophysical jets in both protostellar and black hole environments. We first review the analytic stationary theory of these outflows as well as recent numerical simulations of MHD disk winds. We then focus on simulations that we have done on winds from magnetized disks using the ZEUS 2-D code of Stone and Norman. We treat the Keplerian disk as a fixed platform throughout the simulations. We show that both stationary and episodic, jet-like outflows are driven from disks depending upon their magnetic structure and mass loss rates.
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Sanna, A., A. Kölligan, L. Moscadelli, R. Kuiper, R. Cesaroni, T. Pillai, K. M. Menten i in. "Discovery of a sub-Keplerian disk with jet around a 20 M⊙ young star". Astronomy & Astrophysics 623 (marzec 2019): A77. http://dx.doi.org/10.1051/0004-6361/201833411.
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It is well established that solar-mass stars gain mass via disk accretion, until the mass reservoir of the disk is exhausted and dispersed, or condenses into planetesimals. Accretion disks are intimately coupled with mass ejection via polar cavities in the form of jets and less collimated winds, which allow mass accretion through the disk by removing a substantial fraction of its angular momentum. Whether disk accretion is the mechanism leading to the formation of stars with much higher masses is still unclear. Here, we are able to build a comprehensive picture of the formation of an O-type star by directly imaging a molecular disk, which rotates and undergoes infall around the central star, and drives a molecular jet that arises from the inner disk regions. The accretion disk is truncated between 2000 and 3000 au, it has a mass of about a tenth of the central star mass, and is infalling towards the central star at a high rate (6 × 10−4 M⊙ yr−1), so as to build up a very massive object. These findings, obtained with the Atacama Large Millimeter/submillimeter Array at 700 au resolution, provide observational proof that young massive stars can form via disk accretion much like solar-mass stars.
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Hummel, W., K. Horne, T. R. Marsh i Janet H. Wood. "Line Formation in U Gem and T Leo". International Astronomical Union Colloquium 158 (1996): 87–88. http://dx.doi.org/10.1017/s0252921100038318.
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We present 3-D LTE radiative transfer calculations [1] for H, He and Ca in accretion disks (AD) of dwarf novae in quiescence. The model disk is assumed to be in hydrostatic equilibrium vertically, and to rotate with Keplerian velocities. Calculated emission lines are fitted to phase-averaged, continuum-subtracted spectra of U Gem (Fig. 1) and T Leo (Fig. 2). Up to four parameters of the AD have been fitted: distance D, baryonic number density N, isotropic turbulence Vtu and disk temperature T; the latter two are assumed to be constant throughout the disk. Geometrical parameters are from [2] and [3].
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Vorobyov, Eduard I., Vardan G. Elbakyan, Hauyu Baobab Liu i Michihiro Takami. "Distinguishing between different mechanisms of FU-Orionis-type luminosity outbursts". Astronomy & Astrophysics 647 (marzec 2021): A44. http://dx.doi.org/10.1051/0004-6361/202039391.
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Aims. Accretion and luminosity bursts can be triggered by three distinct mechanisms: the magnetorotational instability (MRI) in the inner disk regions, clump infall in gravitationally fragmented disks, and close encounters with an intruder star. We study all three of these burst mechanisms to determine the disk kinematic characteristics that can help to distinguish between them. Methods. Numerical hydrodynamics simulations in the thin-disk limit were employed to model the bursts in disk environments that are expected for each burst mechanism. Results. We found that the circumstellar disks featuring accretion bursts can bear kinematic features that are distinct for different burst mechanisms, which can be useful when identifying the origin of a particular burst. The disks in the stellar encounter and clump-infall models are characterized by deviations from the Keplerian rotation of tens of per cent, while the disks in the MRI models are characterized by deviations of only a few per cent, which is mostly caused by the gravitational instability that fuels the MRI bursts. Velocity channel maps also show distinct kinks and wiggles, which are caused by gas disk flows that are particular to each considered burst mechanism. The deviations of velocity channels in the burst-hosting disks from a symmetric pattern typical of Keplerian disks are strongest for the clump-infall and collision models, and carry individual features that may be useful for the identification of the corresponding burst mechanism. The considered burst mechanisms produce a variety of light curves with the burst amplitudes varying in the Δm = 2.5−3.7 limits, except for the clump-infall model where Δm can reach 5.4, although the derived numbers may be affected by a small sample and boundary conditions. Conclusions. Burst-triggering mechanisms are associated with distinct kinematic features in the burst-hosting disks that may be used for their identification. Further studies including a wider model parameter space and the construction of synthetic disk images in thermal dust and molecular line emission are needed to constrain the mechanisms that lead to FU Orionis bursts.
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Chakrabarti, Sandip K. "On the Accretion Disk Models by Stationary and Non-Stationary Shock Waves". Symposium - International Astronomical Union 159 (1994): 477. http://dx.doi.org/10.1017/s0074180900176545.
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An important point which emerged from this meeting is that disks in AGNs are not simply thin, Keplerian type; they show more complex behaviour. Chakrabarti (1990a and references therein) has shown that in an inviscid accretion disk with significant angular momentum, the centrifugal barrier is strong enough to produce axisymmetric standing shock wave. Subsequently, this work was extended to include the non-axisymmetric and viscous disks (Chakrabarti, 1990b). Particularly important are the solutions with viscosity, as they show that as the viscosity is increased, the stable becomes weaker and weaker till it disappears completely. This solution has a unifying character that inviscid pressure driven disks have almost constant angular momentum and can have shock discontinuities, but viscous driven disks dissipate angular momentum quick enough not to have centrifugal barrier and therefore no shock waves. Chakrabarti & Molteni (1993), using Smoothed Particle Hydrodynamics have shown that shocks are produced in inviscid disks, exactly where they are predicted.Unlike a Keplerian disk, a disk with a shock has basically two temperature zones. The post shock solution is responsible for the Big Blue Bump and UV excess (Chakrabarti and Wiita, 1992). At the shock location, the disk is ‘bulged’ the hard radiation from this region is intercepted by the cooler pre-shock flow. The shock strength and location are sensitive to input specific energy of the flow. This configuration might be responsible for the ‘zero-lag’ correlated variability of, say, NGC 5548 (Chakrabarti, Haardt, Maraschi & Molendi, AA, submitted) discussed in this meeting. Spiral shocks which may be produced in disks in a binary system can also appear in disks around AGNs; the perturbation may be due to passage of massive objects (Chakrabarti & Wiita, 1993a). They also cause time variations in the double horned pattern from disk line emission (Chakrabarti & Wiita 1993b) as observed in, say ARP 102B. All these observations point that shocks are probably important ingredients in any accretion disk in AGNs
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Curry, Charles, i Ralph E. Pudritz. "Global, Nonaxisymmetric Instabilities in Magnetized Accretion Disks". International Astronomical Union Colloquium 163 (1997): 339–43. http://dx.doi.org/10.1017/s0252921100042822.
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AbstractWe investigate the global stability of a differentially rotating, ideal MHD fluid shell to linear, nonaxisymmetric perturbations. This system, which approximates an accretion disk near its midplane, is known to be unstable to both axisymmetric and nonaxisymmetric local perturbations. Keplerian disks, which are entirely stable in the hydrodynamic case, show the most rapid growth for radially extended shells.
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Ghosh, Subham, i Banibrata Mukhopadhyay. "Forced Linear Shear Flows with Rotation: Rotating Couette–Poiseuille Flow, Its Stability, and Astrophysical Implications". Astrophysical Journal 922, nr 2 (29.11.2021): 161. http://dx.doi.org/10.3847/1538-4357/ac1118.
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Abstract We explore the effect of forcing on the linear shear flow or plane Couette flow, which is also the background flow in the very small region of the Keplerian accretion disk. We show that depending on the strength of forcing and boundary conditions suitable for the systems under consideration, the background plane shear flow, and hence the accretion disk velocity profile, is modified into parabolic flow, which is a plane Poiseuille flow or Couette–Poiseuille flow, depending on the frame of reference. In the presence of rotation, the plane Poiseuille flow becomes unstable at a smaller Reynolds number under pure vertical as well as three-dimensional perturbations. Hence, while rotation stabilizes the plane Couette flow, the same destabilizes the plane Poiseuille flow faster and hence the forced local accretion disk. Depending on the various factors, when the local linear shear flow becomes a Poiseuille flow in the shearing box due to the presence of extra force, the flow becomes unstable even for Keplerian rotation, and hence turbulence will ensue. This helps to resolve the long-standing problem of subcritical transition to turbulence in hydrodynamic accretion disks and the laboratory plane Couette flow.
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Davies, Claire L., i Jane S. Greaves. "Angular momentum evolution during star and planetary system formation". Proceedings of the International Astronomical Union 8, S299 (czerwiec 2013): 210–11. http://dx.doi.org/10.1017/s1743921313008351.
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AbstractWe focused on analysing the role played by protoplanetary disks in the evolution of angular momentum during star formation. If all the angular momentum contained within collapsing pre-stellar cores was conserved during their formation, proto-stars would reach rotation rates exceeding their break-up velocities before they reached the main sequence (Bodenheimer 1995). In order to avoid this occuring, methods by which proto-stars can lose angular momentum must exist. Angular momentum can be transferred from star to disk via stellar magnetic field lines through a process called magnetic braking (Camenzind 1990; Königl 1991). Alternatively, the stellar angular momentum can be lost from the star-disk system entirely via stellar- or disk-winds (e.g. Pelletier & Pudritz 1992; Matt & Pudritz 2005).The proportion of lost stellar angular momentum retained within the protoplanetary disk is important to studies of planetary system formation. If the bulk motion within the disk remains Keplerian, any increase of angular momentum in the disk causes an outward migration of disk material and an expansion of the disk. Therefore, an increase in disk angular momentum may cause a reduction in the disk surface density, often used to indicate the disk's ability to form planets.We made use of multi-wavelength data available in the literature to directly calculate the stellar and disk angular momenta for two nearby regions of star formation. Namely, these were the densely populated and highly irradiated Orion Nebula Cluster (ONC) and the comparitively sparse Taurus-Auriga region. Due to the limited size of the ONC dataset, we produced an average surface density profile for the region. We modelled the stars as solid body rotators due to their fully convective nature (Krishnamurthi et al. 1997) and assumed the disks are flat and undergo Keplerian rotation about the same rotation axis as the star.We observed the older disks within each of the two star forming regions to be preferentially larger and less massive, consistent with viscous accretion theories and disk dispersal. However, when drawing comparisons between the two regions, the ONC sample appeared to have less massive disks than the Taurus-Auriga sample, even though the population of Taurus-Auriga is older. This may suggest an influence of the birth cloud environment on protoplanetary disk evolution.Finally, the older stars within the ONC were observed to harbour disks that contained more angular momentum than their younger counterparts whereas, in the Taurus-Auriga sample, the amount of angular momentum contained in the older and younger samples was consistent. We suggest that the missing disk angular momentum in the older Taurus-Auriga disks may be contained within yet-undetected planets.
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Bogovalov, Sergey, i Maxim Petrov. "Modeling of the Wind/Disk Outflow from Be Stars II: Formation of the Keplerian Disk". Universe 8, nr 11 (7.11.2022): 591. http://dx.doi.org/10.3390/universe8110591.
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Computer modeling of the outflow from Be stars is performed. In our approach, processes of turbulence excitation and turbulent viscosity are added to the conventional model of the radiation driven winds. The objective of our study is to reproduce from the first principles the main features of the outflow from Be stars: a fast polar wind and a slow viscous Keplerian disk at the equator. At sub-critical velocity of rotation up to 0.999 of the critical velocity, our model reproduces the formation of the fast polar wind together with a slow highly turbulent outflow at the equatorial region. This outflow, however, does not reassemble a Keplerian disk. We link this to the absence of the angular moment transfer from the star to the disk. This process provides an increase of the angular momentum of the disk matter with radius. We consider a star with super critical rotation as the simplest way to supply the angular momentum to the disk. In this case, the star surface has a higher azimuthal speed than the matter at the inner edge of the disk. The angular momentum transfer becomes unavoidable. Already at rotation velocity 0.5% above the critical one, a quasi Keplerian disk at the equator is formed with size ∼10 stellar radius. At rotation 1% higher than the critical speed, the disk reaches ∼15 stellar radius. The main conclusion following from our work is that the conventional model of the radiation driven winds is able to reproduce the main features of the outflow from Be stars provided that the process of turbulence excitation and a process of angular momentum supply of the disk from the central source are added in to this model.
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Hawley, J. F. "Keplerian Complexity: Numerical Simulations of Accretion Disk Transport". Science 269, nr 5229 (8.09.1995): 1365–70. http://dx.doi.org/10.1126/science.269.5229.1365.
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Jacobsen, Steffen K., Jes K. Jørgensen, James Di Francesco, Neal J. Evans, Minho Choi i Jeong-Eun Lee. "Organic chemistry in the innermost, infalling envelope of the Class 0 protostar L483". Astronomy & Astrophysics 629 (30.08.2019): A29. http://dx.doi.org/10.1051/0004-6361/201833214.
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Context. Observations of the innermost regions of deeply embedded protostellar cores have revealed complicated physical structures as well as a rich chemistry with the existence of complex organic molecules. The protostellar envelopes, outflow, and large-scale chemistry of Class 0 and Class I objects have been well studied, but while previous works have hinted at or found a few Keplerian disks at the Class 0 stage, it remains to be seen if their presence in this early stage is the norm. Likewise, while complex organics have been detected toward some Class 0 objects, their distribution is unknown as they could reside in the hottest parts of the envelope, in the emerging disk itself, or in other components of the protostellar system, such as shocked regions related to outflows. Aims. In this work, we aim to address two related issues regarding protostars: when rotationally supported disks form around deeply embedded protostars and where complex organic molecules reside in such objects. We wish to observe and constrain the velocity profile of the gas kinematics near the central protostar and determine whether Keplerian motion or an infalling-rotating collapse under angular momentum conservation best explains the observations. The distribution of the complex organic molecules is used to investigate whether they are associated with the hot inner envelope or a possible Keplerian disk. Methods. We observed the deeply embedded protostar, L483, using Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 data from Cycles 1 and 3 with a high angular resolution down to ~0.1′′ (20 au) scales. We present new HCN J = 4–3, HCO+ J = 4–3, CS J = 7–6, and H13CN J = 4–3 observations, along with a range of transitions that can be attributed to complex organics, including lines of CH3OH, CH3OCHO, C2H5OH, NH2CHO, and other species. Results. We find that the kinematics of CS J = 7–6 and H13CN J = 4–3 are best fitted by the velocity profile from infall under conservation of angular momentum and not by a Keplerian profile. The only discernible velocity profile from the complex organics, belonging to CH3OCHO, is consistent with the infall velocity profile derived from CS J = 7–6 and H13CN J = 4–3. The spatial extents of the observed complex organics are consistent with an estimated ice sublimation radius of the envelope at ~50 au, suggesting that the complex organics exist in the hot corino of L483, where the molecules sublimate off the dust grain ice mantles and are injected into the gas phase. Conclusions. We find that L483 does not harbor a Keplerian disk down to at least 15 au in radius. Instead, the innermost regions of L483 are undergoing a rotating collapse and the complex organics exist in a hot corino with a radius of ~40–60 au. This result highlights that some Class 0 objects contain only very small disks, or none at all, and the complex organic chemistry take place on scales inside the hot corino of the envelope in a region larger than the emerging disk.
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Murray, N., i J. Chiang. "Disk Emission Lines". International Astronomical Union Colloquium 159 (1997): 220–21. http://dx.doi.org/10.1017/s0252921100040100.
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AbstractA thin disk illuminated by a central source will produce single-peaked broad emission lines if there is a wind emerging from the disk. The velocity gradient in the wind produces an anisotropic optical depth. For optically thick lines, the emission is strongest along directions perpendicular to the Keplerian velocity of the disk. The resulting line profiles are single peaked even though the emitting gas moves on essentially circular orbits. We argue that the broad emission lines seen in quasars, Seyferts, and luminous cataclysmic variables arise in disk winds.
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Harsono, D., M. V. Persson, A. Ramos, N. M. Murillo, L. T. Maud, M. R. Hogerheijde, A. D. Bosman i in. "Missing water in Class I protostellar disks". Astronomy & Astrophysics 636 (kwiecień 2020): A26. http://dx.doi.org/10.1051/0004-6361/201935994.
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Context. Water is a key volatile that provides insight into the initial stages of planet formation. The low water abundances inferred from water observations toward low-mass protostellar objects may point to a rapid locking of water as ice by large dust grains during star and planet formation. However, little is known about the water vapor abundance in newly formed planet-forming disks. Aims. We aim to determine the water abundance in embedded Keplerian disks through spatially-resolved observations of H218O lines to understand the evolution of water during star and planet formation. Methods. We present H218O line observations with ALMA and NOEMA millimeter interferometers toward five young stellar objects. NOEMA observed the 31,3–22,0 line (Eup∕kB = 203.7 K) while ALMA targeted the 41,4–32,1 line (Eup∕kB = 322.0 K). Water column densities were derived considering optically thin and thermalized emission. Our observations were sensitive to the emission from the known Keplerian disks around three out of the five Class I objects in the sample. Results. No H218O emission is detected toward any of our five Class I disks. We report upper limits to the integrated line intensities. The inferred water column densities in Class I disks are NH218O < 1015 cm−2 on 100 au scales, which include both the disk and envelope. The upper limits imply a disk-averaged water abundance of ≲10−6 with respect to H2 for Class I objects. After taking the physical structure of the disk into account, the upper limit to the water abundance averaged over the inner warm disk with T > 100 K is between ~10−7 and 10−5. Conclusions. Water vapor is not abundant in warm protostellar envelopes around Class I protostars. Upper limits to the water vapor column densities in Class I disks are at least two orders of magnitude lower than values found in Class 0 disk-like structures.
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Watson, W. D., B. K. Wallin i H. W. Wyld. "Maser Radiation from a Turbulent Keplerian Disk: NGC 4258". International Astronomical Union Colloquium 164 (1998): 225–26. http://dx.doi.org/10.1017/s0252921100045310.
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AbstractCalculations are summarized for the spectral and spatial distribution of maser radiation that emerges from a turbulent Keplerian disk when viewed nearly edge-on. A close comparison is made with the refined observational data about the masing accretion disk around the presumed massive black hole at the nucleus of the galaxy NGC 4258.
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Kraus, S., Th Preibisch i K. Ohnaka. "The inner gaseous accretion disk around a Herbig Be star revealed by near- and mid-infrared spectro-interferometry". Proceedings of the International Astronomical Union 3, S243 (maj 2007): 337–44. http://dx.doi.org/10.1017/s1743921307009696.
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AbstractHerbig Ae/Be stars are pre-main-sequence stars of intermediate mass, which are still accreting material from their environment, probably via a disk composed of gas and dust. Here we present a recent study of the geometry of the inner (AU-scale) circumstellar region around the Herbig Be star MWC 147 using long-baseline interferometry. By combining for the first time near- and mid-infrared spectro-interferometry on a Herbig star, our VLTI/AMBER and VLTI/MIDI data constrain not only the geometry of the brightness distribution, but also the radial temperature distribution in the disk. The emission from MWC 147 is clearly resolved and has a characteristic physical size of ∼1.3 AU and ∼9 AU at 2.2 μm and 11 μm respectively. This increase in apparent size towards longer wavelengths is much steeper than predicted by analytic disk models assuming power-law radial temperature distributions. For a detailed modeling of the interferometric data and the spectral energy distribution of MWC 147, we employ 2-D frequency-dependent radiation transfer simulations. This analysis shows that passive irradiated Keplerian dust disks can easily fit the SED, but predict much lower visibilities than observed, so these models can clearly be ruled out. Models of a Keplerian disk with emission from an optically thick inner gaseous accretion disk (inside the dust sublimation zone), however, yield a good fit of the SED and simultaneously reproduce the observed near- and mid-infrared visibilities. We conclude that the near-infrared continuum emission from MWC 147 is dominated by accretion luminosity emerging from an optically thick inner gaseous disk, while the mid-infrared emission also contains strong contributions from the passive irradiated dust disk.
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Bardou, Anne, i Jean Heyvaerts. "Interaction Of A Stellar Magnetic Field With A Turbulent Accretion Disk". International Astronomical Union Colloquium 163 (1997): 205–9. http://dx.doi.org/10.1017/s0252921100042652.
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AbstractMagnetized objects surrounded by a turbulent and keplerian accretion disk are considered. In such systems, magnetic field lines are embedded into the disk. The magnetic field of the central object is assumed to be dipolar in the absence of the accretion disk. In the presence of a turbulent accretion disk, it is shown that the interaction with the disk stretches magnetic field lines along the disk and that most of the non-magnetospheric magnetic flux is expelled outside the disk.
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Watanabe, Y., i J. Fukue. "Accretion-Disk Corona Advected by External Radiation Drag". Symposium - International Astronomical Union 188 (1998): 413–14. http://dx.doi.org/10.1017/s0074180900115785.
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Accretion-disk corona (ADC) is required from observational as well as theoretical reasons. In almost all of traditional studies, however, a stationary corona has been assumed; i.e., the corona gas corotates with the underlying (Keplerian) accretion disk, and the radial motion is ignored. Recently, in the theory of accretion disks a radiative interaction between the gas and the external radiation field has attracted the attention of researchers. In particular the radiation drag between the gas and the external radiation field becomes important from the viewpoint of the angular-momentum removal. We thus examine the effect of radiation drag on the accretion-disk corona above/below the accretion disk (Watanabe, Fukue 1996a, b). We suppose that an accretion disk can be described by the standard disk, and that radiation fields are produced by the central luminous source and the accretion disk, itself. In general an accretion-disk corona under the influence of strong radiation fields dynamically infalls (advected) toward the center.
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Moran, J. M. "Dynamical Models of the Maser in NGC 4258". International Astronomical Union Colloquium 159 (1997): 402–5. http://dx.doi.org/10.1017/s0252921100040574.
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The presence of two quasars symmetrically displaced from the nucleus of the galaxy NGC 4258 (Pietsch et al. 1994) has given rise to some speculation that they might have some dynamical connection with the high-velocity maser emission seen in the nucleus (Burbidge 1996; Ozernoy 1996). The case that the masers define a simple Keplerian disk is very compelling; nonetheless, it is instructive to investigate whether any other dynamical models could fit the available data.The evidence that the masers define a thin Keplerian disk can be found in Miyoshi et al. (1995) and Moran et al. (1995). Some of the relevant data are shown elsewhere in this volume (Fig. 2 of Greenhill’s paper). The basic analysis is as follows. The features near the systemic velocity of 470km s−1 show a linear dependence of line-of-sight velocity versus distance along the major axis, while the redshifted and blueshifted high-velocity features show a nearly Keplerian dependence with distance.
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Gallardo Cava, I., M. Gómez-Garrido, V. Bujarrabal, A. Castro-Carrizo, J. Alcolea i H. Van Winckel. "Keplerian disks and outflows in post-AGB stars: AC Herculis, 89 Herculis, IRAS 19125+0343, and R Scuti". Astronomy & Astrophysics 648 (kwiecień 2021): A93. http://dx.doi.org/10.1051/0004-6361/202039604.
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Context. There is a class of binary post-AGB stars with a remarkable near-infrared excess that are surrounded by Keplerian or quasi-Keplerian disks and extended outflows composed of gas escaping from the disk. The Keplerian dynamics had been well identified in four cases, namely the Red Rectangle, AC Her, IW Car, and IRAS 08544−4431. In these objects, the mass of the outflow represents ~10% of the nebular mass, the disk being the dominant component of the nebula. Aims. We aim to study the presence of rotating disks in sources of the same class in which the outflow seems to be the dominant component. Methods. We present interferometric NOEMA maps of 12CO and 13CO J = 2–1 in 89 Her and 12CO J = 2–1 in AC Her, IRAS 19125+0343, and R Sct. Several properties of the nebula are obtained from the data and model fitting, including the structure, density, and temperature distributions, as well as the dynamics. We also discuss the uncertainties on the derived values. Results. The presence of an expanding component in AC Her is doubtful, but thanks to new maps and models, we estimate an upper limit to the mass of this outflow of ≲3 × 10−5 M⊙, that is, the mass of the outflow is ≲5% of the total nebular mass. For 89 Her, we find a total nebular mass of 1.4 × 10−2 M⊙, of which ~50% comes from an hourglass-shaped extended outflow. In the case of IRAS 19125+0343, the nebular mass is 1.1 × 10−2 M⊙, where the outflow contributes ~70% of the total mass. The nebular mass of R Sct is 3.2 × 10−2 M⊙, of which ~75% corresponds to a very extended outflow that surrounds the disk. Conclusions. Our results for IRAS 19125+0343 and R Sct lead us to introduce a new subclass of binary post-AGB stars, for which the outflow is the dominant component of the nebula. Moreover, the outflow mass fraction found in AC Her is smaller than those found in other disk-dominated binary post-AGB stars. 89 Her would represent an intermediate case between both subclasses.
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Okazaki, Atsuo T. "Some observational appearances of m=1 density waves in Be star disks". Symposium - International Astronomical Union 162 (1994): 380–81. http://dx.doi.org/10.1017/s0074180900215416.
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One-armed (i.e., m = 1) density waves are the only global waves in nearly Keplerian disks (Kato 1983). Their frequencies are much smaller than the angular frequency of disk rotation. Based on this theory, Okazaki (1991) proposed that the long-term V/R variations of Be stars are phenomena caused by the global m = 1 oscillations in the equatorial disks. Hummel and Hanuschik (1993) showed that line profiles of disks with m = 1 perturbation patterns are in agreement with the observed V/R variability.
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Fung, Jeffrey, i Tomohiro Ono. "Cooling-induced Vortex Decay in Keplerian Disks". Astrophysical Journal 922, nr 1 (1.11.2021): 13. http://dx.doi.org/10.3847/1538-4357/ac1d4e.
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Abstract Vortices are readily produced by hydrodynamical instabilities, such as the Rossby wave instability, in protoplanetary disks. However, large-scale asymmetries indicative of dust-trapping vortices are uncommon in submillimeter continuum observations. One possible explanation is that vortices have short lifetimes. In this paper, we explore how radiative cooling can lead to vortex decay. Elliptical vortices in Keplerian disks go through adiabatic heating and cooling cycles. Radiative cooling modifies these cycles and generates baroclinicity that changes the potential vorticity of the vortex. We show that the net effect is typically a spin down, or decay, of the vortex for a subadiabatic radial stratification. We perform a series of two-dimensional shearing box simulations, varying the gas cooling (or relaxation) time, t cool, and initial vortex strength. We measure the vortex decay half-life, t half, and find that it can be roughly predicted by the timescale ratio t cool/t turn, where t turn is the vortex turnaround time. Decay is slow in both the isothermal (t cool ≪ t turn) and adiabatic (t cool ≫ t turn) limits; it is fastest when t cool ∼ 0.1 t turn, where t half is as short as ∼300 orbits. At tens of astronomical units where disk rings are typically found, t turn is likely much longer than t cool, potentially placing vortices in the fast decay regime.
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Bogovalov, S. V., i I. V. Tronin. "Toward the self-consistent model of cold disk accretion". International Journal of Modern Physics D 27, nr 10 (lipiec 2018): 1844005. http://dx.doi.org/10.1142/s0218271818440054.
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Observations of active galactic nuclei show increasing number of cases when the kinetic luminosity of jets exceeds the bolometric luminosity of disks. We develop a model of so-called cold disk accretion when the majority of the angular momentum is carried out by the wind from the disk rather than by turbulent viscous stresses. In this case the luminosity of the disk can be essentially suppressed and kinetic-to-bolometric luminosity ratio can be consistent with the observations. The method of self-consistent numerical solution of the problem of the outflow and disk accretion is proposed in this work. In this problem the angular momentum carried out by the wind is equal to the angular momentum loss by the Keplerian disk with specified accretion mass rate. Thus, the problem of the wind outflow is consistent with the disk accretion. Example of self-consistent solution of the problem by this method is presented.
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Zderic, Alexander, Maria Tiongco, Angela Collier, Heather Wernke, Aleksey Generozov i Ann-Marie Madigan. "A Lopsided Outer Solar System?" Astronomical Journal 162, nr 6 (1.12.2021): 278. http://dx.doi.org/10.3847/1538-3881/ac2def.
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Abstract Axisymmetric disks of eccentric orbits in near-Keplerian potentials are unstable and undergo exponential growth in inclination. Recently, Zderic et al. showed that an idealized disk then saturates to a lopsided mode. Here we show, using N-body simulations, that this apsidal clustering also occurs in a primordial Scattered Disk in the outer solar system, which includes the orbit-averaged gravitational influence of the giant planets. We explain the dynamics using Lynden-Bell's mechanism for bar formation in galaxies. We also show surface density and line-of-sight velocity plots at different times during the instability, highlighting the formation of concentric circles and spiral arms in velocity space.
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Shu, Frank H., Susana Lizano, Daniele Galli, Mike J. Cai i Subhanjoy Mohanty. "The Challenge of Sub-Keplerian Rotation for Disk Winds". Astrophysical Journal 682, nr 2 (16.07.2008): L121—L124. http://dx.doi.org/10.1086/591028.
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Chen, Kaiyou, Jules P. Halpern i Alexei V. Filippenko. "Kinematic evidence for a relativistic Keplerian disk - ARP 102B". Astrophysical Journal 339 (kwiecień 1989): 742. http://dx.doi.org/10.1086/167332.
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