Edge Of Disk Research Articles

The Excitation Conditions of CN in TW Hya

Abstract We report observations of the cyanide anion, CN, in the disk around TW Hya covering the N = 1−0, N = 2−1, and N = 3−2 transitions. Using line-stacking techniques, 24 hyperfine transitions are detected out of the 30 within the observed frequency ranges. Exploiting the super-spectral resolution from the line-stacking method reveals the splitting of hyperfine components previously unresolved by laboratory spectroscopy. All transitions display a similar emission morphology, characterized by an azimuthally symmetric ring, peaking at ≈45 au (0.″75), and a diffuse outer tail extending out to the disk edge at ≈200 au. Excitation analyses assuming local thermodynamic equilibrium (LTE) yield excitation temperatures in excess of the derived kinetic temperatures based on the local line widths for all fine-structure groups, suggesting assumptions of LTE are invalid. Using the 0D radiative transfer code RADEX, we demonstrate that such non-LTE effects may be present when the local H2 density drops to 107 cm−3 and below. Comparison with models of TW Hya find similar densities at elevated regions in the disk, typically z / r ≳ 0.2, consistent with model predictions where CN is formed via vibrationally excited H2 in the disk atmospheric layers where UV irradiation is less attenuated.

On the Edge Singularity of the Actuator Disk Model

AbstractIn this technical brief, the classic actuator disk theory is revisited with a view to shed some light on the singularity of the flow at the edge of the disk where the vortex tube starts and where vorticity is generated. The study is carried out using small perturbation assumption in two-dimensions and simplified boundary conditions in all cases. The problem of the two-dimensional thin cambered plate with constant vorticity distribution is solved and the leading edge singularity is analyzed as it is believed to be relevant to the axisymmetric flow at the actuator disk edge. Next, the velocity components induced by the cylindrical vortex tube of constant vorticity are obtained via the Biot–Savart law and the near edge behavior is investigated. It is shown that the velocity components behavior is consistent with that of the thin cambered plate with constant loading, thus reinforcing the notion that the axisymmetric slip-line behaves as r − R ∝ −xlnx near the disk edge.

Quantitative Fundus Autofluorescence: Advanced Analysis Tools.

PurposeTo use multimodal retinal images (including quantitative fundus autofluorescence [QAF]) for spectral-domain optical coherence tomography (SD-OCT)-based image registration and alignment. For each age decade of healthy adults, normative fine-grained QAF retinal maps are generated and advanced methods for QAF image analysis are applied.MethodsMultimodal retinal images were obtained from 103 healthy subjects (age 19–77 years; unremarkable retina/macula, age-appropriate clear optic media). Custom written FIJI plugins enabled: (1) determination of the fovea in SD-OCT and the edge of the optic disc in infrared (IR) images; (2) alignment and superimposition of multimodal retinal images based on foveal and optic disc position; (3) plotting of normative QAF retinal maps for each decade; and (4) comparison of individual retinas with normative retinas of different decades using newly introduced analysis patterns (QAF97, freehand tool).ResultsSD-OCT based image registration enables easy image registration, alignment, and analysis of different modalities (QAF, IR, and SD-OCT here reported). In QAF, intensities significantly increase with age with two major inclines between the third/fourth and seventh/eighth decades. With aging, the parafoveal area of maximum QAF intensity slightly shifts from temporal-superior to temporal. Compared with standard QAF analysis, refined QAF analysis patterns reveal a more detailed analysis of QAF, especially in the diseased retina.ConclusionsAge-related QAF normative retinal maps can be used to directly compare and classify individual's QAF intensities. Advanced QAF analysis tools will further help to interpret autofluorescence changes in normal aging and in the diseased retina in a multimodal imaging setting.Translational RelevanceAdvanced methods for QAF analysis link basic findings with clinical observations in normal aging and in the diseased macula.

Gap, shadows, spirals, and streamers: SPHERE observations of binary-disk interactions in GG Tauri A

Context.A large portion of stars is found to be part of binary or higher-order multiple systems. The ubiquity of planets found around single stars raises the question of whether and how planets in binary systems form. Protoplanetary disks are the birthplaces of planets, and characterizing them is crucial in order to understand the planet formation process.Aims.Our goal is to characterize the morphology of the GG Tau A disk, one of the largest and most massive circumbinary disks. We also aim to trace evidence for binary-disk interactions.Methods.We obtained observations in polarized scattered light of GG Tau A using the SPHERE/IRDIS instrument in theH-band filter. We analyzed the observed disk morphology and substructures. We ran 2D hydrodynamical models to simulate the evolution of the circumbinary ring over the lifetime of the disk.Results.The disk and also the cavity and the inner region are highly structured, with several shadowed regions, spiral structures, and streamer-like filaments. Some of these are detected here for the first time. The streamer-like filaments appear to connect the outer ring with the northern arc. Their azimuthal spacing suggests that they may be generated through periodic perturbations by the binary, which tear off material from the inner edge of the outer disk once during each orbit. By comparing observations to hydrodynamical simulations, we find that the main features, in particular, the gap size, but also the spiral and streamer filaments, can be qualitatively explained by the gravitational interactions of a binary with a semimajor axis of ~35 au on an orbit coplanar with the circumbinary ring.

Living on the edge: Rossby wave instability and HFQPOs in black hole binaries

Context. The Rossby wave instability (RWI) has been proposed to explain the origin of the high-frequency quasi-periodic oscillations observed in the X-ray emission of astrophysical systems harbouring black holes. Recent numerical computations have proven that the RWI does exist in a general relativistic context and that its presence is associated with a time-variable X-ray emission from the disc. Aims. Using our new Numerical Observatory of Violent Accreting system, NOVAs, we explore the way the RWI impacts an accretion disc orbiting a spinning black hole under realistic astrophysical conditions. Our aim is to study the impact of the presence of the RWI in the very inner part of the accretion disc on known observables and explore some possibly new ones. Methods. We present the first full general relativistic hydrodynamical simulations of the RWI occurring at the last stable orbit of an accretion disc orbiting around a Kerr black-hole. Those simulations, coupled with a full general relativistic ray-tracing, have allowed us to directly compare our simulations with the observables we obtained from the X-ray emission of the disc. Results. Our study shows, for the first time, that the RWI naturally arises near the inner edge of an accretion disc whenever it gets close to its last stable orbit, as predicted analytically. From there, we show that not only does the RWI create a visible timing feature but it also impacts the energy spectrum of the source, which exhibits a high energy extension due to the presence of hot vortices generated by the RWI in the disc. Our study also shows that systems with the RWI present at the inner edge of the disc only exhibit similar behavior to systems in which HFQPOs have been detected.

Pulsed disc accretion driven by Hot jupiters

ABSTRACT We present 2D hydrodynamical simulations of hot Jupiters orbiting near the inner edge of protoplanetary discs. We systemically explore how the accretion rate at the inner disc edge is regulated by a giant planet of different mass, orbital separation, and eccentricity. We find that a massive (with planet-to-star mass ratio ≳0.003) eccentric (ep ≳ 0.1) planet drives a pulsed accretion at the inner edge of the disc, modulated at one or two times the planet’s orbital frequency. The amplitude of accretion variability generally increases with the planet mass and eccentricity, although some non-monotonic dependences are also possible. Applying our simulation results to the T Tauri system CI Tau, where a young hot Jupiter candidate has been detected, we show that the observed luminosity variability in this system can be explained by pulsed accretion driven by an eccentric giant planet.

Optical and Infrared Study of the Obscured B[e] Supergiant High-mass X-Ray Binary IGR J16318–4848*

Abstract The supergiant high-mass X-ray binary IGR J16318–4848 was the first source detected by the INTErnational Gamma-Ray Astrophysics Laboratory satellite in 2003 and distinguishes itself by its high intrinsic absorption and B[e] phenomenon. It is the perfect candidate to study both binary interaction and the environment of supergiant B[e] stars. This study targets the local properties of IGR J16318–4848. We aim to clarify the geometry of this system and distinguish different key emitting regions in the binary. We provide optical to near-infrared (NIR) spectra from the Very Large Telescope/X-Shooter and analyze both fine structures of the lines and the broadband spectral energy distribution by adding archival mid-infrared Spitzer and Herschel data. We also perform a stellar atmosphere and wind modeling of the optical to NIR spectrum using the Potsdam Wolf–Rayet code. We determine the contribution of the irradiated inner edge of the dusty circumbinary disk, derive the velocity of an equatorial stellar wind, and suggest the compact object orbits within the cavity between the star and the disk. We report on flat-topped lines originating from a spherically symmetric disk wind, along with the first detection of what is likely the polar component of the stellar wind. Stellar atmosphere and wind modeling shows that the central star may have a helium-enhanced atmosphere, likely because of its intense wind shedding part of its hydrogen envelope. Finally, we compare the properties of IGR J16318–4848 with a similar source, CI Cameleopardis.

TW Hya: an old protoplanetary disc revived by its planet

Abstract Dark rings with bright rims are the indirect signposts of planets embedded in protoplanetary discs. In a recent first, an azimuthally elongated AU-scale blob, possibly a planet, was resolved with ALMA in TW Hya. The blob is at the edge of a cliff-like rollover in the dust disc rather than inside a dark ring. Here we build time-dependent models of TW Hya disc. We find that the classical paradigm cannot account for the morphology of the disc and the blob. We propose that ALMA-discovered blob hides a Neptune mass planet losing gas and dust. We show that radial drift of mm-sized dust particles naturally explains why the blob is located on the edge of the dust disc. Dust particles leaving the planet perform a characteristic U-turn relative to it, producing an azimuthally elongated blob-like emission feature. This scenario also explains why a 10 Myr old disc is so bright in dust continuum. Two scenarios for the dust-losing planet are presented. In the first, a dusty pre-runaway gas envelope of a ∼40 M⊕ Core Accretion planet is disrupted, e.g., as a result of a catastrophic encounter. In the second, a massive dusty pre-collapse gas giant planet formed by Gravitational Instability is disrupted by the energy released in its massive core. Future modelling may discriminate between these scenarios and allow us to study planet formation in an entirely new way – by analysing the flows of dust and gas recently belonging to planets, informing us about the structure of pre-disruption planetary envelopes.

EX draconis: using eclipses to separate outside-in and inside-out outbursts

ABSTRACT We present a study of the eclipses in the accreting white dwarf EX draconis (EX Dra) during TESS Cycles 14 and 15. During both of the two outbursts present in this data set, the eclipses undergo a hysteretic loop in eclipse-depth/out-of-eclipse-flux space. In each case, the direction in which the loops are executed strongly suggests an outburst that is triggered near the inner edge of the accretion disc and propagates outwards. This in turn suggests that the outbursts in EX Dra are ‘inside out’ outbursts; events predicted by previous hydrodynamic studies of dwarf nova accretion discs and confirmed spectroscopically in a number of other accreting white dwarf systems. We therefore propose that the direction of the loop executed in eclipse-depth/out-of-eclipse flux space be used as a test to phenomenologically distinguish between ‘inside out’ and ‘outside in’ outbursts in other eclipsing dwarf novae; a reliable and purely photometric test to differentiate between these phenomena.

Mechanics of generically creased disks.

Folded structures are often idealized as a series of rigid faces connected by creases acting as revolute hinges. However, real folded structures can deform between creases. An example of particular interest is a disk decorated by multiple radial creases. Such disks are bistable, snapping between a "natural" and "inverted" shape. We investigate the mechanical behavior of these creased disks and propose a new analytical approach to describe their mechanics. Detailed experiments are performed which show that, when indented at the center, a localized dimple forms, precluding the conical shape assumed in previous studies. As the indentation depth increases this dimple expands radially until reaching the disk edge when it snaps to the inverted shape, which has a conical form. We develop an analytical model which approximates each face as a series of rigid facets connected by hinges that can both rotate and stretch. Energy expressions are derived relating hinge rotation and stretching to compatible shell deformations of the facets and equilibrium enforced by minimizing the total strain energy. By increasing the number of facets, the mechanics of the continuum shell is approached asymptotically. The analysis shows that membrane stretching of the faces is required when a conical form of deformation is enforced. However, in the limit of zero thickness, the forming and propagation of a localized dimple is inextensional. This new approach relates the kinematic analysis of rigid origami to the mechanics of thin shells, offering an efficient method to predict the behavior of folded structures.

Studying the Reflection Spectra of the New Black Hole X-Ray Binary Candidate MAXI J1631−479 Observed by NuSTAR: A Variable Broad Iron Line Profile

Abstract We present results from the Nuclear Spectroscopic Telescope Array observations of the new black hole X-ray binary candidate MAXI J1631–479 at two epochs during its 2018–2019 outburst, which caught the source in a disk dominant state and a power-law dominant state. Strong relativistic disk reflection features are clearly detected, displaying significant variations in the shape and strength of the broad iron emission line between the two states. Spectral modeling of the reflection spectra reveals that the inner radius of the optically thick accretion disk evolves from <1.9 to 12 ± 1 r g (statistical errors at 90% confidence level) from the disk dominant to the power-law dominant state. Assuming in the former case that the inner disk radius is consistent with being at the innermost stable circular orbit, we estimate a black hole spin of a* > 0.94. Given that the bolometric luminosity is similar in the two states, our results indicate that the disk truncation observed in MAXI J1631–479 in the power-law dominant state is unlikely to be driven by a global variation in the accretion rate. We propose that it may instead arise from local instabilities in the inner edge of the accretion disk at high accretion rates. In addition, we find an absorption feature in the spectra centered at 7.33 ± 0.03 keV during the disk dominant state, which is evidence for the rare case that an extremely fast disk wind ( ) is observed in a low-inclination black hole binary, with the viewing angle of 29° ± 1° as determined by the reflection modeling.

Diagnostic Value of Systematic Imaging Examination in Embedded Optic Disc Drusen in Adolescents with Mild Visual Impairment.

Aim To evaluate the diagnostic value of systematic ophthalmologic imaging examination in the diagnosis of embedded optic disc drusen (ODD) in adolescents with mild visual impairment. Methods Eleven patients were evaluated through optometric examination, fundus photography, visual field inspection, optical coherence tomography (OCT), ultrasonography (US), and fundus fluorescein angiography (FFA). Of the 11 patients, three also underwent cranial and orbital magnetic resonance imaging (MRI). Results All 11 patients had either no apparent abnormality or only mild refractive abnormalities. In all patients, fundus inspection revealed flushing the optic disc with varying degrees of limited boundary ambiguity and optic disc congestion with disappearance of the fovea. One patient had a visual field defect during the period of edema of ODD, but the visual field returned to normal after the optic disc edema subsided. US revealed discoid acousto-optic masses in front of the optic disc in six patients. OCT showed a slight elevation and thinning of the retinal nerve fiber layer (RNFL) of the optic disc in all patients. Quasicircular, hyperreflex signals of different sizes could be observed below the RNFL. Late-stage FFA revealed focal staining at the edge of the optic disc without fluorescence leakage in all patients. Orbital and cranial MRI findings were normal in the three patients. Conclusion A systematic ophthalmologic imaging examination can not only improve the detection rate of embedded ODD but also avoid excessive examinations and treatments.

Probing the magnetospheric accretion region of the young pre-transitional disk system DoAr 44 using VLTI/GRAVITY

Context. Young stellar objects are thought to accrete material from their circumstellar disks through their strong stellar magnetospheres. Aims. We aim to directly probe the magnetospheric accretion region on a scale of a few 0.01 au in a young stellar system using long-baseline optical interferometry. Methods. We observed the pre-transitional disk system DoAr 44 with VLTI/GRAVITY on two consecutive nights in the K-band. We computed interferometric visibilities and phases in the continuum and in the Brγ line in order to constrain the extent and geometry of the emitting regions. Results. We resolve the continuum emission of the inner dusty disk and measure a half-flux radius of 0.14 au. We derive the inclination and position angle of the inner disk, which provides direct evidence that the inner and outer disks are misaligned in this pre-transitional system. This may account for the shadows previously detected in the outer disk. We show that Brγ emission arises from an even more compact region than the inner disk, with an upper limit of 0.047 au (~5 R⋆). Differential phase measurements between the Brγ line and the continuum allow us to measure the astrometric displacement of the Brγ line-emitting region relative to the continuum on a scale of a few tens of microarcsec, corresponding to a fraction of the stellar radius. Conclusions. Our results can be accounted for by a simple geometric model where the Brγ line emission arises from a compact region interior to the inner disk edge, on a scale of a few stellar radii, fully consistent with the concept of magnetospheric accretion process in low-mass young stellar systems.

Plasmonic Emission of Bullseye Nanoemitters on Bi2Te3 Nanoflakes.

Topological insulators, such as Bi2Te3, have been confirmed to exhibit plasmon radiation over the entire visible spectral range. Herein, we fabricate bullseye nanoemitters, consisting of a central disk and concentric gratings, on the Bi2Te3 nanoflake. Due to the existence of edge plasmon modes, Bi2Te3 bullseye nanostructures are possible to converge light towards the central disk. Taking advantage of the excellent spatial resolution of cathodoluminescence (CL) characterization, it has been observed that plasmonic behaviors depend on the excitation location. A stronger plasmonic intensity and a wider CL spectral linewidth can be obtained at the edge of the central disk. In order to further improve the focusing ability, a cylindrical Pt nanostructure has been deposited on the central disk. Additionally, the finite element simulation indicates that the electric-field enhancement originates from the coupling process between the plasmonic emission from the Bi2Te3 bullseye and the Pt nanostructure. Finally, we find that enhancement efficiency depends on the thickness of the Pt nanostructure.

A point vortex transportation model for yawed wind turbine wakes

In this study, stereo particle imaging velocimetry measurements are performed at multiple streamwise locations behind a yawed wind turbine to reveal the formation mechanisms of the counter-rotating vortex pair (CVP), and a point vortex transportation (PVT) model is proposed to reproduce the top–down asymmetric kidney-shaped wake (also referred to as a curled wake). Results indicate that the CVP formed behind a yawed wind turbine originates from the complex interactions between the hub vortex and the streamwise components of the blade tip vortices, which is fundamentally different from the case of a yawed drag disk where the hub vortex is absent. Specifically, when the yaw angle exceeds a critical value, a small part of the streamwise vorticity shed from the rotor disk edge switches its sign from negative to positive and subsequently merges with the concentrated hub vortex under mutual induction, creating a patch of positive vorticity; meanwhile, the remaining streamwise vorticity distributed along the rotor edge curls and evolves into another patch of negative vorticity. These two patches of streamwise vorticity essentially constitute the CVP. Based on the physics learnt from the experiments, the non-uniform cross-stream velocity fields are first reconstructed by a cloud of point vortices distributed along the rotor edge and a hub vortex located in the rotor centre, and subsequently used to numerically solve a simplified transportation–diffusion equation of the wake velocity deficit, which altogether constitute the PVT model. This physics-based reduced-order model is the first model capable of accurately reproducing the wake deformation behind a yawed wind turbine.

An Investigation of Strain‐Softening Phenomenon in Al–0.1% Mg Alloy during High‐Pressure Torsion Processing

An Al–0.1% Mg alloy is processed by high‐pressure torsion (HPT) at room temperature. The Al–0.1% Mg alloy displays strain‐softening phenomenon through hardness evolution: the hardness values in the disc center area are higher than at the disc edge area after 1/2, 1, and 3 turns, and the size of the hard region in the disc center gradually reduces as the number of turns increases from 1/2 to 3 turns. The hardness values evolve toward homogeneity along the disc diameters after 5 and 10 turns. Electron backscatter diffraction (EBSD) and X‐ray line profile analysis suggest that the lower hardness values at the disc edge area in the Al–0.1% Mg alloy are related to a recovery/recrystallization mechanism where the material is subjected to heavy straining.

Modeling uncertainties in X-ray reflection spectroscopy measurements I: Impact of higher order disk images

There are many simplifications in current relativistic reflection models and this introduces systematic uncertainties in the measurement of the properties of the source. In this paper, we study the impact of the radiation crossing the equatorial plane between the black hole and the inner edge of the accretion disk; that is, the radiation produced by the other side of the disk or circling the black hole one or more times (higher order disk images). For slow-rotating black holes with a larger plunging region, the effect is not very sensitive to the exact inclination angle of the disk. For fast-rotating black holes with a smaller plunging region, the effect is very weak for low inclination angles and becomes more important as the angle increases. We simulate some observations without and with higher order disk images and fit the data with the reflection model RELXILL_NK to check its capability of recovering the correct input parameters. Our results suggest that the effect of higher order disk images can be safely ignored for observations with present and near future X-ray missions, even for tests of the Kerr hypothesis.

Multistep peripherin-2/rds self-assembly drives membrane curvature for outer segment disk architecture and photoreceptor viability

Rod and cone photoreceptor outer segment (OS) structural integrity is essential for normal vision; disruptions contribute to a broad variety of retinal ciliopathies. OSs possess many hundreds of stacked membranous disks, which capture photons and scaffold the phototransduction cascade. Although the molecular basis of OS structure remains unresolved, recent studies suggest that the photoreceptor-specific tetraspanin, peripherin-2/rds (P/rds), may contribute to the highly curved rim domains at disk edges. Here, we demonstrate that tetrameric P/rds self-assembly is required for generating high-curvature membranes in cellulo, implicating the noncovalent tetramer as a minimal unit of function. P/rds activity was promoted by disulfide-mediated tetramer polymerization, which transformed localized regions of curvature into high-curvature tubules of extended lengths. Transmission electron microscopy visualization of P/rds purified from OS membranes revealed disulfide-linked tetramer chains up to 100 nm long, suggesting that chains maintain membrane curvature continuity over extended distances. We tested this idea in Xenopus laevis photoreceptors, and found that transgenic expression of nonchain-forming P/rds generated abundant high-curvature OS membranes, which were improperly but specifically organized as ectopic incisures and disk rims. These striking phenotypes demonstrate the importance of P/rds tetramer chain formation for the continuity of rim formation during disk morphogenesis. Overall, this study advances understanding of the normal structure and function of P/rds for OS architecture and biogenesis, and clarifies how pathogenic loss-of-function mutations in P/rds cause photoreceptor structural defects to trigger progressive retinal degenerations. It also introduces the possibility that other tetraspanins may generate or sense membrane curvature in support of diverse biological functions.

Large-scale Dynamics of Winds Originating from Black Hole Accretion Flows. II. Magnetohydrodynamics

Abstract The great difference in dynamical range between small-scale accretion disk simulations and large-scale or cosmological simulations creates difficulties in tracking the disk wind kinematics. In the first paper of this series, we studied the dynamics of hydrodynamic winds from the outer edge of the accretion disk toward galactic scales. In this paper, we further incorporate magnetic fields by employing a one-dimensional magnetohydrodynamic model, with fiducial boundary conditions set for hot accretion flows. The wind solution is achieved through requiring gas to pass smoothly through the slow, Alfvén, and fast magnetosonic points. Beyond the fast magnetosonic point, physical quantities are found to show power-law dependences with cylindrical radius R, i.e., and . The magnetization of wind is dominant in determining the wind properties. The wind is accelerated to greater terminal velocities with stronger magnetizations. The fiducial parameters result in a terminal velocity of about 0.016c. The dependence of the wind physical quantities on temperature, field line angular velocity, and adiabatic index is also discussed.

Modified Screen Printed Electrode Suitable for Electrochemical Measurements in Gas Phase.

We describe a convenient assembly for screen printed carbon electrodes (SPCE) suitable for analyses in gaseous samples which are of course lacking in supporting electrolytes. It consists of a circular crown of filter paper, soaked in a RTIL or a DES, placed upon a disposable screen printed carbon cell, so as to contact the outer edge of the carbon disk working electrode, as well as peripheral counter and reference electrodes. The electrical contact between the paper crown soaked in RTIL or DES and SPCE electrodes is assured by a gasket, and all components are installed in a polylactic acid holder. As a result of this configuration, a sensitive, fast-responding, membrane-free gas sensor is achieved where the real working electrode surface is the boundary zone of the carbon working disk contacted by the paper crown soaked in the polyelectrolyte. This assembly provides a portable and disposable electrochemical platform, assembled by the easy immobilization onto a porous and inexpensive supporting material such as paper of RTILs or DESs which are characterized by profitable electrical conductivity and negligible vapor pressure. The electroanalytical performance of this device was evaluated by voltammetric and flow injection analyses of oxygen which was chosen as prototype of electroactive gaseous analytes. The results obtained pointed out that this assembly is very profitable for the analysis of gaseous atmospheres, especially when used as detector for FIA in gaseous streams.