Bright Ring Research Articles

Dust Rings and Cavities in the Protoplanetary Disks around HD 163296 and DoAr 44

We model substructure in the protoplanetary disks around DoAr 44 and HD 163296 in order to better understand the conditions under which planets may form. We match archival millimeter-wavelength thermal emission against models of the disks’ structure that are in radiation balance with the starlight heating and in vertical hydrostatic equilibrium, and then we compare to archival polarized scattered near-infrared images of the disks. The millimeter emission arises in the interior, while the scattered near-infrared radiation probes the disks’ outer layers. Our best model of the HD 163296 disk has dust masses 81 ± 13 M ⊕ in the inner ring at 68 au and M ⊕ in the outer ring at 102 au, both falling within the range of estimates from previous studies. Our DoAr 44 model has total dust mass M ⊕. Unlike HD 163296, DoAr 44 as of yet has no detected planets. If the central cavity in the DoAr 44 disk is caused by a planet, the planet’s mass must be at least 0.5 M J and is unlikely to be greater than 1.6 M J. We demonstrate that the DoAr 44 disk's structure with a bright ring offset within a fainter skirt can be formed by dust particles drifting through a plausible distribution of gas.

Effect of continuously flowing liquid Li limiter on particle and heat fluxes during H-mode discharges in EAST

• Particle and heat fluxes were successfully controlled by using continuously flowing liquid Li (FLiLi) limiter in the H mode discharges with high plasma heating power in EAST. • By using flowing liquid Li limiter, the fuel recycling could effectively reduce by ∼ 50% and Zeff could decrease from 2.3 to 1.6. • The decreased recycling and impurity radiation led to the achievement of high energy confinement plasma with the average stored energy increased up to ∼ 290 kJ. • Due to Li vapor shielding effect, ∼40% plasma heat flux was dissipated before arrived at the Li limiter. Particle and heat fluxes were successfully controlled by using a continuously flowing liquid Li (FLiLi) limiter in the H-mode discharges with high plasma heating power in the Experimental Advanced Superconducting Tokamak device. There were strong interactions between the FLiLi limiter and high-power plasma with a ∼ 8.3 MW source heating power, and successively, a bright Li radiation ring was produced, which effectively decreased fuel particle recycling by approximately 50%. Due to Li efflux from FLiLi during a series of high-power discharges, an obvious real-time wall conditioning effect was produced, and fuel particle recycling further decreased. Moreover, the value of Z eff decreased from 2.3 to 1.6 due to a decrease in impurity sources; this was attributed to the accumulation of Li deposited on the first wall, which effectively protected the wall materials. The decreased recycling and impurity radiation achieved high-energy confinement plasma, and the average stored energy increased up to ∼ 290 kJ. Moreover, due to the effect of Li vapor shielding, nearly 30% plasma heat flux was dissipated before it arrived at the Li limiter. These results promote further exploration of liquid Li solutions for the critical challenge of heat flux handling and particle control in fusion power plants.

Terahertz Near‐Field Vortex Beams with Variable Intensity Profiles Based on Geometric Metasurfaces

Electromagnetic waves possessing orbital angular momentum, namely, vortex beams, have attracted considerable attention in the fields ranging from optical communications to quantum science, due to their extraordinary information encoding capabilities. Vortex beams are traditionally exhibited with a doughnut‐shaped intensity distribution, where a null intensity center surrounded by a bright ring, caused by the phase singularity. Herein, geometric metasurface devices that can generate near‐field vortex beams with variable intensity profiles are proposed and experimentally demonstrated. The generation of a vortex beam with tailored intensity profile is realized by integrating the azimuthal nonlinear phase and spiral phase into ring‐shaped anisotropic air‐slit arrays. As proof‐of‐principle examples, multiple geometric metasurfaces that generate vortex beams with CN−fold rotational symmetric or asymmetric intensity profiles in the near‐field are demonstrated in the terahertz domain. This unique capability for terahertz near‐field vortices with variable intensity distributions based on geometric metasurface approach opens an avenue to develop multifunctional integrated systems and system‐on‐chip devices, leading to potential applications in microscopy, integrated photonics, quantum information processing, and optical communication.

Chaotic photon orbits and shadows of a non-Kerr object described by the Hartle–Thorne spacetime

The data from the event horizon telescope have provided a novel view of the vicinity of the horizon of a black hole (BH), by imaging the region around the light-ring. They have also raised hopes for measuring in the near future, features of the image (or the shadow) related to higher order effects of photons travelling in these regions, such as the appearance of higher order bright rings produced by more than one windings of photons around the light-ring. While the prospect of measuring these fine features of Kerr BHs is very interesting in itself, there are some even more intriguing prospects for observing novel features of possible non-Kerr objects, in the case that the subjects of our images are not the BH solutions of general relativity. In the hope of sufficient resolution being available in the future, we explore in this work the structure and properties of null geodesics around a Hartle–Thorne (HT) spacetime that includes a deformation from the Kerr spacetime characterised by the quadrupole deformation δq. These spacetimes have been found to exhibit a bifurcation of the equatorial light-ring to two off-equatorial light-rings in a range of δqs and spin parameters. In addition to this, there is a range of parameters where both the equatorial and the off-equatorial light-rings are present. This results in the formation of a pocket that can trap photon orbits. We investigate the properties of these trapped orbits and find that chaotic behaviour emerges. Some of these chaotic orbits are additionally found to be ‘sticky’ and get trapped close to periodic orbits for long times. We also explore how these novel features affect the shadow and find that the off-equatorial light-rings produce distinctive features that deform its circular shape, while the chaotic behaviour associated to the pocket creates features with fractal structure. These results are shown to be quite general, extending to higher order HT spacetimes.

Lensless light intensity model for quasi-spherical cell size measurement.

Quasi-spherical cell size measurement plays an important role in medical test. Traditional methods such as a microscope and a flow cytometer are either it depends on professionals and cannot be automated, or it is expensive and bulky, which are not suitable for point-of-care test. Lab-on-a-chip technology using the lensless imaging system gives a good solution for obtaining the quasi-spherical cell size. The diffraction effects and the low resolution are the two main problems faced by the lensless imaging system. In this paper, a lensless light intensity model for the quasi-spherical cell size measurement is given. First, the diffraction characteristics of a quasi-spherical cell edge are given. Then, a diffraction model at an arc edge is constructed based on the Fresnel diffraction at a straight edge. Using the diffraction model at an arc edge, we explained the mechanism of the formation of the quasi-spherical cell diffraction fringes. Finally, the light intensity of the first bright ring of the quasi-spherical cell diffraction pattern is used to achieve quasi-spherical cell size measurement. The required equipment and the measurement methods are extremely simple, very suitable for point-of-care test. The experimental results show that the proposed model can realize the statistical measurement of the quasi-spherical cells and the classification of the quasi-spherical cells with a difference of 1 [Formula: see text].

On vortex and dark solitons in the cubic–quintic nonlinear Schrödinger equation

We study topologically charged propagation-invariant eigenstates of the 1+2-dimensional Schrödinger equation with a cubic (focusing)–quintic (defocusing) nonlinear term. First, we revisit the self-trapped vortex soliton solutions. Using a variational ansatz that allows us to describe the solutions as a liquid with a surface tension, we derive a simple formula relating the inner and outer radii of the bright vortex ring. Then, using numerical and variational techniques, we analyse dark soliton solutions for which the wave function density asymptotes to a non-vanishing value. We find an eigenvalue cutoff for the propagation constant that depends on the topological charge l. The variational profile provides simple and very accurate results for l≥2. We also study the azimuthal stability of the eigenstates by a linear analysis finding that they are stable for all values of the propagation constant, at least for small l.

The Double Detonation of a Double-degenerate System, from Type Ia Supernova Explosion to its Supernova Remnant

Type Ia supernovae (SNe) are believed to be caused by the thermonuclear explosion of a white dwarf (WD), but the nature of the progenitor system(s) is still unclear. Recent theoretical and observational developments have led to renewed interest in double-degenerate models, in particular the “helium-ignited violent merger” or “dynamically driven double-degenerate double-detonation” (D6). In this paper we take the output of an existing D6 SN model and carry it into the supernova remnant (SNR) phase up to 4000 yr after the explosion, past the time when all the ejecta have been shocked. Assuming a uniform ambient medium, we reveal specific signatures of the explosion mechanism and spatial variations intrinsic to the ejecta. The first detonation produces an ejecta tail visible at early times, while the second detonation leaves a central density peak in the ejecta that is visible at late times. The SNR shell is off-center at all times, because of an initial velocity shift due to binary motion. The companion WD produces a large conical shadow in the ejecta, visible in projection as a dark patch surrounded by a bright ring. This is a clear and long-lasting feature that is localized, and its impact on the observed morphology is dependent on the viewing angle of the SNR. These results offer a new way to diagnose the explosion mechanism and progenitor system using observations of a Type Ia SNR.

First Sagittarius A* Event Horizon Telescope Results. III. Imaging of the Galactic Center Supermassive Black Hole

We present the first event-horizon-scale images and spatiotemporal analysis of Sgr A* taken with the Event Horizon Telescope in 2017 April at a wavelength of 1.3 mm. Imaging of Sgr A* has been conducted through surveys over a wide range of imaging assumptions using the classical CLEAN algorithm, regularized maximum likelihood methods, and a Bayesian posterior sampling method. Different prescriptions have been used to account for scattering effects by the interstellar medium toward the Galactic center. Mitigation of the rapid intraday variability that characterizes Sgr A* has been carried out through the addition of a “variability noise budget” in the observed visibilities, facilitating the reconstruction of static full-track images. Our static reconstructions of Sgr A* can be clustered into four representative morphologies that correspond to ring images with three different azimuthal brightness distributions and a small cluster that contains diverse nonring morphologies. Based on our extensive analysis of the effects of sparse (u, v)-coverage, source variability, and interstellar scattering, as well as studies of simulated visibility data, we conclude that the Event Horizon Telescope Sgr A* data show compelling evidence for an image that is dominated by a bright ring of emission with a ring diameter of ∼50 μas, consistent with the expected “shadow” of a 4 × 106 M ⊙ black hole in the Galactic center located at a distance of 8 kpc.

Constraining giant planet formation with synthetic ALMA images of the Solar System’s natal protoplanetary disk

New ALMA observations of protoplanetary disks allow us to probe planet formation in other planetary systems, giving us new constraints on planet formation processes. Meanwhile, studies of our own Solar System rely on constraints derived in a completely different way. However, it is still unclear what features the Solar System protoplanetary disk could have produced during its gas phase. By running 2D isothermal hydro-simulations used as inputs for a dust evolution model, we derive synthetic images at millimeter wavelengths using the radiative transfer code RADMC3D. We find that the embedded multiple giant planets strongly perturb the radial gas velocities of the disk. These velocity perturbations create traffic jams in the dust, producing over-densities different from the ones created by pressure traps and located away from the planets’ positions in the disk. By deriving the images atλ= 1.3 mm from these dust distributions, we show that very high resolution observations are needed to distinguish the most important features expected in the inner part (<15 AU) of the disk. The traffic jams, observable with a high resolution, further blur the link between the number of gaps and rings in disks and the number of embedded planets. We additionally show that a system capable of producing eccentric planets by scattering events that match the eccentricity distributions in observed exoplanets does not automatically produce bright outer rings at large radii in the disk. This means that high resolution observations of disks of various sizes are needed to distinguish between different giant planet formation scenarios during the disk phase, where the giants form either in the outer regions of the disks or in the inner regions. In the second scenario, the disks do not present planet-related features at large radii. Finally, we find that, even when the dust temperature is determined self-consistently, the dust masses derived observationally might be off by up to a factor of ten compared to the dust contained in our simulations due to the creation of optically thick regions. Our study clearly shows that in addition to the constraints from exoplanets and the Solar System, ALMA has the power to constrain different stages of planet formation already during the first few million years, which corresponds to the gas disk phase.

Müllerian mimicry and the coloration patterns of sympatric coral snakes

Abstract Coral snakes in the genus Micrurus are venomous, aposematic organisms that signal danger to predators through vivid coloration. Previous studies found that they serve as models to several harmless species of Batesian mimics. However, the extent to which Micrurus species engage in Müllerian mimicry remains poorly understood. We integrate detailed morphological and geographical distribution data to investigate if coral snakes are Müllerian mimics. We found that coloration is spatially structured and that Micrurus species tend to be more similar where they co-occur. Though long supposed, we demonstrate for the first time that coral snakes might indeed be Müllerian mimics as they show some convergence in coloration patterns. Additionally, we found that the length of red-coloured rings in Micrurus is conserved, even at large geographic scales. This finding suggests that bright red rings may be under more substantial stabilizing selection than other aspects of coloration and probably function as a generalized signal for deterring predators.

Effectiveness of Lymphatic Contrast Enhanced Ultrasound in the diagnosis of Cervical Lymph node metastasis from papillary thyroid carcinoma

Cervical lymph node metastasis (CLNM) is common in patients with papillary thyroid carcinoma (PTC), which is responsible for tumor staging and surgical strategy. The accurate preoperative identification of CLNM is essential. In this study, twenty consecutive patients with PTC received a parenchyma injection of Sonazoid followed by contrast enhanced ultrasound (CEUS) to identify CLNM. The specific lymphatic CEUS (LCEUS) signs for diagnosing CLNM were summarized, which were further compared with the resected specimens to get the pathological basis. After the injection of contrast agent, lymphatic vessel and lymph node (LN) could be exclusively displayed as hyperperfusion on LCEUS. The dynamic perfusion process of contrast agent in CLNM over time can be clearly visualized. Perfusion defect and interruption of bright ring were the two characteristic LCEUS signs in diagnosing CLNM. After comparing with pathology, perfusion defect was correlated to the metastatic foci in medulla and interruption of bright ring was correlated to the tumor seeding in marginal sinus (all p values < 0.001). The diagnostic efficacies of these two signs were high (perfusion defect vs. interruption of bright ring: AUC, 0.899, 95% CI 0.752–1.000 vs. 0.904, 0.803–1.000). LCEUS has advantages in identifying CLNM from PTC. The typical LCEUS signs of CLNM correlated with pathology.

The Variability of the Black Hole Image in M87 at the Dynamical Timescale

Abstract The black hole images obtained with the Event Horizon Telescope (EHT) are expected to be variable at the dynamical timescale near their horizons. For the black hole at the center of the M87 galaxy, this timescale (5–61 days) is comparable to the 6 day extent of the 2017 EHT observations. Closure phases along baseline triangles are robust interferometric observables that are sensitive to the expected structural changes of the images but are free of station-based atmospheric and instrumental errors. We explored the day-to-day variability in closure-phase measurements on all six linearly independent nontrivial baseline triangles that can be formed from the 2017 observations. We showed that three triangles exhibit very low day-to-day variability, with a dispersion of ∼3°–5°. The only triangles that exhibit substantially higher variability (∼90°–180°) are the ones with baselines that cross the visibility amplitude minima on the u–v plane, as expected from theoretical modeling. We used two sets of general relativistic magnetohydrodynamic simulations to explore the dependence of the predicted variability on various black hole and accretion-flow parameters. We found that changing the magnetic field configuration, electron temperature model, or black hole spin has a marginal effect on the model consistency with the observed level of variability. On the other hand, the most discriminating image characteristic of models is the fractional width of the bright ring of emission. Models that best reproduce the observed small level of variability are characterized by thin ring-like images with structures dominated by gravitational lensing effects and thus least affected by turbulence in the accreting plasmas.

Correlation between corneal tomography and postphacoemulsification positive dysphotopsia

ObjectivesThe aim was to compare between patients who have positive dysphotopsia after uncomplicated phacoemulsification surgery and those who do not have regarding their corneal tomographic findings.BackgroundDysphotopsia is a disturbance of vision and includes light phenomena such as haloes, the subjective perception of a bright ring around a light source. It occurs owing to optical nonconformities in the optical path such as cataract or optical boundaries.Patients and methodsThis is a prospective interventional study that was conducted for 1 year on 20 patients with acquired cataracts. Preoperative corneal tomography and visual assessment were carried out, and then postoperative periodic follow-up for 6 months was done with clinical and visual assessment for dysphotopsia.ResultsThis study shows that 40% of eyes (eight eyes) had higher order aberration with preoperative positive dysphotopsia and 60% of eyes (12 eyes) showed no higher order aberration with no preoperative positive dysphotopsia. Postoperative assessment of positive dysphotopsia showed that patients with no higher order aberrations complained of positive dysphotopsia and patients with higher order aberrations complained of positive dysphotopsia but more severe than before.ConclusionThis study concluded that there is a correlation between corneal tomography and postphacoemulsification positive dysphotopsia, which affects visual satisfaction of patients after phacoemulsification surgery.

Multiplexed Generation of Generalized Vortex Beams with On‐Demand Intensity Profiles Based on Metasurfaces

AbstractOptical vortex beams (VB) have provided a new degree of freedom for carrying optical information due to the unbounded number of orthogonal orbital angular momentum (OAM) channels. Due to the presence of phase singularity, VBs possess a dark zone in the center surrounded by a bright ring whose radius is directly related to the OAM carried by the beam. Here multiplexed generalized vortex beams (GVB) are demonstrated with various custom‐defined closed‐loop beam profiles, including polygons, star and windmill, by tailoring the local phase gradient along the azimuthal direction. By utilizing different polarization channels of metasurfaces, multiple GVBs with independent intensity profiles are generated. This approach provides a playground for realizing various optical modulating capabilities, such as precise particle manipulation, optical source, and OAM encryption.

The Irradiation Instability of Protoplanetary Disks

Abstract The temperature in most parts of a protoplanetary disk is determined by irradiation from the central star. Numerical experiments of Watanabe and Lin suggested that such disks, also called “passive disks,” suffer from a thermal instability. Here we use analytical and numerical tools to elucidate the nature of this instability. We find that it is related to the flaring of the optical surface, the layer at which starlight is intercepted by the disk. Whenever a disk annulus is perturbed thermally and acquires a larger scale height, disk flaring becomes steeper in the inner part and flatter in the outer part. Starlight now shines more overhead for the inner part and so can penetrate into deeper layers; conversely, it is absorbed more shallowly in the outer part. These geometric changes allow the annulus to intercept more starlight, and the perturbation grows. We call this the irradiation instability. It requires only ingredients known to exist in realistic disks and operates best in parts that are both optically thick and geometrically thin (inside 30 au, but can extend to further reaches when, e.g., dust settling is considered). An unstable disk develops traveling thermal waves that reach order unity in amplitude. In thermal radiation, such a disk should appear as a series of bright rings interleaved with dark shadowed gaps, while in scattered light it resembles a moving staircase. Depending on the gas and dust responses, this instability could lead to a wide range of consequences, such as ALMA rings and gaps, dust traps, vertical circulation, vortices, and turbulence.

The steady-state hydrodynamics of a long-lived disc: planetary system architecture and prospects of observing a circumplanetary disc shadow in V4046 Sgr

ABSTRACT Recent imaging of the disc around the V4046 Sgr spectroscopic binary revealed concentric regions of dust rings and gaps. The object’s proximity and expected equilibrated state due to its old age (&amp;gt;20 Myr) make it a superb testbed for hydrodynamical studies in direct comparison to observations. We employ two-dimensional hydrodynamical simulations of gas and multiple dust species to test whether the observed structure conforms with the presence of giant planets embedded in the disc. We then perform radiative transfer (RT) calculations of sky images, which we filter for the telescope response for comparison with near-infrared (NIR) and millimetre observations. We find that the existing data are in excellent agreement with a flared disc and the presence of two giant planets, at $9$ and $20\, {\rm au}$, respectively. The different ring widths are recovered by diffusion-balanced dust trapping within the gas pressure maxima. In our RT model, the diffusion in vertical direction is reduced in comparison to the radial value by a factor of 5 to recover the spectral energy distribution. Further, we report a previously unaddressed, azimuthally confined intensity decrement on the bright inner ring in the NIR scattered light observation. Our model shows that this decrement can be explained by a shadow cast by a circumplanetary disc around the same giant planet that creates the inner cavity in the hydrodynamical simulations. We examine the shape of the intensity indentation and discuss the potential characterization of a giant planet and its associated disc by its projected shadow in scattered light observations.

Molecules with ALMA at Planet-forming Scales (MAPS). XIV. Revealing Disk Substructures in Multiwavelength Continuum Emission

Abstract Constraining dust properties of planet-forming disks via high-angular-resolution observations is fundamental to understanding how solids are trapped in substructures and how dust growth may be favored or accelerated therein. We use ALMA dust continuum observations of the Molecules with ALMA at Planet-forming Scales (MAPS) disks and explore a large parameter space to constrain the radial distribution of solid mass and maximum grain size in each disk, including or excluding dust scattering. In the nonscattering model, the dust surface density and maximum grain size profiles decrease from the inner disks to the outer disks, with local maxima at the bright ring locations, as expected from dust trapping models. The inferred maximum grain sizes from the inner to outer disks decrease from 1 cm to 1 mm. For IM Lup, HD 163296, and MWC 480 in the scattering model, two solutions are compatible with their observed inner disk emission: one solution corresponding to a maximum grain size of a few millimeters (similar to the nonscattering model), and the other corresponding to a size of a few hundred micrometers. Based on the estimated Toomre parameter, only IM Lup—which shows a prominent spiral morphology in millimeter dust—is found to be gravitationally unstable. The estimated maximum Stokes number in all the disks lies between 0.01 and 0.3, and the estimated turbulence parameters in the rings of AS 209 and HD 163296 are close to the threshold where dust growth is limited by turbulent fragmentation. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.

(Invited) Understanding the Electroluminescence Signature of High-Voltage Vertical GaN Pin Diodes with Different Edge Termination Designs

GaN has superior properties, such as a wide band gap and high critical electric field that make it promising material for future power semiconductor devices. Edge termination for GaN power devices remains a subject of significant interest. In this work, different edge termination designs were systematically evaluated and compared by utilizing broadband electroluminescence technique under various reverse bias conditions. Edge termination is a crucial step in power devices fabrication process, using nitrogen implant is a common step in GaN PiN diode. In this work, Nitrogen ion implantation was used to form junction termination extension (JTE) and Guard Rings (GR). A full 2” wafer was fabricated in a foundry process to build a high current 1.2kV class GaN vertical diodes on non-homogenous GaN substrate. In silicon power devices, a smooth tapered implanted doping profiles are often achieved through a controlled diffusion of the implanted dopant island during activation. Activation and diffusion of acceptor dopants via ion implantation is neither well controlled nor understood in GaN. In this work, based JTE terminations, GR termination and a combination of both were compared. We are comparing several devices on the same wafer type and same fabrication process but with different edge termination designs; and spatially resolving their spectrum, by utilizing the electroluminescence mapping technique to acquire a series of broadband images under high voltage reverse bias. There is a clear difference in the electroluminescence signature. This is the first time we show the impact of edge termination on the evolution of these defects and the transport path of the leakage current. The leakage current, and hence the electroluminescence signature is changing as well with the termination design. All the termination and guard ring designs were based on Nitrogen implant. The nitrogen implant doses and energy are chosen to create enough damage in the p-type region. Stress testing is in-progress to evaluate the impact of these defects on failure mechanisms. JTE only design show a leakage current as a bright ring on the outer perimeter of the device active region closer to trench isolation while a GR only design brings the leakage current near the anode. A combination of both termination designs results in scattered leakage points on the outer perimeter of the device. Simulation results of the filed profiles of the different structures and hyperspectral EL and Raman spectroscopy are in progress along with temperature stressing to understand the nitrogen diffusion mechanisms in GaN. This study will have an impact on the future of GaN power devices and mature its process to compete with SiC technology. Figure 1

Photothermocapillary Method for the Nondestructive Testing of Solid Materials and Thin Coatings.

The photothermocapillary (PTC) effect is a deformation of the free surface of a thin liquid layer on a solid material that is caused by the dependence of the coefficient of surface tension on temperature. The PTC effect is highly sensitive to variations in the thermal conductivity of solids, and this is the basis for PTC techniques in the non-destructive testing of solid non-porous materials. These techniques analyze thermal conductivity and detect subsurface defects, evaluate the thickness of thin varnish-and-paint coatings (VPC), and detect air-filled voids between coatings and metal substrates. In this study, the PTC effect was excited by a “pumped” Helium-Neon laser, which provided the monochromatic light source that is required to produce optical interference patterns. The light of a small-diameter laser beam was reflected from a liquid surface, which was contoured by liquid capillary action and variations in the surface tension. A typical contour produces an interference pattern of concentric rings with a bright and wide outer ring. The minimal or maximal diameter of this pattern was designated as the PTC response. The PTC technique was evaluated to monitor the thickness of VPCs on thermally conductive solid materials. The same PTC technique has been used to measure the thickness of air-filled delaminations between a metal substrate and a coating.

Image of the thin accretion disk around compact objects in the Einstein\u2013Gauss\u2013Bonnet gravity

We study the optical appearance of a thin accretion disk around compact objects within the Einstein–Gauss–Bonnet gravity. Considering static spherically symmetric black holes and naked singularities we search for characteristic signatures which can arise in the observable images due to the modification of general relativity. While the images of the Gauss–Bonnet black holes closely resemble the Schwarzschild black hole, naked singularities possess a distinctive feature. A series of bright rings are formed in the central part of the images with observable radiation 10^3 times larger than the rest of the flux making them observationally significant. We elucidate the physical mechanism, which causes the appearance of the central rings, showing that the image is determined by the light ring structure of the spacetime. In a certain region of the parametric space the Gauss–Bonnet naked singularities possess a stable and an unstable light ring. In addition the gravitational field becomes repulsive in a certain neighbourhood of the singularity. This combination of features leads to the formation of the central rings implying that the effect is not specific for the Einstein–Gauss–Bonnet gravity but would also appear for any other compact object with the same characteristics of the photon dynamics.