Edge Of Disk Research Articles

Orbital evolution of a circumbinary planet in a gaseous disk

Sub-Jupiter classed circumbinary planets discovered in close-in binary systems have orbits just beyond the dynamically unstable region, which is determined by the eccentricity and mass ratio of the host binary stars. These planets are assumed to have formed beyond the snow line and migrated to the current orbits rather than forming in situ. We propose a scenario in which a planet formed beyond the snow line and migrated to the inner edge of the circumbinary disk, which was within the unstable area, and then moved to the current orbit through outward transportation. This outward transportation is driven by the balance of orbital excitation of the central stars inside the gravitationally unstable region and damping by the gas-drag force. We carried out N-body simulations with a dissipating circumbinary protoplanetary disk for binary systems with different eccentricities and mass ratios. Planets are more likely to achieve a stable orbit just beyond the unstable region in less eccentric binary systems. This result is not as sensitive to mass ratio as it is to eccentricity. These dependencies are consistent with the data from observed binary systems hosting circumbinary planets. We find CBPs’ orbits close to the instability boundaries are explained by our orbital evolution scenario.

On the centrifugal granulation characteristics by rotary disk: Effect of outer edge structure

Atomizer configurations are pivotal for centrifugal granulation to recovery heat recovery from high-temperature blast furnace slag. In this study, water and water/glycerol mixtures were selected as the working medium analogizing to real molten blast furnace slag. We visualized their granulation processes on five sets of disks with long-flat (LF), short-flat (SF), sharp (S), trapezoid (T) and circular (C) edges. The disk edges are found with considerable impact on the liquid film movement: the LF- and SF-edge disks allow for the adherence of liquid film on the side walls while the rest disks suppress such adherences. The underlying reason for the adherence was theoretically analysed and ascribed to the intricate trade-off between centrifugal force, surface tension and adhesion force. Indicators including adherence distance, critical flowrate and droplet size were considered to assess these disks. The LF- and SF-edge disks contribute to larger critical flowrate and smaller droplet size compared to S-, T- and C-edge disks. The present study shed light on the effect of disk edges on granulation characteristics and provides new insights into atomizer design towards better granulation performance of blast furnace slag.

Construction of three-dimensional finite element model and biomechanical study on patient with with cervical spondylotic myelopathy

To establish a three-dimensional finite element model (FEM) of the neck, to analyze the differences in neck biomechanics between patient with cervical spondylotic myelopathy (CSM) and healthy subject and to provide biomechanics basis for the pathogenesis of CSM. Methods: A patient with CSM was enrolled in a mechanical simulation experiment. Three-dimensional CT scan was performed, and three-dimensional FEM of the neck was constructed. A heathy subject was selected as a control according to the patient's age, gender, height, and weight. Three-dimensional FEM was used to compare the stress differences in the vertebral body, intervertebral disc, ligament and spinal cord under the normal stress of the cervical spine and the maximum stress of the posterior reclining motion. Results: Successfully constructed FEM model of CSM patient and control, and performed mechanical analysis, the most obvious difference in cervical vertebral body force was at C5-C6 segment in CSM patients. The maximum stress site of control and patient was at the anterior edge of the vertebral body. The maximum stress of the vertebral body in the CSM patient was less than that of the control. The stress distribution of the intervertebral disc was irregular in the CSM patient, and the maximum stress was concentrated on both sides of the posterior edge of the intervertebral disc. The stress distribution of the ligaments of the CSM patient was uneven. The maximum stress was in the posterior longitudinal ligament. The range of neck movement in extension of the CSM patient was restricted. Conclusion: Compared with the healthy subject, the balance of the vertebral body, intervertebral disc, ligament and limited range of motion of the CSM patient has been changed, which may be related to the mechanical pathogenesis of cervical spondylotic myelopathy.

Separating extended disc features from the protoplanet in PDS 70 using VLT/SINFONI

Transition discs are prime targets to look for protoplanets and study planet-disc interactions. We present VLT/SINFONI observations of PDS~70, a transition disc with a recently claimed embedded protoplanet. We take advantage of the angular and spectral diversity present in our data for an optimal PSF modeling and subtraction using principal component analysis (PCA). We report the redetection of PDS 70 b, both the front and far side of the outer disc edge, and the detection of several extended features in the annular gap. We compare spectral differential imaging applied before (PCA-SADI), and after (PCA-ASDI) angular differential imaging. Our tests suggest that PCA-SADI better recovers extended features, while PCA-ASDI is more sensitive to point sources. We adapted the negative fake companion (NEGFC) technique to infer the astrometry of the companion, and derived $r = 193.5 \pm 4.9 \mathrm{mas}$ and PA = 158.7deg $\pm$ 3.0deg. We used both NEGFC and ANDROMEDA to infer the $K$-band spectro-photometry of the protoplanet, and found results consistent with recent VLT/SPHERE observations, except for their 2018/02 epoch measurement in the $K2$ filter. Finally, we derived an upper limit of $\dot{M_b} < 1.26 \times 10^{-7} \big[ \frac{5 M_{\rm Jup}}{M_b} \big] \big[ \frac{R_b}{R_{\rm Jup}}\big] M_{\rm Jup} $ yr$^{-1}$ for the accretion rate of the companion based on an adaptation of PCA-SADI/PCA-ASDI around the Br$\gamma$ line.

Electronic structure of a mesoscopic superconducting disk: Quasiparticle tunneling between the giant vortex core and the disk edge

The electronic structure of the giant vortex states in a mesoscopic superconducting disk is studied in a dirty limit using the Usadel approach. The local density of states profiles are shown to be strongly affected by the effect of quasiparticle (QP) tunneling between the states localized in the vortex core and the ones bound to the sample edge. Decreasing temperature leads to a crossover between the edge-dominated and core-dominated regimes in the magnetic field dependence of the tunneling conductance. This crossover is discussed in the context of the efficiency of quasiparticle cooling by the magnetic field induced QP traps in various mesoscopic superconducting devices.

How Gas Accretion Feeds Galactic Disks

Abstract Numerous observations indicate that galaxies need a continuous gas supply to fuel star formation and explain the star formation history. However, direct observational evidence of gas accretion remains rare. Using the EAGLE cosmological hydrodynamic simulation suite, we study cold gas accretion onto galaxies and the observational signatures of the cold gas kinematics. For EAGLE galaxies at z = 0.27, we find that cold gas accretes onto galaxies anisotropically with typical inflow speeds between 20 and 60 km s−1. Most of these galaxies have comparable mass inflow rates and star formation rates, implying that the cold inflowing gas plausibly accounts for sustaining the star-forming activities of the galaxies. As motivation for future work to compare the cold gas kinematics with measurements from quasar sightline observations, we select an EAGLE galaxy with an extended cold gas disk, and we probe the cold gas using mock quasar sightlines. We demonstrate that by viewing the disk edge on, sightlines at azimuthal angles below 10° and impact parameters out to 60 pkpc can detect cold gas that corotates with the galaxy disk. This example suggests that cold gas disks extending beyond the optical disks possibly explain the sightline observations that detect corotating cold gas near galaxy major axes.

Beryllium-10 production in gaseous protoplanetary disks and implications for the astrophysical setting of refractory inclusions

Calcium-aluminum-rich inclusions (CAIs), the oldest known solids of the solar system, show evidence for the past presence of short-lived radionuclide beryllium-10, which was likely produced by spallation during protosolar flares. While such 10Be production has hitherto been modeled at the inner edge of the protoplanetary disk, I calculate here that spallation at the disk surface may reproduce the measured 10Be/9Be ratios at larger heliocentric distances. Beryllium-10 production in the gas prior to CAI formation would dominate that in the solid. Interestingly, provided the Sun’s proton to X-ray output ratio does not decrease strongly, 10Be/9Be at the CAI condensation front would increase with time, explaining the reduced values in a (presumably early) generation of CAIs with nucleosynthetic anomalies. CAIs thus need not have formed very close to the Sun and may have condensed at 0.1–1 AU where sufficiently high temperatures originally prevailed.

Simulation of voltage/current waveforms and contact area of pulsed surface discharge on water

Propagation of a surface discharge on water is evaluated using simulation results of the voltage/current waveforms and discharge contact area. Voltage/current waveforms are calculated using an exponential function which assumes the resistance of water decreases with increasing discharge contact area. A conductive disk having a given potential is used to model the discharge contact area and the temporal variation of the radius of the disk is discussed as the discharge propagation. The calculation in the current field is replaced by a calculation of the electrostatic field using the similarity between current and electrostatic fields. The calculation of the electrostatic field is conducted by a charge simulation method. The discharge phenomena are classified into two stages which are the breakdown of needle-to-water gap and the surface discharge propagation on water. The electrostatic field calculation at needle-to-water gap is performed to determine the initial discharge contact area. Expansion of the contact area in the creepage direction, is evaluated by the electric field calculation at the edge of the conductive disk. The expansion terminates when the field becomes lower than 26 kV/cm. The velocity of the expansion increases with the applied voltage. The maximum contact radius increases with decreasing conductivity of water under the same applied voltage. The tendency of simulation results of the expansion of the contact area are consistent with the previous observation results of the discharge propagation.

Plasmonic emission of hybrid Au/Ag bullseye nanostructures

Bullseye nanostructures with different central disk diameters and numbers of concentric rings have been fabricated in Au/Ag metallic films on glass substrates by focused ion beam milling. The Au/Ag bimetallic nanoresonator is expected to provide chemical stability and outstanding plasmonic property. A novel hybrid plasmonic emission has been observed by cathodoluminescence in the scanning electron microscope. It is found that the hybrid plasmon amplitude of the bullseye structure highly depends on the excitation position. The plasmonic intensity is the maximum when the beam is located at the edge of the central disk, and it can be tuned by selecting the disk size and the number of grooves. Additionally, the finite element simulation reveals that the bimetallic bullseye structure strongly confines the optical radiation, and the electric field distribution directly relates to the emission wavelength.

Fraunhofer Lines in the Center-to-Limb Transition over the Solar Disk

Two-dimensional spectra of the Sun (from the center to the limb of the disk) in wavelength ranges of λ = 532.0–532.8 and 539.1–539.9 nm were registered with the ATsU-5 telescope (the Russian abbreviation ATsU corresponds to the Astronomical Coelostat Mounting) of the Main Astronomical Observatory of the National Academy of Sciences of Ukraine (MAO NASU) after replacing the regular main mirror by a short-focus one (with a focal length of 1 m). An advantage of the applied method is that the spectrum is registered simultaneously for different heliocentric positions on the solar disk. The observational data were reduced for the influence of light scattered in the spectrograph, the atmospheric-stray light, the spectrograph instrumental profile, and some aberrations. The center-to-limb ratios of the spectra are compared to the data available in the literature. The data on variations in the profiles of eleven spectral lines in transition from the center to the limb of the solar disk were obtained. The revealed nonmonotonicity of these changes is explained by inhomogeneities in physical conditions on the surface of the Sun. In general, the depths of the studied Fe I lines demonstrate the decreasing tendency in the strength of lines when passing toward the limb. For most lines, the full widths at half maximum increase toward the disk edge. The equivalent widths show differently directed variations. The parameters of the line Mn I λ 539.4 nm behave in a different way: all three analyzed parameters grow toward the disk edge; however, at the extreme limb, the depth and the equivalent width also start to decrease. The limb-effect of lines was measured; it exhibits the highest value when the core positions in weak lines are compared. For strong lines, the limb-effect is strongest while comparing the middle parts of the line bisectors.

Laminar spread of a circular liquid jet impinging axially on a rotating disc

The steady laminar annular spread of a thin liquid film generated by a circular jet which impinges perpendicularly in direction of gravity on the centre of a rotating disc is examined both analytically and numerically. Matched asymptotic expansions of the flow quantities provide the proper means for studying the individual flow regimes arising due to the largeness of the Reynolds number formed with the radius of the jet, its slenderness and the relative magnitude of the centrifugal body force. This is measured by a suitably defined Rossby number,$Ro$. The careful analysis of jet impingement predicts a marked influence of gravity and surface tension on the film flow, considered in the spirit of a shallow-water approach, only through the vorticity imposed by the jet flow. Accordingly, associated downstream conditions are disregarded as the local Froude and Weber numbers are taken to be sufficiently large. Hence, the parabolic problem shaped from the governing equations in a rigorous manner describes the strongly supercritical spread of a developed viscous film past an infinite disc, essentially controlled by$Ro$. Its numerical solutions are discussed for a wide range of values of$Ro$. The different flow regimes reflecting varying effects of viscous shear and centrifugal force are elucidated systematically to clarify the surprising richness of flow phenomena. Special attention is paid to the cases$Ro\gg 1$and$Ro\ll 1$. The latter, referring to relatively high disc spin, implies a delicate breakdown of the asymptotic flow structure, thus requiring a specific analytical and numerical treatment. Finally, the impact of gravity and capillarity and thus of the disc edge on the film flow is envisaged in brief.

A Microalgae Biocomposite-Integrated Spinning Disk Bioreactor (SDBR): Toward a Scalable Engineering Approach for Bioprocess Intensification in Light-Driven CO2 Absorption Applications

A scalable, solar-energy-driven microbial spinning disk gas absorber–converter technology has been developed by a novel combination of advanced photoreactive biocomposite materials with a continuous thin film flow spinning disc bioreactor (SDBR). Chlorella vulgaris microalgae were incorporated into a porous paper biocomposite for the first time with the addition of chitosan for cell integration within the paper matrix. A 10-cm-diameter SDBR with an immobilized C. vulgaris biocomposite paper enabled high photoactivity and CO2 biofixation at a spin speed of 300 rpm over 15 h of operation in the presence of bicarbonate in the liquid medium and 5% CO2 in the gas environment. Practically all C. vulgaris cells in the biocomposite successfully remained attached to the disk under conditions equivalent to 5g at the disc edge. Overall, the increased CO2 biofixation with a greatly reduced biocomposite surface area and the high cell retention in this proof-of-concept technology highlight the bioprocess intensificatio...

L1 Stream Deflection and Ballistic Launching at the Disk Bow Shock: An Absorption-line Velocity Analysis in Semi-detached Binaries

Abstract Observations of semi-detached interacting binaries reveal orbital modulation in the optical, UV, and X-ray bands, indicating the presence of absorbing material obscuring the disk and accreting primary star at specific orbital phases consistent with L1 stream material overflowing the disk edge. We simulate the L1 stream interaction with the disk using tests particles within the context of the Roche model in the restricted three-body problem. At the disk bow shock the L1 stream particles are deflected and launched onto ballistic trajectories above the disk (as would normally occurs at the front of a detached shock in the hypersonic flow past a blunt body). At a given scale height, the material is assumed to continue without being affected by the disk, while at lower altitude it is being launched at an increasing elevation, as well as gradually being dragged by the Keplerian flow. Near the disk midplane (z ≪ H) the material is assumed to become part of the disk. We follow the stream material ballistic trajectories over the disk surface, where they reach a maximum height z/r at a binary phase Φ ∼ 0.75 and land on the disk at a smaller radius around phase Φ ∼ 0.5. The phase of the maximum height, the phase of the landing site, and the phase of the hot spot itself, all decrease significantly with decreasing radius. The radial velocity for each L1 stream ballistic trajectory along the line of sight (of the observer) to the hot inner parts of the disk is computed as a function of the orbital phase for a binary configuration matching the dwarf nova U Geminorum. The computed velocity amplitudes, phases, and pattern match the observed velocity offsets of the metal lines in the FUSE spectrum of U Gem during outburst. As ballistic trajectories are much easier to compute than realistic 3D hydrodynamical simulations, we propose the use of the L1 stream deflection and ballistic launching as a way to analyze the absorption-line orbital variability in semi-detached binaries and to assess or confirm, with some limitations, system parameters such as the mass ratio, inclination, and disk outer radius.

The corona contracts in a black-hole transient.

The geometry of the accretion flow around stellar-mass black holes can change on timescales of days to months1-3. When a black hole emerges from quiescence (that is, it 'turns on' after accreting material from its companion) it has a very hard (high-energy) X-ray spectrum produced by a hot corona4,5 positioned above its accretion disk, and then transitions to a soft (lower-energy) spectrum dominated by emission from the geometrically thin accretion disk, which extends to the innermost stable circular orbit6,7. Much debate persists over how this transition occurs and whether it is driven largely by a reduction in the truncation radius of the disk8,9 or by a reduction in the spatial extent of the corona10,11. Observations of X-ray reverberation lags in supermassive black-hole systems12,13 suggest that the corona is compact and that the disk extends nearly to the central black hole14,15. Observations of stellar-mass black holes, however, reveal equivalent (mass-scaled) reverberation lags that are much larger16, leading to the suggestion that the accretion disk in the hard-X-ray state of stellar-mass black holes is truncated at a few hundreds of gravitational radii from the black hole17,18. Here we report X-ray observations of the black-hole transient MAXI J1820+07019,20. We find that the reverberation time lags between the continuum-emitting corona and the irradiated accretion disk are 6 to 20 times shorter than previously seen. The timescale of the reverberation lags shortens by an order of magnitude over a period of weeks, whereas the shape of the broadened iron K emission line remains remarkably constant. This suggests a reduction in the spatial extent of the corona, rather than a change in the inner edge of the accretion disk.

Angiogenesis-related factors in the placenta of pregnant women with congenital heart diseases

To study the features of angiogenesis of the placental villous chorion in women whose gestation took place in congenital heart disease (CHD). Thirty-five placentas obtained from women with full-term pregnancy, including 20 cases of non-operated CHD and 15 as a result of physiological pregnancy and childbirth (a control group), were studied. A placental morphological examination was made according to the standard scheme using routine stains and immunohistochemical techniques involving reactions with mouse monoclonal antibodies against VEGF, CD34, and SMA. The placentas of women with CHD showed a set of pathological changes, including impaired chorionic villous maturation and marked dystrophic and necrobiotic changes, the latter being more common in the placental marginal zones. Placental VEGF expression in women with CHD was significantly higher than that in the controls, especially at the edge of the placental disc. On the contrary, CD34 expression in all placental sections was lower in CHD. The distribution of SMA in the myofibroblasts of chorionic villous vessels in CHD was characterized by diffuse growth of actin expression. The specific volume of the cell surface with a positive reaction to actin significantly increased in the center, especially in the peripheral zone. Thus, the analysis of the studies could establish that hemodynamic disturbance during gestation complicated by CHD was accompanied by remodeling of the villous chorion. Pathological changes in the placental barrier complicate metabolism and gas exchange in the fetoplacental complex. Microvascular remodeling is an important mechanism of placental adaptation to circulatory hypoxic conditions in the presence of CHD and a prerequisite for successful pregnancy termination and childbirth in disease.

Effect of hole edge chamfering on stress concentration at joining end in shrink fitted of hollow disk and cylinder

Roller chains are widely used for power transmission on many kinds of industrial machinery, including conveyors, cars, motorcycles, bicycles, and so forth. This study focuses on the fitting portion between the ring plate and the pin because the stress concentration of this connection sometimes causes final breakage. First, if shrink-fitting a pin to a plate, stress concentration occurs along the hole edge even under no external load. As a result of shrinkage fit of this pin, the stress concentration under external load is totally different from stress concentration of ordinary hole alone. Therefore, in this paper, as a fundamental model of the joint problem between a plate and a pin, an axisymmetric problem of a cylinder fitted in a hollow disk is studied. Then, the effect of chamfering on the hole edge of the hollow disk is discussed. Also, the e between the case where the hollow disk surface and the cylinder are the same surface and the case where the cylindrical end surface protrudes from the hollow disk are also clarified. The circumferential stress can be reduced by chamfering even when the cylinder does not protrude or protrude.

The formation of rings and gaps in wind-launching non-ideal MHD discs: three-dimensional simulations

Previous axisymmetric investigations in two dimensions (2D) have shown that rings and gaps develop naturally in non-ideal magnetohydrodynamic (MHD) disk-wind systems, especially in the presence of ambipolar diffusion (AD). Here we extend these 2D simulations to three dimensions (3D) and find that rings and gaps are still formed in the presence of a moderately strong ambipolar diffusion. The rings and gaps form from the same basic mechanism that was identified in the 2D simulations, namely, the redistribution of the poloidal magnetic flux relative to the disk material as a result of the reconnection of a sharply pinched poloidal magnetic field lines. Thus, the less dense gaps are more strongly magnetized with a large poloidal magnetic field compared to the less magnetized (dense) rings. The rings and gaps start out rather smoothly in 3D simulations that have axisymmetric initial conditions. Non-axisymmetric variations arise spontaneously at later times, but they do not grow to such an extent as to disrupt the rings and gaps. These disk substructures persist to the end of the simulations, lasting up to 3000 orbital periods at the inner edge of the simulated disk. The longevity of the perturbed yet still coherent rings make them attractive sites for trapping large grains that would otherwise be lost to rapid radial migration due to gas drag. As the ambipolar diffusivity decreases, both the disk and the wind become increasingly turbulent, driven by the magnetorotational instability, with tightly-wound spiral arms becoming more prominent in the disk.

Relativistic Proton Levels from Region AR 12673 (GLE #72) and the Heliospheric Current Sheet as a Sun–Earth Magnetic Connection

On 2017 September 10 Neutron Monitors (NMs) apparatus located at ground level and high latitudes detected an increase in the counting rate associated to solar energetic particles (SEPs) emission from X8.2-class solar flare and its associated CME. This was the second-highest flare of the current solar cycle. The origin was the active region AR 12673 when it was located at the edge of the west solar disk, magnetically poorly connected with Earth. However, there was a peculiar condition: the solar protons accelerated by the CME shocks were injected within a heliospheric current sheet (HCS) region when Earth was crossing this region. We show that often HCS and SEPs propagation are closely related. If the source locations of SEPs are within or close to HCS, the HCS play the role of a Sun–Earth magnetic connection. SEPs drift around HCS paths, and SEPs are also drift in a wide range of longitudes by the HCSs. In some cases, and especially when Earth crosses the HCS sector, a fraction of these particles can reach Earth with a harder energetic particle flux, triggering a ground-level enhancement (GLE). The blast on 2017 September 10, which triggered the GLE #72, was the second in the current solar cycle. We show that the two GLEs, including all sub-GLEs observed in the current solar cycle, comes from solar explosions that happened within an HCS structure; this behavior is also observed in the GLEs of the previous solar cycle. In general, solar explosions from active regions poorly connected with Earth can trigger GLEs, through the mechanism described above. In all cases, the SEPs drift processes by HCS structures provides an efficient particle transport, allowing the observation of these solar transient events.

Unconventional origin of supersoft X-ray emission from a white dwarf binary

Supersoft X-ray sources are stellar objects that emit X-rays with temperatures of about 1 million kelvin and luminosities well in excess of what can be produced by stellar coronae. It has generally been presumed that the objects in this class are binary star systems in which mass transfer leads to nuclear fusion on the surface of a white dwarf1. Classical novae—the runaway fusion events on the surfaces of white dwarfs—generally have supersoft phases, and it is often stated that the bright steady supersoft X-ray sources seen from white dwarfs accreting mass at a high rate are undergoing steady nuclear fusion1. Here, we report the discovery of a transient supersoft source in the Small Magellanic Cloud without any signature of nuclear fusion having taken place. This discovery indicates that the X-ray emission probably comes from a ‘spreading layer’2—a belt on the surface of the white dwarf near the inner edge of the accretion disk in which a large fraction of the total accretion energy is emitted—and (albeit more tentatively) that the accreting white dwarf is relatively massive. We thus establish that the presence of a supersoft source cannot always be used as a tracer of nuclear fusion, in contradiction with decades-old consensus about the nature of supersoft emission. Accretion onto the surface of a white dwarf typically generates supersoft X-ray emission and broad emission lines due to nuclear fusion. ASASSN-16oh exhibits no visible broad lines, implying there is no surface fusion, and instead, a belt around the dwarf called a spreading layer is the source of the supersoft X-ray emission.

Inner disk structure of the classical T Tauri star LkCa 15

Context. Magnetospheric accretion has been thoroughly studied in young stellar systems with full non-evolved accretion disks, but it is poorly documented for transition disk objects with large inner cavities. Aims. We aim at characterizing the star-disk interaction and the accretion process onto the central star of LkCa 15, a prototypical transition disk system with an inner dust cavity that is 50 au wide. Methods. We obtained quasi-simultaneous photometric and spectropolarimetric observations of the system over several rotational periods. We analyzed the system light curve and associated color variations, as well as changes in spectral continuum and line profile to derive the properties of the accretion flow from the edge of the inner disk to the central star. We also derived magnetic field measurements at the stellar surface. Results. We find that the system exhibits magnetic, photometric, and spectroscopic variability with a period of about 5.70 days. The light curve reveals a periodic dip, which suggests the presence of an inner disk warp that is located at the corotation radius at about 0.06 au from the star. Line profile variations and veiling variability are consistent with a magnetospheric accretion model where the funnel flows reach the star at high latitudes. This leads to the development of an accretion shock close to the magnetic poles. All diagnostics point to a highly inclined inner disk that interacts with the stellar magnetosphere. Conclusions. The spectroscopic and photometric variability on a timescale of days to weeks of LkCa 15 is remarkably similar to that of AA Tau, the prototype of periodic dippers. We therefore suggest that the origin of the variability is a rotating disk warp that is located at the inner edge of a highly inclined disk close to the star. This contrasts with the moderate inclination of the outer transition disk seen on the large scale and thus provides evidence for a significant misalignment between the inner and outer disks of this planet-forming transition disk system.