Disk Properties Research Articles

Study of Microstructure and Mechanical Properties by Torsional Behavior in Axial Closed Die Rolling Forming

The impact of the torsional component on the microstructure and mechanical characteristics of a titanium alloy is examined in this work using a combination of numerical simulation and experimental validation. During the axial closed die rolling (ACDR) forming, the combined effects of compressive and torsional deformation cause a significant increase in the specimen’s cumulative strain. The specimen’s shear strain changes most significantly at the height of H/2. The α-phase has a greater propensity to slip on the conical surface, followed by the cylindrical surface, according to SEM and EBSD analyses. The basal surface has the highest resistance to slip. The formation of a fine isometric α-phase occurs when the compressive component causes the α-phase to become more prone to breakage and fracture. A larger α-phase will form because of the torsional component’s influence, which increases the likelihood that the α-phase will slip and exhibit bending and twisting. With a difference in strength of less than 1 percent and a difference in plasticity between the tangential and radial directions of less than 5 percent, the mechanical properties of the TC11 disks formed by the ACDR show a greater degree of isotropy. The specimens show a tough fracture mode, with radial performance outperforming tangential performance, according to fracture morphology analysis.

Predicting HCN, HCO^+, multitransition CO, and dust emission of star-forming galaxies. Extension to luminous infrared galaxies and the role of cosmic-ray ionization

The specific star formation rate of star-forming main sequence galaxies significantly decreased since $z 1.5$ because the molecular gas fraction and star formation efficiency decreased. The gas velocity dispersion decreased within the same redshift range and is apparently correlated with the star formation efficiency (inverse of the molecular gas depletion time). However, the radio--infrared (IR) correlation has not changed significantly since $z 1.5$. The theory of turbulent clumpy star-forming gas disks together with the scaling relations of the interstellar medium describes the large- and small-scale properties of galactic gas disks. We extend our previous work on the IR multitransition molecular line, and radio continuum emission of local and high-z star-forming and starburst galaxies to local and $z 0.5$ luminous IR galaxies. The model reproduces the IR luminosities, CO, HCN, and HCO$^+$ line luminosities, and the CO spectral line energy distributions of these galaxies. We derived CO(1-0) and HCN(1-0) conversion factors for all galaxy samples. The relation between the star formation rate per unit area and the H$_2$ surface density cannot be fit simply for all redshifts. The star formation efficiency, the product of the gas turbulent velocity dispersion, and the angular velocity of the galaxies are tightly correlated. Galaxies with lower stellar masses can in principle compensate their gas consumption via star formation by radial viscous gas accretion. The limiting stellar mass increases with redshift. The radio continuum emission is directly proportional to the density of cosmic-ray (CR) electrons, but the molecular line emission depends on the CR ionization rate via the gas chemistry. The normalization of the CR ionization rate we found for the different galaxy samples is higher by about a factor of three to five than the normalization for the solar neighborhood. This means that the mean yield of low-energy CR particles for a given star formation rate per unit area is higher by about three to ten times in external galaxies than was observed by Voyager I.

Magnetic seed generation by plasma heat flux in accretion disks

Magnetic batteries are potential sources that may drive the generation of a seed magnetic field, even if this field is initially zero. These batteries can be the result of nonaligned thermodynamic gradients in plasmas, as well as of special and general-relativistic effects. So far, magnetic batteries have only been studied in ideal magnetized fluids. We studied the nonideal fluid effects introduced by the energy flux in the vortical dynamics of a magnetized plasma in curved space-time. We propose a novel mechanism for generating a heat-flux-driven magnetic seed within a simple accretion disk model around a Schwarzschild black hole. We used the 3+1 formalism for the splitting of the space-time metric into space-like and time-like components. We studied the vortical dynamics of a magnetized fluid with a heat flux in the Schwarzschild geometry in which thermodynamic and hydrodynamic quantities are only dependent on the radial coordinate. Assuming that the magnetic field is initially zero, we estimated the linear time evolution of the magnetic field due to the inclusion of nonideal fluid effects. When the thermodynamic and hydrodynamic quantities vary only radially, the effect of the coupling between the heat flux, the space-time curvature, and the fluid velocity acts as the primary driver for an initial linearly time-growing magnetic field. The plasma heat flux completely dominates the magnetic field generation at a specific distance from the black hole, where the fluid vorticity vanishes. This distance depends on the thermodynamical properties of the Keplerian plasma accretion disk. These properties control the strength of the nonideal effects in the generation of seed magnetic fields. We find that heat flux is the main driver of a seed magnetic field in black hole accretion disks if the geometry, plasma dynamics, and thermodynamics share the same axial symmetry. This suggests that nonideal fluid effects may play a major role in the magnetization of astrophysical plasmas.

Understanding Factors Contributing to Glaucoma in Populations of African Descent

Glaucoma is the leading cause of irreversible blindness globally, with the commonest subtype being primary open angle glaucoma (POAG). POAG is characterised by an increase in intraocular pressure (IOP), optic nerve damage and irreversible visual field loss. People of African descent (AD) are significantly more susceptible to POAG when compared to people of European descent (ED), and the reasons for this are complex and multifaceted. The vast level of genetic diversity in AD populations has allowed, through genome-wide association studies (GWAS), for the identification of several single nucleotide polymorphisms (SNPs) as well as differences in mitochondrial haplogroups, which could explain the pathophysiology underlying the increased susceptibility of AD populations to POAG. The altered expression of genes such as MYOC as well as the expression of inflammatory mediators influencing reactive astrocytes have also been implicated. There are also several differences in morphology between AD and ED eyes which must be considered, including differences in central corneal thickness (CCT) and corneal hysteresis (CH) as well as variation in properties of optic discs. The link between all the aforementioned factors and the increased prevalence of POAG in AD populations will be explored in this review.

Observing planetary gaps in the gas of debris disks

Recent ALMA observations discovered consequent amounts (i.e., up to a few 10−1 M⊙) of CO gas in debris disks that were expected to be gas-free. This gas is in general estimated to be mostly composed of CO, C, and O (i.e., H2-poor), unlike the gas present in protoplanetary disks (H2-rich). At this stage, the majority of planet formation already occurred, and giant planets might be evolving in these disks. While planets have been directly observed in debris disks (e.g., β Pictoris), their direct observations are challenging due to the weak luminosity of the planets. In this paper, with the help of hydrodynamical simulations (with FARGO3D) coupled with a radiative transfer code (RADMC-3D) and an observing tool (CASA), we show that planet-gas interactions can produce observable substructures in this late debris disk stage. While it is tricky to observe gaps in the CO emission of protoplanetary disks, the unique properties of the gaseous debris disks allow us to observe planetary gaps in the gas. Depending on the total mass of the gaseous debris disk, kinks can also be observed. We derive a simple criterion to estimate in which conditions gaps would be observable and apply it to the known gaseous debris disk surrounding HD 138813. In our framework, we find that planets as small as 0.5 MJ can produce observable gaps and investigate under which conditions (i.e., gas and planets characteristics) the substructure become observable with ALMA. The first observations of planet-gas interactions in debris disks can lead to a new way to indirectly detect exoplanets, reaching a population that could not be probed before, such as giant planets that are too cold to be detected by direct imaging.

Binary orbit and disks properties of the RW Aur system using ALMA observations

Context. The dynamical interactions between young binaries can perturb the material distribution of their circumstellar disks, and modify the planet formation process. In order to understand how planets form in multiple stellar systems, it is necessary to characterize both their binary orbit and their disks properties. Aims. In order to constrain the impact and nature of the binary interaction in the RW Aur system (bound or unbound), we analyzed the circumstellar material at 1.3 mm wavelengths, as observed at multiple epochs by the Atacama Large (sub-)millimeter Array (ALMA). Methods. We analyzed the disk properties through parametric visibility modeling, and we used this information to constrain the dust morphology and the binary orbital period. Results. We imaged the dust continuum emission of RW Aur with a resolution of 3 au, and we find that the radius enclosing 90% of the flux (R90%) is 19 au and 14 au for RW Aur A and B, respectively. By modeling the relative distance of the disks at each epoch, we find a consistent trend of movement for the disk of RW Aur B moving away from the disk of RW Aur A at an approximate rate of 3 mas yr−1 (about 0.5 au yr−1 in sky-projected distance). By combining ALMA astrometry, historical astrometry, and the dynamical masses of each star, we constrain the RW Aur binary stars to be most likely in a high-eccentricity elliptical orbit with a clockwise prograde orientation relative to RW Aur A, although low-eccentricity hyperbolic orbits are not ruled out by the astrometry. Our analysis does not exclude the possibility of a disk collision during the last interaction, which occurred 295−74+21 yr ago relative to beginning of 2024. Evidence for the close interaction is found in a tentative warp of 6 deg in the inner 3 au of the disk of RW Aur A, in the brightness temperature of both disks, and in the morphology of the gas emission. A narrow ring that peaks at 6 au around RW Aur B is suggestive of captured material from the disk around RW Aur A.

Accretion disc dynamics in extragalactic black hole X-ray binaries: a comprehensive study of M33 X–7, NGC 300 X–1, and IC 10 X–1

ABSTRACT Extragalactic black hole X-ray binaries (BH-XRBs) are the most intriguing X-ray sources as some of them are ‘home’ to the most massive stellar-mass BHs ever found. In this work, we conduct a comprehensive study of three massive, eclipsing extragalactic BH-XRBs i.e. M33X-7, NGC300X-1, and IC10X-1 and using entire X-ray observations available from XMM–Newton and NuSTAR till date. Preliminary analysis using diskbb and power-law models shows that the sources have steep spectra and sub-Eddington luminosities (L<0.69 L$_{\mathrm{ Edd}}$), with major flux contribution from non-thermal component, resembling the relatively uncharted steep power-law state (SPL). To understand the accretion disc properties in this state, we explore alternate modelling scenario that reveals the presence of a ‘hot’ ($kT_{\mathrm{ in}}=1\!-\!2$ keV) slim-disc (diskpbb) with radial temperature profile $T(r)\propto r^{-p}$ ($p=0.5\!-\!0.66$), along with a cooler ($kT_{\mathrm{ in}}=0.1\!-\!0.2$ keV) standard thermal disc (diskbb). We carry out the continuum-fitting method using relativistic slim-disc model (slimbh) and estimate the mass range of M33 X–7, NGC300X-1, and IC10X-1 is to be 9–15 M$_{\odot }$, 9–28 M$_{\odot }$, and 10–30 M$_{\odot }$, respectively. Further, eclipse periods are determined by modelling the light curve, using which we estimate the size of the eclipsing bodies. Modelling of the eclipse spectra revealed the complete obscuration of soft spectral component during eclipse, implying the emission of hard component from an extended accretion region. Based on our findings, we provide an inference on geometry of accretion disc in these wind-fed systems and compare their properties with the other two extragalactic BH-XRBs.

Investigating the Mean Temperature of Accretion Disks and Mass Transfer Rates in Cataclysmic Variable Stars through Orbital Characteristics

Cataclysmic variable (CV) stars, characterized by their dynamic binary systems composed of a white dwarf and a donor red dwarf star, exhibit intricate mass transfer processes crucial for understanding their evolutionary pathways. This study delved into the theoretical investigation of mass transfer processes occurring within non-magnetic CV stars analyzing their orbital characteristics. A selection of eleven CV systems, encompassing a diverse range of subcategories, were chosen for the analysis of this research. Well-established Fourier and Lomb-Scargle algorithms were utilized to identify the most effective algorithm in determining the periodicity of their light curves. The calculated orbital periods for the aforementioned CV sample were then leveraged to determine the mean temperature of their accretion disks. This determination was achieved through established techniques which used spectroscopic Balmer emission lines and Stromgren photometric observations. These techniques provide robust measurements of the physical properties of accretion disks within CVs. Finally, a strong correlation was established between mean temperature of the disk which determined through spectroscopic method and system’s mass transfer rate which determined via various techniques and algorithms.

Co-Sintering Anode Materials with Garnet Electrolytes for Solid-State Batteries

Li7La3Zr2O12 (LLZ) has garnered considerable attention as the solid electrolyte among oxide-based materials due to its notable Li-ion conductivity and stability against Li metal. Nevertheless, LLZ necessitates high-temperature sintering to achieve enhanced ionic conductivity, which inadvertently fosters the formation of undesired interphases between the LLZ electrolyte and electrode materials. Addressing this challenge necessitates a reduction in sintering temperature. While there are numerous studies on co-sintering LLZ with cathode materials, the analogous investigations regarding anode materials remain scarce. Consequently, the selection of anode materials suitable for LLZ-based all-solid-state batteries has yet to progress significantly. Thus, this study endeavors to identify anode materials compatible with LLZ for co-sintering and enhancing electrode performance. In the realm of anode materials, achieving both reaction suppression during sintering and high energy density is paramount. Predicting reactions between different materials typically relies on thermodynamic calculations. This study focuses on the Li-concentration between diverse materials, serving as the driving force behind the reaction rate. Hence, we investigate the relationship between the lithium concentration in the electrode material and LLZ reactivity.Bi5Nb3O15, TiNb2O7, CeO2-SrLi2Ti6O14, SrLi2Ti6O14, Li2Ni(WO4)2, Li3Ni2SbO6, Li2SnO3, Li2TiO3 and Li3SbO4 were selected as the anode candidate. All anode materials and Bi-substituted LLZ (Bi-LLZ) were synthesized via solid-state reaction. The resulting anode material and LLZ were mixed at a volume ratio of 1:0.85 and press-formed into the disk, which was subsequently sintered at temperatures ranging from 650°C–850°C. The crystal structure of the sintered disk was characterized via X-ray diffraction, while microstructure observations were conducted using SEM-EDS and TEM-EDS. The electrical properties of the composite anode disks were evaluated using AC impedance spectroscopy and DC polarization methods. To assess the electrode properties of the composite anode disks, the charge-discharge tests were performed using a liquid electrolyte.XRD measurement post co-sintering was conducted to evaluate the reactivity of anode candidates with Bi-LLZ. The relationship between the Li-concentration of anode materials (C Li: mol/cm3) and the impurity phase ratio post co-sintering was investigated. The reaction between anode materials and LLZ can be categorized into two groups based on lithium concentration. Highly reactive materials exhibit lower C Li than Bi-LLZ, while low-reactive materials possess higher C Li than LLZTB. When the Li-concentration in the anode material was low, both LLZ and the anode material vanished entirely, and new reaction products emerged. Conversely, high Li-concentration materials maintained both peaks, indicating minimal reaction progress. Furthermore, we demonstrated that the composite anode based on higher CLi materials performs effectively. Thus, increasing the Li-concentration in the anode material to the same level or higher than that in LLZO can suppress the reaction during sintering.

Disk2Planet: A Robust and Automated Machine Learning Tool for Parameter Inference in Disk–Planet Systems

We introduce Disk2Planet, a machine-learning-based tool to infer key parameters in disk–planet systems from observed protoplanetary disk structures. Disk2Planet takes as input the disk structures in the form of 2D density and velocity maps, and outputs disk and planet properties, that is, the Shakura–Sunyaev viscosity, the disk aspect ratio, the planet–star mass ratio, and the planet’s radius and azimuth. We integrate the Covariance Matrix Adaptation Evolution Strategy, an evolutionary algorithm tailored for complex optimization problems, and the Protoplanetary Disk Operator Network, a neural network designed to predict solutions of disk–planet interactions. Our tool is fully automated and can retrieve parameters in one system in 3 minutes on an Nvidia A100 graphics processing unit. We empirically demonstrate that our tool achieves percent-level or higher accuracy, and is able to handle missing data and unknown levels of noise.

Superradiance scattering of electromagnetic and gravitational fields and thin accretion disk around non-commutating Kerr black hole

We consider the non-commutative (NC) Kerr black hole where the mass of the central object is smeared over a region of linear size b, b is the strength of the NC character of spacetime. For the spacetime under consideration, we calculate the amplification factor for electromagnetic and gravitational fields and study various properties of a thin accretion disk. The expression for the amplification factor is obtained with the help of the asymptotic matching technique. The amplification factor is then plotted against frequency for various values of the spin a and the NC parameter b. Though the amplification factor increases with a but decreases with b, the cut-off frequency up to which we have amplification increases with a and b. We then study the effect of the spin and the NC nature of spacetime on the energy flux, temperature distribution, emission spectrum, energy conversion efficiency, and the radius of the innermost stable circular orbit of a thin accretion disk around the black hole with the help of the steady-state Novikov–Thorne model. Our study reveals that these quantities increase with the spin and the NC parameter. We also find that the disk around the NC Kerr black is hotter and more luminous than that around the Kerr black hole and the NC Schwarzschild black hole. We can conclusively infer from our investigation that the NC nature of spacetime has a significant impact on the superradiance phenomenon as well as on various properties of thin accretion disks.

Reducing the Brace Correction Stress on the Secondary Lumbar Curve Results in Excellent Muscle, Bone, and Disc Mechanical Performance: A Musculoskeletal Finite Element Simulation of AIS Patient With Rigo A3.

The biomechanical mechanism of brace intervention on bone, muscle, and disc should be comprehensively considered for AIS patients. We aimed to developmentally construct a musculoskeletal finite element model of adolescent idiopathic scoliosis to simulate the coupling of corrective forces and analyze the mechanical properties of bone, muscle, and disc. Investigateing, more effective clinical interventions to break the vicious cycle of patients during growth. A finite element model, including muscle, bone, and disc, was established using computed tomography data of a patient with RigoA3 adolescent idiopathic scoliosis. The three-point force coupling, antigravity, and bending effects of the Chêneau brace were simulated, and the correction force of the secondary lumbar bend was gradually reduced while observing the mechanical characteristics of bone, muscle, and disc. The correction force in line with symmetrical spine growth was comprehensively evaluated. The correction rate of the main thoracic (MT) curve, the intervertebral space height on the concave side of the vertebrae at the apex, and the stress ratio of the intervertebral discs were optimal when the maximum corrective pressure threshold was reached. However, the proximal thoracic (PT) curve was aggravated and the axial forces on the concave side were unbalanced. At this time, the biomechanical performance of the model is also not optimal. The correction rate of the Cobb Angle of the MT curve decreased with the decrease of the correction pressure in the lumbar region. When reduced to 25% of the maximum threshold, the convex side of disc stress, intervertebral space, and muscle axial force is more in line with the biomechanical mechanism of correction and can avoid sacrificing the PT curve. Downward adjustment of the corrective force to the secondary lumbar curve, using the Chêneau brace, results in better primary thoracic curvature mechanics in the musculoskeletal finite element model, suggesting that breaking the vicious cycle of scoliosis progression to guide benign spinal growth is beneficial.

Biomechanics of the intervertebral disc : Consequences of degenerative changes

The intervertebral disc represents the flexible connection between two adjacent vertebral bodies. Intervertebral discs, therefore, give the spine its enormous range of motion. At the same time, intervertebral discs distribute the load evenly over the bony vertebral bodies to ensure load transfer from the upper body to the pelvis, provide sufficient stability, and absorb shocks during everyday movements as well as under extreme loads. The two tissue regions of the intervertebral disc, the central fluid-rich core (nucleus pulposus) and the lamellae of the outer fibrous ring (annulus fibrosus) experience different stresses under load and movement. This article summarizes current knowledge on the biomechanical properties of the intervertebral disc and explains how these are altered by degeneration and which surgical treatment options for degenerated and herniated discs are advisable from abiomechanical perspective.

Experimental investigations of Tribological properties of AISID3 Disc and TiN Coated Carbide Pin in LN2 Environment based on Taguchi Technique

Experimental investigations of Tribological properties of AISID3 Disc and TiN Coated Carbide Pin in LN2 Environment based on Taguchi Technique

Correlation Between Radio Loudness and the Eddington Ratio in Quasars

ABSTRACTQuasars can be categorized into radio‐loud and radio‐quiet populations based on radio properties. The physical mechanisms underlying this dichotomy have long been an active area of investigation. In this work, we analyze multi‐wavelength data from 851 quasars matched between the SDSS DR14 and FIRST catalogs, requiring emission line measurements with signal‐to‐noise ratios > 3, we fit quasar optical continuum spectra and compute the radio loudness, luminosities, and Eddington ratios. We classify quasars as radio‐loud or radio‐quiet using a dividing line of . We find that the distribution of the Eddington ratio and radio luminosity is different between the radio‐loud and radio‐quiet quasars, and the correlation between the Eddington ratio and radio loudness is disparate as well. The Eddington ratio shows a weakly positive correlation with radio loudness in both the whole sample and radio‐loud quasars, which imply that the Eddington ratio contributes to the radio loudness but it is not the dominant factor and that additional factors influence relativistic jet production in radio‐loud quasars. However, the Eddington ratio is anti‐correlated with radio loudness in radio‐quiet quasars, potentially related to the properties of the accretion disk.

Gaia/GSP-spec spectroscopic properties of γ Doradus pulsators

Context. The third Data Release of the ESA Gaia mission has provided a large sample of new gravity-mode pulsators, among which more than 11 600 are γ Dor stars. Aims. The goal of the present work is to present the spectroscopic parameters of these γ Dor pulsators estimated by the GSP-Spec module that analysed millions of Gaia spectra. Such a parametrisation could help confirm their γ Dor nature and provide their chemo-physical properties. Methods. The Galactic positions, kinematics, and orbital properties of these new Gaia pulsators were examined in order to define a sub-sample belonging to the Milky Way thin disc, in which these young stars should preferentially be found. The stellar luminosities, radii, and astrometric surface gravities were estimated without adopting any priors from uncertain stellar evolution models. These parameters, combined with the GSP-Spec effective temperatures, spectroscopic gravities, and metallicities were then validated by comparison with recent literature studies. Results. Most stars are found to belong to the Galactic thin disc, as expected. It is also found that the derived luminosities, radii, and astrometric surface gravities are high quality and have values typical of genuine γ Dor pulsators. Moreover, we show that Teff and [M/H] of pulsators with high enough S/N spectra or slow to moderate rotation rates are robust. This allowed to define a sub-sample of genuine slow-rotating Gaiaγ Dor pulsators. Their Teff were found to be between ∼6500 and ∼7800 K, log(g) is around 4.2, and the luminosities and stellar radii peak at ∼5 L⊙ and ∼1.7 R⊙, The median metallicity is close to the Solar value, although γ Dor with higher and lower metallicities by about ±0.5 dex were also identified. The [α/Fe] content is fully consistent with the chemical properties of the Galactic disc. Conclusions.Gaia/DR3 spectroscopic properties of γ Dor stars therefore confirm the nature of these pulsators and allow to chemo-physically parametrise a new large sample of such stars. Moreover, future Gaia data releases should drastically increase the number of γ Dor stars with parameters spectroscopically derived with good precision.

Impact of H I cooling and study of accretion disks in asymptotic giant branch wind-companion smoothed particle hydrodynamic simulations

Context. High-resolution observations reveal that the outflows of evolved low- and intermediate-mass stars harbour complex morphological structures that are linked to the presence of one or multiple companions. Hydrodynamical simulations provide a way to study the impact of a companion on the shaping of the asymptotic giant branch (AGB) star out-flow. Aims. Using smoothed particle hydrodynamic (SPH) simulations of an AGB star undergoing mass loss, which also has a binary companion, we study the impact of including H I atomic line cooling on the flow morphology. We also study how this affects the properties of the accretion disks that form around the companion. Methods. We used the PHANTOM code to perform high-resolution 3D SPH simulations of the interaction of a solar-mass companion with the outflow of an AGB star, using different wind velocities and eccentricities. We compared the model properties, computed with and without the inclusion of H I cooling. Results. The inclusion of H I cooling produces a sizeable decrease in the temperature, up to one order of magnitude, in the region closely surrounding the companion star. As a consequence, the morphological irregularities and relatively energetic (bipolar) outflows that were obtained without H I cooling no longer appear. In the case of an eccentric orbit and a low wind velocity, these morphologies are still highly asymmetric, but the same structures recur at every orbital period, making the morphology more regular. Flared accretion disks, with a (sub-)Keplerian velocity profile, are found to form around the companion in all our models with H I cooling, provided the accretion radius is small enough. The disks have radial sizes ranging from about 0.4 to 0.9 au and masses around 10−7−10−8 M⊙. For the considered wind velocities, mass accretion onto the companion is up to a factor of 2 higher than predicted by the standard Bondi Hoyle Littleton rate, ranging between ~4 to 21% of the AGB wind mass loss rate. The lower the wind velocity at the location of the companion, the larger and the more massive the disk and the higher the mass accretion efficiency. In eccentric systems, the disk size, disk mass, and mass accretion efficiency vary, depending on the orbital phase. Conclusions. H I cooling is an essential ingredient to properly model the medium around the companion where density-enhanced wind structures form and it favours the formation of an accretion disk.

Constraints on the accretion properties of quasi-periodic erupters from GRMHD simulations

Some apparently quiescent supermassive black holes (BHs) at centers of galaxies show quasi-periodic eruptions (QPEs) in the X-ray band, the nature of which is still unknown. A possible origin for the eruptions is an accretion disk. However, the properties of such disks are restricted by the timescales of recurrence and the duration of the flares. In this work, we test the possibility that the temporal properties of known QPEs can be explained by accretion from a compact accretion disk with an outer radius out g and we focus on a particular object, GSN 069. We ran several 3D general relativistic magnetohydrodynamic (GRMHD) simulations with the H-AMR code of thin and thick disks and studied how the initial disk parameters such as thickness, magnetic field configuration, magnetization, and Kerr parameter affect the observational properties of QPEs. We show that accretion onto a slowly rotating BH through a small, moderately thin accretion disk with an initially low plasma beta can explain the observed time between outbursts and the lack of evidence for a variable jet emission. In order to form such a disk, the accreting matter should have a low net angular momentum. A potential source for such low angular momentum matter with a quasi-periodic feeding mechanism might be a tight binary of wind-launching stars. Apart from their primary application, our results can also be useful for general studies of systems with small accretion disks, in which evolution occurs very rapidly so that the disks cannot be considered stationary. For such systems, it is important to understand how the initial conditions affect the results.

Recovering chemical bimodalities in observed edge-on stellar disks: Insights from AURIGA simulations

The well-known bimodal distribution of Milky Way disk stars in the [α/Fe]–metallicity plane is often used to define thick and thin disks. In external edge-on galaxies, there have been attempts to identify this type of bimodality using integral field spectroscopy (IFS) data. However, for unresolved stellar populations, observations only contain integrated information, making these studies challenging. We assessed the ability to recover chemical bimodalities in IFS observations of edge-on galaxies, using 24 Milky Way-mass galaxies from the AURIGA zoom-in cosmological simulations. We first analyzed the distribution of single stellar particles in the [Mg/Fe]–[Fe/H] plane, finding that bimodality is frequent but not ubiquitous and often unclear. Then we produced mock IFS [Mg/Fe] and [Fe/H] maps of galaxies seen edge on, and considered integrated stellar-population properties (projected and spatially binned). We investigated how the distribution of stars in the [Mg/Fe]–[Fe/H] plane is affected by edge-on projection and spatial binning. Bimodality is preserved, while distributions change their shapes. Naturally, broad distributions of individual star particles are narrowed into smaller [Mg/Fe] and [Fe/H] ranges for spatial bins. We observe continuous distributions from high [Mg/Fe] and low [Fe/H], to lower [Mg/Fe] values and higher [Fe/H]. Despite being continuous, these distributions are bimodal in most cases. The overlap in [Fe/H] is small, and different [Mg/Fe] components show up as peaks instead of sequences (even when the latter are present for individual particles). The larger the spatial bins, the narrower the [Mg/Fe]–[Fe/H] distribution. This narrowing helps amplify the density of different [Mg/Fe] peaks, often leading to a clearer bimodality in mock IFS observations than for original star particles. We also assessed the correspondence of chemical bimodalities with the distinction between geometric thick and thin disks. Their individual particles have different distributions, but mostly overlap in [Mg/Fe] and [Fe/H]. However, integrated properties of geometric thick and thin disks in mock maps do mostly segregate into different regions of the [Mg/Fe]–[Fe/H] plane. In bimodal distributions, they correspond to the two distinct peaks. Our results show that this approach can be used for bimodality studies in future IFS observations of edge-on external galaxies.

Energy-dependent and Energy-integrated Two-moment General-relativistic Neutrino Transport Simulations of a Hypermassive Neutron Star

We compare two-moment-based energy-dependent and three variants of energy-integrated neutrino transport general-relativistic magnetohydrodynamics simulations of a hypermassive neutron star. To study the impacts due to the choice of the neutrino transport schemes, we perform simulations with the same setups and input neutrino microphysics. We show that the main differences between energy-dependent and energy-integrated neutrino transport are found in the disk and ejecta properties, as well as in the neutrino signals. The properties of the disk surrounding the neutron star and the ejecta in energy-dependent transport are very different from the ones obtained using energy-integrated schemes. Specifically, in the energy-dependent case, the disk is more neutron-rich at early times and becomes geometrically thicker at later times. In addition, the ejecta is more massive and, on average, more neutron-rich in the energy-dependent simulations. Moreover, the average neutrino energies and luminosities are about 30% higher. Energy-dependent neutrino transport is necessary if one wants to better model the neutrino signals and matter outflows from neutron star merger remnants via numerical simulations.