Disk Properties Research Articles

Probing Accretion Physics with Gravitational Waves

Gravitational-wave observations of extreme mass ratio inspirals (EMRIs) offer the opportunity to probe the environments of active galactic nuclei (AGN) through the torques that accretion disks induce on the binary. Within a Bayesian framework, we study how well such environmental effects can be measured using gravitational wave observations from the Laser Interferometer Space Antenna (LISA). We focus on the torque induced by planetary-type migration on quasicircular inspirals, and use different prescriptions for geometrically thin and radiatively efficient disks. We find that LISA could detect migration for a wide range of disk viscosities and accretion rates, for both $\alpha$ and $\beta$ disk prescriptions. For a typical EMRI with masses $50M_\odot+10^6M_\odot$, we find that LISA could distinguish between migration in $\alpha$ and $\beta$ disks and measure the torque amplitude with $\sim 20\%$ relative precision. Provided an accurate torque model, we also show how to turn gravitational-wave measurements of the torque into constraints on the disk properties. Furthermore, we show that, if an electromagnetic counterpart is identified, the multimessenger observations of the AGN EMRI system will yield direct measurements of the disk viscosity. Finally, we investigate the impact of neglecting environmental effects in the analysis of the gravitational-wave signal, finding 3$\sigma$ biases in the primary mass and spin, and showing that ignoring such effects can lead to false detection of a deviation from general relativity. This work demonstrates the scientific potential of gravitational observations as probes of accretion-disk physics, accessible so far through electromagnetic observations only.

Disk or Companion: Characterizing Excess Infrared Flux in Seven White Dwarf Systems with Near-infrared Spectroscopy

Excess infrared flux from white dwarf stars is likely to arise from a dusty debris disk or a cool companion. In this work, we present near-infrared spectroscopic observations with Keck/MOSFIRE, Gemini/GNIRS, and Gemini/Flamingos-2 of seven white dwarfs with infrared excesses identified in previous studies. We confirmed the presence of dust disks around four white dwarfs (Gaia J0611–6931, Gaia J0006+2858, Gaia J2100+2122, and WD 0145+234) as well as two new white dwarf–brown dwarf pairs (Gaia J0052+4505 and Gaia J0603+4518). In three of the dust disk systems, we detected for the first time near-infrared metal emissions (Mg i, Si I, and possibly Fe I) from a gaseous component of the disk. We developed a new Markov Chain Monte Carlo framework to constrain the geometric properties of each dust disk. In three systems, the dust disk and the gas disk appear to coincide spatially. For the two brown dwarf–white dwarf pairs, we identified broad molecular absorption features typically seen in L dwarfs. The origin of the infrared excess around Gaia J0723+6301 remains a mystery. Our study underlines how near-infrared spectroscopy can be used to determine sources of infrared excess around white dwarfs, which has now been detected photometrically in hundreds of systems.

The GRAVITY young stellar object survey

Context. T Tauri stars are known to be the cradle of planet formation. Most exoplanets discovered to date lie at the very inner part of the circumstellar disk (<1 au). The innermost scale of young stellar objects is therefore a compelling region to be addressed, and long-baseline interferometry is a key technique to unveil their mysteries. Aims. We aim to spatially and spectrally resolve the innermost scale (≤1 au) of the young stellar system CI Tau to constrain the inner disk properties and better understand the magnetospheric accretion phenomenon. Methods. The high sensitivity offered by the combination of the four 8-m class telescopes of the Very Large Telescope Interferometer (VLTI) allied with the high spectral resolution (R ~ 4000) of the K-band beam combiner GRAVITY offers a unique capability to probe the sub-au scale of the CI Tau system, tracing both dust (continuum) and gas (Brγ line) emission regions. We developed a physically motivated geometrical model to fit the interferometric observables – visibilities and closure phases (CP) – and constrained the physical properties of the inner dusty disk. The continuum-corrected pure line visibilities have been used to estimate the size of the Hydrogen I Brγ emitting region. Results. From the K-band continuum study, we report a highly inclined (i ~ 70°) resolved inner dusty disk, with an inner edge located at a distance of 21 ± 2 R★ from the central star, which is significantly larger than the dust sublimation radius (Rsub = 4.3 to 8.6 R★). The inner disk appears misaligned compared to the outer disk observed by ALMA and the non-zero closure phase indicates the presence of an asymmetry that could be reproduced with an azimuthally modulated ring with a brighter south-west side. From the differential visibilities across the Brγ line, we resolved the line-emitting region, and measured a size of 4.8- 1.0+ 0.8 R★. Conclusions. The extended inner disk edge compared to the dust sublimation radius is consistent with the claim of an inner planet, CI Tau b, orbiting close in. The inner-outer disk misalignment may be induced by gravitational torques or magnetic warping. The size of the Brγ emitting region is consistent with the magnetospheric accretion process. Assuming it corresponds to the magnetospheric radius, it is significantly smaller than the co-rotation radius (Rcor= 8.8 ± 1.3 R★), which suggests an unstable accretion regime that is consistent with CI Tau being a burster.

Tunable Physical Properties of VSe2 hexagonal disks

Transition metal dichalcogenides (TMDs) belonging to the family of two-dimensional (2D) materials have received a great deal of research interest over the past few decades due to their unique electronic, optical, mechanical, and magnetic properties as compared to their three-dimensional (3D) counterparts. Magnetism in reduced dimensions, such as in 2D materials, is an underexplored phenomenon, though it has potential for numerous applications, including the fabrication of memory devices and spintronics devices. In this work, we report the structural, morphological, and magnetic characterization of hexagonal disks of VSe2 prepared by the hydrothermal method. The structural and morphological characterization confirms the formation of hexagonal disks of 1T-VSe2. The magnetic measurements show that hexagonal VSe2 is paramagnetic in the entire range of this study, from 5–300 K, with an S–type isothermal magnetization behavior at low temperatures. The field cooling (FC) data collected at an applied magnetic field of 0.5T reveals a hump at a temperature of 118 K, which can be correlated to the charge density wave (CDW) transition point. The increase in CDW transition temperature from 107 K (bulk) to 118 K indicates a decrease in VSe2 thickness. The detailed analysis shows a tunability in the physical properties of VSe2 with its thickness.

Transition disc nature of post-AGB binary systems confirmed by mid-infrared interferometry

Context. Many properties of circumbinary discs around evolved post-asymptotic giant branch (post-AGB) binary systems are similar to those of protoplanetary discs around young stars. The deficits of near-infrared (near-IR) flux in the spectral energy distributions (SEDs) of these systems hints towards large dust-free cavities that are reminiscent of transition discs as are commonly observed around young stars. Aims. We aim to assess the size of the inner rim of six post-AGB binary systems with lack in the near-IR like this. We used resolved mid-infrared (mid-IR) high-angular resolution observations of VLTI/MATISSE and VLTI/MIDI. The inner rim of only one such system was previously resolved. We compared these inner rim sizes to five systems with available MATISSE data that were identified to host a disc starting at the dust sublimation radius. Methods. We used geometric ring models to estimate the inner rim sizes, the relative flux contributions of the star, the ring, and an over-resolved emission, the orientation of the ring, and the spectral dependences of the components. Results. We find that the inner dust rims of the targets with a lack of near-IR excess in their SEDs are ∼2.5 to 7.5 times larger than the theoretical dust sublimation radii, and inner rim sizes of the systems that do not show this deficit are similar to those of their theoretical dust sublimation radii. The physical radii of the inner rims of these transition discs around post-AGB binaries are 3–25 au, which are larger than the disc sizes inferred for transition discs around young stars with VLTI/MIDI. This is due to the higher stellar luminosities of post-AGB systems compared to young stars, implying larger dust sublimation radii and thus larger physical inner radii of the transition disc. Conclusions. With mid-IR interferometric data, we directly confirm the transition disc nature of six circumbinary discs around post-AGB binary systems. Future observational and modelling efforts are needed to progress in our understanding of the structure, origin, and evolution of these transition discs.

GaiaData Release 3

Context.The motion of stars has been used to reveal details of the complex history of the Milky Way, in constant interaction with its environment. Nevertheless, to reconstruct the Galactic history puzzle in its entirety, the chemo-physical characterisation of stars is essential. PreviousGaiadata releases were supported by a smaller, heterogeneous, and spatially biased mixture of chemical data from ground-based observations.Aims.GaiaData Release 3 opens a new era of all-sky spectral analysis of stellar populations thanks to the nearly 5.6 million stars observed by the Radial Velocity Spectrometer (RVS) and parametrised by the GSP-Spec module. In this work, we aim to demonstrate the scientific quality ofGaia’s Milky Way chemical cartography through a chemo-dynamical analysis of disc and halo populations.Methods.Stellar atmospheric parameters and chemical abundances provided byGaiaDR3 spectroscopy are combined with DR3 radial velocities and EDR3 astrometry to analyse the relationships between chemistry and Milky Way structure, stellar kinematics, and orbital parameters.Results.The all-skyGaiachemical cartography allows a powerful and precise chemo-dynamical view of the Milky Way with unprecedented spatial coverage and statistical robustness. First, it reveals the strong vertical symmetry of the Galaxy and the flared structure of the disc. Second, the observed kinematic disturbances of the disc – seen as phase space correlations – and kinematic or orbital substructures are associated with chemical patterns that favour stars with enhanced metallicities and lower [α/Fe] abundance ratios compared to the median values in the radial distributions. This is detected both for young objects that trace the spiral arms and older populations. Severalα, iron-peak elements and at least one heavy element trace the thin and thick disc properties in the solar cylinder. Third, young disc stars show a recent chemical impoverishment in several elements. Fourth, the largest chemo-dynamical sample of open clusters analysed so far shows a steepening of the radial metallicity gradient with age, which is also observed in the young field population. Finally, theGaiachemical data have the required coverage and precision to unveil galaxy accretion debris and heated disc stars on halo orbits through their [α/Fe] ratio, and to allow the study of the chemo-dynamical properties of globular clusters.Conclusions.GaiaDR3 chemo-dynamical diagnostics open new horizons before the era of ground-based wide-field spectroscopic surveys. They unveil a complex Milky Way that is the outcome of an eventful evolution, shaping it to the present day.

Extending the theory of propagating fluctuations: the first fully relativistic treatment and analytical Fourier–Green’s functions

ABSTRACT The aperiodic variability ubiquitously observed from accreting black hole X-ray binary systems is generally analysed within the framework of the so-called ‘theory of propagating fluctuations’. In this paper we derive the Fourier transforms of the Green’s function solutions of the thin disc equations. These solutions suffice to describe all possible solutions through standard convolution techniques. Solutions are found for both Newtonian discs and general relativistic solutions with a vanishing ISCO stress. We use this new relativistic theory to highlight the Kerr black hole spin dependence of a number of observable variability properties of black hole discs. The phase lags, coherence, and power density spectra of Kerr discs are shown to be strong functions of black hole spin. Observations of the aperiodic variability of black hole accretion sources may now, at least in principle, offer a new avenue to directly constrain black hole spins.

Super-spinning Kerr attractors: Observational signatures of accretion tori and proto-jets

We study accretion tori and proto-jets in the field of central Kerr super-spinning attractors, exposing distinctions between Kerr naked singularities (NSs) and black holes (BHs). We focus on the spacetime regions very close to the central singularity, interior of the ergoregion, especially for slowly spinning NSs, where repulsive gravity effects emerge, discussing the causal structure in relation to tori contained, partially contained and confined in the ergoregion. We explore particularly regions close to the attractor rotational axis and the poles, where very slowly spinning tori, with momenta ℓ≈0, and axial cusp, constrained by the light surfaces, are relevant. Proto-jets (constraining jet emission) proved to be a signature in comparison with BH case, pointing out the emergence of very fast spinning tori in the ergoregion, very slow tori, double tori with internal cusp, and the presence of an axial cusp. The accretion disks properties point out very faster spinning attractors (extremely super spinning NSs). Providing distinguishable physical characteristics of jets and accretion tori, the differences between the BH and NS accretion scenarios, emerging from this analysis, constitute astrophysical tracers distinguishing NSs from BHs, and possible strong NSs observational signature of the primordial Kerr superspinars predicted by string theory.

Toward a population synthesis of disks and planets

Aims. We want to find the distribution of initial conditions that best reproduces disc observations at the population level. Methods. We first ran a parameter study using a 1D model that includes the viscous evolution of a gas disc, dust, and pebbles, coupled with an emission model to compute the millimetre flux observable with ALMA. This was used to train a machine learning surrogate model that can compute the relevant quantity for comparison with observations in seconds. This surrogate model was used to perform parameter studies and synthetic disc populations. Results. Performing a parameter study, we find that internal photoevaporation leads to a lower dependency of disc lifetime on stellar mass than external photoevaporation. This dependence should be investigated in the future. Performing population synthesis, we find that under the combined losses of internal and external photoevaporation, discs are too short lived. Conclusions. To match observational constraints, future models of disc evolution need to include one or a combination of the following processes: infall of material to replenish the discs, shielding of the disc from internal photoevaporation due to magnetically driven disc winds, and extinction of external high-energy radiation. Nevertheless, disc properties in low-external-photoevaporation regions can be reproduced by having more massive and compact discs. Here, the optimum values of the α viscosity parameter lie between 3 × 10−4 and 10−3 and with internal photoevaporation being the main mode of disc dispersal.

Изучение структуры и кинематики Галактики по данным о классических цефеидах

Classical Cepheids are important for studying the properties of the galactic disk, the spiral structure of the Galaxy, its rotation, evolution, etc. This article provides an overview of the main results of studying the structure and kinematics of the Galaxy, which were obtained by various scientific teams using classical Cepheids. The main attention is paid to the results of studying the Galaxy obtained by the authors of this work. The following issues are considered: a) the nature of the spatial distribution of Cepheids in the Galaxy, both near the equatorial plane of the Galaxy and in the vertical direction; in particular, the relationship of Cepheids with the large-scale Warp of the galactic disk is considered; b) the use of young Cepheids to refine the parameters of the spiral pattern of the Galaxy; c) the use of young Cepheids to refine the rotation parameters Galaxies and perturbation velocities caused by the influence of the galactic spiral density wave.

Morphology of the gas-rich debris disk around HD 121617 with SPHERE observations in polarized light

Context. Debris disks are the signposts of collisionally eroding planetesimal circumstellar belts, whose study can put important constraints on the structure of extrasolar planetary systems. The best constraints on the morphology of such disks are often obtained from spatially resolved observations in scattered light. In this paper, we investigate the young (~16 Myr) bright gas-rich debris disk around HD 121617. Aims. We use new scattered light observations from VLT/SPHERE to characterize the morphology and the dust properties of the debris disk. From these properties, we can then derive constraints on the physical and dynamical environment of this system, for which significant amounts of gas have been detected. Methods. The disk morphology is constrained by linear polarimetric observations in the J band. Based on our modeling results and archival photometry, we also model the spectral energy distribution (SED) to put constraints on the total dust mass and dust size distribution. Finally, we explore different scenarios that could explain these new constraints. Results. We present the first resolved image in scattered light of the debris disk around HD 121617. We fit the morphology of the disk, finding a semi-major axis of 78.3 ± 0.2 au, an inclination of 43.1 ± 0.2°, and a position angle of the major axis with respect to north of 239.8 ± 0.3°, which is compatible with the previous continuum and CO detection with ALMA. Our analysis shows that the disk has a very sharp inner edge, possibly sculpted by a yet-undetected planet or gas drag. While less sharp, its outer edge is steeper than expected for an unperturbed disk, which could also be due to a planet or gas drag, but future observations probing the system farther from the main belt would help explore this possibility further. The SED analysis leads to a dust mass of 0.21 ± 0.02 M⊕ and a minimum grain size of 0.87 ± 0.12 μm, smaller than the blowout size by radiation pressure, which is not unexpected for very bright collisionally active disks.

Testing the Interaction between a Substellar Companion and a Debris Disk in the HR 2562 System

The HR 2562 system is a rare case where a brown dwarf companion resides in a cleared inner hole of a debris disk, offering invaluable opportunities to study the dynamical interaction between a substellar companion and a dusty disk. We present the first ALMA observation of the system as well as the continued Gemini Planet Imager monitoring of the companion’s orbit with six new epochs from 2016 to 2018. We update the orbital fit, and in combination with absolute astrometry from GAIA, place a 3σ upper limit of 18.5 M J on the companion’s mass. To interpret the ALMA observations, we used radiative transfer modeling to determine the disk properties. We find that the disk is well resolved and nearly edge-on. While the misalignment angle between the disk and the orbit is weakly constrained, due to the short orbital arc available, the data strongly support a (near) coplanar geometry for the system. Furthermore, we find that the models that describe the ALMA data best have inner radii that are close to the companion’s semimajor axis. Including a posteriori knowledge of the system’s SED further narrows the constraints on the disk’s inner radius and places it at a location that is in reasonable agreement with (possibly interior to) predictions from existing dynamical models of disk truncation by an interior substellar companion. HR 2562 has the potential over the next few years to become a new test bed for dynamical interaction between a debris disk and a substellar companion.

Ultrathin GaN quantum wells in AlN nanowires for UV-C emission

Molecular beam epitaxy growth and optical properties of GaN quantum disks in AlN nanowires were investigated, with the purpose of controlling the emission wavelength of AlN nanowire-based light emitting diodes. Besides GaN quantum disks with a thickness ranging from 1 to 4 monolayers, a special attention was paid to incomplete GaN disks exhibiting lateral confinement. Their emission consists of sharp lines which extend down to 215 nm, in the vicinity of AlN band edge. The room temperature cathodoluminescence intensity of an ensemble of GaN quantum disks embedded in AlN nanowires is about 20% of the low temperature value, emphasizing the potential of ultrathin/incomplete GaN quantum disks for deep UV emission.

Modelling dark matter halo spin using observations and simulations: application to UGC 5288

ABSTRACT Dark matter (DM) halo properties are extensively studied in cosmological simulations but are very challenging to estimate from observations. The DM halo density profile of observed galaxies is modelled using multiple probes that trace the DM potential. However, the angular momentum distribution of DM halos is still a subject of debate. In this study, we investigate a method for estimating the halo spin and halo concentration of low surface brightness (LSB), gas-rich dwarf barred galaxy UGC 5288, by forward modelling disc properties derived from observations – stellar and gas surface densities, disc scalelength, H i rotation curve, bar length, and bar ellipticity. We combine semi-analytical techniques, N-body/SPH, and cosmological simulations to model the DM halo of UGC 5288 with both a cuspy Hernquist profile and a flat-core pseudo-isothermal profile. We find that the best match with observations is a pseudo-isothermal halo model with a core radius of rc = 0.23 kpc and halo spin of λ = 0.08 at the virial radius. Although our findings are consistent with previous core radius estimates of the halo density profile of UGC 5288, as well as with the halo spin profiles of similar mass analogues of UGC 5288 in the high-resolution cosmological-magneto-hydrodynamical simulation TNG50, there still remain some uncertainties as we are limited in our knowledge of the formation history of the galaxy. Additionally, we find that the inner halo spin (r < 10 kpc) in barred galaxies is different from the unbarred ones, and the halo spin shows weak correlations with bar properties.

Multi-wavelength aperture polarimetry of debris disc host stars

ABSTRACT Debris discs around main sequence stars have been extensively characterized from infrared to millimetre wavelengths through imaging, spectroscopic, and total intensity (scattered light and/or thermal emission) measurements. Polarimetric observations have only been used sparingly to interpret the composition, structure, and size of dust grains in these discs. Here, we present new multiwavelength aperture polarization observations with parts-per-million sensitivity of a sample of twelve bright debris discs, spanning a broad range of host star spectral types, and disc properties. These measurements were mostly taken with the HIgh Precision Polarimetric Instrument on the Anglo-Australian Telescope. We combine these polarization observations with the known disc architectures and geometries of the discs to interpret the measurements. We detect significant polarization attributable to circumstellar dust from HD 377 and HD 39060, and find tentative evidence for HD 188228 and HD 202628.

Mid-infrared blends and continuum signatures of dust drift and accretion in protoplanetary disks

Context. The mid-infrared (MIR) emission of molecules such as H2O, HCN, OH, CO2, and C2H2, has been identified in the Spitzer Infrared Spectrograph (IRS) spectra of many protoplanetary disks. According to the modelling results, the blend strengths are affected by different disk properties such as the gas mass and dust content in the disks. An observational correlation between HCN and water blend fluxes has been noted, specifically related to a changing disk gas mass. Aims. We aim to find out whether the explanation for the observed flux correlation between HCN and water in the MIR could also be attributed to other properties and processes taking place in disks, such as the evolution of dust grains. We also consider what the consequences of these results would be in relation to the disk evolution. Methods. We used pre-existing ProDiMo radiation thermal-chemical disk models exploring a range of properties such as the disk gas mass, disk inner radius, dust size power law distribution, and, finally, time-dependent dust evolution. From these models, we computed the MIR fluxes of HCN and H2O blends. Simultaneously, we derived the spectral indices from the simulated spectral energy distributions (SEDs) in the Spitzer IRS regime. Finally, we compared these quantities with the observed data. Results. The MIR blend fluxes correlation between HCN and water can be explained as a consequence of dust evolution, namely, changes in the dust MIR opacity. Other disk properties, such as the disk inner radius and the disk flaring angle, can only partially cover the dynamic range of the HCN and water blend observations. At the same time, the dynamic range of the MIR SED slopes is better reproduced by the disk structure (e.g. inner radius, flaring) than by the dust evolution. Our model series do not reproduce the observed trend between continuum flux at 850 µm and the MIR HCN/H2O blend ratio. However, our models show that this continuum flux is not a unique indicator of disk mass and it should therefore be used jointly with complementary observational data for optimal results. Conclusions. The presence of an anti-correlation between MIR H2O blend fluxes and the MIR SED is consistent with a scenario where dust evolves in disks, producing lower opacity and stronger features in the Spitzer spectral regime, while the gas eventually becomes depleted at a later stage, leaving behind an inner cavity in the disk.

Analysis of metallicities of open clusters in the Galactic disc

ABSTRACT The metallicities of open clusters (OCs) are probes for many Galactic disc properties, such as age-metallicity relation and abundance gradient evolution. In recent years, a large number of newly found OCs or OC candidates have been reported. However, the metallicity values of OCs in the Galactic disc in different works vary from each other. In particular, the cluster metallicities in our previous work (hereafter LISC I), which are determined from Gaia’s photometric data, are obviously smaller than most other catalogues. This work aims to investigate the metallicities of Galactic disc OCs in LISC I. We redetermine the mean metallicities of 79 OCs using the spectroscopic data of Large Sky Area Multi-Object Fiber Spectroscopic Telescope DR8 and get obvious discrepancies between the two works. The causes of the difference are studied by using two different isochrones and uncertainties in colour-magnitude diagram fitting process. We find that the evolutionary models adopted and, to a lesser extent, the fitting methods are mainly responsible for the discrepant values of LISC I metallicities. We also propose a linear relationship to correct for the LISC I metallicity, which should only be used to provide more reliable [Fe/H] values in the absence of spectroscopic determinations.

Analysing the SEDs of protoplanetary disks with machine learning

Context. The analysis of spectral energy distributions (SEDs) of protoplanetary disks to determine their physical properties is known to be highly degenerate. Hence, a full Bayesian analysis is required to obtain parameter uncertainties and degeneracies. The main challenge here is computational speed, as one proper full radiative transfer model requires at least a couple of CPU minutes to compute. Aims. We performed a full Bayesian analysis for 30 well-known protoplanetary disks to determine their physical disk properties, including uncertainties and degeneracies. To circumvent the computational cost problem, we created neural networks (NNs) to emulate the SED generation process. Methods. We created two sets of MCFOST Monte Carlo radiative transfer disk models to train and test two NNs that predict SEDs for continuous and discontinuous disks, with 18 and 26 free model parameters, respectively. A Bayesian analysis was then performed on 30 protoplanetary disks with SED data collected by the FP7-Space DIANA project to determine the posterior distributions of all parameters. We ran this analysis twice, (i) with old distances and additional parameter constraints as used in a previous study, to compare results, and (ii) with updated distances and free choice of parameters to obtain homogeneous and unbiased model parameters. We evaluated the uncertainties in the determination of physical disk parameters from SED analysis, and detected and quantified the strongest degeneracies. Results. The NNs are able to predict SEDs within ~1 ms with uncertainties of about 5% compared to the true SEDs obtained by the radiative transfer code. We find parameter values and uncertainties that are significantly different from previous values obtained by χ2 fitting. Comparing the global evidence for continuous and discontinuous disks, we find that 26 out of 30 objects are better described by disks that have two distinct radial zones. The analysed sample shows a significant trend for massive disks to have small scale heights, which is consistent with lower midplane temperatures in massive disks. We find that the frequently used analytic relationship between disk dust mass and millimetre-flux systematically underestimates the dust mass for high-mass disks (dust mass ≥10−4 M⊙). We determine how well the dust mass can be determined with our method for different numbers of flux measurements. As a byproduct, we created an interactive graphical tool that instantly returns the SED predicted by our NNs for any parameter combination.

Massive pre-main-sequence stars in M17

Context.The young massive-star-forming region M17 contains optically visible massive pre-main-sequence stars that are surrounded by circumstellar disks. Such disks are expected to disappear when these stars enter the main sequence. The physical and dynamical structure of these remnant disks are poorly constrained, especially the inner regions where accretion, photo-evaporation, and companion formation and migration may be ongoing.Aims.We aim to constrain the physical properties of the inner parts of the circumstellar disks of massive young stellar objects B243 (6M⊙) and B331 (12M⊙), two systems for which the central star has been detected and characterized previously despite strong dust extinction.Methods.Two-dimensional radiation thermo-chemical modelling with PRODIMOof double-peaked hydrogen lines of the Paschen and Brackett series observed with X-shooter was used to probe the properties of the inner disk of the target sources. The model was modified to treat these lines. Additionally, the dust structure was studied by fitting the optical and near-infrared spectral energy distribution.Results.B243 features a hot gaseous inner disk with dust at the sublimation radius at ~3 AU. The disk appears truncated at roughly 6.5 AU; a cool outer disk of gas and dust may be present, but it cannot be detected with our data. B331 also has a hot gaseous inner disk. A gap separates the inner disk from a colder dusty outer disk starting at up to ~100 AU. In both sources the inner disk extends to almost the stellar surface. Chemistry is essential for the ionization of hydrogen in these disks.Conclusions.The lack of a gap between the central objects and these disks suggests that they accrete through boundary-layer accretion. This would exclude the stars having a strong magnetic field. Their structures suggest that both disks are transitional in nature, that is to say they are in the process of being cleared, either through boundary-layer accretion, photo-evaporation, or through companion activity.

Preparation and characterization of UHMWPE reinforced with polyester fibers for artificial cervical disc replacement (ACDR)

The purpose of this paper is to report on the preparation and improvement of a biocomposite material made from ultra-high molecular weight polyethylene for the replacement of natural discs. Such replacements are necessary due to intervertebral disc degradation as humans age, which can cause persistent pain due to nerve compression and high friction between vertebrae that can lead to vertebral corrosion. The material was shown to have excellent mechanical properties such as low coefficient of friction, and biocompatibility; however, it degraded with time due to wear failure. Moreover, The wear resistance was related to many factors, such as toughness. In the methodology of the current study, UHMWPE is reinforced with different percent of polyester (2, 4, 6, 8, 10%) to improve the mechanical properties of the polymer disc, thus enhancing its toughness and providing its high bearing ability for the load. The findings revealed that the tensile strength and modulus of elasticity improved by 43.415% and 34.286%, respectively, with the 6% polyester fibers due to the excellent entanglement between the matrix and reinforcing phase. The other mechanical properties, such as flexural strength and modulus, impact strength, fracture toughness, and compression strength, were also enhanced in this study. The highest value at 6% polyester fiber was found to be due to good bonding and adhesion between the polymer and polyester fibers. The Fourier Transformation Spectroscopy (FTIR) showed a shift on some peaks. The originality of this work is that the improvements due to the new bio-composite polymers for artificial implant cervical discs can open many applications in future for these materials.