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A new particle-based code for Lagrangian stochastic models applied to stellar turbulent convection
No full textContext. The inclusion of convection in stellar evolution models, mostly based on mixing length theories, lacks realism, especially near convective-radiative interfaces. Furthermore, the interaction of convection with oscillations is poorly understood, giving rise to surface effects that currently prevent us from accurately predicting seismic frequencies, and therefore from fully exploiting the asteroseismic data of low-mass stars.
Aims. Our aim was to develop a new formalism to model the one-point statistics of stellar convection, to implement it in a new numerical code, and to validate this implementation against benchmark cases.
Methods. This new formalism is based on Lagrangian probability density function (PDF) methods, where a Fokker-Planck equation for the PDF of particle-based turbulent properties is integrated in time. The PDF equation was established so that the underlying transport equations for all first- and second-order moments of the turbulent flow are identical to the exact ones stemming from first principles. We then developed a Monte Carlo implementation of this method, where the flow is represented by a large number of notional particles acting as realisations of the PDF. Notional particles interact with each other through the time- and space-dependent mean flow, which is estimated from the particle realisations through a scheme similar to smoothed particle hydrodynamics.
Results. We established a model for the evolution of turbulent properties along Lagrangian trajectories applicable to stellar turbulent convection, with the minimum number of physical assumptions necessary to close the system. In particular, no closure is needed for the non-linear advection terms, which are included exactly through the Lagrangian nature of the formalism. The numerical implementation of this new formalism allows us to extract time-dependent maps of the statistical properties of turbulent convection in a way that is not possible in grid-based large-eddy simulations, in particular the turbulent pressure, Reynolds stress tensor, internal energy variance and convective flux
SDSS-V LVM: Resolving physical conditions in the Trifid Nebula
No full textAims. The chemical abundance of the interstellar medium sets the initial conditions for star formation and provides a probe of chemical galaxy evolution models. However, unresolved inhomogeneities in the electron temperature can lead to a systematic underestimation of the abundances. We aim to directly test this effect.
Methods. We used the SDSS-V Local Volume Mapper to spatially map the physical conditions of the Trifid Nebula (M 20), a Galactic H I
Solving multi-objective optimization problem in Bipolar Hesitant Fuzzy environment
No full textMulti-objective optimization problems are pervasive in various fields, ranging from engineering and economics to environmental management and decision-making processes. These problems involve the simultaneous optimization of multiple conflicting objectives, often leading to complex and non-linear relationships between decision variables. To tackle such intricate problems, this article introduces a novel approach: Bipolar Hesitant Fuzzy Optimization (BHFO) method. This method extends traditional fuzzy, hesitant fuzzy and bipolar fuzzy optimization techniques by incorporating bipolar hesitant fuzzy sets (BHFS), which allow decision-makers to assign degrees of hesitation and bipolarity to their preferences, reflecting the inherent uncertainty and ambiguity associated with real-world decision-making. This approach recognizes that decision-makers may not always be completely certain about their preferences, which is a common scenario in practical multi-objective optimization problems. In this article, we present the theoretical foundations of the BHFO method, including the representation of the parameter as generalized bipolar parabolic fuzzy numbers and operations on these numbers. The proposed approach empowers decision-makers to navigate the complexities of multi-objective optimization problems effectively, accommodating hesitant and bipolar preferences. Furthermore, we illustrate the application of the BHFO method by solving multi objective production planning problem and the result is compared with the other existing methods
Structural colour and photonic mechanisms in the blow flies
No full textStructural colours in natural organisms are created by complex photonic architectures giving rise to remarkable visual appearances. In arthropods, these structures are usually made of biopolymers and comprise photonic crystals. They are often iridescent, i.e., their colours depend on the incidence and observation angles. Despite the interest of the scientific community in a large variety of species including those belonging to butterflies and beetles, some orders such as dipterans have been overlooked so far. In this work, the structural colours from the abdomens of two dipteran species, namely Calliphora vicina and Lucilia richardsi blow flies, with different displayed colours were investigated by spectrophotometry and optical simulations. Using electron microscopy, we identified multilayer photonic structures as the primary mechanism responsible for their visual appearances, with possible additional thin-film interference in C. vicina. In addition, the dipterans’ colours were analysed in terms of chromaticity as well as with respect to the visual sensitivities of the species and the ones of some of their predators. The reflectance spectra of the blow flies investigated were found to correlate with high absorption by their own and their predators’ photoreceptors. These findings indicate that structural colouration in blow flies may influence not only communication with conspecifics but also interactions with predators
Efficient modeling of Lyman-
No full textThe Lyman-α forest opacity fluctuations observed from high-redshift quasar spectra have been proven to be extremely successful in probing the late phase of the reionization epoch. For ideal modeling of these opacity fluctuations, one of the main challenges is to satisfy the extremely high dynamic range requirements of the simulation box, resolving the Lyman-α forest while probing the large cosmological scales. In this study, we adopted an efficient approach to model Lyman-α opacity fluctuations in a coarse simulation volume, utilizing the semi-numerical reionization model SCRIPT (including inhomogeneous recombination and radiative feedback) integrated with a realistic photoionization background fluctuation generating model. Our model crucially incorporates ionization and temperature fluctuations, which are consistent with the reionization model. After calibrating our method with respect to high-resolution full hydrodynamic simulation, Nyx, we compared the models with available observational data at the redshift range, z = 5.0 − 6.1. With a fiducial reionization model (reionization end at z = 5.8), we demonstrated that the observed scatter in the effective optical depth can be matched reasonably well by tuning the free parameters of our model, (i.e., the effective ionizing photon mean free path and the mean photoionization rate). We further pursued an MCMC-based parameter space exploration, utilizing the available data to put constraints on the above free parameters. Our estimation prefers a slightly higher photoionization rate and slightly lower mean free path than the previous studies, which is also a consequence of temperature fluctuations. This study holds significant promise for efficiently extracting important physical information about the Epoch of Reionization, utilizing the wealth of available and upcoming observational data
Life in the dark
No full textContext. Free-floating (rogue) planets are thought to be numerous in the Galaxy and may retain their moons after ejection from their natal systems. If those satellites acquire or preserve orbital eccentricity, tidal dissipation can provide a long-lasting internal heat source, potentially creating urable environments (capable of enabling abiogenesis) in the absence of stellar radiation.
Aims. We explore (i) whether moons remain dynamically bound to planets expelled by a core-collapse (Type II) supernova, (ii) how the explosion reshapes their orbits, and (iii) under which circumstances tidal heating can sustain urable subsurface oceans that meet the minimal conditions for life to originate.
Methods. We carried out 4412 three-dimensional N-body simulations with an 8th-order Runge–Kutta scheme, modelling homologous stellar mass loss for progenitors of 10 M⊙. Post-explosion orbital elements of single moons and resonant moon systems were analysed, and tidal heating power was estimated with a constant phase-lag prescription for several tidal dissipation functions and moon densities.
Results. All simulated moons survive the supernova and remain bound to their planets. The explosion excites moon eccentricities up to ≃7 × 10−4 and ≃3 × 10−3 for single moons of planets with circular and eccentric orbits, respectively. For resonant pairs, an eccentricity of ≲2 × 10−2 is preserved. The semi-major axis of the moons changes by ≲0.2%. For 12–15% of cases – preferentially moons at a ≤ 15 Rp and with e ≥ 10−3 – the specific tidal heating power lies between 0.1 and 10 times what is estimated on Europa or Enceladus, sufficient to maintain liquid oceans beneath an ice crust. Eccentricity damping timescales exceed the age of the Solar System for a ≥ 10 Rp, implying billions of years of continuous heating on the moons.
Conclusions. Moons of rogue planets ejected via Type II supernova explosions are both dynamically stable and, in a significant minority of configurations, tidally active enough to host long-lived subsurface oceans. Such worlds represent promising targets for future searches for extraterrestrial life
COSMOS2025: The COSMOS-Web galaxy catalog of photometry, morphology, redshifts, and physical parameters from JWST, HST, and ground-based imaging
No full textWe present COSMOS2025, the COSMOS-Web catalog of photometry, morphology, photometric redshifts, and physical parameters for more than 700 000 galaxies in the Cosmic Evolution Survey (COSMOS) field. This catalog is based on our James Webb Space Telescope 255 h COSMOS-Web program, which provides deep near-infrared imaging in four NIRCam (F115W, F150W, F277W, F444W) and one MIRI (F770W) filter over the central ~0.54 deg2 (~0.2 deg2 for MIRI) in COSMOS. These data are combined with ground- and space-based data to derive photometric measurements of NIRCam-detected sources using both fixed-aperture photometry (on the space-based bands) and a profile-fitting technique on all 37 bands spanning 0.3 μm to 8 μm. We provide morphology for all sources from complementary techniques including profile fitting and machine-learning classification. We derive photometric redshifts, physical parameters, and non-parametric star formation histories from spectral energy distribution (SED) fitting. The catalog has been extensively validated against previous COSMOS catalogs and other surveys. Photometric redshift accuracy measured using spectroscopically confirmed galaxies out to z ~ 9 reaches σMAD = 0.012 at mF444W < 28 and remains at σMAD ≲ 0.03 as a function of magnitude, color, and galaxy type. This represents a factor of ~2 improvement at 26 AB mag compared to COSMOS2020. The catalog is approximately 80% complete at log(M⋆/M⊙) ~ 9 at z ~ 10 and at log(M⋆/M⊙) ~ 7 at z ~ 0.2, representing a gain of 1 dex compared to COSMOS2020. COSMOS2025 represents the definitive COSMOS-Web catalog. It is provided with complete documentation, together with redshift probability distributions, and it is ready for scientific exploitation today
Velocity field of an active region filament from GRIS infrared He I and IRIS ultraviolet observations
No full textContext. Plasma flow measurements in solar active region filaments are rare, particularly in the infrared and ultraviolet ranges that probe the chromosphere and transition region. In addition, previous studies generally focused on prominences and filaments near the solar limb.
Aims. This study presents a multi-wavelength, multi-instrument analysis of an active region filament observed on the solar disk on November 9 and 10, 2020. Our goal is to characterize the plasma flows in the filament using spectroscopic measurements in both the infrared and ultraviolet spectral ranges. This is important for understanding the mechanisms for filament support, mass loading, and energy balance. Furthermore, this also offers observational benchmarks for filament modeling and simulations.
Methods. Spectra from the IRIS satellite, including the Mg I
Establishing a relationship between the cosmological 21 cm power spectrum and interferometric closure phases
No full textContext. Measurements of the cosmic 21 cm background need to achieve a high dynamic range to isolate it from bright foreground emissions. Instrumental calibration inaccuracies can compromise the spectral fidelity of the smooth foreground continuum, thereby limiting the dynamic range of the measurement and potentially precluding the detection of the cosmic line signal. In light of this calibration challenge, recent work has proposed using the calibration-independent closure phase to search for the spectral fluctuations of the cosmic 21 cm background signal. However, so far there has been only a heuristic understanding of the mapping between closure phases and the cosmological power spectrum of the background line signal.
Aims. This work aims to establish a more accurate mathematical relationship between closure phase measurements and the cosmological power spectrum of the background line signal.
Methods. Building on previous work, we treat the cosmic signal component as a perturbation to the closure phase and use a delay spectrum approach to estimate the power of the perturbing signal. We establish the relationship between this estimate and the cosmological power spectrum using standard Fourier transform techniques, and validate it using simulated observations from the Hydrogen Epoch of Reionization Array (HERA).
Results. We find that, statistically, the power spectrum estimate from closure phases is approximately equal to the true cosmological power spectrum convolved with a foreground-dependent window function, provided that the signal-to-foreground ratio is small. Compared with standard approaches, the foreground dependence of the window function results in an increased amount of mode-mixing and a more pronounced proliferation of foreground power along the line-of-sight dimension of the cylindrical power spectrum. These effects can be mitigated by flagging instances where the window function is broad. Crucial to gaining the necessary sensitivity, this mapping will allow us to average the measurements of closure triads of different shapes based on their imprint in cylindrical Fourier space
Constraints on the
No full textContext. JWST provides a unique dataset for studying the earliest stages of reionisation at z > 9, promising insights into the first galaxies. Many JWST/NIRSpec prism spectra of z > 5 galaxies have revealed smooth Lyman-alpha breaks, implying damping wing scattering by neutral hydrogen.
Aims. We investigate what current prism spectra imply about the intergalactic medium (IGM) at z > 6 and how best to use NIRSpec spectra to recover IGM properties. We use a sample of 99 z ∼ 5.5 − 13 galaxies with high S/N prism spectra in the public archive, including 12 at z > 10.
Methods. We analyse these spectra using damping wing sightlines from inhomogeneous reionising IGM simulations, mapping between the distance of a source from the neutral IGM and the average IGM neutral fraction. We marginalise over absorption by local neutral hydrogen around the galaxies and Lyman-alpha emission.
Results. We observe a decline in the median and variance of flux around the Lyα break with increasing redshift, consistent with an increasingly neutral IGM, as ionized regions become smaller and rarer. At z ≳ 9 the spectra become consistent with an almost fully neutral IGM. We find S/N > 15 per pixel is required to robustly estimate IGM properties from prism spectra. We fit a sub-sample of high S/N spectra and infer mean IGM neutral fractions of (> 0.70 excluding GNz11) at z ≈ 6.5, 9.3. We also investigate local HI absorption, finding a median column density of log10NH