Phase Curves Research Articles

A search for non-transiting exoplanets with optical light phase curves from TESS Southern ecliptic sectors

ABSTRACT Phased photometric variation provides a method for discovering potential non-transiting exoplanets in high-precision time-series photometry. Applying a Lomb–Scargle algorithm, we search for phased photometric variation in a selection of 140 000 bright dwarf stars with full-frame image light curves from the Southern ecliptic hemisphere of the Transiting Exoplanet Survey Satellite (TESS) mission. We fit the phased photometric variation signal for these candidates using a three-component model comprised of atmospheric reflection/emission, tidal ellipsoidal distortion, and Doppler beaming contributions. We find 27 candidate signals that can be attributed to short-period, massive planets. Our candidates have periods ranging from 0.74 to 1.98 d, and photometric variations with amplitudes ranging from 94 to 528 ppm. The host stars are all bright (9 < T < 11) F- and G-type dwarf stars. We estimate the radial velocity semi-amplitudes to be in excess of 60 m s−1 for each candidate, easily within reach of current high-precision spectrographs. If confirmed, these candidates would be the first non-transiting exoplanets discovered with TESS.

The tidal deformation and atmosphere of WASP-12 b from its phase curve

Context. Ultra-hot Jupiters present a unique opportunity to understand the physics and chemistry of planets, their atmospheres, and interiors at extreme conditions. WASP-12 b stands out as an archetype of this class of exoplanets, with a close-in orbit around its star that results in intense stellar irradiation and tidal effects. Aims. The goals are to measure the planet’s tidal deformation, atmospheric properties, and also to refine its orbital decay rate. Methods. We performed comprehensive analyses of the transits, occultations, and phase curves of WASP-12b by combining new CHEOPS observations with previous TESS and Spitzer data. The planet was modeled as a triaxial ellipsoid parameterized by the second-order fluid Love number of the planet, h2, which quantifies its radial deformation and provides insight into the interior structure. Results. We measured the tidal deformation of WASP-12b and estimated a Love number of h2 = 1.55−0.49+0.45 (at 3.2σ) from its phase curve. We measured occultation depths of 333 ± 24 ppm and 493 ± 29 ppm in the CHEOPS and TESS bands, respectively, while the nightside fluxes are consistent with zero, and also marginal eastward phase offsets. Our modeling of the dayside emission spectrum indicates that CHEOPS and TESS probe similar pressure levels in the atmosphere at a temperature of ~2900 K. We also estimated low geometric albedos of Ag = 0.086 ± 0.017 and Ag = 0.01 ± 0.023 in the CHEOPS and TESS passbands, respectively, suggesting the absence of reflective clouds in the high-temperature dayside of the planet. The CHEOPS occultations do not show strong evidence for variability in the dayside atmosphere of the planet at the median occultation depth precision of 120 ppm attained. Finally, combining the new CHEOPS timings with previous measurements refines the precision of the orbital decay rate by 12% to a value of −30.23 ± 0.82 ms yr−1, resulting in a modified stellar tidal quality factor of Q′★ = 1.70 ± 0.14 × 105. Conclusions. WASP-12 b becomes the second exoplanet, after WASP-103b, for which the Love number has been measured from the effect of tidal deformation in the light curve. However, constraining the core mass fraction of the planet requires measuring h2 with a higher precision. This can be achieved with high signal-to-noise observations with JWST since the phase curve amplitude, and consequently the induced tidal deformation effect, is higher in the infrared.

Main-belt and Trojan asteroid phase curves from the ATLAS survey

ABSTRACT Sparse and serendipitous asteroid photometry obtained by wide field surveys such as the Asteroid Terrestrial-impact Last Alert System (ATLAS) is a valuable resource for studying the properties of large numbers of small Solar System bodies. We have gathered a large data base of ATLAS photometry in wideband optical cyan and orange filters, consisting of 9.6 × 107 observations of 4.5 × 105 main belt asteroids and Jupiter Trojans. We conduct a phase curve analysis of these asteroids considering each apparition separately, allowing us to accurately reject outlying observations and to remove apparitions and asteroids not suitable for phase curve determination. We obtain a data set of absolute magnitudes and phase parameters for over 100 000 selected asteroids observed by ATLAS, $\sim 66\, 000$ of which had sufficient measurements to derive colours in the ATLAS filters. To demonstrate the power of our data set we consider the properties of the Nysa–Polana complex, for which the ATLAS colours and phase parameters trace the S-like and C-like compositions amongst family members. We also compare the properties of the leading and trailing groups of Jupiter Trojans, finding no significant differences in their phase parameters or colours as measured by ATLAS, supporting the consensus that these groups were captured from a common source population during planetary migration. Furthermore, we identify ∼9000 asteroids that exhibit large shifts in derived absolute magnitude between apparitions, indicating that these objects have both elongated shapes and spin axes with obliquity ∼90 degrees.

Secondary eclipse and day-night modulation of exoplanets observed by transiting exoplanet survey satellite

Astronomers have identified over five thousand extrasolar planets since the discovery of the first solar-like star in 1995. These systems exhibit greater diversity than our solar system, providing insights into their formation and evolution. To understand these exoplanets and their habitability, it is crucial to examine their atmosphere composition. The Transiting Exoplanet Survey Satellite (TESS) can detect reflected light from exoplanets with high accuracy, providing valuable insights into their formation and potential for life in the Universe. Planetary reflection can be detected by monitoring the light curve, which is the sum of stellar flux and planetary reflection. Orbiting planets may also reveal their presence by modulating reflected starlight, showing day-night variations in observers sight lines. However, these flux variations are extremely small, at a level of 0.01%, making detection difficult. This study developed an efficient Python program to search for secondary eclipse and day-night modulation on the TESS light curves of over four hundred known short-period transiting exoplanets. The program automatically identifies and rejects low-quality photometric data points in light curves, folding high-quality light curves in the orbital phase determined by primary transits. The phase-folded average light curves have high photometric precision, suitable for detecting secondary eclipse and day-night modulation. The program successfully identified planetary reflection in seventeen transiting exoplanetary systems, larger than the current TESS sample by twice. The program plans to upgrade to search for orbital phase modulation in non-transit exoplanets, taking advantage of the high precision of TESS photometry.

Time-resolved Hubble Space Telescope Wide Field Camera 3 Spectrophotometry Reveals Inefficient Day-to-night Heat Redistribution in the Highly Irradiated Brown Dwarf SDSS 1557B

Brown dwarfs (BDs) in ultra-short-period orbits around white dwarfs (WDs) offer a unique opportunity to study the properties of tidally locked, fast-rotating (1–3 hr), and highly irradiated atmospheres. Here we present phase-resolved spectrophotometry of the WD–BD binary SDSS 1557, which is the fifth WD–BD binary in our six-object sample. Using the Hubble Space Telescope Wide Field Camera 3 Near-infrared G141 instrument, the 1.1–1.7 μm phase curves show rotational modulations with semiamplitudes of 10.5% ± 0.1%. We observe a wavelength-dependent amplitude, with longer wavelengths producing larger amplitudes, while no wavelength-dependent phase shifts were identified. The phase-resolved extracted BD spectra exhibit steep slopes and are nearly featureless. A simple radiative energy redistribution atmospheric model re-creates the hemisphere-integrated brightness temperatures at three distinct phases and finds evidence for weak redistribution efficiency. Our model also predicts a higher inclination than previously published. We find that SDSS 1557B, the second most irradiated BD in our sample, is likely dominated by clouds on the nightside, whereas the featureless dayside spectrum is likely dominated by H− opacity and a temperature inversion, much like the other highly irradiated BD EPIC 2122B.

The EBLM project – XIII. The absolute dynamical masses of the circumbinary planet host TOI-1338/BEBOP-1, and applications to the study of exoplanet atmospheres

ABSTRACT High-contrast eclipsing binaries with low mass M-dwarf secondaries are precise benchmark stars to build empirical mass–radius relationships for fully convective low-mass ($\rm M_{\star } \lt 0.35\, M_{\odot }$) dwarf stars. The contributed light of the M-dwarf in such binaries is usually much less than one per cent at optical wavelengths. This enables the detection of circumbinary planets from precise radial velocity measurements. High-resolution cross-correlation techniques are typically used to detect exoplanet atmospheres. One key aspect of these techniques is the post-processing, which includes the removal of telluric and spectral lines of the host star. We introduce the application of such techniques to optical high-resolution spectra of the circumbinary planet-host TOI-1338/BEBOP-1, turning it effectively into a double-lined eclipsing binary. By using simulations, we further explore the impact of post-processing techniques for high-contrast systems. We detect the M-dwarf secondary with a significance of 11σ and measure absolute dynamical masses for both components. Compared to previous model-dependent mass measurements, we obtain a four times better precision. We further find that the post-processing results in negligible systematic impact on the radial velocity precision for TOI-1338/BEBOP-1 with more than $96.6\,$ per cent (1σ) of the M-dwarf’s signal being conserved. We show that these methods can be used to robustly measure dynamical masses of high-contrast single-lined binaries providing important benchmark stars for stellar evolution particularly near the bottom of the main sequence. We also demonstrate how to retrieve the phase curve of an exoplanet with high-resolution spectroscopy using our data.

Hot Jupiter diversity and the onset of TiO/VO revealed by a large grid of non-grey global circulation models

ABSTRACT The population of hot Jupiters is extremely diverse, with large variations in their irradiation, period, gravity, and chemical composition. To understand the intrinsic planet diversity through the observed population level trends, we explore the a priori scatter in the population created by the different responses of atmospheric circulation to planetary parameters. We use the SPARC/MITgcm three-dimensional global circulation model to simulate 345 planets spanning a wide range of instellation, metallicity, gravity, and rotation periods typical for hot Jupiters, while differentiating between models with and without titanium oxide (TiO)/vanadium oxide (VO) in their atmosphere. We show that the combined effect of the planetary parameters leads to a large diversity in the ability of atmospheres to transport heat from day-side to night-side at a given equilibrium temperature. We further show that the hotspot offset is a non-monotonic function of planetary rotation period and explain our findings by a competition between the rotational and divergent parts of the circulation. As a consequence, hotspot offset and phase curve amplitude are not necessarily correlated. Finally, we compare the observables from our grid to the population of Spitzer and Hubble observations of hot Jupiters. We find that the sudden jump in brightness temperature observed in the Spitzer secondary eclipse measurements can be naturally explained by the cold-trapping of TiO/VO at approximately 1800 K. Spectra, phase curves and thermal structures from the model grid used in this study are available to the community, for more details see the data availability section.

Toward Atmospheric Retrievals of Panchromatic Light Curves: ExPLOR-ing Generalized Inversion Techniques for Transiting Exoplanets with JWST and Ariel

Conventional atmospheric retrieval codes are designed to extract information, such as chemical abundances, thermal structures, and cloud properties, from fully “reduced” spectra obtained during transit or eclipse. Reduced spectra, however, are assembled by fitting a series of simplified light curves to time-series observations, wavelength by wavelength. Thus, spectra are postprocessed summary statistics of the original data, which by definition do not encode all the available information (i.e., astrophysical signal, model covariance, and instrumental noise). Here, we explore an alternative inversion strategy where the atmospheric retrieval is performed on the light curve directly, i.e., closer to the data. This method is implemented in EXoplanet Panchromatic Light curve Observation and Retrieval (ExPLOR), a novel atmospheric retrieval code inheriting from the TauREx project. By explicitly considering time in the model, ExPLOR naturally handles transits, eclipses, phase curves, and other complex geometries for transiting exoplanets. In this paper, we have validated this new technique by inverting simulated panchromatic light curves. The model was tested on realistic simulations of a WASP-43 b-like exoplanet as observed with the James Webb Space Telescope (JWST) and Ariel telescope. By comparing our panchromatic light-curve approach against conventional spectral retrievals on mock scenarios, we have identified key breaking points in information and noise propagation when employing past literature techniques. Throughout the paper, we discuss the importance of developing “closer-to-data” approaches such as the method presented in this work, and highlight the inevitable increase in model complexity and computing requirements associated with the recent JWST revolution.

Asymmetry in the atmosphere of the ultra-hot Jupiter WASP-76 b

Context. WASP-76 b has been a recurrent subject of study since the detection of a signature in high-resolution transit spectroscopy data indicating an asymmetry between the two limbs of the planet. The existence of this asymmetric signature has been confirmed by multiple studies, but its physical origin is still under debate. In addition, it contrasts with the absence of asymmetry reported in the infrared (IR) phase curve. Aims. We provide a more comprehensive dataset of WASP-76 b with the goal of drawing a complete view of the physical processes at work in this atmosphere. In particular, we attempt to reconcile visible high-resolution transit spectroscopy data and IR broadband phase curves. Methods. We gathered 3 phase curves, 20 occultations, and 6 transits for WASP-76 b in the visible with the CHEOPS space telescope. We also report the analysis of three unpublished sectors observed by the TESS space telescope (also in the visible), which represents 34 phase curves. Results. WASP-76 b displays an occultation of 260 ± 11 and 152 ± 10 ppm in TESS and CHEOPS bandpasses respectively. Depending on the composition assumed for the atmosphere and the data reduction used for the IR data, we derived geometric albedo estimates that range from 0.05 ± 0.023 to 0.146 ± 0.013 and from <0.13 to 0.189 ± 0.017 in the CHEOPS and TESS bandpasses, respectively. As expected from the IR phase curves, a low-order model of the phase curves does not yield any detectable asymmetry in the visible either. However, an empirical model allowing for sharper phase curve variations offers a hint of a flux excess before the occultation, with an amplitude of ~40 ppm, an orbital offset of ~ −30°, and a width of ~20º. We also constrained the orbital eccentricity of WASP-76 b to a value lower than 0.0067, with a 99.7% confidence level. This result contradicts earlier proposed scenarios aimed at explaining the asymmetry observed in high-resolution transit spectroscopy. Conclusions. In light of these findings, we hypothesise that WASP-76 b could have night-side clouds that extend predominantly towards its eastern limb. At this limb, the clouds would be associated with spherical droplets or spherically shaped aerosols of an unknown species, which would be responsible for a glory effect in the visible phase curves.

The Unusual Brightness Phase Curve of (65803) Didymos

On 2022 September 26, NASA's Double Asteroid Redirection Test (DART) successfully hit Dimorphos, the smaller companion of the binary system formed with the asteroid (65803) Didymos. Both the binary system and the impact event were imaged by the Light Italian Cubesat for Imaging of Asteroids, detached from DART 15 days before the impact. Images from the onboard LUKE red, green, and blue camera together with ground-based observations enabled the reconstruction of Didymos's brightness phase curve, with phase angles ranging from 2.35° to 107.7°. The opposition effect regime was studied using the exponential-linear equation, the “Shevchenko” function and the linear-by-parts model while the IAU-official HG1G2 magnitude system was applied to the full phase curve. The opposition effect indicates an unusual asteroid surface for an S type, with characteristics similar to M-type asteroids. While the HG1G2 parameters from the full phase curve place Didymos well among asteroids of the taxonomic C complex. Didymos’s phase curve parameters when compared to near-Earth asteroids are very close to the Q type (1862) Apollo, indicating possible depletion of fine submicrometric grains through resurfacing. Didymos's geometric albedo (0.15 ± 0.01) is reported to be 30%–45% smaller than the average geometric albedo for near-Earth S types (0.26 ± 0.04). We propose that Didymos might be an LL ordinary chondrite analog containing albedo-suppressing, shock-darkened/impact melt minerals that have undergone resurfacing processes in the past. A comparison with meteorites indicates that, less likely, Didymos could also contain materials analog to carbon-bearing brecciated L3 ordinary chondrites.

Quantitative grain size estimation on airless bodies from the negative polarization branch

Context. Sunlight scattered from the surface of an airless body is generally partially polarized, and the corresponding polarization state includes information about the scattering surface, such as albedo, surface grain sizes, composition, and taxonomic types. Most polarimetric studies on airless bodies thus far have focused on optical wavelengths (λ ≲ 1 µm). Aims. We conducted polarimetry of two large airless bodies, the Dawn mission targets (1) Ceres and (4) Vesta, in the near-infrared region. We further investigated the change in the polarimetric phase curves over the wavelengths expected from previous works. Methods. We used the Nishiharima Infrared Camera (NIC) installed at the Nishi-Harima Astronomical Observatory (NHAO) to observe these objects at multiple geometric configurations in the J, H, and Ks bands (λ ~ 1.2–2.3 µm). Results. Polarimetric parameters were determined and compared with previously reported experimental results. In particular, Vesta exhibits a characteristic change in the negative polarization branch as the wavelength increases to the Ks band, which we interpret as an indication of the dominant existence of D ~ 10–20 µm particles. Our approach is supported by empirical reasoning and coincides well with an independent, theory-driven approach based on thermal modeling. Conclusions. This work demonstrates how near-infrared polarimetry can be utilized to quantitatively determine the particle size of airless objects. This finding will have important implications for asteroid taxonomy and regolith evolution.

Super-Earth LHS3844b is Tidally Locked

Short-period exoplanets on circular orbits are thought to be tidally locked into synchronous rotation. If tidally locked, these planets must possess permanent day- and night-sides, with extreme irradiation on the dayside and none on the nightside. However, so far the tidal locking hypothesis for exoplanets is supported by little to no empirical evidence. Previous work showed that the super-Earth LHS 3844b likely has no atmosphere, which makes it ideal for constraining the planet’s rotation. Here we revisit the Spitzer phase curve of LHS 3844b with a thermal model of an atmosphere-less planet and analyze the impact of nonsynchronous rotation, eccentricity, tidal dissipation, and surface composition. Based on the lack of observed strong tidal heating we rule out rapid nonsynchronous rotation (including a Mercury-like 3:2 spin–orbit resonance) and constrain the planet's eccentricity to less than ∼0.001 (more circular than Io's orbit). In addition, LHS 3844b’s phase curve implies that the planet either still experiences weak tidal heating via a small-but-nonzero eccentricity (requiring an undetected orbital companion), or that its surface has been darkened by space weathering; of these two scenarios we consider space weathering more likely. Our results thus support the hypothesis that short-period rocky exoplanets are tidally locked, and further show that space weathering can significantly modify the surfaces of atmosphere-less exoplanets.

The laboratory PROGRA2 database to interpret the linear polarization and brightness phase curves of light scattered by solid particles in clouds and layers

Laboratory measurements of the brightness and linear polarization of the light scattered by clouds of particles are necessary to interpret remote sensing measurements of dust in space and in planetary atmospheres. For 30 years, such laboratory measurements were conducted by the PROGRA2 project for particles with different natures, sizes and shapes. The resulting database contains the brightness and linear polarization curves for 170 samples and at 4 wavelengths in the visible and near infra-red domains. The samples cover most of the particles that we expect to find in space and in planetary atmospheres. The particles can be compact, porous or aggregated, with sizes up to hundreds of µm; the monomers of aggregates can have sizes as small as 10 nm. The measurements were obtained for clouds of randomly oriented particles levitated on the ground conditions by an air draught technique, and under microgravity conditions during parabolic flights. Complementary measurements were obtained for deposited particles in layers to compare the main characteristics of the phase curves using the same sample. After a description of the instruments and of the samples under study, we present the database and the main results already obtained with PROGRA2. The phase curves often differ for deposited and levitating particles. Such phase curves are related to different physical properties of the particles, and can be compared to modelling calculations. In case of agregated particles, we discuss the influence of the monomers on the phase curves. Finally, the main results obtained for dust analogs of differents object of the solar system are compared to observations.

Estimation of constitutive parameters for shape memory polymer thermo-mechanical cycle by an integrated simulation and inverse optimization method

In this work, a method for inverse optimization of shape memory polymer material parameters is proposed to determine the intrinsic model parameters more quickly and accurately for simulated experimental test analysis. First, the basic mechanical properties of the material are characterized experimentally and the parameters of the generalized Maxwell model based on SMP material are fitted. Then, a joint simulation inversion optimization method is built in the ISIGHT-MATLAB-ABAQUS integrated environment to optimize the time domain Prony series parameters using downhill simplex optimization algorithm. The results show that the average errors of the stress curves before and after the optimization of the cooling solid phase and the experimental results are 0.31 MPA and 0.23 MPA, respectively, and the average errors of the strain curves in the warming recovery phase are 1.70% and 0.40%, respectively. After the inversion optimization, the average errors of the stress curves are optimized by 25.8% and the average errors of the strain curves are optimized by 76.5%. This method makes the simulation results more stable with the experimental results, which can effectively reduce the experimental cost and promote the shape memory property of SMP to be widely used in engineering.

Exomoon Phase Curves: Toroidal Exosphere Simulations of Exo‐Ios Orbiting 8 Exoplanets in Alkali Spectroscopy

AbstractToroidal atmospheres and exospheres characterized at exoplanets may be fueled by volcanically active exomoons, often referred to as exo‐Ios. We study the neutral outgassing and volatile evolution of a close‐orbiting, evaporating satellite at eight candidate exoplanet‐exomoon systems WASP‐49,‐96,‐69,‐17 b, XO‐2N b, HAT‐P‐1 b, HD‐189733 b, and HD‐209458 b by developing a 3‐D test‐particle Monte Carlo simulation, Simulating the Evolution of Ring Particles Emergent from Natural Satellites. The module is coupled to dishoom, approximating the minimum mass‐flux needed to reproduce observations of alkali line profiles identified in dozens of transmission spectra. We focus on sputtered neutral sodium, limited by photoionization and radiative effects. By considering Earth‐, Io‐, and Enceladus‐like masses, we systematically simulate the imprint of a non‐hydrostatic medium (characteristic of volcanic exospheres) in density and velocity space using a novel Delaunay tesselation field estimator algorithm. Our results demonstrate how exomoons can considerably modulate gas density observations probed near exoplanet transit, depending on the orbital phase of the putative satellite at the time of observation. The density evolution, therefore, manifests on orbital timescales as “exomoon phase curves” from shadow to occultation. We find two regimes of density evolution, characteristic of a: (a) localized cloud and (b) an azimuthally symmetric exoring/torus, degenerate with an exoplanet atmosphere, ranging from ∼109.5±0.5 cm−2 to ∼1015±0.25 cm−2 at our leading candidate WASP‐69b I. In certain orbital architectures, the smallest evaporating satellite mass surprisingly generates the brightest sodium signal, fueling optimism for discovering photometrically indiscernible rocky exomoons. We suggest long baseline monitoring of alkali and SO2 systems in spectroscopy to search for the temporal and spatial variability predicted here.

The radiative and dynamical impact of clouds in the atmosphere of the hot Jupiter WASP-43 b

Context. Hot Jupiters are tidally locked gaseous exoplanets that exhibit large day-night temperature contrasts. Their cooler nightsides are thought to host clouds, as has been suggested by numerous observations. However, the exact nature of these clouds, their spatial distribution, and their impact on atmospheric dynamics, thermal structure, and spectra is still unclear. Aims. We investigate the atmosphere of WASP-43 b, a short period hot Jupiter recently observed with James Webb Space Telescope (JWST), to understand the radiative and dynamical impact of clouds on the atmospheric circulation and thermal structure. We aim to understand the impact of different kinds of condensates potentially forming in WASP-43 b, with various sizes and atmospheric metallicities. Methods. We used a 3D global climate model (GCM) with a new temperature-dependent cloud model that includes radiative feedbacks coupled with hydrodynamical integrations to study the atmospheric properties of WASP-43 b. We produced observables from our GCM simulations and compared them to spectral phase curves from various observations to derive constraints on the atmospheric properties. Results. We show that clouds have a net warming effect, meaning that the greenhouse effect caused by clouds is stronger than the albedo cooling effect. We show that the radiative effect of clouds has various impacts on the dynamical and thermal structure of WASP-43 b. Depending on the type of condensates and their sizes, the radiative-dynamical feedback will modify the horizontal and vertical temperature gradient and reduce the wind speed. For super-solar metallicity atmospheres, fewer clouds form in the atmosphere, leading to a weaker feedback. Comparisons with spectral phase curves observed with HST, Spitzer, and JWST indicate that WASP-43 b's nightside is cloudy and rule out sub-micron Mg2SiO4 cloud particles as the main opacity source. Distinguishing between cloudy solarand cloudy super-solar-metallicity atmospheres is not straightforward, and further observations of both reflected light and thermal emission are needed.

Pre-impact Thermophysical Properties and the Yarkovsky Effect of NASA DART Target (65803) Didymos

The NASA Double Asteroid Redirection Test (DART) spacecraft impacted the secondary body of the binary asteroid (65803) Didymos on 2022 September 26 and altered its orbit about the primary body. Before the DART impact, we performed visible and mid-infrared observations to constrain the pre-impact thermophysical properties of the Didymos system and to model its Yarkovsky effect. Analysis of the photometric phase curve derives a Bond albedo of 0.07 ± 0.01, and a thermophysical analysis of the mid-infrared observations derives a thermal inertia of 320 ± 70 J m−2 K−1 s−1/2 and a thermal roughness of 40° ± 3° rms slope. These properties are compatible with the ranges derived for other S-type near-Earth asteroids. Model-to-measurement comparisons of the Yarkovsky orbital drift for Didymos derives a bulk density of 2750 ± 350 kg m−3, which agrees with other independent measures based on the binary mutual orbit. This bulk density indicates that Didymos is spinning at or near its critical spin-limit at which self-gravity balances equatorial centrifugal forces. Furthermore, comparisons with the post-impact infrared observations presented in Rivkin et al. indicate no change in the thermal inertia of the Didymos system following the DART impact. Finally, orbital temperature simulations indicate that subsurface water ice is stable over geologic timescales in the polar regions if present. These findings will be investigated in more detail by the upcoming ESA Hera mission.

Large Eddy Simulation Combined with System Identification Method to Analyze Non-Premixed Flame Transfer Function

ABSTRACT The heat release response (HRR) of the flame is a pivotal aspect of combustion instability investigation, commonly characterized by the Flame Transfer Function (FTF). This study employed a combination of large eddy simulation (LES) and system identification (SI) techniques to derive the FTF for a methane-air non-premixed swirling burner. The influence of memory time and excitation signals within the LES+SI was investigated as only a few studies have been conducted in this direction so far, and validated against experimental data. Variations in memory time led to notable shifts in frequency and amplitude for gain peaks and valleys, with modest effects on phase delay within the 20–140 Hz range. The number of corner frequencies increased with memory time, whereby smaller memory times flattened the gain curve and underestimated phase delay, and larger memory times intensified curve undulations, distorting finer details. By minimizing the Mean Relative Error (MRE) between LES+SI results and experimental data, the optimized memory time of 0.017 s was identified, which closely aligned with the convection time of 0.0167 s. Consequently, convection time could be referenced in a priori estimation approach for memory time in a non-premixed swirling burner. In comparing FTF obtained from different excitation signals, the Superimposed Sinusoidal Signal (SINE) excelled in the gain curve within the 20–100 Hz range, accurately capturing the 30 Hz gain peak and 80 Hz valley, while the Broadband White Noise (BBWN) excelled in the phase curve within the same range, both yielding a smaller mean relative error (MRE). However, the Discrete Random Binary Signal (DRBS) demonstrated the best consistency with experimental data within the 100–190 Hz range, and boasted an MRE of 38.01% and 28.55% respectively for the gain and phase curve within the entire frequency range. Consequently, we inferred that DRBS functioned as the excitation signal with the most minimal identification error.

Deletion and insertion tampering detection for speech authentication based on fluctuating super vector of electrical network frequency

The current digital speech deletion and insertion tampering detection methods mainly employes the extraction of phase and frequency features of the Electrical Network Frequency (ENF). However, there are some problems with the existing approaches, such as the alignment problem for speech samples with different durations, the sparsity of ENF features, and the small number of tampered speech samples for training, which lead to low accuracy of deletion and insertion tampering detection. Therefore, this paper proposes a tampering detection method for digital speech deletion and insertion based on ENF Fluctuation Super-vector (ENF-FSV) and deep feature learning representation. By extracting the parameters of ENF phase and frequency fitting curves, feature alignment and dimensionality reduction are achieved, and the alignment and sparsity problems are avoided while the fluctuation information of phase and frequency is extracted. To solve the problem of the insufficient sample size of tampered speech for training, the ENF Universal Background Model (ENF-UBM) is built by a large number of untampered speech samples, and the mean vector is updated to extract ENF-FSV. Considering the shallow representation of ENF features with not highlighting important features, we construct an end-to-end deep neural network to strengthen the attention to the abrupt fluctuation information by the attention mechanism to enhance the representational power of the ENF-FSV features, and then the deep ENF-FSV features extracted by the Residual Network (ResNet) module are fed to the designed classification network for tampering detection. The experimental results show that the method in this paper exhibits higher accuracy and better robustness in the Carioca, New Spanish, and ENF High-sampling Group (ENF-HG) databases when compared with the state-of-the-art methods.

Nomogram combining pre-operative clinical characteristics and spectral CT parameters for predicting the WHO/ISUP pathological grading in clear cell renal cell carcinoma.

To develop a novel clinical-spectral-computed tomography (CT) nomogram incorporating clinical characteristics and spectral CT parameters for the preoperative prediction of the WHO/ISUP pathological grade in clear cell renal cell carcinoma (ccRCC). Seventy-three ccRCC patients who underwent spectral CT were included in this retrospective analysis from December 2020 to June 2023. The subjects were pathologically divided into low- and high-grade groups (WHO/ISUP 1/2, n = 52 and WHO/ISUP 3/4, n = 21, respectively). Information on clinical characteristics, conventional CT imaging features, and spectral CT parameters was collected. Multivariate logistic regression analyses were conducted to create a nomogram combing clinical data and image data for preoperatively predicting the pathological grade of ccRCC, and the area under the curve (AUC) was utilized to assess the predictive performance of the model. Multivariate logistic regression analyses revealed that age, systemic immune-inflammation index (SII), and the slope of the spectrum curve in the cortex phase (CP-K) were independent predictors for predicting high-grade ccRCC. The clinical-spectral-CT model exhibited high evaluation efficacy, with an AUC of 0.933 (95% confidence interval [CI]: 0.878-0.998; sensitivity: 0.810; specificity: 0.923). The calibration curve revealed that the predicted probability of the clinical-spectral-CT nomogram could better fit the actual probability, with high calibration. The Hosmer-Lemeshow test showed that the model had a good fitness (χ2 = 5.574, p = 0.695). The clinical-spectral-CT nomogram has the potential to predict WHO/ISUP grading of ccRCC preoperatively.