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In this paper, we present photometric and spectroscopic observations of the subluminous Type Ia supernova (SN Ia) 2012ij, which has an absolute B -band peak magnitude M B , max = âˆ' 17.95 ± 0.15 mag. The B -band light curve exhibits a fast postpeak decline with Î" m 15(B) = 1.86 ± 0.05 mag. All the R - and I / i -band light curves show a weak secondary peak/shoulder feature at about 3 weeks after the peak, like some transitional subclass of SNe Ia, which could result from an incomplete merger of near-infrared (NIR) double peaks. The spectra are characterized by Ti ii and strong Si ii λ 5972 absorption features that are usually seen in low-luminosity objects like SN 1999by. The NIR spectrum before maximum light reveals weak carbon absorption features, implying the existence of unburned materials. We compare the observed properties of SN 2012ij with those predicted by the sub-Chandrasekhar-mass and the Chandrasekhar-mass delayed-detonation models and find that both optical and NIR spectral properties can be explained to some extent by these two models. By comparing the secondary maximum features in the I and i bands, we suggest that SN 2012ij is a transitional object linking normal SNe Ia to typical 91bg-like ones. From the published sample of SNe Ia from the Carnegie Supernova Project II, we estimate that the fraction of SN 2012ijâ€"like SNe Ia is not lower than ∼2%. [ABSTRACT FROM AUTHOR]

The optical light curves of quiescent black hole low-mass X-ray binaries often exhibit significant nonellipsoidal variabilities, showing the photospheric radiation of the companion star is veiled by other sources of optical emission. Assessing this “veiling” effect is critical to the black hole mass measurement. Here in this work, we carry out a strictly simultaneous spectroscopic and photometric campaign on the prototype of black hole low-mass X-ray binary A0620-00. We find that for each observation epoch, the extra optical flux beyond a pure ellipsoidal modulation is positively correlated with the fraction of veiling emission, indicating the accretion disk contributes most of the nonellipsoidal variations. Meanwhile, we also obtain a K2V spectral classification of the companion, as well as the measurements of the companion’s rotational velocity v sin i = 83.8 ± 1.9 km sâˆ'1 and the mass ratio between the companion and the black hole q = 0.063 ± 0.004. [ABSTRACT FROM AUTHOR]

This is the fourth paper in the series of analyses of times of minimum and period variations in W UMa eclipsing binaries, and the implications for mass exchange in these systems. In this paper, the systems discussed in Papers 1–3 for which analyses are relatively complete are sorted into three sections, arranged in order of degree of confidence that mass exchange occurrence is established and that the present rate of exchange has been determined. The higher-confidence systems are: 44 Boo, RZ Cam, VW LMi, AU Ser; the intermediate-confidence systems are: TY Boo, V1191 Cyg, AP Leo, ER Ori; and the lower-confidence systems are: AB And, XY Boo, AC Boo, AH Cnc, VW Cep, EZ Hya, XY Leo, W UMa, and GR Vir. A fourth section describes promising cases that require additional data and/or analyses. For the higher-confidence systems, selected analyses of the times of minimum and of the most comprehensive light curve (LC) and radial velocity (RV) suites of data have yielded mean mass changes to the more massive component of dM 1 /dt = +2.37 (13) × 10−7 M ʘ /y for 44 Boo, +4.00 (14) × 10−8 M ʘ /y for RZ Com, +2.53 (7) × 10−7 M ʘ /y for VW LMi, and -1.98 (11) × 10−7 M ʘ /y for AU Ser. [ABSTRACT FROM AUTHOR]

Abstract—The paper provides a review of important results of studies of chemically peculiar and related magnetic stars. More than 90 papers published in the world leading astronomical journals mainly in 2019 were analyzed. The most important results: high-accuracy photometric light curves were obtained during the TESS satellite; we discovered several dozen of new chemically peculiar magnetic stars; it was shown that large magnetic spots on cool stars exist for tens of years practically unchanged; we found several new magnetic white dwarfs with very weak fields; a strong magnetic white dwarf with a rotation period of about 100 years was discovered. New data have been obtained to better understand the mechanisms of formation and evolution of magnetic stars. [ABSTRACT FROM AUTHOR]

Underwater images suffer from severe color attenuation and contrast reduction due to the poor and complex lighting conditions in the water. Most mainstream methods employing deep learning typically require extensive underwater paired training data, resulting in complex network structures, long training time, and high computational cost. To address this issue, a novel ZeroReference Parameter Estimation Network (Zero-UAE) model is proposed in this paper for the adaptive enhancement of underwater images. Based on the principle of light attenuation curves, an underwater adaptive curve model is designed to eliminate uneven underwater illumination and color bias. A lightweight parameter estimation network is designed to estimate dynamic parameters of underwater adaptive curve models. A tailored set of non-reference loss functions are developed for underwater scenarios to fine-tune underwater images, enhancing the network's generalization capabilities. These functions implicitly control the learning preferences of the network and effectively solve the problems of color bias and uneven illumination in underwater images without additional datasets. The proposed method examined on three widely used real-world underwater image enhancement datasets. Experimental results demonstrate that our method performs adaptive enhancement on underwater images. Meanwhile, the proposed method yields competitive performance compared with state-of-the-art other methods. Moreover, the Zero-UAE model requires only 17K parameters, minimizing the hardware requirements for underwater detection tasks. What'more, the adaptive enhancement capability of the Zero-UAE model offers a new solution for processing images under extreme underwater conditions, thus contributing to the advancement of underwater autonomous monitoring and ocean exploration technologies. [ABSTRACT FROM AUTHOR]

In this paper, we present results of refining the characteristics of the eclipsing pre-cataclysmic variable SDSS J162256.6+473051 based on a model analysis of its optical radiation. We used the spectra of the system obtained with the 6-m BTA telescope of SAO RAS and the data from its multi-band photometric observations with the 1.5-m Russian-Turkish telescope RTT150. Calculations of the optical radiation of SDSS J162256.6+473051 were carried out using the method of irradiated atmosphere models. When analyzing the spectra of the system at the minimum brightness, we found the following atmospheric parameter estimates of the sdB sub-dwarf: K, , [He/H] . The light curves of SDSS J162256.6+473051 were modeled and a complete set of fundamental parameters of the system was obtained. Their satisfactory agreement with the literature data allows us to conclude that the characteristics of similar systems with weak reflection effects can be analyzed together, even when they are determined using different methods of radiation modeling. [ABSTRACT FROM AUTHOR]

Current methods of performing Initial Orbit Determination (IOD) in near-earth orbital regions cannot be directly extended to cislunar space due to changes in gravitational models that must be utilized. For the case of cislunar orbits, the Moon’s gravitational influence necessitates that orbital motions be described by three-body dynamics. Three-body dynamics produce orbits that are generally not elliptical, fixed to an orbital plane, or geometrically simple. This change in assumptions that can be made complicates the task of performing IOD and has led to the investigation of alternative methods and features to classify cislunar orbit parameters. In this paper, we explore the potential of utilizing Machine Learning (ML) algorithms to constrain potential IOD search spaces to specific cislunar families. We accomplish this by training the ML classifier to predict cislunar family from a light curve. To generate training data for this ML effort, we introduce a novel simulation pipeline that produces radiometrically validated light curves using the Digital Imaging and Remote Sensing Image Generation (DIRSIG™) engine. This pipeline ingests various parameters, including: initial Circular Restricted Three-Body Problem (CR3BP) state vectors, satellite material properties, telescope optical properties, and satellite 3D models. The pipeline produces light curves capturing the influence of these factors on the observed visual magnitude signature as a function of elapsed time and phase angle. This pipeline was utilized to produce approximately 3500 light curves of various cislunar orbital families as captured from the perspective of two observing locations: the spaced-based Earth-Moon L1 point, and a Lunar surface based point. These light curves were used as training datasets for neural network models to perform classification of cislunar family via input time-series vectors consisting of two features: visual magnitude and phase angle. Our machine learning technique first uses a warping technique to construct constant sized observational input of the light curves into a multi-layer perceptron, the architecture of which was chosen by a search over a large landscape of possibilities optimizing for validation prediction accuracy. The selected model was then trained on various scenarios of input data, again doing a search over several available hyper-parameters. It was found that the trained models were able to achieve test data-set accuracy of 93.4% for light curves captured from the face of the moon, and 87.5% when combined with light curves captured from the space-based L1 point. [ABSTRACT FROM AUTHOR]

Aims. Our aim in this paper is to refine the orbital and physical parameters of the HATS-2 planetary system and study transit timing variations and atmospheric composition thanks to transit observations that span more than 10 yr and that were collected using different instruments and pass-band filters. We also investigate the orbital alignment of the system by studying the anomalies in the transit light curves induced by starspots on the photosphere of the parent star. Methods. We analysed new transit events from both ground-based telescopes and NASA's TESS mission. Anomalies were detected in most of the light curves and modelled as starspots occulted by the planet during transit events. We fitted the clean and symmetric light curves with the JKTEBOP code and those affected by anomalies with the PRISM+GEMC codes to simultaneously model the photometric parameters of the transits and the position, size, and contrast of each starspot. Results. We found consistency between the values we found for the physical and orbital parameters and those from the discovery paper and ATLAS9 stellar atmospherical models. We identified different sets of consecutive starspot-crossing events that temporally occurred in less than five days. Under the hypothesis that we are dealing with the same starspots, occulted twice by the planet during two consecutive transits, we estimated the rotational period of the parent star and, in turn the projected and the true orbital obliquity of the planet. We find that the system is well aligned. We identified the possible presence of transit timing variations in the system, which can be caused by tidal orbital decay, and we derived a low-resolution transmission spectrum. [ABSTRACT FROM AUTHOR]

The paper describes a target setting of searching for apsidal motion in 21 eclipsing binaries. We estimate the capability of its determination for the systems of interest in the coming years, as well as present results of observations in 2009–2018, in which the minima of the light curves of these stars have been obtained. The accuracy of orbital period determination of the studied binaries is 10–100 times greater in comparison with the previously available data. For two systems, photometric elements are determined. As a by-product of the study, a close eclipsing binary of the W UMa type was discovered. [ABSTRACT FROM AUTHOR]

Synthesis methods for light and radial velocity curves are currently one of the main tools for studying close binary systems (CBSs). The paper gives a brief review of the history and development of the methods and their implementations in Sternberg Astronomical Institute of Moscow State University (SAI MSU), where a set of computer programs has been created to analyze observations of CBSs of various types. As a demonstration, we present the results of the analysis by our algorithms for three interesting CBSs at different evolutionary stages. An analysis of the unusual light curves of the recently discovered pre-cataclysmic binary GPX-TF16E-48 was performed using the Roche model with spots on the normal star. The X-ray light curves of the microquasar SS433 were analyzed using a precessing accretion disk model. The highly elliptical Wolf‒Rayet binary WR22 was studied in the frame of the Roche model accounting for the absorption by the powerful wind of the Wolf–Rayet star using space-based photometric observations. As a result of this detailed analysis of the light curves and involving spectroscopic information, the parameters of the CBSs and their components were found. This paper is based on a presentation made in the astrophysical memorial seminar "Novelties in Understanding the Evolution of Binary Stars", dedicated to the 90th anniversary of Professor M.A. Svechnikov. [ABSTRACT FROM AUTHOR]

Context. Modern-day time-domain photometric surveys collect a lot of observations of various astronomical objects and the coming era of large-scale surveys will provide even more information on their properties. Spectroscopic follow-ups are especially crucial for transients such as supernovae and most of these objects have not been subject to such studies. Aims. Flux time series are actively used as an affordable alternative for photometric classification and characterization, for instance, peak identifications and luminosity decline estimations. However, the collected time series are multidimensional and irregularly sampled, while also containing outliers and without any well-defined systematic uncertainties. This paper presents a search for the best-performing methods to approximate the observed light curves over time and wavelength for the purpose of generating time series with regular time steps in each passband. Methods. We examined several light curve approximation methods based on neural networks such as multilayer perceptrons, Bayesian neural networks, and normalizing flows to approximate observations of a single light curve. Test datasets include simulated PLAsTiCC and real Zwicky Transient Facility Bright Transient Survey light curves of transients. Results. The tests demonstrate that even just a few observations are enough to fit the networks and improve the quality of approximation, compared to state-of-the-art models. The methods described in this work have a low computational complexity and are significantly faster than Gaussian processes. Additionally, we analyzed the performance of the approximation techniques from the perspective of further peak identification and transients classification. The study results have been released in an open and user-friendly Fulu Python library available on GitHub for the scientific community. [ABSTRACT FROM AUTHOR]

KIC 9406652, one of the recently identified IW And-type dwarf novae, is the best target for studying the tilted disk in cataclysmic variable stars. In a previous paper by Kimura et al. (2020b, PASJ, 72, 94), we analyzed its Kepler light curves and found that its orbital light curves during the brightening stage were dominated by the reflection effect of the secondary star and varied with the orientation of the tilted disk; the amplitude was maximized at the minimum of the super-orbital signal and the phase of the light maximum shifted to an earlier one with the advance of the super-orbital phase. We argued in that work that this was direct evidence of the retrogradely precessing tilted disk as the secondary star acts like a reflecting object. In order to confirm this interpretation, we have performed numerical modeling of orbital light curves in this paper. We have succeeded in reproducing the main characteristics of the observed orbital light curves by a simple model in which the secondary star is irradiated by the tilted disk. We have also constrained the inclination angle, i , of the binary system and the tilt angle, θ, of the disk purely from photometric considerations. The best-fitting parameter set is found to be i ∼ 45° and |$\theta \sim {2{_{.}^{\circ}}0}$|⁠ , respectively. The orbital inclination thus estimated is consistent with that obtained from the spectroscopic considerations within the uncertainty limit. On the other hand, the tilt angle of the disk could be underestimated by using only the semi-amplitude of super-orbital signals. [ABSTRACT FROM AUTHOR]

1RXS J083842.1−282723 is a nearly synchronous magnetic cataclysmic variable with a simple X-ray light curve. While its orbital period was fairly well established at P orb = 98.4 minutes from optical spectroscopy, indirect estimates of P spin/ P orb ranged from 0.90 to 0.96 because the short X-ray light curves could not determine the beat period to a factor of 2. We analyze a recent 50 days TESS observation, and ground-based optical time-series photometry spanning 9 yr, that together measure precise beat, orbit, and spin periods and enable the X-ray and optical modulations to be phase aligned. Although the X-ray light curves do not distinguish between a beat period of 16.11 or 32.22 hr, all of the optical evidence favors the longer value, with complete pole switching of accretion every half beat cycle. This would require P spin/ P orb = 0.952. Long-term optical monitoring also shows a decline in accretion rate, and a change in the beat-folded light curve. It would be useful to obtain a new X-ray/optical observation of at least 32 hr duration to examine any associated change in accretion structure, and to confirm the spin and beat periods. [ABSTRACT FROM AUTHOR]

In this paper, by treating the cosmological constant as a thermodynamic pressure, we study the thermodynamics and phase transitions of the dyonic AdS black holes in Gauss-Bonnet-Scalar gravity, where the conformal scalar field is considered. In a more general extended phase space, we first verified the first law of black hole thermodynamics, and find that it is always true. Meanwhile, the corresponding Smarr relation is also obtained. Then, we found that this black hole exhibits interesting critical behaviors in six dimensions, i.e., two swallowtails can be observed simultaneously. Interestingly, in a specific parameter space, we observed the small/intermediate/large black hole phase transitions, with the triple point naturally appearing. Additionally, the small/large black hole phase transition, similar to the liquid/gas phase transition of the van der Waals fluids, can also be found in other parameter regions. Moreover, we note that the novel phase structure composed of two separate coexistence curves discovered in the dyonic AdS black holes in Einstein-Born-Infeld gravity disappears in Gauss-Bonnet-Scalar gravity. This suggests that this novel phase structure may be related to gravity theory, and importantly, it is generally observed that the triple point is a universal property of dyonic AdS black holes. On the other hand, we calculated the critical exponents near the critical points and found that they share the same values as in mean field theory. Finally, it is true that these results will provide some deep insights into the interesting thermodynamic properties of the dyonic AdS black holes in the background of conformal scalar fields. [ABSTRACT FROM AUTHOR]

Underwater images often suffer from degradation due to scattering and absorption. With the development of artificial intelligence, fully supervised learning-based models have been widely adopted to solve this problem. However, the enhancement performance is susceptible to the quality of the reference images, which is more pronounced in underwater image enhancement tasks because the ground truths are not available. In this paper, we propose a light-enhanced pixel fusion network (LEPF-Net) to solve this problem. Specifically, we first introduce a novel light enhancement block (LEB) based on the residual block (RB) and the light enhancement curve (LE-Curve) to restore the cast color of the images. The RB is adopted to learn and obtain the feature maps from an original input image, and the LE-Curve is used to renovate the color cast of the learned images. To realize the superb detail of the repaired images, which is superior to the reference images, we develop a pixel fusion subnetwork (PF-SubNet) that adopts a pixel attention mechanism (PAM) to eliminate noise from the underwater image. The PAM adapts weight allocation to different levels of a feature map, which leads to an enhancement in the visibility of severely degraded areas. The experimental results show that the proposed LEPF-Net outperforms most of the existing underwater image enhancement methods. Furthermore, among the five classic no-reference image quality assessment (NRIQA) indicators, the enhanced images obtained by LEPF-Net are of higher quality than the ground truths from the UIEB dataset. [ABSTRACT FROM AUTHOR]

The paper presents the first results of the ongoing spectropolarimetric monitoring of magnetic fields of stars, whose chemically peculiar nature has been previously revealed with the 1-m SAO RAS telescope. We selected the sample candidates using the photometric data of the Kepler and TESS space missions. The efficiency of the method of searching for new CP stars based on photometric light curves has been confirmed. We present the magnetic field measurements and estimate the atmospheric parameters of the objects under study. [ABSTRACT FROM AUTHOR]

The electromagnetic emission from the nonrelativistic ejecta launched in neutron star mergers (either dynamically or through a disk wind) has the potential to probe both the total mass and composition of this ejecta. These observations are crucial in understanding the role of these mergers in the production of r -process elements in the Universe. However, many properties of the ejecta can alter the light curves and we must both identify which properties play a role in shaping this emission and understand the effects these properties have on the emission before we can use observations to place strong constraints on the amount of r -process elements produced in the merger. This paper focuses on understanding the effect of the velocity distribution (amount of mass moving at different velocities) for lanthanide-rich ejecta on the light curves and spectra. The simulations use distributions guided by recent calculations of disk outflows and compare the velocity-distribution effects to those of ejecta mass, velocity, and composition. Our comparisons show that uncertainties in the velocity distribution can lead to a factor of 2–4 uncertainties in the inferred ejecta mass based on peak infrared luminosities. We also show that early-time UV or optical observations may be able to constrain the velocity distribution, reducing the uncertainty in the ejecta mass. [ABSTRACT FROM AUTHOR]

Sub-TeV or TeV γ -rays have been convincingly detected in the afterglows of some gamma-ray bursts (GRBs). The relativistic jet associated with GRBs may be surrounded by a cocoon and thus the thermal photons of the cocoon pervading the emission region of the jet can be upscattered to the very-high-energy regime (e.g., sub-TeV/TeV) by the electrons in the jet. In this scenario, the electrons in the jet cool down and thus the jet emission in the low-energy regime, e.g., the X-ray or optical, may be suppressed. In this paper, we study the effect of the cocoon's thermal photons on the jet emission in the low-energy regime. We find that the jet emission in the low-energy regime is significantly suppressed when the emission region of the jet is just encircled by a hot cocoon. Correspondingly, there is a sharp decay in the light curves of the jet emission in the low-energy regime, which can be understood to signify strong TeV emission in GRBs. Since the radius of the cocoon expands with the observer time t obs, the suppression of the jet emission in the low-energy regime may be relieved and thus the light curves of the jet emission would return to those of emission without a cocoon-external inverse-Compton cooling effect. For a long-lasting jet with power ∝ (1 + t obs / t c) α , an internal plateau followed by a sharp decay may generally appear. [ABSTRACT FROM AUTHOR]

This paper outlines a multi-system approach for ground-based optical observations and the characterization of satellites in geostationary orbit. This multi-system approach is based on an in-depth analysis of the key factors to consider for light curve analysis of Earth's orbiting satellites. Light curves have been observed in different spectral bands using two different systems. The first system is specialized for astronomical observations and consists of a telescope equipped with an sCMOS camera and Sloan photometric filters. In contrast, the second system is a more cost-effective solution designed for professional non-astronomical applications, incorporating DSLR cameras equipped with RGB channels associated with a Bayer mask and photographic lenses. This comparative analysis aims to highlight the differences and advantages provided by each system, stressing their respective performance characteristics. The observed light curves will be presented as a function of the phase angle, which depends on the relative positions of the observer, the object, and the Sun. This angle plays an important role in optimizing the visibility of Earth's orbiting satellites. Finally, multiband observations of different satellites will be compared to seek an associated spectral signature, which may allow the identification of structurally similar objects through optical observations. [ABSTRACT FROM AUTHOR]

In this paper, we report the results of the detailed temporal and spectral studies of the BeXRB J21347 + 4737 based on the data from the nuclear spectroscopic telescope array (NuSTAR) and Swift/XRT in a wide energy range of 0.5–50 keV. Coherent pulsation with a period of 322.738 ± 0.018 s was found in the light curve, implying the source pulsation has spun down by 0.341 s yr - 1 when compared with the coherent pulsation estimated from XMM Newton >7 years ago. The pulse profile of the source demonstrates energy dependence and has evolved with time. The pulse fraction of the source observed by NuSTAR initially decreases with energy up to ∼ 15 keV, followed by a non-monotonic increasing trend above 15 keV. The source spectrum can be well approximated by an absorbed power-law model with modification by an exponential cutoff at high energies. The absorbed flux of the source is 4 × 10 - 11 erg cm - 2 s - 1 and its corresponding luminosity is 3.5 × 10 35 erg s - 1 . The study of pulse-phase resolved spectroscopy shows a strong variation of spectral parameters on the phase. No additional emission or absorption features in the form of Fe line or cyclotron lines were observed both in the phase-averaged and phase-resolved spectra of IGR J21347 + 4737. [ABSTRACT FROM AUTHOR]

Compared with the international meteor surveillance systems, the ground wide angle camera (GWAC) system exhibits characteristics such as images with the resolution of 4K × 4K and single-site observation. These characteristics present challenges for meteor detection in the GWAC system. Consequently, this paper proposes a new meteor detection algorithm for the GWAC system on the base of the solely mini-GWAC system data algorithm. The new algorithm consists of the following key steps: (1) to compare differences between adjacent frames, applying block-based image binarization thresholds, and incorporating median filtering to reduce noise; (2) to adopt the probabilistic Hough transform (PHT) to identify moving objects and cluster them based on the origin moment of the line segments, while assessing the credibility of clustering; (3) to introduce the so-called maximum disappearance frame for moving objects in the tracking algorithm, enhancing the ability to track multi-frame moving objects. The utilization of the line segment inclination angle of the moving object as the direction of movement facilitates the tracking of multiple moving objects, thereby reducing the probability of mistakenly selecting single-frame moving objects; (4) to leverage the light curves of single-frame moving objects to select meteors to enhance the accuracy of meteor detection. Comparative experiments demonstrate that our proposed algorithm processes each frame image in just 0.39 s, achieving an accuracy of 89.8% in the dataset of 5856 adjacent frames. The experimental results indicate that the algorithm achieved an accuracy of 90.27% when applied in the meteor detection of the image data captured by the GWAC system from Dec. 10th to 19th in 2019 and 2021, obtaining excellent detection results. [ABSTRACT FROM AUTHOR]

Most of the stars in the Universe are M spectral class dwarfs, which are known to be the source of bright and frequent stellar flares. In this paper, we propose new approaches to discover M-dwarf flares in ground-based photometric surveys. We employ two approaches: a modification of a traditional method of parametric fit search and a machine learning algorithm based on active anomaly detection. The algorithms are applied to Zwicky Transient Facility (ZTF) data release 8, which includes the data from the ZTF high-cadence survey, allowing us to reveal flares lasting from minutes to hours. We analyse over 35 million ZTF light curves and visually scrutinize 1168 candidates suggested by the algorithms to filter out artefacts, occultations of a star by an asteroid, and other types of known variable objects. The result of this analysis is the largest catalogue of ZTF flaring stars to date, representing 134 flares with amplitudes ranging from −0.2 to −4.6 mag, including repeated flares. Using Pan-STARRS DR2 colours, we assign a spectral subclass to each object in the sample. For 13 flares with well-sampled light curves and available geometric distances from Gaia DR3, we estimate the bolometric energy. This research shows that the proposed methods combined with the ZTF's cadence strategy are suitable for identifying M-dwarf flares and other fast transients, allowing for the extraction of significant astrophysical information from their light curves. [ABSTRACT FROM AUTHOR]

This paper investigates the frequency of transiting planetary systems around metal-polluted white dwarfs using high-cadence photometry from ULTRACAM and ULTRASPEC on the ground and space-based observations with TESS. Within a sample of 313 metal-polluted white dwarfs with available TESS light curves, two systems known to have irregular transits are blindly recovered by box-least-squares and Lomb–Scargle analyses, with no new detections, yielding a transit fraction of |$0.8_{-0.4}^{+0.6}$|  per cent. Planet detection sensitivities are determined using simulated transit injection and recovery for all light curves, producing upper limit occurrences over radii from dwarf to Kronian planets, with periods from 1 h to 27 d. The dearth of short-period, transiting planets orbiting polluted white dwarfs is consistent with engulfment during the giant phases of stellar evolution, and modestly constrains dynamical re-injection of planets to the shortest orbital periods. Based on simple predictions of transit probability, where |$(R_* + R_{\rm p})/a\simeq 0.01$|⁠ , the findings here are nominally consistent with a model where 100 per cent of polluted white dwarfs have circumstellar debris near the Roche limit; however, the small sample size precludes statistical confidence in this result. Single transits are also ruled out in all light curves using a search for correlated outliers, providing weak constraints on the role of Oort-like comet clouds in white dwarf pollution. [ABSTRACT FROM AUTHOR]

We present a software package designed to produce photometric light curves and measure rotation periods from full-frame images taken by the Transiting Exoplanet Survey Satellite (TESS), which we name ' tessilator '. tessilator is the only publicly available code that will run a full light curve and rotation period (⁠|$P_{\rm rot}$|⁠) analysis based on just a (list of) target identifier(s) or sky position(s) via a simple command-line prompt. This paper sets out to introduce the rationale for developing tessilator , and then describes the methods, considerations, and assumptions for: extracting photometry; dealing with potential contamination; accounting for natural and instrumental systematic effects; light-curve normalization and detrending; removing outliers and unreliable data; and finally, measuring the |$P_{\rm rot}$| value and several periodogram attributes. Our methods have been tuned specifically to optimize TESS light curves and are independent from the pipelines developed by the TESS Science Processing Operations Center (SPOC), meaning tessilator can, in principle, analyse any target across the entire celestial sphere. We compare tessilator |$P_{\rm rot}$| measurements with TESS -SPOC-derived light curves of 1560 (mainly solar-type and low-mass) stars across four benchmark open clusters (Pisces–Eridanus, the Pleiades, the Hyades, and Praesepe) and a sample of nearby field M-dwarfs. From a vetted subsample of 864 targets we find an excellent return of |$P_{\rm rot}$| matches for the first three open clusters (⁠|$\gt 85$|  per cent) and a moderate (⁠|$\sim 60$|  per cent) match for the 700 Myr Praesepe and MEarth sample, which validates tessilator as a tool for measuring |$P_{\rm rot}$|⁠. The tessilator code is available at https://github.com/alexbinks/tessilator. [ABSTRACT FROM AUTHOR]

The thermal evolution of isolated neutron stars is a key element in unravelling their internal structure and composition and establishing evolutionary connections among different observational subclasses. Previous studies have predominantly focused on one-dimensional or axisymmetric two-dimensional models. In this study, we present the thermal evolution component of the novel three-dimensional magnetothermal code MATINS (MAgneto-Thermal evolution of Isolated Neutron Star). MATINS employs a finite volume scheme and integrates a realistic background structure, along with state-of-the-art microphysical calculations for the conductivities, neutrino emissivities, heat capacity, and superfluid gap models. This paper outlines the methodology employed to solve the thermal evolution equations in MATINS , along with the microphysical implementation that is essential for the thermal component. We test the accuracy of the code and present simulations with non-evolving magnetic fields of different configurations (all with electrical currents confined to the crust and a magnetic field that does not thread the core), to produce temperature maps of the neutron star surface. Additionally, for a specific magnetic field configuration, we show one fully coupled evolution of magnetic field and temperature. Subsequently, we use a ray-tracing code to link the neutron star surface temperature maps obtained by MATINS with the phase-resolved spectra and pulsed profiles that would be detected by distant observers. This study, together with our previous article focused on the magnetic formalism, presents in detail the most advanced evolutionary code for isolated neutron stars, with the aim of comparison with their timing properties, thermal luminosities and the associated X-ray light curves. [ABSTRACT FROM AUTHOR]

7P/Pons–Winnecke is a near-Earth short-period comet of a moderate activity level. In this paper, we present the analysis of observations performed during a favorable apparition of the comet in 2021, indicating its status as a transitional ageing comet. The sublimation starts when the comet is close to the Sun, at a distance of RON = 1.76 ± 0.1 AU, and continues for ~13 months, which is apparently caused by residual reserves of water ice. The dust production rate of the comet is not high even at perihelion (<150 kg/s), and the 1.4-percent active portion of the nucleus area is sufficient to provide this mass loss. The photometric age of the comet is PAGE = 54.4 comet years; being combined with a light curve amplitude of ASEC(1;1) = 5.5m, this age corresponds to the state of a transitional middle-aged comet. [ABSTRACT FROM AUTHOR]

Following the widespread practice of exoplanetary transit simulations, various presumed components of an extrasolar system can be examined in numerically simulated transits, including exomoons, rings around planets, and the deformation of exoplanets. Template signals can then be used to efficiently search for light curve features that mark specific phenomena in the data, and they also provide a basis for feasibility studies of instruments and search programs. In this paper, we present a method for exocomet transit light curve calculations using arbitrary dust distributions in transit. The calculations, spanning four distinct materials (carbon, graphite, pyroxene, and olivine), and multiple dust grain sizes (100–300 nm, 300–1000 nm, and 1000–3000 nm) encompass light curves in VRJHKL bands. We also investigated the behavior of scattering colors. We show that multicolor photometric observations are highly effective tools in the detection and characterization of exocomet transits. They provide information on the dust distribution of the comet (encoded in the light curve shape), while the color information itself can reveal the particle size change and material composition of the transiting material, in relation to the surrounding environment. We also show that the typical cometary tail can result in the wavelength dependence of the transit timing. We demonstrate that multi-wavelength observations can yield compelling evidence for the presence of exocomets in real observations. [ABSTRACT FROM AUTHOR]

γ Cassiopeiae (B0.5IVe) is the noted prototype of a subgroup of classical Be stars exhibiting hard thermal X-ray emission. This paper reports results from a 23 yr optical campaign on this star with an automated photometric telescope (APT). A series of unstable long cycles of length 56–91 days has nearly ceased over the last decade. Also, we revise the frequency of the dominant coherent signal at 0.82238 days−1. This signal's amplitude has nearly disappeared in the last 15 yr but has somewhat recovered its former strength. We confirm the presence of secondary nonradial pulsation signals found by other authors at frequencies 1.24, 2.48, and 5.03 days−1. The APT data from intensively monitored nights reveal rapidly variable amplitudes among these frequencies. We show that peculiarities in the 0.82 days−1 waveform exist that can vary even over several days. Although the 0.82 days−1 frequency is near the star's presumed rotational frequency, because of its phase slippage with respect to a dip pattern in its far-UV light curve, it is preferable to consider the UV pattern, not the 0.82 days−1 signal, as associated with rotational modulation. We also find hints of the UV dip pattern in periodograms of seasonal data early in our program. [ABSTRACT FROM AUTHOR]

In this paper, we study stellar light curves from the Transiting Exoplanet Survey Satellite (TESS) for the presence of stellar flares. The main aim is to detect stellar flares using 2 minute cadence data and to perform a statistical analysis. To find and analyze stellar flares, we prepared the automatic software WARPFINDER. We implemented three methods described in this paper: trend, difference, and profile fitting. Automated searches for flares was accompanied by visual inspection. Using our software we analyzed the 2 minute cadence light curves of 330,000 stars located in the first 39 sectors of TESS observations. As a result, we detected over 25,000 stars showing flare activity with the total number of more than 140,000 flares. This means that about 7.7% of all the analyzed objects are flaring stars. The estimated flare energies range between 1031 and 1036 erg. We prepared a preliminary preview of the statistical distribution of parameters such as the flare duration, amplitude, and energy, and compared it with previous results. The relationship between stellar activity and spectral type, temperature, and mass was also statistically analyzed. Based on the scaling laws, we estimated the average values of the magnetic field strength and length of the flare loops. In our work, we used both single (about 60%), and double (about 40%) flare profiles to fit the observational data. The components of the double profile are supposed to be related to the direct heating of the photosphere by nonthermal electrons and back-warming processes. [ABSTRACT FROM AUTHOR]

Determining the types of light curves has been a challenge due to the massive amount of light curves generated by large sky survey programs. In the literature, the light curves classification methods are overly dependent on the imaging quality of the light curves, so the classification results are often poor. In this paper, a new method is proposed to classify the Kepler light curves from Quarter 1, and consists of two parts: feature extraction and classification neural network construction. In the first part, features are extracted from the light curves using three different methods, and then the features are fused (transform domain features, light curve flux statistics features, and Kepler photometry features). In the second part, a classification neural network RLNet, based on Residual Network (ResNet) and Long Short Term Memory (LSTM), is proposed. The experiment involved the classification of approximately 150,000 Kepler light curves into 11 categories. The results show that this new method outperforms seven other methods in all metrics, with an accuracy of 0.987, a minimum recall of 0.968, and a minimum precision of 0.970 under all categories. [ABSTRACT FROM AUTHOR]

In the present paper, we define the three cases of the geometric phase equations associated with a monochromatic linearly polarized light wave traveling along an optical fiber in three-dimensional Walker manifold (M, ge f). Walker manifolds have many applications in mathematics and theoretical physics. We are working in the context of a pseudo-Riemannian manifold (i.e. a manifold equipped with a non-degenerate arbitrary signature metric tensor). That is, we generalize the motion of the light wave in the optical fiber and the associated electromagnetic curves that describe the motion of a charged particle under the influence of an electromagnetic field over a Walker space defined as a pseudo-Riemannian manifold with a light-like distribution, parallel to the Levi-Civita junction. These manifolds (especially Lorentzian) are important in physics because of their applications in general relativity. Then, we obtain the Rytov curves related to the cases of geometric phase models. Moreover, we give some examples and visualize the evolution of the electric field along the optical fiber in (M, ge f) via MAPLE program. [ABSTRACT FROM AUTHOR]

This paper investigates a new methodology to search for periods in light curves of high-energy gamma-ray sources such as active galactic nuclei (AGNs). High-energy light curves have significant stochastic components, making period detection somewhat challenging. In our model, periodic terms, drifts of the light curves, and random walk with a correlation between flux points due to colored noise are taken into account independently. The parameters of the model are obtained directly from a Markov Chain Monte Carlo minimization. The time periods found are compared to the output of the publicly available Agatha program. The search method is applied to high-energy periodic AGN candidates from the Fermi-LAT catalog. The significance of periodic models over pure noise models is discussed. Finally, the variability of the period and amplitude of oscillating terms is studied on the most significant candidates. [ABSTRACT FROM AUTHOR]

We characterize the variability in nearly continuous optical observations of the bright radio-loud quasar 3C 273 and nine additional active galactic nuclei detected with the Fermi Gamma-ray Space Telescope Large Area Telescope (Fermi-LAT). Optical observations were obtained during the K2 mission with the Kepler spacecraft for periods of 49 to 83 days conducted with ≃1 minute (short) or ≃30 minutes (long) cadences in 2015–2017. 3C 273 was quiescent during the course of the observations, varying by only a factor of 1.02. Three objects, PKS 0047+023, PKS 1216-10, and PKS B2320-035, were active, varying by factors of 1.8–3.4. Six other objects were comparatively quiet, varying by factors of less than 1.4. Power spectral densities (PSDs) were calculated for each object. Overall, the slopes of most PSDs, as well as those we reported in an earlier paper, were in the range −2.0 to −2.7 and are consistent with those produced by turbulence in the relativistic jet, and not by "hot spots" in the disk emission. Mechanisms operating in the jet other than turbulence, such as "mini-jets" or "jet-in-jets", may also produce the observed range of PSD slopes. Both accretion disk and jet models are plausible origins for the 3C 273 optical variability during the K2 observations. [ABSTRACT FROM AUTHOR]

Type IIb supernovae (SNe IIb) present a unique opportunity for investigating the evolutionary channels and mechanisms governing the evolution of stripped-envelope SN progenitors due to a variety of observational constraints. Comparison of these constraints with the full distribution of theoretical properties not only helps determine the prevalence of observed properties in nature, but can also reveal currently unobserved populations. In this follow-up paper, we use the large grid of models presented in Sravan et al. to derive distributions of single and binary SNe IIb progenitor properties and compare them to constraints from three independent observational probes: multiband SN light curves, direct progenitor detections, and X-ray/radio observations. Consistent with previous work, we find that while current observations exclude single stars as SN IIb progenitors, SN IIb progenitors in binaries can account for them. We also find that the distributions indicate the existence of an unobserved dominant population of binary SNe IIb at low metallicity that arise due to mass transfer initiated on the Hertzsprung Gap. In particular, our models indicate the existence of a group of highly stripped (envelope mass ∼0.1–0.2M☉) progenitors that are compact (<50R☉) and blue (Teff ≲ 105 K) with ∼104.5–105.5L☉ and low-density circumstellar mediums. As discussed in Sravan et al., this group is necessary to account for SN IIb fractions and likely exist regardless of metallicity. The detection of the unobserved populations indicated by our models would support weak stellar winds and inefficient mass transfer in SN IIb progenitors. [ABSTRACT FROM AUTHOR]

Supernova explosions emit debris including neutrinos and antineutrinos. In a previous paper these were linked to a hypothetical acceleron field and the variations in this acceleron field as the blast reached Earth were investigated as a cause for accelerated nuclear decays. In this paper some of the collateral reactions which would result are investigated to see if they are consistent with known things. This includes the known detections which are associated with Supernova 1987A and other supernovae. Also, the rate of supernova detections on Earth is considered. One cannot induce stars to explode, so we must be content with what has been observed. We find that there are no observations available at present which would rule out the existence of the acceleron field and the associated particle, as long as it has a mass within a specified range. Also, the recent discovery of uranium's presence in the spectra of some galactic halo stars is discussed in the context of the acceleron mechanism. A separate paper will discuss the dependence of supernova light curves on the nuclear decay of relevant nuclei. [ABSTRACT FROM AUTHOR]

With the advent of space-based precision photometry missions, the quantity and quality of starspot light curves has greatly increased. This paper presents a large number of starspot models and their resulting light curves to (1) better determine light-curve metrics and methods that convey useful physical information and (2) understand how the underlying degeneracies of the translation from physical starspot distributions to the resulting light curves obscure that information. We explore models of relatively active stars at several inclinations while varying the number of (dark) spots, random spot distributions in position and time, timescales of growth and decay, and differential rotation. We examine the behavior of absolute and differential variations of individual intensity dips and overall light curves and demonstrate how complex spot distributions and behaviors result in light curves that typically exhibit only one or two dips per rotation. Unfortunately, simplistic "one- or two-spot" or "active longitude" descriptions or modeling of light curves can often be highly misleading. We also show that short "activity cycles" can easily be simply due to random processes. It turns out to be quite difficult to disentangle the competing effects of spot lifetime and differential rotation, but under most circumstances, spot lifetime is the more influential of the two. Many of the techniques tried to date only work when spots live for many rotations. These include autocorrelation degradation for spot lifetimes and periodograms for both global and differential rotation. Differential rotation may be nearly impossible to accurately infer from light curves alone unless spots live for many rotations. The Sun and solar-type stars its age or older are unfortunately the most difficult type of case. Further work is needed to have increased confidence in light-curve inferences. [ABSTRACT FROM AUTHOR]

It is generally supposed that a transition from the normal decay phase (decay slope ∼−1) to a steeper phase (decay slope ∼−2) could be suggested as a jet break. The jet opening angle θjet is then calculated from the jet break time of the afterglow light curve. This allows the derivation of the collimation-corrected energy Ejet of those gamma-ray bursts (GRBs). We extensively searched for the GRBs with jet break features from multiwavelength afterglow light curves, and 138 GRBs with significant breaks were collected. The jet break times of those GRBs mainly range from 1000 to 106 s, and the distribution of the collimation-corrected energy Ejet peaks at ∼1050 erg. We also confirmed the Eγ,iso−Ep,i, Ejet−Ep,i and Eγ,iso−θjet relations, and found Eγ,iso−Tj,z−Ep,i relation remains tight with more multiwavelength data. This tight Eγ,iso−Tj,z−Ep,i relation is also conformed by different groups of our selected GRBs in the paper. In addition, another two new and tighter correlations among Ejet−Tj,z−Ep,i are well confirmed for different circumburst mediums in this paper. We suggest that those tight three-parameter correlations are more physical, and could be widely applied to constrain the cosmological parameters. [ABSTRACT FROM AUTHOR]

In the present paper, we obtained the first orbital solution for the newly discovered W UMa systems: GSC 3983-0544 and GSC 4502-1040. We used the most recent version of the Wilson-Devinney code to model the light curves of the two systems. The spectral type of the components of the two systems was adopted and the accepted solutions revealed some absolute parameters, which enable us to draw a preliminary picture of their evolutionary status. [ABSTRACT FROM AUTHOR]

Near Earth Object (NEO) 2020 SO is believed to be a Centaur rocket booster from the mid 1960's that was temporarily recaptured by the Earth. 2020 SO entered Earth's Hill sphere in November 2020, with close approaches in December 2020 and February 2021, where it became bright enough (approximately 14 V magnitude) to be observed by Raven-class (< 1 m) telescopes. In this paper, 2020 SO's spin state and reflective properties are estimated using data collected from multiple telescope sites around the world during both close approaches. The 95% Highest Posterior Density (HPD) region and Maximum A Posteriori (MAP) spin state and reflective properties of 2020 SO are estimated using Bayes' theorem via Markov Chain Monte Carlo (MCMC) sampling of a predictive light curve simulation that is based on an anisotropic Phong reflection model. We estimate ten parameters at the start of an observation epoch: attitude quaternion (4), angular velocity vector (3), and diffusive/specular reflectivity parameters (3). Using a Fourier fitting and least squares minimization technique we find a joint-estimated period of 9.328 ± 0.275 s at a 2 σ confidence level in the light curves of 2020 SO that further provides support for it being an artificial object as the current most rapidly rotating known asteroid is 2017 QG18 with a period over 1.3 times slower. The method of light curve inversion employed in this paper can be applied directly to other NEOs given photometric observations with a high enough temporal density and knowledge of some approximate physical properties of the object. [ABSTRACT FROM AUTHOR]

MRK 421 is a giant elliptical galaxy in the Ursa Major constellation whose core has all the properties of a BL Lac object. It manifests a high activity and variability from the radio to gamma-ray ranges on time scales from a few hours to more than 10 years. MRK 421 has a large companion— a spiral, probably, also active galaxy (MRK 421-5). This paper presents the results of an analysis of observations (in the V, R, and I bands) as part of a joint Latvian-Ukrainian project for study of the variability of bright AGN. In addition, the light curves of MRK 421 from the AAVSO data base (American Association of Variable Star Observers) are analyzed to confirm the results of periodogram analysis. Ultimately, over the time interval studied here, MRK 421 is suspected of having a cyclical variability with a characteristic time in the range of 9.3-13.4 days determined by two different methods (approximation of the data by sinusoids and the CLEANest method), which is confirmed by an analysis of longer observations of MRK 421 in the V band (with AAVSO data). The longer variability of MRK 421 was also analyzed. It was found that in the V, R, and I light curves from AAVSO the maxima of the LS-periodograms correspond to periods of 1.6-1.7 years. This is close to earlier results from an analysis of historical light curves of MRK 421 obtained by other authors. The AAVSO data also indicate the presence in MRK 421 of a longer cycle of brightness variation with a characteristic time of 20-30 years. [ABSTRACT FROM AUTHOR]

In this paper, we examine the trajectory, orbital, and radiometric characteristics of the bolide event occurring off the coast of southern Florida and the Grand Bahama Island on April 13, 2021. An object measuring about 1.3 m in diameter entered the atmosphere at approximately 02:16:40 UTC at a velocity of 16 km s−1. It took an almost due north course between Florida and Grand Bahama Island, terminating in the Atlantic Ocean. No fragments have been recovered up to the date of submission of this paper. We used a fragmentation model to infer the internal structure of the object. We found that the best fit to the light curve and height of the peak energy deposition is with a weak stony meteor, with a density of about 2000 kg m−3, that disrupted and fragmented quickly, over a time interval of 1.5 s, or over a distance of about 11 km in altitude, between 45 and 34 km. We find that the impactor had a preatmospheric mass of 2.5 ± 0.5 t, resulting in a diameter of about 1.34 ± 0.09 m. We performed a backward integration of the trajectory to determine an orbit and found that the impacting object was a Jupiter family comet with a semimajor axis of about 3.6 AU, and an inclination of 9°, which is consistent with our analysis from the fragmentation model. We could not find a suitable candidate for a parent body. [ABSTRACT FROM AUTHOR]

Context. Understanding the effects of rotation in stellar evolution is key to modelling early-type stars, half of which have equatorial velocities over 100 km s−1. The nearby star Altair is an example of such fast-rotating stars, and furthermore, it has the privilege of being modelled by a detailed 2D concordance model that reproduces most of its observables. Aims. The aim of this paper is to include new asteroseismic frequencies to improve our knowledge of Altair, especially its age. Methods. We processed images of Altair obtained during July 2022 by the Transiting Exoplanet Survey Satellite using the halo photometry technique to obtain its light curve over this observation period. Results. By analysing the light curve, we derived a set of 22 new frequencies in the oscillation spectrum of Altair and confirmed 12 previously known frequencies. Compared with model predictions, we could associate ten frequencies with ten axisymmetric modes. This identification is based on the modelled visibility of the modes. Moreover, nine of the modelled frequencies can be adjusted to simultaneously match their corresponding observed frequencies, once the core hydrogen mass fraction of the concordance model is set to Xcore/Xini ≃ 0.972, with Xini = 0.739. Using the combined results of a 1D MESA model computing the pre-main sequence and a 2D time-dependent ESTER model computing the main sequence, we find that this core hydrogen abundance sets the age of Altair to 88 ± 10 Myr, which is slightly younger than previous estimates. [ABSTRACT FROM AUTHOR]

Context. Periodic quasi-stellar objects (QSOs) are considered as candidates of supermassive binary black hole (BBH) systems in galactic centers. The periodicity of their light curves can be interpreted as being due to the Doppler boosting caused by the rotation of the two black holes (BHs). Further confirmation of these candidates may require different lines of observational evidence. Aims. Assuming the Doopler boosting scenario, in this paper we investigate the (coherent) variations of broad emission lines (BELs) and continuum light curves for active BBH systems surrounded by a circumbinary broad-line region (cBLR) and focus on their dependence on the eccentric orbital configuration. Methods. We calculated the variation of continuum light according to the motion of BBHs on elliptical orbits, with simplified orbital orientation for demonstration, the Doppler enhanced or weakened photoionization of each BLR cloud by the central BBH sources and its variation by assuming a shifted Γ-distribution of BLR clouds for a simple BLR geometry, and finally obtain the coherent variation of the continuum and the BELs. Results. We find that the amplitude and variation pattern of the continuum light curves and the evolution of the BEL profiles both sensitively depend on the eccentric orbital configuration of BBH systems, especially when the eccentricity is high. If only the secondary BH is active, the variation amplitudes of continuum light curves and BELs both increase with increasing BBH inclination angles and orbital eccentricities, but decrease with increasing BBH mass ratio. If both BHs are active, the asymmetry in the ionization of BLR clouds at different areas caused by the Doppler boosting effect of the secondary BH is weakened due to that of the primary BH at the opposite direction, which leads to systematically smaller variation amplitudes of both continuum light curves and BELs compared with those in the cases where only secondary the BH is activated. Conclusions. The coherent variations of the BEL profiles with the continuum light for those periodic QSOs provide an important way to confirm the existence of BBHs in their center. Future joint analysis of the light curves and multi-epoch observed BEL profiles for periodic QSOs may lead to the identification of a number of BBH systems. [ABSTRACT FROM AUTHOR]