Observatory Research Articles

Detection of thioacetaldehyde (CH_3CHS) in TMC-1 : Sulfur-oxygen differentiation along the hydrogenation sequence

In recent years, the chemistry of sulfur in the interstellar medium has experienced renewed interest due to the detection of a large variety of molecules containing sulfur. We report the first identification in space of a new S-bearing molecule, thioacetaldehyde (CH_3CHS), which is the sulfur counterpart of acetaldehyde (CH_3CHO). The astronomical observations are part of QUIJOTE, a Yebes,40m Q-band line survey of the cold dense cloud TMC-1 . We detected seven individual lines corresponding to A and E components of the four most favorable rotational transitions of CH_3CHS covered in the Q band (31.0-50.3 GHz). Assuming a rotational temperature of 9 K, we derive a column density of 9.8,times,10^10 cm^-2 for CH_3CHS, which implies that it is 36 times less abundant than its oxygen counterpart CH_3CHO. By comparing the column densities of the O- and S-bearing molecules detected in TMC-1 we find that as molecules increase their degree of hydrogenation, sulfur-bearing molecules become less abundant than their oxygen analog. That is, hydrogenation seems to be less favored for S-bearing molecules than for O-bearing ones in cold sources such as TMC-1 . We explored potential formation pathways to CH_3CHS and implemented them into a chemical model, which underestimates the observed abundance of thioacetaldehyde by several orders of magnitude, however. Quantum chemical calculations carried out for one of the potential formation pathways, the S + C_2H_5 reaction, indicate that formation of CH_3CHS is only a minor channel in this reaction.

Research on Conjecture of Dark Energy

An in-depth exploration of the origin of dark energy is undertaken. Dark energy is a fascinating and mysterious concept within the realm of astrophysics. It was discovered through a series of astronomical observations and theoretical studies. For instance, the observation of distant supernovae revealed the accelerating expansion of the universe, leading to the postulation of an unknown forcedark energy. The crucial role played by dark energy in the universe is then delved into. It is now widely accepted that dark energy is responsible for accelerating the expansion of the universe. This has significant implications for the understanding of the cosmos and its ultimate fate. Next, the relationship between other matter in relation to celestial bodies and dark energy is examined. Black holes and dark matter are two important components of the universe that have a complex interaction with dark energy. Having immense gravitational pulls, black holes and dark matter, which is believed to make up a large portion of the total matter in the universe, both influence the distribution and behavior of dark energy. The current inferences about dark energy and some famous hypotheses put forward by renowned scientists are also discussed. These hypotheses range from modifications of general relativity to the existence of extra dimensions and new forms of matter. Finally, personal thoughts and speculations on the relationship between dark energy and the higher-dimensional universe are offered. The idea of a higher-dimensional universe has intrigued scientists for decades, and there is growing interest in exploring whether dark energy could be related to these hidden dimensions. This could potentially open up new avenues for understanding the fundamental nature of the universe and its mysteries

Addressing Distribution Discrepancies in Pulsar Candidate Identification via Bayesian-neural-network-based Multimodal Incremental Learning

Abstract With the advancement of astronomical observation technology and the substantial increase in data volume, traditional methods for pulsar identification are increasingly challenged by the dynamic nature of data distributions. To address this, our study introduces a multimodal incremental learning approach utilizing Bayesian neural networks. This method enables the model to adapt to new data distributions while preserving the knowledge of previous data. In our experiments, we utilized pulsar data sets from two telescopes and compared our new method with traditional techniques. The research results demonstrate that our method performs comparably to traditional methods across all evaluation metrics, while showing a significant improvement in handling data distribution discrepancy, with the F1-score increasing from approximately 70% to over 95%. Specifically, our model achieved an accuracy of 97.93%, a recall of 96.13%, and an F1-score of 97.02% under conditions of distributional disparities. These findings not only confirm the model's capability to adapt to dynamic data environments but also effectively address the challenges of data distribution discrepancy, significantly enhancing the predictive accuracy of pulsar identification in the context of evolving and variable radio frequency interference environments.

Astronomical Observatories in Thrace: Archaeoastronomical Data as Indication of Ancient Sun-Related Spiritual Practices (3rd-1st millennia BC)

In the past rock-cut monuments were used for horizon or meridional observations of solstices and equinoxes. This study focuses on three of the better studied through the means of archaeoastronomy monuments in Thrace – Tangardak kaya, Harman kaya and Zaychi vrah (Cabyle). The additional carvings of Tangadak kaya womb-cave suggest that it was used not simply for Sun-observation, but also for ancient Sun-related spiritual practices during the winter solstice. Similar practices were used two millennia later in the Golyama Arsenalka Thracian Tomb’s domed chamber, which shows that in Thrace there was a millennial continuity of ancient spiritual beliefs.

Why the Real Atmosphere Has More Energy than Climate Models: Implications for Ground-Based Telescopes

The calculation of Gibbs free energy via the statistical multifractal analysis of airborne observations indicates that the atmosphere is not at local thermodynamic equilibrium. Both climate models and meteorological analyses assume that it is. Satellite retrievals use spectroscopic data taken at equilibrium in laboratories, leading to apparent consistency that is to some degree faulty. Line shapes of radiatively active species, the rotational energy of molecular nitrogen and oxygen, and the translational energy of all molecules are involved, resulting in less energy in models than exists in the real atmosphere. The resulting formulation of turbulence is from the smallest scales up and has implications for astronomical observation by adaptive optics. Kolmogorov (isotropy) is not evident. The effect of temperature on the overhead water vapour column at ground-based telescopes is also open to the effects of climate change. The degree to which the dynamic operational temperature differs from that obtained by the use of local thermodynamic equilibrium assumptions needs to be established by observational measurements. Some of the considerations will apply to the atmospheres of exoplanets with regard to photochemistry and signatures of life.

Modal Noise Mitigation and Scrambling Performance of a Compound Scrambler

Abstract Fiber scrambling is integral to high-precision calibration systems for radial velocity (RV) measurements, crucial in the quest for exoplanet discovery. Coherent light sources, like laser frequency combs, often induce laser speckles, a form of modal noise, which can result in spectra calibration errors. The starlight collected in astronomical observations is often polychromatic light. This study investigates the speckle-like mode noise generated under incoherent light, identifying a clear correlation between fiber length and the intensity of this noise. Remarkably, experiments using LED illumination showed that fibers shorter than 2 m exhibit significant speckle-like noise, manifesting as distinctive ripple-like structures, a newly identified phenomenon referred to as modal patterns. Mitigation techniques, including squeezing and vibrating methods, can reduce contrast and suppress modal patterns effectively. To further enhance scrambling performance, a novel fiber scrambling approach, the compound scrambler, is proposed. This design integrates laser polishing, thermal heating, and fiber tapering techniques to enhance near-field uniformity. Utilizing a combination of non-circular and graded index fibers, the compound scrambler achieves notable improvements in scrambling gain (SG). A refined nondestructive fabrication method, leveraging the superior scrambling effect of non-circular fibers and the efficiency of adiabatic taper structures, achieves a high SG of 1064. These findings contribute to advancing high-precision spectrograph design, offering practical solutions to enhance RV measurement accuracy. The compound scrambler's integrity and modular design promise stability, longevity, and scalability, holding immense potential for astronomical instrumentation.

Theoretical investigation of the A1Π–X1Σ+, B1Σ+–X1Σ+, C1Σ+–X1Σ+, and E1Π–X1Σ+ transitions of the CO molecule

Potential energy and dipole moment curves for CO are calculated using a high level theory and diabatised. The resulting curves are used to compute electronic spectra of CO found in agreement with laboratory and astronomical observations.

Absorption spectra of PS in the ultraviolet and infrared region.

The line list is essential for accurately modeling various astrophysical phenomena, such as stellar photospheres and atmospheres of extrasolar planets. This paper introduces a new line database for the PS molecule spanning from the ultraviolet to the infrared regions, covering wavenumbers up to 45000cm-1 and containing over ten million transitions between 150,458 states with total angular momentum J<160. Accurate line intensities for rotational, vibrational and electronic transitions are generated by using the general purpose variational code DUO. Before applying the DUO program, the potential energy curves (PECs), the electric dipole transition moments (EDTMs) and the spin-orbit coupling (SOC) matrix need to be provided, which are computed by an ab initio method at the icMRCI level. The DUO program is executed to generate two files - a state file and a transition file, which are provided to the ExoCross program which supply cross sections, intensities, partition functions, lifetimes and quantum number assignments. The cross-sections and intensities for the observed transitions are necessary for the correct modeling of the spectra. Tests of the line lists show that our predictions not only provide a favorable comparison with the experimental spectrum but also a cornerstone for various astronomical observations.

The Normative Basis of Islamic Astronomy For The Transformation of Prayer Schedules To Digital And Its Accuracy

The provisions for prayer times have been determined based on the instructions contained in the Qur'an and Sunnah. The Prophet gave an example of starting a prayer time based on the shadow of an object perpendicular to the sun's position relative to the earth. For example, the midday prayer is set when the sun is at its culmination. This shows that the determination of the start of the prayer time is based on the observation of the sun which must be in a certain position for each prayer time. These provisions are transformed into a set of mathematical formulas based on ongoing astronomical observations. In subsequent developments, this prayer schedule will not only be in hard copy form but also in the form of a website and Android application. Several Android applications display the starting schedule for prayers in a place that is different from the others. Every android application that displays prayer times should refer to the initial provisions of the times stipulated in the Shari'a and Fiqh, not limited to mere calculations, nor is there an API which is a common reference for program developers. There needs to be a unified standard calculation system for the android application for prayer times. It is also necessary to make a standard API and Indonesian standards in accordance with the fiqh provisions for the start of prayer times set in Indonesia.

Enhanced detection and identification of satellites using an all-sky multi-frequency survey with prototype SKA-Low stations

Abstract With the low Earth orbit environment becoming increasingly populated with artificial satellites, rockets, and debris, it is important to understand the effects they have on radio astronomy. In this work, we undertake a multi-frequency, multi-epoch survey with two SKA-Low station prototypes located at the SKA-Low site, to identify and characterise radio frequency emission from orbiting objects and consider their impact on radio astronomy observations. We identified 152 unique satellites across multiple passes in low and medium Earth orbits from 1.6 million full-sky images across 13 selected ≈ 1 MHz frequency bands in the SKA-Low frequency range, acquired over almost 20 days of data collection. Our algorithms significantly reduce the rate of satellite misidentification, compared to previous work, validated through simulations to be &lt; 1%. Notably, multiple satellites were detected transmitting unintended electromagnetic radiation, as well as several decommissioned satellites likely transmitting when the Sun illuminates their solar panels. We test alternative methods of processing data, which will be deployed for a larger, more systematic survey at SKA-Low frequencies in the near future. The current work establishes a baseline for monitoring satellite transmissions, which will be repeated in future years to assess their evolving impact on radio astronomy observations.

Determination of dynamic and physical characteristics of near-Earth asteroids based on observations from 2022–2023

Astrometric and multicolor photometric observations of near-Earth asteroids have been made at the SBG telescopes of the Kourovka Astronomical Observatory of the UrFU and the Zeiss-1000 telescope of the Simeiz Observatory in 2022–2023. Improved orbital elements were obtained for seven asteroids from astrometric observations at the SBG telescope. Axial rotation periods were estimated from photometric observations for seven asteroids. Color indices for six asteroids were obtained from photometric observations in B, V, R, and I filters.

Infrared Spectroscopy of Isocyano-Polycyclic Aromatic Hydrocarbons: The NC Stretch.

Anharmonic computations reveal an intense, narrow (20 cm-1, 0.043 μm) absorption feature at approximately 2160 cm-1 (4.63 μm) in the vibrational spectra of 14 prototypical singly isocyano-substituted polycyclic aromatic hydrocarbons (NC-PAHs) attributed to the NC stretching mode. The intrinsically bright NC stretching mode and strong anharmonic coupling to other states in this region of the spectrum, along with the presence of multiple isomers of each NC-PAH, creates a complex, intense band for each molecule alone, and for the group of molecules as a whole. The NC stretching feature is shifted approximately 130 cm-1 to lower frequency compared to the CN stretching feature of cyano-substituted PAHs. This shift is due to the weaker NC bond as a result of the zwitterionic character of the NC-PAHs. Advanced resonance polyad matrices are utilized in the second order vibrational perturbation treatment, providing in-depth understanding of the spectroscopic characteristics of each vibrational transition. These detailed spectroscopic data are provided for use in analysis of future laboratory experiments and the search for NC-PAHs in astronomical observations. Such data will be vital to the continued benchmarking of computational methodologies for use in exotic, substituted PAHs that have never been studied before.

Study of observed changes in the first harmonic amplitude of the daily precipitation amount series in the territory of Russia

Using the data from weather observation stations, an assessment of the statistical significance of the first harmonic amplitude of the average long-term daily precipitation amount series in Russia in 1961–2020 and their changes in 1991–2020 compared to 1961–1990 is made. It is shown that at most stations the first harmonic has a reliable value different from the noise, except for eleven stations in the southern regions of the European Part of Russia. It is revealed that, on average, there is a significant decrease in the first harmonic amplitudes of the daily precipitation series across Russia. An analysis of the spatial distribution of the studied quantities is performed and the presence of large areas with their homogeneous character is demonstrated.

Monthly High‐Resolution Historical Climate Data for North America Since 1901

ABSTRACTInterpolated grids of historical climate variables are widely used in climate change impact and adaptation research. Here, we contribute monthly historical time series grids since 1901 for our data product ClimateNA, which integrates historical data and future projections to generate high‐resolution gridded data and point estimates for North America. The historical climate grids in this study are based on interpolations of monthly anomalies (change factors) with thin‐plate splines, but a novel aspect is that we rely on high‐quality 1961–1990 normal estimates from ClimateNA to serve as reference for the change factor calculations instead of the reference being derived from station data itself. This allowed us to utilise records from 66,282 climate stations for interpolations, regardless of their temporal coverage. Another aspect that deviates from standard practice is that we reduce overfitting by optimising thin‐plate splines at a 0.5° grid level instead of fitting weather station observations directly. The high‐resolution grids generated with this approach compared favourably with other time series products, such as Daymet and advanced multi‐source products, such as MSWEP, in statistical and mapped visual comparisons, and provide additional historical coverage since the beginning of the 20th century.

The Multimodal Universe: 100 TB of Machine Learning Ready Astronomical Data

Abstract We present the Multimodal Universe, a new framework collating over 100 TB of multimodal astronomical data for its first release, spanning images, spectra, time series, tabular and hyper-spectral data. This unified collection enables a wide variety of machine learning (ML) applications and research across astronomical domains. The dataset brings together observations from multiple surveys, facilities, and wavelength regimes, providing standardized access to diverse data types. By providing uniform access to this diverse data, the Multimodal Universe aims to accelerate the development of ML methods for observational astronomy that can work across the large differences in astronomical datasets. The framework is actively supported and is designed to be extended whilst enforcing minimal self consistent conventions making contributing data as simple and practical as possible.

Defective flux and splicing abnormality restoration of stellar spectra in LAMOST based on deep learning

Abstract Sky surveys such as the Large Sky Area Multi-Object Fibre Spectroscopic Telescope can capture numerous spectra. However, many factors in astronomical observations, such as observation conditions and instrumental effects, can degrade spectrum quality, resulting in defective fluxes and splicing abnormality. These factors significantly reduce the precision of scientific information extracted from such spectra. In the past, these flux values were considered unreliable and their utilization was low. Thus, it is crucial to develop and utilize spectra restoration algorithms to improve spectra quality and enable further scientific exploration. Unfortunately, few research has been done on these low-quality spectra. In this paper, we propose a novel spectrum restoration algorithm, which is called the Anomaly Spectra Restoration Generative Adversarial Nets (Anomaly_GANs) based on Generative Adversarial Networks (GANs). The experiment shows that the performance of Anomaly_GANs is better than those of other methods concerning spectrum restoration. Therefore, our method can serve as an effective approach for spectrum restoration, providing a suitable replacement for previous methods.

Optimization Design of Pt/C Multilayer Supermirrorsfor Hard X-rays

Aperiodic multilayers have important applications in hard X-rays astronomical observations due to their broadband responses. This paper presents an optimization model of Pt/C power-law graded stack multilayers using the IMD software. The reflectivity expression of multilayers was derived from the reflection theory of X-ray multilayers and Fresnel recursion formulas. Then, the effects of maximum bi-layer thickness ([Formula: see text]), ratio of high-density material thickness to bi-layer thickness ([Formula: see text]), power-law index ([Formula: see text]), number of bi-layers ([Formula: see text]), grazing incidence angle ([Formula: see text]), interfacial roughness ([Formula: see text]), and photon energy ([Formula: see text]) on the reflectivity were analyzed. The calculation results showed that the [Formula: see text], [Formula: see text] and [Formula: see text] control the shift of response range, absorption peak and Bragg peaks, respectively. And the decrease of [Formula: see text] and increase of [Formula: see text] and [Formula: see text] can result in the reduction of reflectivity at different energies. Additionally, an optimized multilayer structure was proposed according to the extremum of merit function, which can achieve a broadband reflectivity of no less than 0.6 from 1[Formula: see text]keV up to 80[Formula: see text]keV. These results can provide important references for the response characteristic analysis and optimization design of multilayers.

Eppur si muove: Evidence of disc precession or a sub-milliparsec SMBH binary in the QPE-emitting galaxy GSN 069

X-ray quasi-periodic eruptions (QPEs) are intense soft X-ray bursts from the nuclei of nearby low-mass galaxies typically lasting about one hour and repeating every few hours. Their physical origin remains a matter of debate, although so-called impact models appear promising. These models posit a secondary orbiting body piercing through the accretion disc around the primary supermassive black hole (SMBH) in an extreme mass-ratio inspiral (EMRI) system. In this work, we study the QPE timing properties of GSN 069, the first galactic nucleus in which QPEs have been identified. We primarily focus on observed minus calculated (O-C) diagrams. The O-C data in GSN 069 are consistent with a super-orbital modulation of several tens of days, whose properties do not comply with the impact model. We suggest that rigid precession of a misaligned accretion disc or, alternatively, the presence of a second SMBH forming a sub-milliparsec binary with the inner EMRI is needed to reconcile the model with the data. In both cases, the quiescent accretion disc emission should also be modulated on similar timescales. Current X-ray monitoring indicates that this might be the case, although a longer baseline of higher cadence observations is needed to confirm the tentative X-ray flux periodicity on firm statistical grounds. Future dedicated monitoring campaigns will be crucial for testing the overall impact-plus-modulation model in GSN 069 and to distinguish between the two proposed modulating scenarios. If our interpretation is correct, QPEs in GSN 069 represent the first electromagnetic detection of a short-period EMRI system in an external galaxy, paving the way to future multi-messenger astronomical observations. Moreover, QPEs encode unique information on SMBHs inner environments, which can be used to gain insights on the structure and dynamics of recently formed accretion flows and to possibly infer the presence of tight SMBH binaries in galactic nuclei.

Ground-Based Cloud Image Segmentation Method Based on Improved U-Net

Cloud image segmentation is a technique that divides images captured by meteorological satellites or ground-based observations into different regions or categories. By extracting the distribution, shape, and dynamic features of clouds, it provides precise data support for the meteorological and environmental fields, significantly influencing photovoltaic (PV) power generation forecasting, astronomical telescope observatory site selection, and weather forecasting. A ground-based cloud image segmentation model based on an improved U-Net is proposed, which adopts an overall encoder–decoder structure. In the encoder phase, this paper constructs a dilated convolution–atrous spatial pyramid pooling (ASPP)–dilated convolution structure to enhance early cloud feature extraction. Dilated convolution is a novel type of convolution that expands the receptive field by inserting holes into standard convolution, thereby capturing a larger range of contextual information. ASPP maintains high resolution while paying attention to both local details and global structures of the image. In the decoder stage, the bicubic interpolation method is used for up-sampling to restore the feature map resolution and improve the clarity of the segmented image. The bicubic interpolation method refers to the use of cubic polynomial functions to interpolate the pixel values of the input image. In addition, this paper designs a novel skip connection layer structure between the encoder and decoder, composed of a depthwise separable path (DS path) and an improved channel spatial attention module (Im-CSAM) connected in sequence. The DS path combines depthwise separable convolutions and residual structures to facilitate information exchange between high-level and low-level features. The Im-CSAM is a modular attention mechanism that focuses on important cloud features in spatial and channel dimensions to enhance segmentation accuracy. Experiments show that compared to the traditional U-Net, the accuracy, precision, and MIoU of this model improved by 2.2%, 4.1%, and 5.0%, respectively, in the SWINySEG dataset, and by 3.2%, 3.6%, and 5.8%, respectively, in the TCDD dataset, proving that the improved method has a better generalization ability and segmentation performance.

Bouguer and Lambert’s pioneering contributions to goniophotometric reflectance measurements and models: retrospective

Written independently and published in the same year, 1760, Bouguer’s Traité d’optique and Lambert’s Photométria are the foundations of photometry. We discuss their thoughts and pioneering contributions to the measurement and modeling of light reflected by matte materials, as well as the scattering of sunlight by the Moon and other planets toward Earth. With the law that now bears his name, Lambert introduced an approximation that is still widely used today, thanks to its simplicity. Bouguer presented the first goniophotometric measurements of diffuse reflectance. He developed models representing a rough surface by a set of either small hemispheres for astronomical observations or small randomly oriented facets to describe matte materials. In the latter case, he proposed a graphical representation of the distribution of surface asperities. We look at how Bouguer’s work has been perceived over time, and in particular how it gave rise to the microfacet models developed from the end of the 20th century and widely used in computer graphics. This historical overview highlights the relevance of these two 18th-century scientists’ reflections, which are a source of inspiration for new perspectives in the photometric characterization of matte materials.