Observatory Research Articles

A Galaxy Image Augmentation Method Based on Few-shot Learning and Generative Adversarial Networks

Galaxy morphology classifications based on machine learning are a typical technique to handle enormous amounts of astronomical observation data, but the key challenge is how to provide enough training data for the machine learning models. Therefore this article proposes an image data augmentation method that combines few-shot learning and generative adversarial networks. The Galaxy10 DECaLs data set is selected for the experiments with consistency, variance, and augmentation effects being evaluated. Three popular networks, including AlexNet, VGG, and ResNet, are used as examples to study the effectiveness of different augmentation methods on galaxy morphology classifications. Experiment results show that the proposed method can generate galaxy images and can be used for expanding the classification model’s training set. According to comparative studies, the best enhancement effect on model performance is obtained by generating a data set that is 0.5–1 time larger than the original data set. Meanwhile, different augmentation strategies have considerably varied effects on different types of galaxies. FSL-GAN achieved the best classification performance on the ResNet network for In-between Round Smooth Galaxies and Unbarred Loose Spiral Galaxies, with F1 Scores of 89.54% and 63.18%, respectively. Experimental comparison reveals that various data augmentation techniques have varied effects on different categories of galaxy morphology and machine learning models. Finally, the best augmentation strategies for each galaxy category are suggested.

Cloud Identification and Reconstruction from All-sky Camera Images Based on Star Photometry Estimation

Cloud cover significantly influences ground-based optical astronomical observations, with nighttime astronomy often relying on visible light all-sky cameras for cloud detection. However, existing algorithms for processing all-sky cloud images typically require extensive manual intervention, posing challenges in identifying clouds with pronounced extinction characteristics. Furthermore, there is a lack of effective means for detailed visualization of cloud cover. To address these issues, this paper proposes a method that reconstructs the cloud distribution and thickness from all-sky images through star identification and photometry. Specifically, a high-precision star coordinate to the pixel position imaging model calibration method based on the star recognition for fisheye lenses is investigated, resulting in an all-sky rms error of less than 0.87 pixels. Based on the comprehensive reference star catalog, an optimized star extraction method based on SExtractor is developed to handle the difficulty of image source detection in all-sky cloud images. The optical thickness and distribution of cloud layers is calculated through star matching and extinction measurements. Finally, contingent upon the capability of camera and catalog star density, seven cloud layer reconstruction methods are proposed based on meshing and machine learning techniques, achieving a reconstruction accuracy of up to 1.°8. The processing results from real observed images indicate that the proposed method offers a straightforward calibration process and delivers excellent cloud cover extraction and reconstruction outcomes, thereby providing practical value in telescope dynamic scheduling, site characterization and the development of observation strategies.

Contamination of spectroscopic observations by satellite constellations

Context. With the onset of large telecommunication constellations, the number of satellites on low orbits has dramatically increased over the past years, raising concerns among the astronomical community about their impact on observations. Aims. Since spectroscopic observations represent a large fraction of professional astronomical observations and given that spectro-graphs lack spatial information that can reveal the presence of a satellite, this paper is focused on how satellites affect spectroscopic optical observations. Methods. We simulated how often satellites contaminate spectrograph observations by using realistic constellations with over 400 000 objects. We counted the satellites that crossed a representative 10 × 1" slit during a 1000 s exposure, for different solar elevations and observation directions. We also measured how a satellite affects a spectrum by using real data from different scientific targets and a scaled solar analog as the satellite. We then used standard tools to measure astrophysical parameters and compare them with the clean spectrum. Results. As expected, the fraction of affected spectra varies dramatically with the direction of the observation and the elevation of the sun, with a maximum of 10% at twilight down to no contamination when the sun reaches −30°, with a nightly average of ~2%. The probability of a satellite crossing over the astronomical target will be further reduced depending on the target’s apparent size. Because of the fast motion of the satellites and the limiting magnitude of the spectrographs, high-resolution instruments are essentially blind to most satellites. For lower resolution spectrographs, the effect on the measured astrophysical parameters depends strongly on the signal-to-noise ratio of the exposure, longer exposures on brighter targets being the least affected at ≲1%. Satellites that are brighter and/or higher than the constellation satellites, while less numerous, can also contaminate the spectra. Conclusions. Satellites (either coming from a large constellation or not) have the potential to contaminate spectra. While the fraction of affected spectra is likely to remain low even with a number of satellites about 100× larger than today, some of these contaminated spectra will be difficult to identify, as is already the case with existing satellites and asteroids. The best mitigation is to ensure that their brightness is fainter than V = 7 and that the satellites’ absolute magnitude V1000 km is also fainter than 7, and whenever possible to shoot multiple exposures.

CSS_J154915.7+375506: a low-mass-ratio marginal contact binary system with a hierarchical third body

ABSTRACT We presented the multifilter light curves of CSS_J154915.7+375506 inaugurally, which were observed by the 1.5-m Astronomicheskiy Zerkalniy Telescope 22 ( AZT-22) telescope at Maidanak Astronomical Observatory. A low-resolution spectrum obtained by Large-sky-Area Multi-Object fiber Spectroscopic Telescope reveals that it is an A-type (spectral A type) close binary. By analysing the BVRI total-eclipse light curves, we are able to derive a reliable photometric solution for this system, which indicates that CSS_J154915.7+375506 is an extremely low mass ratio (q = 0.138) marginal contact binary system. The location in the Hertzsprung–Russell (HR) diagram shows that its secondary component with a much smaller mass is the more evolved one, indicating that the mass ratio reversal occurred. The present secondary component had transferred a significant amount of mass to the present primary one. By the combination of a total of 20 times of minimum, we investigated its O–C (observed minus calculated) curve. A periodic oscillation and a possible period decrease have been detected. As the period decreases, the system will evolve towards the contact phase. This makes CSS_J154915.7+375506 a valuable case to study the formation scenario of contact binaries through mass reversal. The periodic oscillation suggested a third body with a minimal mass of $0.91\, {\rm M}_{\odot }$, which is larger than that of the less massive component in the central binary. This implies that the secondary body was not replaced by the third body during early stellar interactions, indicating that it is a fossil system and retains its original dynamical information.

Supernova dust destruction in the magnetized turbulent ISM

Dust in the interstellar medium (ISM) is critical to the absorption and intensity of emission profiles used widely in astronomical observations, and necessary for star and planet formation. Supernovae (SNe) both produce and destroy ISM dust. In particular the destruction rate is difficult to assess. Theory and prior simulations of dust processing by SNe in a uniform ISM predict quite high rates of dust destruction, potentially higher than the supernova dust production rate in some cases. Here we show simulations of supernova-induced dust processing with realistic ISM dynamics including magnetic field effects and demonstrate how ISM inhomogeneity and magnetic fields inhibit dust destruction. Compared to the non-magnetic homogeneous case, the dust mass destroyed within 1 Myr per SNe is reduced by more than a factor of two, which can have a great impact on the ISM dust budget.

Blind multi-Poissonian image deconvolution with sparse log-step gradient prior.

Blind image deconvolution plays a very important role in the fields such as astronomical observation and fluorescence microscopy imaging, in which the noise follows Poisson distribution. However, due to the ill-posedness, it is a very challenging task to reach a satisfactory result from a single blurred image especially when the power of the Poisson noise is at a high level. Therefore, in this paper, we try to achieve high-quality restoration results with multi-blurred images which are contaminated by Poisson noise. Firstly, we design a novel sparse log-step gradient prior which adopts a mixture of logarithm and step functions to regularize the image gradients and combine it with the Poisson distribution to formulate the blind multi-image deconvolution problem. Secondly, we incorporate the methods of variable splitting and Lagrange multiplier to convert the original problem into sub-problems, then we alternately solve them to achieve the estimation of all the blur kernels of corresponding blurred images. Besides, we also design a non-blind multi-image deconvolution algorithm which is based on the log-step gradient prior to reach the final restored image. Experimental results on both synthetic and real-world blurred images show that the proposed prior is very capable of suppressing negative artifacts caused by ill-posedness. The algorithm can achieve restored image of very high quality which is competitive with some state-of-the-art methods.

Autonomous Robotic Capabilities in Space Exploration: From Mars to Beyond

The historical timeline of automated systems functioning in space settings spans around 75 years, whereas the existence of practical automated equipment to facilitate astronomical observation dates back over 200 years. Over time, physical servomechanisms have seen advancements in both hardware and software capabilities, enabling their successful operation on the Martian surface and even during journeys to the heliopause, which marks the outer boundary of interstellar space. Contemporary spaceflight operations exemplify a growing capacity to provide decentralized coordination across several automated systems, intricate communication networks, and diverse communities of scientists and engineers. This article examines the impact of autonomous robotic functionalities on space explorations, specifically emphasizing the investigation of Mars' surface. The article examines the use of robotic systems in past missions, specifically focusing on their application in activities like as the identification and analysis of water ice deposits, study of geological features, and the deployment of sensor devices. The article further emphasizes the achievements of autonomous operations in missions conducted in Earth's orbit, as well as the progress made in developing autonomy for operations in close vicinity to minor celestial bodies. This research explores the Chang'e 4 lunar mission and the OSIRIS-REx mission as instances of autonomous exploration and sample gathering on minor celestial bodies. The research also encompasses the exploration of prospective autonomy in forthcoming expeditions to oceanic realms and distant locales.

Prebiotic Astrochemistry from Astronomical Observations and Laboratory Spectroscopy.

The discovery of more than 200 gas-phase chemical compounds in interstellar space has led to the speculation that this nonterrestrial synthesis may play a role in the origin of life. These identifications were possible because of laboratory spectroscopy, which provides the molecular fingerprints for astronomical observations. Interstellar chemistry produces a wide range of small, organic molecules in dense clouds, such as NH2COCH3, CH3OCH3, CH3COOCH3, and CH2(OH)CHO. Carbon (C) is also carried in the fullerenes C60 and C70, which can preserve C-C bonds from circumstellar environments for future synthesis. Elusive phosphorus has now been found in molecular clouds, the sites of star formation, in the molecules PO and PN. Such clouds can collapse into solar systems, although the chemical/physical processing of the emerging planetary disk is uncertain. The presence of molecule-rich interstellar starting material, as well as the link to planetary bodies such as meteorites and comets, suggests that astrochemical processes set a prebiotic foundation.

NGTS-28Ab: a short period transiting brown dwarf

ABSTRACT We report the discovery of a brown dwarf orbiting a M1 host star. We first identified the brown dwarf within the Next Generation Transit Survey data, with supporting observations found in TESS sectors 11 and 38. We confirmed the discovery with follow-up photometry from the South African Astronomical Observatory, SPECULOOS-S, and TRAPPIST-S, and radial velocity measurements from HARPS, which allowed us to characterize the system. We find an orbital period of ∼1.25 d, a mass of $69.0^{+5.3}_{-4.8}$ MJ, close to the hydrogen burning limit, and a radius of 0.95 ± 0.05 RJ. We determine the age to be >0.5 Gyr, using model isochrones, which is found to be in agreement with spectral energy distribution fitting within errors. NGTS-28Ab is one of the shortest period systems found within the brown dwarf desert, as well as one of the highest mass brown dwarfs that transits an M dwarf. This makes NGTS-28Ab another important discovery within this scarcely populated region.

A portable S-DIMM developed for preliminary measurement of seeing for Solar Site Survey: Theory and one case study

Imaging quality is highly important for astronomical observations. The imaging quality of a telescope depends not only on the capabilities of the telescope itself but also on its location. When distant stars pass the atmosphere, due to the presence of atmospheric turbulence, the imaging quality becomes degraded. The atmospheric coherence length is the most commonly used parameter to evaluate the influence of the local atmospheric turbulence on telescopes. It is used to describe the degree of atmospheric attenuation of image quality. For the preliminary estimation of atmospheric daytime seeing from a lot of candidate sites, we have developed a portable S-DIMM (PS-DIMM),which is mainly composed of a light-duty tracking mount, a 9 cm aperture lens barrel and a Canon 60D SLR camera. With the PS-DIMM the daytime seeing of a site can be well estimated by measuring the relative displacement variance of the edge positions at both ends of the Sun’s diameter. The principle of PS-DIMM is introduced in this paper. The simultaneous seeing measurements by it and the traditional S-DIMM were carried out at the Fuxian Lake Solar Station, showing a very well correlated between them but with an offset of 2.6 cm. In contrast to the traditional S-DIMM, PS-DIMM offers the advantages of reduced weight and enhanced portability. The utilization of PS-DIMM has played an important role in the early stages of the site survey for the next-generation solar telescopes.

Frequency and photometric analysis of the δ Scuti stars SDSS J231559.32 + 595654.1 and ASAS J080529-1357.5

We carried out multi-bandpass BVRI CCD photometric observations for the two δ Scuti stars SDSS J231559.32 + 595654.1 (SDSS23 + 59) and ASAS J080529-1357.5 (ASAS08-13) at Kottamia Astronomical Observatory (KAO). The star SDSS23 + 59 has δ Scuti-type with a low amplitude pulsating variable, and the star ASAS08-13 is classified as a high amplitude δ Scuti-type. The time-series light curve data for each star was analyzed using the discrete Fourier transform (DFT), which revealed a dominant fundamental mode (f0) of oscillation and associated harmonics. The photometric analysis of the two stars suggests SDSS23 + 59 is a star that can pulsate in a short period mode (P = 0.111314d ± 0.000012) with low amplitude (0.101–0.09), and the star ASAS08-13 can pulsate in a short period mode (P = 0.10052247 ± 0.00000281) with high amplitude (0.186–0.168 mag). The nonradial modes for SDSS23 + 59 and radial modes for ASAS08-13 are detected. We calculated new times of maximum light for both stars and combined them with those from other sources (ZTF and AAVSO) to update their corresponding linear ephemerides. The O − C diagram gives us a primary indication that the period of the star is increasing at the rate of (1/P) dP/dt = 3.410(0.006)×10 -10 yr−1 and 2.7321(0.0092)x10-6 yr−1 for SDSS23 + 59 and ASAS08-13 respectively. The physical parameters are calculated, and the positions of the stars on the P-Teff, M−L, M−R, and Teff-log g are investigated.

Can astronomical observations be used to constrain crucial chemical reactions? The methoxy case. SOLIS XVIII

ABSTRACT To understand the origin of interstellar molecules we rely on astrochemical models, the gas-phase networks of which contain ≥7000 reactions. However, just a tiny fraction of them have parameters derived in laboratory experiments. Theoretical quantum mechanical (QM) calculations can also provide this information. Unfortunately, sometimes theoretical predictions and experimental values disagree, as is the case for the paradigmatic reaction CH3OH + OH → CH3O + H2O. Both laboratory experiments and QM calculations found an unexpected increase in the rate coefficients with decreasing temperature. However, experimental and theoretical estimates of the rate coefficients diverge by up to two orders of magnitude at the low temperatures of interest in interstellar chemistry. This work aims to test whether astronomical observations can help untangle this confusing situation. To this end, we first carried out new QM calculations to derive the rate coefficients of the major destruction reaction of the methoxy radical, CH3O + H, and then we compared astronomical observations from the IRAM/NOEMA Large Programme SOLIS with astrochemical model predictions. Our new rate coefficient for the CH3O + H reaction is 5–10 times larger than that in the astrochemical data base KIDA in the 10–100 K range. When including the new methoxy destruction rate coefficients, the comparison between observations and model predictions favours the rate coefficients of the CH3OH + OH reaction from QM calculations. We conclude that QM calculations are an important alternative to laboratory experiments when it comes to the harsh conditions of interstellar objects and that astronomical observations can be used to constraint the rate coefficients of relevant reactions.

Multitarget scattering imaging based on Nonnegative Matrix Factorization beyond the optical memory effect

Speckle correlation technique is limited by the optical memory effect (OME) range, and aliasing phenomenon occurs in multitarget information beyond the range. Here, we propose a multitarget scattering imaging method based on Nonnegative Matrix Factorization (NMF) beyond the OME, which can separate and interpret the single target information from the aliasing information. Based on the study of the multitarget aliasing speckle autocorrelation model, we apply NMF to unmix the multitarget speckle autocorrelation beyond the OME, and combine with phase retrieval (PR) technology to recover the target. Our approach requires only single-shot speckle information without prior information to realize wide-field multitarget imaging. This work provides potential value for biomedical imaging and astronomical observation, and helps to broaden the application scope of speckle correlation technique.

Fundamental Limits of Few-Layer NbSe2 Microbolometers at Terahertz Frequencies.

The rapid development of infrared spectroscopy, observational astronomy, and scanning near-field microscopy has been enabled by the emergence of sensitive mid- and far-infrared photodetectors. Superconducting hot-electron bolometers (HEBs), known for their exceptional signal-to-noise ratio and fast photoresponse, play a crucial role in these applications. While superconducting HEBs are traditionally crafted from sputtered thin films such as NbN, the potential of layered van der Waals (vdW) superconductors is untapped at THz frequencies. Here, we introduce superconducting HEBs made from few-layer NbSe2 microwires. By improving the interface between NbSe2 and metal leads, we overcome impedance mismatch with RF readout, enabling large responsivity THz detection (0.13 to 2.5 THz) with a minimal noise equivalent power of 7 pW/ and nanosecond-range response time. Our work highlights NbSe2 as a promising platform for HEB technology and presents a reliable vdW assembly protocol for custom bolometer production.

Single‐Photon Time‐Stretch Infrared Spectroscopy

AbstractSensitive mid‐infrared (MIR) spectroscopy is highly demanded in various fields ranging from industrial inspection, biomedical diagnosis to astronomical observation. However, the detection sensitivity of conventional MIR spectrometers is severely limited by excessive noises for existing infrared sensors, which hinders widespread use in photon‐scarce scenarios. Here, a broadband MIR single‐photon time‐stretch spectrometer is devised and implemented based on high‐fidelity spectral upconversion and time‐correlated coincidence counting. Specifically, a nanophotonic supercontinuum illumination covering 2.4–4.2 µm is nonlinearly converted to the near‐infrared band, where low‐loss single‐mode fiber and high‐performance silicon detector can be leveraged to facilitate dispersive operation and sensitive detection, respectively. The arrival time for the dispersed upconversion photons is precisely registered with a low‐timing‐jitter photon counter, which enables us to obtain a high spectral resolution about 0.5 cm−1 under a low‐light‐level illumination down to 0.14 photons/nm/pulse. In comparison to previous MIR upconversion spectrometers, the presented time‐stretch architecture favors single‐pixel simplicity and high‐throughput acquisition for the single‐photon spectral measurement. The achieved MIR spectroscopic features of broadband spectral coverage, sub‐wavenumber resolution, single‐photon sensitivity, and room‐temperature operation would stimulate immediate applications in material and life sciences.

Evaluation of the astrometric capability of Multi-Channel Imager and simulated calculation of proper motion of M31

Introduction: The Multi-Channel Imager (MCI), one of the back-end modules of the future China Space Station Telescope (CSST), is designed for high-precision spacebased astronomical observations. This paper evaluates the astrometric capability of the MCI based on simulated observational images and Gaia data: the M31 galaxy is selected as a representative case to validate the astrometric capability by calculating the proper motions (PMs) of the M31 member stars.Method: We analyze the stellar centroids of the simulated images in the R, I and G bands, positional uncertainty of 2.5 mas for brighter foreground reference stars from the Gaia DR3 catalog and of 7.5 mas for the fainter M31 member stars, are adopted respectively. The theoretical PMs are generated from the adopted velocity field model, rotation curve, and stellar surface density profile. And the simulated observed PMs are generated from the aforementioned position uncertainties and theoretical PMs.Result: We conclude that the precision of the MCI derived PMs strongly depends on the number of astrometric epochs per year. Specifically, uncertainty of 10 μas/yr is achievable with 10 epochs per year, and of 5 μas/yr with 50 epochs ignoring possible systematic effects. And symmetrically distributed observed fields yield better M31 kinematic parameters.Discussion: Unknown systematic errors, space environment effects on detectors, dithering strategies, and observation schedules can affect the PMs of M31, the above issues need further analysis and validation in future work.

Madeira: 300 years of an astronomical site

The history of science in islands is not a well worked out discipline. This article offers the first thorough historical account of astronomical activities at Madeira, from the discovery of the uninhabited island in the fifteenth century (600 years ago), through its establishment as an astronomical observatory (300 years ago) and up to the recent past.

Formation and Evolution Mechanisms for Organic Matter in Space

Organic compounds are a major component of dust in molecular clouds, alongside silicates and water ice, due to the high abundances of elements that make up these compounds in the Galaxy. The initial molecular inventory of the Solar System, inherited from the molecular cloud, was modified and new complex molecules were formed in the protoplanetary disk and planetesimals. Because astronomical observations mainly target gas, while cosmochemical evidence deals with solid phases, it is crucial to link discrepant knowledge on organic species through state-of-the-art modeling. This chapter reviews the latest understanding of surface reactions on inter-stellar dusts, gas–dust reactions in the protoplanetary disk, and alteration processes on planetesimals in the early Solar System.

Introducing LensCharm

Strong gravitational lensing, a phenomenon rooted in the principles of general relativity, grants us a unique window into the distant cosmos by offering a direct probe into dark matter and providing independent constraints on the Hubble constant. These research objectives call for the utmost precision in the estimation of the lens mass and the source brightness distributions. Recent strides in telescope technology promise to provide an abundance of yet undiscovered strong-lensing systems, presenting observations of unprecedented quality. Realizing the full potential of these advancements hinges on achieving the highest fidelity in both source and lens reconstruction. In this study, we introduce LensCharm, a novel Bayesian approach for strong-lensing signal reconstruction. Unlike more prevalent methods, LensCharm enables the nonparametric reconstruction of both the source and lens concurrently, along with their associated uncertainties. We showcase the distinctive strengths of our approach through comprehensive analyses of both real-world and simulated astronomical data, underscoring its superiority in achieving precise reconstructions. We have made LensCharm publicly accessible, envisioning its empowerment of the next generation of astronomical observation reconstructions and cosmological constraints derived from strong gravitational lensing.

Hydrodynamic Simulations of Oxygen–Neon Classical Novae as Galactic 7Li Producers and Potential Accretion-induced Collapse Progenitors* *We dedicate this paper to the memory of R. Mark Wagner. Friend, collaborator, exemplary observational astronomer, and contributor to studies of classical novae and transient objects for more than 40 years. He will be missed.

We report on studies of classical nova (CN) explosions where we follow the evolution of thermonuclear runaways (TNRs) on oxygen–neon (ONe) white dwarfs (WDs). Using NOVA, a 1D hydrodynamic computer code, we accrete solar matter until the TNR is ongoing and then switch to a mixed composition. This approach is guided by the results of multidimensional studies of TNRs in WDs, which find that sufficient mixing with WD core material occurs after the TNR is well underway, and levels of enrichment of the CNONeMg elements are reached that agree with observations of CN ejecta abundances. Because the amount of accreted material is inversely proportional to the oxygen abundance, by first accreting solar matter, the amount of accreted material is larger than in those simulations with an initially enriched composition. We vary the mass of the WD (from 0.6 M ⊙ to 1.35 M ⊙) and the composition of the mixed materials. Our results show large enrichments of 7Be in the ejected gases, implying that ONe CNe and CO CNe may be responsible for a significant fraction (∼100 M ⊙) of the Galactic 7Li (∼1000 M ⊙). The production of 22Na and 26Al in CN explosions and the γ-ray emission predicted by our simulations are discussed. The WDs in all our simulations eject less material than they accrete and we predict that the WD is growing in mass as a consequence of the CN outburst. ONe CNe, therefore, may be an important channel for accretion-induced collapse events.