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The results of new photometric observations of the chromospherically active star ET Dra, performed using telescopes of the Zvenigorod INASAN Observatory, the Russian-Cuban Observatory in the territory of the Republic of Cuba (Havana), and the Terskol INASAN Observatory (a total of 8 sets of observations) with the addition of archival observations of the Kamogata Wide-field Survey. Variations in the shape of the light curve caused by the rotational modulation of a star with spots on the surface, as well as studies of the long-term variability of the star's brightness, were investigated based on the data acquired in 2018–2023. Characteristic changes in the ET Dra light curve were noted including a decrease of the stellar brightness in the filter, its cyclic variations, and subsequent brightness increase. The shape of the phase curve and the duration of the extended minimum of brightness vary. During the HJD 245 9670–245 9715 interval, the amplitude of the star's brightness variability reached a maximum value of more than 0.4m, as it was in 1990. The surface temperature inhomogeneities maps were calculated and estimates of the spottedness parameter S of the object were performed for each of the 8 sets of observations. Maximum value of parameter S was 32.2‒33.5%. Based on the constructed power spectra, the values of possible cycles of long-term activity of the star were obtained as 570 and 1160d (1.56 and 3.18 years, respectively). [ABSTRACT FROM AUTHOR]

We present the results of our identification of 11 X-ray sources detected on the half of the sky in the 4–12 keV energy band on the combined map of the first five all-sky surveys with the Mikhail Pavlinsky ART-XC telescope onboard the SRG observatory. All these sources were also detected by the SRG/eROSITA telescope in the 0.2–8 keV energy band, whose data have allowed us to improve their positions and to investigate their X-ray spectra. Five of them have been detected in X-rays for the first time, while the remaining ones have already been known previously, but their nature has remained unknown. We have taken optical spectra for nine sources with the 1.6-m AZT-33IK telescope at the Sayan Observatory (the Institute of Solar–Terrestrial Physics, the Siberian Branch of the Russian Academy of Sciences); for two more objects we have analyzed the archival spectra from SDSS and the 6dF survey. The objects are classified as Seyfert galaxies (seven Sy1, three Sy1.9, and one Sy2) at redshifts . Our analysis of the X-ray spectra has revealed a noticeable intrinsic absorption ( cm ) in two of the four Seyfert 2 galaxies (Sy1.9–2). The spectrum of one more of them (SRGA J000132.9+240237) cannot be described within the model of an absorbed Comptonization continuum, which may point to a strong absorption and a significant contribution of the reflected radiation. However, the available SRG all-sky survey data are not enough to obtain reliable constraints on the absorption column density in this object, which is also interesting in that it is radio loud. Longer X-ray observations are required to refine the physical properties of this active galactic nucleus. [ABSTRACT FROM AUTHOR]

In this paper, we present a project of a multi-channel wide-field optical sky monitoring system with high temporal resolution—Small Aperture Imaging Network Telescope (SAINT)— mostly built from off-the-shelf components and aimed towards searching and studying optical transient phenomena on the shortest time scales. The instrument consists of twelve channels each containing 30 cm (F/1.5) GENON Max objectives mounted on separate ASA DDM100 mounts with pointing speeds up to 50 deg/s. Each channel is equipped with a 4128 × 4104 pixel Andor Balor sCMOS detector and a set of photometric g r i z filters and linear polarizers. At the heart of every channel is a custom-built reducer-collimator module allowing rapid switching of an effective focal length of the telescope—due to it the system is capable of operating in either wide-field survey or narrow-field follow-up modes. In the first case, the field of view of the instrument is 470 square degrees (39 sq.deg. for a single channel) and the detection limits (5 σ level at 5500 Å) are 12.5, 16.5, 19, 21 with exposure times of 20 ms, 1 s, 30 s and 20 min, correspondingly. In the second, follow-up (e.g., upon detection of a transient of interest by either a real-time detection pipeline, or upon receiving an external trigger) regime, all telescopes are oriented towards the single target, and SAINT becomes an equivalent to a monolithic 1-meter telescope, with the field of view reduced to 11 ′ × 11 ′ , and the exposure times decreased down to 0.6 ms (1684 frames per second). Different channels may then have different filters installed, thus allowing a detailed study—acquiring both color and polarization information—of a target object with the highest possible temporal resolution. The telescopes are located in two pavilions with sliding roofs and are controlled by a cluster of 25 computers that both govern their operation and acquire and store up to 800 terabytes of data every night, also performing its real-time processing using a dedicated fast image subtraction pipeline. Long-term storage of the data will require a petabyte class storage. The operation of SAINT will allow acquiring an unprecedented amount of data on various classes of astrophysical phenomena, from near-Earth to extragalactic ones, while its multi-channel design and the use of commercially available components allows easy expansion of its scale, and thus performance and detection capabilities. [ABSTRACT FROM AUTHOR]

We present the results of the optical identification and spectroscopic redshift measurements of 216 galaxy clusters detected in the SRG/eROSITA all-sky X-ray survey. The spectroscopic observations were performed in 2020–2023 with the 6-m BTA telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences, the 2.5-m telescope at the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Moscow State University, the 1.6-m AZT-33IK telescope at the Sayan Solar Observatory of the Institute of Solar–Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences, and the 1.5-m Russian–Turkish telescope (RTT-150) at the TÜBİTAK Observatory. For all of the galaxy clusters presented here the spectroscopic redshift measurements have been obtained for the first time. Of these, 139 galaxy clusters have been detected for the first time in the SRG/eROSITA survey and 22 galaxy clusters are at redshifts , including three at . Deep direct images with the rizJK filters have also been obtained for four distant galaxy clusters at . For these observations we chose the most massive clusters and, therefore, most of the galaxy clusters presented here with the spectroscopic redshifts measured by us will most likely enter in future into the cosmological samples of galaxy clusters from the SRG/eROSITA survey. [ABSTRACT FROM AUTHOR]

This paper presents an approach to accurately determine the orbits of Medium Earth Orbit (MEO) and Geosynchronous Earth Orbit (GEO) space objects by utilizing data from an electro-optical sensor (Optical Satellite Tracking Station (OSTS), Kottamia Observatory station). The proposed method combines an extended and unscented Kalman filter with a semi-analytical propagation model. The effectiveness of this approach is demonstrated through numerical simulations and comparisons with traditional orbit determination techniques. The results drawn from this study show that when comparing both methods, the unscented semi-analytical Kalman filter provided more accurate orbital state estimates and required less time and fewer observations to converge. [ABSTRACT FROM AUTHOR]

Detection, observation and description of supernovae associated with gamma-ray bursts are currently topical tasks in the field of transient phenomena. From the moment an assumption is made about the relationship of the gamma-ray burst with a supernova to obtaining the parameters of the latter, many steps must be taken, and each of them introduces uncertainty and systematics into the final result. In this paper, we analyze the selective effects that arise during the determination of the parameters of supernovae associated with gamma-ray bursts and discuss possible options for taking them into account and minimizing them. [ABSTRACT FROM AUTHOR]

The Russian–Turkish 1.5-m telescope (hereafter RTT-150) takes an active part in the work on the ground optical support of observations by the Russian Spectrum–Röntgen–Gamma (SRG) observatory (with the participation of Germany) aimed at the identification and classification of new X-ray sources detected by the SRG telescopes. The instrumental capabilities of RTT-150 (occasionally, without any significant usage of telescope time and detriment for astrophysical programs) are used in astrometric observations to control the correction of the orbit of the SRG space observatory itself. In these cases, RTT-150 provides the Ballistic Center of the Keldysh Institute of Applied Mathematics of the Russian Academy of Sciences with high-precision astrometric measurements of the SRG position, which have been used to successfully keep it in its operational orbit for more than three years of its exploitation. Beginning from the stage of flight to the zone of the Lagrange point in July 2019 and at the main phase of the all-sky survey mission until March 2023, 96 sets (with a duration of about 30 min each) of high-precision positional observations with more than 5000 astrometric and photometric measurements were carried out at the RTT-150 observing facility. In most cases, the positional accuracy of the measurements dependent on seeing and apparent SRG brightness agrees with the accuracy of the provided ephemerides, and in declination and right ascension, respectively. In the summer months in projection onto the central region of the Galaxy in fields extremely rich in sources, the astrometric accuracy is , sufficient for the SRG detection after the corrections and subsequent refinements of its trajectory. Geographically, RTT-150 is the southernmost instrument among the Russian telescopes for the ground astrophysical support of SRG. This fact is also extremely important in positional SRG observations at the lowest positions in declination . We present the results of our astrometric and photometric observations with RTT-150 and our astrometric data reduction technique in various fields up to those extremely rich in sources. [ABSTRACT FROM AUTHOR]

In this paper, we present a project of a multi-channel wide-field optical sky monitoring system with high temporal resolution—Small Aperture Imaging Network Telescope (SAINT)— mostly built from off-the-shelf components and aimed towards searching and studying optical transient phenomena on the shortest time scales. The instrument consists of twelve channels each containing 30 cm (F/1.5) GENON Max objectives mounted on separate ASA DDM100 mounts with pointing speeds up to 50 deg/s. Each channel is equipped with a 4128 × 4104 pixel Andor Balor sCMOS detector and a set of photometric griz filters and linear polarizers. At the heart of every channel is a custom-built reducer-collimator module allowing rapid switching of an effective focal length of the telescope—due to it the system is capable of operating in either wide-field survey or narrow-field follow-up modes. In the first case, the field of view of the instrument is 470 square degrees (39 sq.deg. for a single channel) and the detection limits (5σ level at 5500 Å) are 12.5, 16.5, 19, 21 with exposure times of 20 ms, 1 s, 30 s and 20 min, correspondingly. In the second, follow-up (e.g., upon detection of a transient of interest by either a real-time detection pipeline, or upon receiving an external trigger) regime, all telescopes are oriented towards the single target, and SAINT becomes an equivalent to a monolithic 1-meter telescope, with the field of view reduced to 11′ × 11′, and the exposure times decreased down to 0.6 ms (1684 frames per second). Different channels may then have different filters installed, thus allowing a detailed study—acquiring both color and polarization information—of a target object with the highest possible temporal resolution. The telescopes are located in two pavilions with sliding roofs and are controlled by a cluster of 25 computers that both govern their operation and acquire and store up to 800 terabytes of data every night, also performing its real-time processing using a dedicated fast image subtraction pipeline. Long-term storage of the data will require a petabyte class storage. The operation of SAINT will allow acquiring an unprecedented amount of data on various classes of astrophysical phenomena, from near-Earth to extragalactic ones, while its multi-channel design and the use of commercially available components allows easy expansion of its scale, and thus performance and detection capabilities.

The Burst Observer and Optical Transient Exploring System (BOOTES) was first designed as an asset of autonomous telescopes that started to be deployed in 1998, taking 24 years to be fully developed around the earth. Nowadays BOOTES has became a global network of robotic telescopes, being the first one present in all continents, as of 2022. Here we present the details of the network and review its achievements over the last 2 decades regarding follow-up observations of high-energy transient events. Moreover, considering the recent operations of neutrino and gravitational wave detectors, some hot-topic expectations related to robotic astronomy are discussed within the framework of multi-wavelength astrophysics.

We present the results of our identification of 14 X-ray sources detected in the eastern Galactic sky () in the 4–12 keV energy band on the combined map of the first five all-sky surveys (from December 2019 to March 2022) with the Mikhail Pavlinsky ART-XC telescope onboard the SRG observatory. All 14 sources are reliably detected by the SRG/eROSITA telescope in the 0.2–8 keV energy band. Six of them have been detected in X-rays for the first time, while the remaining ones have already been known previously as X-ray sources, but their nature has remained unknown. We have taken optical spectra for 12 sources with the 1.6-m AZT-33IK telescope at the Sayan Observatory (the Institute of Solar–Terrestrial Physics, the Siberian Branch of the Russian Academy of Sciences). For two more objects we have analyzed the archival spectra taken during the 6dF survey. All objects have turned out to be Seyfert galaxies (one NLSy1, three Sy1, four Sy1.9, and six Sy2) at redshifts –0.238. Based on data from the eROSITA and ART-XC telescopes onboard the SRG observatory, we have obtained X-ray spectra for all objects in the energy range 0.2–12 keV. In four of them the intrinsic absorption exceeds cm at a 90 confidence level, with one of them being probably heavily obscured ( cm with 90 confidence). This paper continues our series of publications on the identification of hard X-ray sources detected during the all-sky survey with the SRG orbital X-ray observatory. [ABSTRACT FROM AUTHOR]

Based on a comparison of the SRG/eROSITA catalog of X-ray active stars and the Gaia catalog, we have obtained a sample of 502 peculiar objects for which Gaia, on the one hand, detects statistically significant parallaxes or proper motions and, on the other hand, records signs of a nonzero optical extent. On the –color diagram these objects are significantly separated from the bulk of the stars and are located in the region typical for active galactic nuclei (AGNs). According to the SIMBAD database, of them are AGNs and galaxies with spectroscopic redshifts and only are confirmed objects in our Galaxy. Our spectroscopic observations of 19 unidentified objects with the RTT-150 telescope have shown that 18 of them are AGNs at redshifts 0.01–0.3 and one object is an M star in our Galaxy. We discuss various scenarios for the appearance of such peculiar objects. [ABSTRACT FROM AUTHOR]

We present information about the first results of work on the study of stars at the optical station of the Russian–Cuban Observatory. The observatory consists of two stations – optical and geodynamic, created by the Institute of Astronomy of the Russian Academy of Sciences and the Institute of Applied Astronomy of the Russian Academy of Sciences together with the Institute of Geophysics and Astronomy of the Republic of Cuba. The main instrument of the observatory is a 20-cm wide-field robotic telescope with a CCD camera and a photometric filter wheel. In late 2021 and early 2022, the first photometric studies of the active stars V410 Tau and FR Cnc were carried out. [ABSTRACT FROM AUTHOR]

Maneuver detection and estimation is deemed crucial for maintaining catalogs of Resident Space Objects (RSOs) as it helps to avoid sets of duplicated objects and track correlation issues. In fact, maneuvers, along with launches and break-up events, are the main source of potential new object detections during RSOs cataloging activities. For the continuous and reliable provision of Space Situational Awareness (SSA) and Space Traffic Management (STM) services, a challenging trade-off between detection time and characterization accuracy of maneuvers needs to be performed. In this paper, two novel and operationally feasible methodologies are proposed for maneuver detection and estimation. The first, a track-to-orbit methodology, uses a pre-maneuver orbit to linearize the dynamics and estimate the single burn that minimizes the residuals of the post-maneuver tracks. The second, an orbit-to-orbit methodology, estimates the double burn that solves a minimization problem between the pre-maneuver and post-maneuver orbits. Both methods, based on an optimal control approach, are not only proposed to tackle the maneuver estimation problem but also to be integrated on operational and robust association frameworks. Results are presented for optical scenarios with both simulated and real data, providing insightful conclusions on the capabilities, performance and limitations of the proposed methods. Particular emphasis is given to the importance of the track association, since a single track is usually not enough to perform a reliable estimation of the maneuver. Besides, the capability of the methods to provide a solution to the association problem, even when not perfectly characterizing the true maneuver, is discussed. [ABSTRACT FROM AUTHOR]

We present the results of our identification of 17 X-ray sources detected in the 4–12 keV energy range by the Mikhail Pavlinsky ART-XC telescope during the first year of the SRG all-sky survey. Three of them have been discovered by the ART-XC telescopes, while the remaining ones have already been known previously as X-ray sources, but their nature has remained unknown. We took optical spectra for nine sources located in the northern sky () with the 1.6-m AZT-33IK telescope at the Sayan Observatory (the Institute of Solar–Terrestrial Physics, the Siberian Branch of the Russian Academy of Sciences) and the 1.5-m Russian–Turkish telescope at the TÜBITAK National Observatory. For the remaining objects we have analyzed the archival optical spectra taken during the 6dF survey. All of the investigated objects have turned out to be Seyfert galaxies (eight of type 1, seven of type 2, and two of intermediate type 1.8) at redshifts up to . Based on data from the eROSITA and ART-XC telescopes onboard the SRG observatory, we have obtained X-ray spectra in the energy range 0.2–20 keV for eight sources. A significant intrinsic absorption ( cm ) has been detected in three of them, with two of them being probably strongly absorbed ( cm ). This paper is a continuation of the series of publications on the optical identification of active galactic nuclei detected by the ART-XC telescope. [ABSTRACT FROM AUTHOR]

The fast visualization and manipulation of individual carbon nanotubes (CNTs) has always been a significant technology for their fundamental research. Here, a fast and facile approach is proposed to realize the optical observation of individual suspended CNTs and CNT networks under conventional optical microscopes with the assistance of tar nanodroplets from smoke. The nanodroplets deposited on CNTs render them with strong light scattering to visible light, thus making the CNTs visible under optical microscopes. This visualization method is controllable, environmentally friendly, low‐cost, and can be completed in just a few seconds in ambient conditions. Besides, the tar nanodroplets can be easily removed from the CNTs by laser irradiation. More importantly, the smoke sources are widely available and there are no strict requirements for operating conditions. This smoke‐assisted visualization method shows great potential in the fundamental research of CNTs. [ABSTRACT FROM AUTHOR]

Abstract Here, we introduce a low-cost airglow imaging system developed for observing plasma bubble signatures in 630.0-nm airglow emission from the F region of the ionosphere. The system is composed of a small camera, optical filter, and fish-eye lens, and is operated using free software that automatically records video from the camera. A pilot system was deployed in Ishigaki Island in the southern part of Japan (Lat 24.4, Lon 124.4, Mlat 19.6) and was operated for ~ 1.5 years from 2014 to 2016 corresponding to the recent solar maximum period. The pilot observations demonstrated that it was difficult to identify the plasma bubble signature in the raw image captured every 4 s. However, the quality of the image could be improved by reducing the random noise of instrumental origin through an integration of 30 consecutive raw images obtained in 2 min and further by subtracting the 1-h averaged background image. We compared the deviation images to those from a co-existing airglow imager of OMTIs, which is equipped with a back-illuminated cooled CCD camera with a high quantum efficiency of ~ 90%. It was confirmed that the low-cost airglow imager is capable of imaging the spatial structure of plasma bubbles, including their bifurcating traces. The results of these pilot observations in Ishigaki Island will allow us to distribute the low-cost imager in a wide area and construct a network for monitoring plasma bubbles and their space weather impacts on satellite navigation systems.

Abstract We evaluate the capability of a low-cost all-sky imager (ASI), which has been operative in Longyearbyen (78.1° N, 15.5° E), Norway, to detect 630.0 nm airglow signatures of polar cap patches. The ASI is composed of a small camera, with a charge-coupled device (CCD), manufactured by Watec Co. Ltd., a fish-eye lens, and an optical filter whose central wavelength is 632.0 nm and full-width half maximum (FWHM) is 10 nm. In Longyearbyen, another ASI equipped with a cooled electron-multiplying charge-coupled device (EMCCD) camera has been operative for observations of polar cap patches. We compare the images from the two systems and investigate the performance of the low-cost ASI. On the night of December 4, 2013, a series of polar cap patches were observed by the EMCCD ASI. The low-cost ASI also detected regions of enhanced 630.0 nm airglow passing through the fields-of-view. The quality of the raw images from the low-cost ASI obtained every 4 s were visibly much worse than that of the EMCCD ASI. However, an integration of 7–15 consecutive images made it possible to capture the temporal evolution and spatial structure of the patches, for example, their anti-sunward propagation and finger-like structures along the trailing edge. The estimated values of the absolute optical intensity from the low-cost ASI were found to be consistent with those from the EMCCD ASI, whereby the offset was

Abstract Gamma-ray bursts (GRBs) are the most energetic and mysterious events in the Universe, which are observed in all ranges of electromagnetic spectrum. Most valuable results about physics of GRB are obtained by optical observations. GRBs are initially detected in gamma-rays with poor localization accuracy, and an optical counterpart should be found. The faster the counterpart is found, the more it can give to physics. This first phase, as a rule, corresponds to an early afterglow. The next phases of the observations are multicolor photometry, polarimetry, spectroscopy, and few days later the search for a supernova or kilonova associated with the GRB, and finally, observations of the host galaxy. To manage the problem of fast optical observations, telescopes with a small aperture are suitable. They can have a large field of view, which is necessary to cover initial localizations of GRBs. The sensitivity of the telescope+detector may be sufficient to record statistically significant light curve with fine time resolution. We describe one of the networks of telescopes with a small aperture IKI-GRB FuN, and present the results of early optical observation of GRB sources, and discuss the design requirements of the optical observations for effective GRB research in the next decade.

We present the first results of our program of optical observations for galaxy clusters from the Lockman Hole X-ray survey with the eROSITA telescope onboard the SRG space observatory. We present the results of spectroscopic redshift measurements for 11 galaxy clusters that have been identified optically among the extended X-ray sources of the SRG/eROSITA survey using data from optical and infrared sky surveys. The spectroscopic observations were carried out in late 2019–early 2020 with the 1.6-m AZT-33IK telescope of the Sayan Observatory and the 6-m SAO RAS telescope (Bolshoi Teleskop Azimutalnyi, BTA). [ABSTRACT FROM AUTHOR]

We present the results of our identification of eight objects from the preliminary catalogue of X-ray sources detected in the 4–12 keV energy band by the Mikhail Pavlinsky ART-XC telescope onboard the SRG observatory during the first all-sky survey. Three of them (SRGA J005751.0+210846, SRGA J , SRGA J232446.8+440756) have been discovered by the ART-XC telescope, while five have already been known previously as X-ray sources, but their nature has remained unestablished. The last five sources have also been detected in soft X-rays by the eROSITA telescope of the SRG observatory. Our optical observations have been carried out at the 1.6-m AZT-33IK telescope of the Sayan Observatory and the 1.5-m Russian–Turkish telescope (RTT-150). All of the investigated objects have turned out to be active galactic nuclei (AGNs) at redshifts from 0.019 to 0.283. Six of them are Seyfert 2 galaxies (including one Seyfert 1.9 galaxy), one (SRGA J005751.0+210846) is a "hidden" AGN (in an edge-on galaxy), and one (SRGA J224125.9+760343) is a narrow-line Seyfert 1 galaxy. The latter object is characterized by a high X-ray luminosity ( erg s in the 4–12 keV band) and, according to our black hole mass estimate (), an accretion rate close to the Eddington limit. All three AGNs discovered by the ART-XC telescope (which are not detected by the eROSITA telescope) are characterized by a high absorption column density ( cm ). The results obtained confirm the expectations that the ART-XC telescope is an efficient instrument in searching for heavily obscured and other interesting AGNs in the nearby () Universe. The SRG sky survey will last for another 3 years or more, which must allow many such objects to be discovered. [ABSTRACT FROM AUTHOR]

We present the results of our spectroscopic redshift measurements for galaxy clusters detected previously from Planck all-sky survey data as well as Sloan Digital Sky Survey and WISE all-sky survey data. The redshifts have been measured for 23 clusters, including four galaxy clusters from the second Planck catalogue of Sunyaev–Zeldovich sources. The main spectroscopic observations were carried out during 2019–early 2020 at the 1.6-m AZT-33IK telescope of the Sayan Observatory and the 1.5-m Russian–Turkish telescope (RTT-150). Some of the data have been obtained previously at the 3.5-m Calar Alto telescope. Out of the 23 clusters in this sample, 14 objects are located in the half of the sky where the rights to the data from the eROSITA sky survey onboard the SRG orbital X-ray observatory belong to the Russian side. All these clusters were detected with the eROSITA telescope in the course of the sky survey during 2020. On the whole, we have measured the spectroscopic redshifts for 220 galaxy clusters within our program of optical identifications of galaxy clusters from the Planck catalogue during several years. Many of them have already been detected in the SRG/eROSITA survey; a significant fraction of these objects are among the most massive galaxy clusters of the eROSITA sky survey and will most likely enter into cosmological samples of clusters from this survey. [ABSTRACT FROM AUTHOR]

The study of near-Earth space includes the detection and investigation of an increasing number of space debris objects by ground-based optical telescopes. There is no natural cleansing of space in the geostationary region. The telescope Zeiss-2000 with a two-meter aperture of the Terskol observatory is the largest optical instrument regularly used for space debris investigations. One of the main purposes in «Astronomy in the Elbrus region» international program’s boundaries is the detection and characterization of small fragments of debris,which are invisible for smaller telescopes. During observations on photometric nights we usually detect 4-5 unknown fragments of 17-21st star magnitude. In this article, we present orbital parameters and physical characteristics of several small-sized fragments of the space debris detected at the Terskol observatory in 2016-2017.

The initial orbit determination (IOD) of the very‐short‐arc (VSA) and the association between them are the key steps for expanding the catalogue with optical observations obtained from ground‐based or space ‐based telescopes. For this reason, the distance search method for IOD and the geometrical method for their association were proposed. With optical observations from ground ‐based small telescopes array at Changchun Observatory, National Astronomical Observatories, China Academy of Sciences in Changchun and simulated observations from space‐based telescope, the IOD and the association between the IODs are performed. The successful rates of getting an IOD solution for an optical arc with the distance search method is about 90%. For two kinds of observations. The IOD association results show that the true positive (assert that they are from same object for IODs from a same object) rate is over 80% in most cases. Ant the effects on the association accuracy of filtered different IODs are analyzed in depth. With actual optical observations obtained at Changchun, the results of IOD and their association show the validity of the IOD method and association method used in this paper and they can be used to expand the space object catalogue. [ABSTRACT FROM AUTHOR]

We present the observing program proposed by Paris and Côte d'Azur Observatories for monitoring solar activity during the upcoming cycle 25 and providing near real time images and movies of the chromosphere for space-weather research and applications. Two optical instruments are fully dedicated to this task and we summarize their capabilities. Short-term and fast-cadence observations of the chromosphere will be performed automatically at Calern observatory (Côte d'Azur), where dynamic events, as flare development, Moreton waves, filament instabilities and Coronal Mass Ejections onset, will be tracked. This new set of telescopes will operate in 2021 with narrow bandpass filters selecting Hα and CaII K lines. We present the instrumental design and a simulation of future images. At Meudon, the Spectroheliograph is well adapted to the long-term and low-cadence survey of chromospheric activity by recently improved and optimized spectroscopic means. Surface scans deliver daily (x, y, λ) datacubes of Hα, CaII K and CaII H line profiles. We describe the nature of available data and emphasize the new calibration method of spectra. [ABSTRACT FROM AUTHOR]

Here, we introduce a low-cost airglow imaging system developed for observing plasma bubble signatures in 630.0-nm airglow emission from the F region of the ionosphere. The system is composed of a small camera, optical filter, and fish-eye lens, and is operated using free software that automatically records video from the camera. A pilot system was deployed in Ishigaki Island in the southern part of Japan (Lat 24.4, Lon 124.4, Mlat 19.6) and was operated for ~ 1.5 years from 2014 to 2016 corresponding to the recent solar maximum period. The pilot observations demonstrated that it was difficult to identify the plasma bubble signature in the raw image captured every 4 s. However, the quality of the image could be improved by reducing the random noise of instrumental origin through an integration of 30 consecutive raw images obtained in 2 min and further by subtracting the 1-h averaged background image. We compared the deviation images to those from a co-existing airglow imager of OMTIs, which is equipped with a back-illuminated cooled CCD camera with a high quantum efficiency of ~ 90%. It was confirmed that the low-cost airglow imager is capable of imaging the spatial structure of plasma bubbles, including their bifurcating traces. The results of these pilot observations in Ishigaki Island will allow us to distribute the low-cost imager in a wide area and construct a network for monitoring plasma bubbles and their space weather impacts on satellite navigation systems. [ABSTRACT FROM AUTHOR]

We present the results of spectroscopic redshift measurements for galaxy clusters from the catalogue compiled previously from Planck all-sky survey data in combination with Sloan Digital Sky Survey (SDSS) and WISE data in the optical and infrared ranges. Most of these clusters are massive objects that will also be detected in future all-sky surveys, such as the eROSITA all-sky X-ray survey onboard the Spectrum–Roentgen–Gamma (SRG) space observatory. The spectroscopic observations of these galaxy clusters have been carried out with the 1.5-m Russian–Turkish telescope (RTT150), the 1.6-m Sayan Observatory AZT-33IK telescope, and the 6-m SAO RAS telescope (Bolshoi Teleskop Azimutalnyi, BTA). The spectroscopic redshift measurements have been obtained for 67 galaxy clusters, including 12 galaxy clusters from the second Planck catalogue of Sunyaev–Zeldovich sources. [ABSTRACT FROM AUTHOR]

An example of simultaneous spectroscopic redshift measurements for a large number of galaxies in a cluster by multiobject spectroscopy with the medium- and low-resolution TFOSC spectrograph at the RussianTurkish 1.5-m telescope (RTT150) is presented. The redshifts of galaxies in the cluster at detected previously by the SunyaevZeldovich signal in the Planck all-sky survey have been measured. The spectra of 16 cluster galaxies, 9 of which were determined as ellipticals, were taken in one observation with an exposure time of 3 h and high-quality redshift measurements were made for them. We show that the redshifts of galaxies with magnitudes to , whose number in the TFOSC field can reach dozens, depending on the cluster richness and distance, can be measured in one observation with the TFOSC spectrograph using multiobject masks. Such measurements may be required to refine the redshifts of clusters and to estimate their masses by the dynamical method. [ABSTRACT FROM AUTHOR]

Simulation modelling of the observability of low Earth orbit (LEO) objects was performed using optical surveillance facilities depending on their geographic location and time of year. Orbital data for LEO objects from the open-access catalogue of the near-Earth space objects of the US Combined Space Operations Center (CSpOC) were taken as the initial data for the simulation. The simulation results revealed a complex relationship between the pattern of observability of a LEO object, its orbital parameters and location of the optical surveillance facility, in particular, for Sun-synchronous orbits (SSO) and observing facilities located near the equator. We also discuss variations in the frequency of passes of LEO objects into the field of view (FOV) and in the duration of their observation while passing through the FOV for optical surveillance facilities at three alternative locations. The obtained results and modelling techniques can be further used in the location planning of new optical observing facilities. [ABSTRACT FROM AUTHOR]

We continue the study begun in Karasev et al. (2018) and present the results of our optical identifications of four hard X-ray sources from the INTEGRAL sky surveys. Having first improved the positions of these objects in the sky with the X-ray telescope (XRT) of the Swift observatory, we have identified their counterparts using optical and infrared sky survey data. Then, we have obtained optical spectra for the putative counterparts with the RTT-150 Russian-Turkish telescope and the AZT-33IK telescope. This has allowed the nature of the objects under study to be established. The sources IGR J11079+7106 and IGR J12171+7047 have turned out to be extragalactic in nature and be Seyfert 1 and 2 galaxies, respectively, with the second object being characterized by a large absorption column density. The source IGR J18165−3912 is most likely an intermediate polar with a very high luminosity. The fourth source, IGR J20596+4303, is a chance superposition of two objects—a Seyfert 2 galaxy and a cataclysmic variable. [ABSTRACT FROM AUTHOR]

A remarkable, large‐amplitude, mountain wave (MW) breaking event was observed on the night of 21 June 2014 by ground‐based optical instruments operated on the New Zealand South Island during the Deep Propagating Gravity Wave Experiment (DEEPWAVE). Concurrent measurements of the MW structures, amplitudes, and background environment were made using an Advanced Mesospheric Temperature Mapper, a Rayleigh Lidar, an All‐Sky Imager, and a Fabry‐Perot Interferometer. The MW event was observed primarily in the OH airglow emission layer at an altitude of ~82 km, over an ~2‐hr interval (~10:30–12:30 UT), during strong eastward winds at the OH altitude and above, which weakened with time. The MWs displayed dominant horizontal wavelengths ranging from ~40 to 70 km and temperature perturbation amplitudes as large as ~35 K. The waves were characterized by an unusual, "saw‐tooth" pattern in the larger‐scale temperature field exhibiting narrow cold phases separating much broader warm phases with increasing temperatures toward the east, indicative of strong overturning and instability development. Estimates of the momentum fluxes during this event revealed a distinct periodicity (~25 min) with three well‐defined peaks ranging from ~600 to 800 m2/s2, among the largest ever inferred at these altitudes. These results suggest that MW forcing at small horizontal scales (<100 km) can play large roles in the momentum budget of the mesopause region when forcing and propagation conditions allow them to reach mesospheric altitudes with large amplitudes. A detailed analysis of the instability dynamics accompanying this breaking MW event is presented in a companion paper, Fritts et al. (2019, https://doi.org/10.1029/2019jd030899). Key Points: Multi‐instrument characterization of a mesospheric mountain wave exhibit a unique, large‐amplitude "saw‐tooth" wave breaking signatureUnexpected large‐amplitude mesospheric mountain waves accompany weak winds over low orography due to favorable propagation conditionsVery large mesospheric mountain wave momentum fluxes ~400‐800 m2/s2 are sustained for multiple wave periods [ABSTRACT FROM AUTHOR]

A new generation telescope for objects at Geosynchronous Earth Orbit (GEO) was developed by Shanghai Astronomical Observatory at the end of 2017, it's called FocusGEO telescope. The goal is to observe nearly all the GEO objects over the observation station near real-time. FocusGEO telescope consists of three refracting telescopes of 18 cm aperture and 22 cm focal length, forming a super-large rectangular field of view(FOV) of 3 × 9.5°×9.5°. Each 15 min FocusGEO telescope scans a strip of sky 112.9°long × 28.3°high, almost fully covers the GEO belt over the station. In early 2018, FocusGEO observations were carried out at the Lijiang Observatory site of Yunnan Observatory, the results show that FocusGEO can observe about 380 GEO objects over the station per night. Its observation completeness is over 90% to GEO objects catalogued by USSTRATCOM. In the case of exposure for 5 s, FocusGEO can observe 15 magnitude GEO objects. The observation precision is about 3″ in azimuth and elevation. [ABSTRACT FROM AUTHOR]

We present the results of optical identifications and spectroscopic redshift measurements for galaxy clusters from the second Planck catalogue of Sunyaev-Zeldovich sources. We used the data of observations with the 1.5-m Russian-Turkish telescope (RTT150), the 1.6-m Sayan Observatory AZT-33IK telescope, the 3.5-m Calar Alto telescope, and the 6-m SAO RAS telescope (Bolshoi Teleskop Azimutalnyi, BTA). For the observations we selected Sunyaev-Zeldovich sources unidentified with galaxy clusters with known redshifts. The observations have been carried out for three years, as a result of which we obtained direct images in various filters for a set of galaxy clusters and spectra for the brightest red-sequence galaxies of these clusters. For 38 galaxy clusters we obtained spectroscopic redshift measurements. [ABSTRACT FROM AUTHOR]

Abstract Single crystals of (H 2 NNH 3) 3 CdBr 5 were grown and their properties were investigated. DSC, DTG, structural studies, optical polarized microscopy observations and dielectric studies are presented. TGA showed the stability of the substance up to about 455 K and decomposition above this temperature. DSC studies revealed the first order structural phase transitions at 294/292 on heating/cooling runs. X-ray structural studies showed a change of symmetry from orthorhombic to monoclinic and the transition seems to belong to the mmmF2/m Aizu's species. In optical studies performed with a polarizing microscope, the ferroelastic type of domain structure and the phase front appearance were observed. Dielectric measurements clearly evidenced the first-order phase transition as a jump-like decrease of permittivity on cooling and increase on heating. Structural and dielectric studies indicate the order-disorder character of the phase transition. Highlights • Examination of the structural phase transition in the (H 2 NNH 3) 3 CdBr 5 was performed. • The transition proceeds between two centrosymmetric groups Cmcm ↔ P 2 1 / m. • The transition is of the first order and has the order – disorder character. • Ferroelastic domain structure is typical for the mmmF2/m of the Aizu's species. [ABSTRACT FROM AUTHOR]

The study of near-Earth space includes the detection and investigation of an increasing number of space debris objects by ground-based optical telescopes. There is no natural cleansing of space in the geostationary region. The telescope Zeiss-2000 with a two-meter aperture of the Terskol observatory is the largest optical instrument regularly used for space debris investigations. One of the main purposes in «Astronomy in the Elbrus region» international program's boundaries is the detection and characterization of small fragments of debris,which are invisible for smaller telescopes. During observations on photometric nights we usually detect 4-5 unknown fragments of 17-21st star magnitude. In this article, we present orbital parameters and physical characteristics of several small-sized fragments of the space debris detected at the Terskol observatory in 2016-2017. [ABSTRACT FROM AUTHOR]

Researchers have extensively used convolutional neural networks to detect meteor falls on Earth. However, when dealing with limited available data, these networks may need more robustness to classify new real-world images correctly. This study proposes an optimized training approach of a pre-trained model with an attention mechanism to achieve better generalization results in such a scenario. We compare two architectures, an optimized base model and another version with an attention mechanism. Furthermore, we present a new and publicly available optical meteor dataset that merges several public data sources. We used the merged dataset to train classification models combined with a stratified five-fold cross-validation strategy to determine the reliability of the prediction. The experimental results from both architectures showed good and similar performance. To further determine the best architecture, we performed an additional analysis with visual explanations in new observations. The architecture with an attention mechanism was the best model achieving a false alarm ratio of 2.6% and an accuracy of 97%. [ABSTRACT FROM AUTHOR]

The correlation between meteorological data collected at the optical wide-field patrol network (OWL-Net) Station No. 1 and the seeing of satellite optical observation data was analyzed. Meteorological data and satellite optical observation data from June 2014 to November 2015 were analyzed. The analyzed meteorological data were the outdoor air temperature, relative humidity, wind speed, and cloud index data, and the analyzed satellite optical observation data were the seeing full-width at half-maximum (FWHM) data. The annual meteorological pattern for Mongolia was analyzed by collecting meteorological data over four seasons, with data collection beginning after the installation and initial set-up of the OWL-Net Station No. 1 in Mongolia. A comparison of the meteorological data and the seeing of the satellite optical observation data showed that the seeing degrades as the wind strength increases and as the cloud cover decreases. This finding is explained by the bias effect, which is caused by the fact that the number of images taken on the less cloudy days was relatively small. The seeing FWHM showed no clear correlation with either temperature or relative humidity.

We present the results of our optical identifications of several hard X-ray sources from the INTEGRAL all-sky survey obtained over 14 years of observations. Having improved the positions of these objects in the sky with the X-ray telescope (XRT) of the Swift observatory and the XMMNewton observatory, we have identified their counterparts using optical and infrared sky survey data. We have obtained optical spectra for more than half of the objects from our sample with the RTT-150 and AZT-33IK telescopes, which have allowed us to establish the nature of the objects and to measure their redshifts. Six sources are shown to be extragalactic in origin and to belong to Seyfert 1 and 2 galaxies (IGR J01017+6519, IGR J08215-1320, IGR J08321-1808, IGR J16494-1740, IGR J17098-2344, IGR J17422-2108); we have failed to draw definitive conclusions about the nature of four more objects (IGR J11299-6557, IGR J14417-5533, IGR J18141-1823, IGR J18544+0839), but, judging by circumstantial evidence, they are most likely also extragalactic objects. For one more object (IGR J18044-1829) no unequivocal identification has been made. [ABSTRACT FROM AUTHOR]

Geosynchronous Earth Orbit (GEO) satellites are widely used because of their unique characteristics of high-orbit and remaining permanently in the same area of the sky. Precise monitoring of GEO satellites can provide a key reference for the judgment of satellite operation status, the capture and identification of targets, and the analysis of collision warning. The observation using ground-based optical telescopes plays an important role in the field of monitoring GEO targets. Different from distant celestial bodies, there is a relative movement between the GEO target and the background reference stars, which makes the conventional observation method limited for long focal length telescopes. CCD drift-scan photoelectric technique is applied on monitoring GEO targets. In the case of parking the telescope, the good round images of the background reference stars and the GEO target at the same sky region can be obtained through the alternating observation of CCD drift-scan mode and CCD stare mode, so as to improve the precision of celestial positioning for the GEO target. Observation experiments of GEO targets were carried out with 1.56-meter telescope of Shanghai Astronomical Observatory. The results show that the application of CCD drift-scan photoelectric technique makes the precision of observing the GEO target reach the level of 0.2″, which gives full play to the advantage of the long focal length of the telescope. The effect of orbit improvement based on multi-pass of observations is obvious and the prediction precision of extrapolating to 72-h is in the order of several arc seconds in azimuth and elevation. [ABSTRACT FROM AUTHOR]

We present analysis of five nights of R-band observations of Comet 29P/Schwassmann-Wachmann 1 (SW1) taken on September 2008 which show the comet undergoing an outburst. Coma morphology shows a projected asymmetric shell of material expanding radially and four linear features on the northern side of the coma at position angles 37°, 78°, 300°, and 353°. Using the measured projected radial outflow velocity of 0.11 ±0.02 km/s for the shell material, we calculate an outburst time of UT 2008-09-21.03 ±0.95 days. By tracking the inner and outer extent of the northern linear features, we found that the features are fully contained within the expanding shell of material. This suggested both shell and linear features originated during the same event and activity originating from different regions on the nuclear surface are not necessary to generate both types of morphological structure observed. A 3-D Monte Carlo coma model was used to model the outburst. Morphological features present in the observations were modeled allowing constraints to be placed on the spin state of SW1’s nucleus. The evolution of morphological features allows constraints on the rotation period P assuming an outburst duration Δt and the spin period constraints are expressed in terms of their ratio P/ Δt . Since the spin-pole orientation could not be constrained, four spin-pole orientations were chosen for modeling the coma. Spin-period constraints for each assumed pole orientation are discussed. Overall, modeling suggested either a spin period on the order of days, a spin-pole orientation nearly along the sub-Earth direction, or a combination of both. To place an independent constraint on the outburst duration, radial surface-brightness profiles of the observations were compared with profiles from synthetic models, giving an upper-limit of Δt ≤ 1.5 days. Longer outbursts resulted in a higher number of dust grains in close proximity to the nucleus during the observations and a profile slope too steep to model observations. Lastly, from photometry of the five nights of observation, a lower limit of (1.8 ± 0.07) × 10 9 kg was estimated for the total amount of dust emitted during the outburst. Assuming the outburst was triggered by either the sublimation of pure CO or CO 2 ice and a dust to gas ratio of ∼4 ( Rosetta results for Comet 67P, Rotundi et al. 2015), a lower limit for the outburst duration on the order of hours was obtained. [ABSTRACT FROM AUTHOR]

A method to deal with uncertainties in initial orbit determination (IOD) is presented. This is based on the use of Taylor differential algebra (DA) to nonlinearly map uncertainties from the observation space to the state space. When a minimum set of observations is available, DA is used to expand the solution of the IOD problem in Taylor series with respect to measurement errors. When more observations are available, high order inversion tools are exploited to obtain full state pseudo-observations at a common epoch. The mean and covariance of these pseudo-observations are nonlinearly computed by evaluating the expectation of high order Taylor polynomials. Finally, a linear scheme is employed to update the current knowledge of the orbit. Angles-only observations are considered and simplified Keplerian dynamics adopted to ease the explanation. Three test cases of orbit determination of artificial satellites in different orbital regimes are presented to discuss the feature and performances of the proposed methodology. [ABSTRACT FROM AUTHOR]

The capabilities of the new medium- and low-resolution spectrograph installed recently on the 1.6-m AZT-33IK telescope at the Sayan Observatory of the Institute of Solar-Terrestrial Physics to solve the problems of ground-based optical support for the future all-skyX-ray survey of the SRGobservatory are discussed. Results of the test observations of galaxy clusters, active galactic nuclei (AGNs) and quasars, and cataclysmic variables performed immediately after the installation of the spectrograph on the telescope are presented. The results of these observations show that the AZT-33IK telescope equipped with the new medium- and low-resolution spectrograph can provide a substantial fraction of the necessary optical observations in the program of ground-based optical support for the all-sky survey of the SRG observatory. [ABSTRACT FROM AUTHOR]