Ground-based observations around 1.4 mu m are normally limited by strong absorption of telluric water-vapor. However, Dome A, Antarctica has exceptionally dry conditions that offer a unique opportunity for observations in this band. We designed a new filter covering 1.34-1.48 mu m, namely W ' , and installed it on the Antarctic Infrared Binocular Telescope (AIRBT) at Dome A in 2025. AIRBT comprises two identical 15 cm optical tube assemblies and two InGaAs cameras equipped with J and W ' filters, respectively. With this Early Data Release (EDR), we aim to evaluate the performance of the W ' band at Dome A to observe objects with water-vapor features. This EDR covers similar to 20 deg2 in the Galactic plane using similar to 20,000 images in three nights. For 2 s exposures, the 5 sigma limiting magnitude histogram peaks at J similar to 11.5 mag (Vega) and W 'similar to 9.9 mag, respectively. The J-W ' versus J - H color-color diagram distinguishes ultracool candidates with water-vapor-absorption features from reddened early type stars. Furthermore, later-type stars tend to exhibit stronger water-vapor absorption. Some sources show larger Delta W ' than Delta J across the three nights, which we attribute to variations of their water-vapor-absorption depth. We conclude that it will be efficient to search for ultracool stars and estimate their spectral subtypes using W ' band imaging at Dome A, where the atmospheric transmission is high and stable.

The Multi-Channel Imager (MCI) is a powerful near-ultraviolet (NUV) and visible imager onboard the Chinese Space Station Survey Telescope (CSST). The MCI provides three imaging channels, which are the NUV channel, the Blue channel and the Red channel, with the wavelength ranges of 255-430 nm, 430-700 nm, and 700-1000 nm, respectively. MCI's three channels can target the same field simultaneously, which is unique compared to other imagers onboard the Hubble Space Telescope (HST) or the James Webb Space Telescope (JWST). Each channel employs a CCD focal plane of 9216 & times; 9232 pixels and similar to 7.' 5 & times;7.' 5 field of view (FOV), which are greater than or similar to 4 times the FOVs of HST imagers. The MCI's three channels feature unprecedented sensitivities and FOVs, complementing the NUV and visible capabilities of the CSST for high-precision photometry and weak-signal detection, which would help build a new standard-star system and the deepest UV-Optical exposures for CSST. Rich filter sets of MCI would help explore other areas of science such as local emission line mapping, searching for high-z Ly alpha emitters, etc. Here we present key design features, results of current ground tests, and suggest observing strategies for the MCI.

Accretion onto supermassive black holes (SMBHs) powers active galactic nuclei (AGNs) and drives feedback that shapes galaxy evolution. Constraining AGN accretion disk structure is therefore essential for understanding black hole growth and feedback processes. However, direct constraints on disk size remain rare—particularly from long-term, multiseason spectroscopic reverberation mapping (RM), which is critical for isolating the intrinsic disk response from the broad-line region (BLR). We present results from an intensive multiwavelength RM campaign of NGC 4151 during its brightest state in nearly two decades. This represents the third high-cadence monitoring over the past decade, capturing accretion states spanning the transitional regime between thin and thick disks, making NGC 4151 the only AGN with continuum RM observations across such a wide range in accretion states. Combining spectroscopy from the Lijiang 2.4 m telescope with coordinated Swift UV/X-ray monitoring, we measure interband continuum lags from UV to optical. The wavelength-dependent lags follow a tight τ ∝ λ ^4/3 relation, consistent with reprocessing in a thin disk, but exceed theoretical predictions by a factor of 6.6. Our lag spectrum reveals clear excesses near the Balmer and possibly Paschen jumps, confirming diffuse continuum (DC) contamination from the BLR. By comparing the three campaigns, we discover a nonmonotonic lag–luminosity trend (>3 σ ), which cannot be explained by DC emission alone. We propose that the lags reflect combined disk and BLR contributions, and present the first evidence that the DC component follows an intrinsic Baldwin effect. These results offer new insights into SMBH mass measurements and theoretical models of AGN inner structure.

Optical variability is a key observational probe for studying the accretion dynamics and central engine physics of Active Galactic Nuclei (AGNs). The quality and completeness of light curves have a direct impact on variability studies, particularly for faint AGNs and high-redshift AGNs. To improve the quality of long-term light curves for AGNs, we bin and stack multi-epoch images balancing the image depths and temporal resolution. As a case study, we apply this method to Zwicky Transient Facility (ZTF) observations in the Extended Groth Strip (EGS) field, where the overlapping region covers an area of about 370 arcmin^2 and includes g-band and r-band data taken from March 2018 to December 2024. The co-added images are approximately 2.0 to 2.5 magnitudes deeper than the ZTF single-epoch images. With co-added images, we construct light curves for 73 AGNs in the EGS field. Compared to the traditional ZTF light curves, our light curves maintain consistent long-term variability trends but with higher photometric precision. Furthermore, this method can help detect AGNs with weak variability which are missed from the traditional ZTF data due to the noisy light curves or below the detection limit in ZTF's single-epoch exposure. Among the 73 AGNs, the majority exhibit a bluer-when-brighter (BWB) trend on long-term timescales, which is consistent with previous studies. This work offers insights for optimizing AGN light curves in both current and upcoming all-sky time-domain surveys.

Infrared time-domain surveys remain significantly underdeveloped compared with their optical counterparts. We have developed the Antarctic Infrared Binocular Telescope (AIRBT) to study the dynamic infrared sky at Dome A, Antarctica, taking advantage of the superb infrared observational conditions at this site. AIRBT consists of two identical 15 cm f /3 optical tube assemblies and two cost-effective indium gallium arsenide (InGaAs) cameras equipped with J and H filters, respectively. The cameras have 640 × 512 15 μ m pixels, giving a scale of 6 . ″ 9 pixel −1 and a field of view of 1.22 × 0.97 deg 2 . We characterize the performance of the InGaAs cameras, including bias, readout noise, dark current, nonlinearity, and photon transfer curve (PTC). Our analysis highlights the distinct behaviors of InGaAs cameras compared with charge-coupled devices. The bias and readout noise show temperature dependence. In addition, the noise measured from the PTCs has additional components increasing with exposure time. On-sky tests were conducted in 2022 October including system calibration, limiting depth, and photometric precision. For a single 3 s exposure, we achieved 5 σ limiting magnitudes of 11.2 mag (Vega system) in J band and 9.7 mag in H band. The best photometric precision reached 20 mmag at the bright end, which could be further improved to sub-percent levels through image stacking. AIRBT was installed at Dome A in 2023 January, and scientific observations began as soon as darkness set in.

Located at Dome A, the highest point on the Antarctic plateau, China’s Kunlun station is a premier ground-based photometric observatory. Its cold, dry, and stable atmosphere allows continuous observation for over 40 days during polar winter, ideal for detecting short-period transiting exoplanets. Since 2008, the Antarctic Survey Telescopes (AST3) project has pursued the CHESPA program to search for exoplanet candidates. During the austral winters in 2016 and 2017, the AST3-II telescope surveyed fields located in the southern continuous viewing zone of the Transiting Exoplanet Survey Satellite (TESS). This paper presents the second data release from CHESPA, encompassing photometric data for over 85,000 bright ( m _i ≤ 15) stars. The survey achieved a photometric precision of approximately 2 mmag at optimal brightness levels. To illustrate the data quality, we present a catalog of 203 newly identified variable stars showing brightness variations over 5 mmag based on the 2017 observations, as compared to Data Release 1. Among these, 26 are newly recognized periodic variables that are not listed in the AAVSO database ( https://www.aavso.org/ ), and 86 are in the TESS Candidate Target List. These variables required rigorous examination to eliminate false-positive signals in the transiting exoplanets search.

Cameras with a super-wide field of view, defined here as being at least 20 degrees on one side, are widely used in site testing and time-domain astronomy. However, they intrinsically require optics with non-linear projections, making it challenging to use traditional astrometric methods. We have developed a generalized astrometric method that is applicable to images with super-wide fields of view. We applied the method to images from an all-sky camera and obtained the astrometric solutions. The positional accuracy we achieve in analysing 5170 all-sky images is typically 0.4 pixels in $(x,y)$. Our method is a generalized method suitable for all images with super-wide fields of view.

Low sky brightness is crucial for ground-based astronomical observations, because it limits the observational capability to detect fainter sources. Lenghu, located on the Tibetan Plateau in China, has been identified as an high-quality astronomical site in China, including dark sky in optical band. In this work, we will report the preliminary results of near-infrared sky brightness measurements at Lenghu. Utilizing a wide-field small telescope equipped with an InGaAs camera, we have been conducting long-term monitoring of near-infrared sky brightness in the J and H' bands, respectively, since January 2024. For each image, photometry and astrometry were performed, then sky background was calibrated by standard stars from the 2MASS catalog. This report includes preliminary results on the sky brightness at zenith in the J and H' bands, as well as their variations with solar elevation at Lenghu. Our initial results indicate that the near-infrared sky brightness at Lenghu is comparable to that of other world-class sites, and long-term monitoring will be continued.

Recently, InGaAs cameras have been utilized in time domain astronomical observations in the infrared bands, taking advantage of their improved performance. However, the noise levels of InGaAs cameras remain high compared to Charge coupled device (CCD) in optical bands, thereby limiting the signal-to-noise ratio for photometry. We characterize noise of Ninox 640 SU InGaAs camera. We test the noise components originating from bias, dark current, and flat, and analyze the readout noise, dark current, non-linearity, and the variation in responses between pixels. Bias and readout noise of CCD in optical band are stable. The frame with the minimum integration time of camera is generally considered as bias, and the readout noise is calculated based on it. However, count and noise of InGaAs camera are still unstable during a short period of integration time, prompting a detailed discussion on bias selection and readout noise calculation methods. The photon transfer curve (PTC), which represents the variance as a function of signal, is commonly employed to determine gain of camera from the slope. However, our PTCs exhibit varying slopes corresponding to different levels of brightness in the light source, indicating a non-constant slope. Consequently, we maintain a fixed integration time while increasing the signal level by intensifying the light source. This adjustment yields constant PTC slopes, consistent with the expectation, thereby suggesting the presence of additional noise that increases with integration time. Therefore, when measuring the gain of InGaAs cameras via PTC, it is imperative to opt for fixing exposure time and changing light brightness. Following the characterization of the noise components, we will develop correction methods for each noise and apply these methods to frames obtained from astronomical time domain observations. Finally, we will discuss the potential of InGaAs cameras in infrared time domain observations.

ABSTRACT AST3-2 is the second of the three Antarctic Survey Telescopes, aimed at wide-field time-domain optical astronomy. It is located at Dome A, Antarctica, which is by many measures the best optical astronomy site on the Earth’s surface. Here we present the data from the AST3-2 automatic survey in 2016 and the photometry results. The median 5σ limiting magnitude in i-band is 17.8 mag and the light-curve precision is 4 mmag for bright stars. The data release includes photometry for over 7 million stars, from which over 3500 variable stars were detected, with 70 of them newly discovered. We classify these new variables into different types by combining their light-curve features with stellar properties from surveys such as StarHorse.

Atmospheric seeing is one of the most important parameters for evaluating and monitoring an astronomical site. Moreover, being able to predict the seeing in advance can guide observing decisions and significantly improve the efficiency of telescopes. However, it is not always easy to obtain long-term and continuous seeing measurements from a standard instrument such as differential image motion monitor (DIMM), especially for those unattended observatories with challenging environments such as Dome A, Antarctica. In this paper, we present a novel machine learning-based framework for estimating and predicting seeing at a height of 8 m at Dome A, Antarctica, using only the data from a multi-layer automated weather station (AWS). In comparison with DIMM data, our estimate has a root mean square error (RMSE) of 0.18 arcsec, and the RMSE of predictions 20 minutes in the future is 0.12 arcsec for the seeing range from 0 to 2.2 arcsec. Compared with the persistence, where the forecast is the same as the last data point, our framework reduces the RMSE by 37 percent. Our method predicts the seeing within a second of computing time, making it suitable for real-time telescope scheduling.

ABSTRACT Dome A in Antarctica has many characteristics that make it an excellent site for astronomical observations, from the optical to the terahertz. Quantitative site testing is still needed to confirm the site’s properties. In this paper, we present a statistical analysis of cloud cover and aurora contamination from the Kunlun Cloud and Aurora Monitor (KLCAM). KLCAM is an automatic unattended all-sky camera aiming for long-term monitoring of the usable observing time and optical sky background at Dome A. It was installed at Dome A in January 2017, worked through the austral winter, and collected over 47 000 images over 490 d. A semi-quantitative visual data analysis of cloud cover and auroral contamination was carried out by five individuals. The analysis shows that the night sky was free of clouds for 83 per cent of the time, which ranks Dome A highly in a comparison with other observatory sites. Although aurorae were detected somewhere on an image for nearly 45 per cent of the time, the chance of a point on the sky being affected by an aurora is small. The strongest auroral emission lines can be filtered out with customized filters.

Dome A, Antarctica, has been thought to be one of the best astronomical sites on the Earth for decades. Since it was first visited by astronomers in 2008, dozens of facilities for astronomical observation and site testing were deployed. Due to its special geographical location, the data and message exchange between Dome A and the domestic control center could only depend on Iridium. Because the link bandwidth of Iridium is extremely limited, the network traffic cost is quite expensive and the network is rather unstable, the commonly used data transfer tools, such as rsync and scp, are not suitable in this case. In this paper, we design and implement a data transfer tool called NBFTP (narrow bandwidth file transfer protocol) for the astronomical observation of Dome A. NBFTP uses a uniform interface to arrange all types of data and matches specific transmission schemes for different data types according to rules. Break-point resuming and extensibility functions are also implemented. Our experimental results show that NBFTP consumes 60% less network traffic than rsync when detecting the data pending to be transferred. When transferring small files of 1KB, the network traffic consumption of NBFTP is 40% less than rsync. However, as the file size increases, the network traffic consumption of NBFTP tends to approach rsync, but it is still smaller than rsync.

ABSTRACT The 0.5-m Antarctic Survey Telescopes (AST3) were designed for time-domain optical/infrared astronomy. They are located in Dome A, Antarctica, where they can take advantage of the continuous dark time during winter. Since the site is unattended in winter, everything for the operation, from observing to data reduction, had to be fully automated. Here, we present a brief overview of the AST3 project and some of its unique characteristics due to its location in Antarctica. We summarize the various components of the survey, including the customized hardware and software, that make complete automation possible.

Seeing—the angular size of stellar images blurred by atmospheric turbulence—is a critical parameter used to assess the quality of astronomical sites at optical/infrared wavelengths. Median values at the best mid-latitude sites are generally in the range of 0.6–0.8 arcseconds 1 – 3 . Sites on the Antarctic plateau are characterized by comparatively weak turbulence in the free atmosphere above a strong but thin boundary layer 4 – 6 . The median seeing at Dome C is estimated to be 0.23–0.36 arcseconds 7 – 10 above a boundary layer that has a typical height of 30 metres 10 – 12 . At Domes A and F, the only previous seeing measurements have been made during daytime 13 , 14 . Here we report measurements of night-time seeing at Dome A, using a differential image motion monitor 15 . Located at a height of just 8 metres, it recorded seeing as low as 0.13 arcseconds, and provided seeing statistics that are comparable to those at a height of 20 metres at Dome C. This indicates that the boundary layer was below 8 metres for 31 per cent of the time, with median seeing of 0.31 arcseconds, consistent with free-atmosphere seeing. The seeing and boundary-layer thickness are found to be strongly correlated with the near-surface temperature gradient. The correlation confirms a median thickness of approximately 14 metres for the boundary layer at Dome A, as found from a sonic radar 16 . The thinner boundary layer makes it less challenging to locate a telescope above it, thereby giving greater access to the free atmosphere.

The Gemini Infrared Multi-Object Spectrograph (GIRMOS) is a four-channel adaptive-optics-assisted integralfield spectrograph being designed for the Gemini 8-meter telescopes. Deployed behind the Gemini-North Adaptive Optics (GNAO) system, it will provide spatially-resolved spectra over the 0.9-2.4 um wavelength range for four fields simultaneously. Its multi-object adaptive optics will provide additional correction of the target fields, beyond that achieved by the GNAO system, enabling integral-field spectroscopy with near-diffraction-limited resolution and unprecedented sensitivity. A parallel imaging channel will view the field of regard and provide a simultaneous imaging capability. The primary science objectives include mapping chemical abundances, star formation and kinematics in high-redshift galaxies, and studies of stellar populations, star formation and supermassive black holes in nearby galaxies. In order to support the science programs, GIRMOS requires a system that enables photometric, spectroscopic and astrometric calibration. The GIRMOS Calibration System (CAL) serves this purpose, uniformly illuminating the spectroscopic and imaging channels with both continuous and narrow-line light for flat-field and wavelength calibration. In order to replicate the light path through the instrument as closely as possible, the CAL optical system matches both the pupil position and the focal ratio of the beam delivered to the instrument by GNAO. CAL also includes a metrology system, employing focal-plane masks, to permit precise calibration of the positions of the pick-off arms of the object selection system, and to map optical distortion and instrument flexure. This paper summarizes the key requirements of the CAL system, presents its conceptual design and discusses its expected performance.

Time series data of celestial objects are commonly used to study valuable and unexpected objects such as extrasolar planets and supernova in time domain astronomy. Due to the rapid growth of data volume, traditional manual methods are becoming extremely hard and infeasible for continuously analyzing accumulated observation data. To meet such demands, we designed and implemented a special tool named AstroCatR that can efficiently and flexibly reconstruct time series data from large-scale astronomical catalogues. AstroCatR can load original catalogue data from Flexible Image Transport System (FITS) files or databases, match each item to determine which object it belongs to, and finally produce time series datasets. To support the high-performance parallel processing of large-scale datasets, AstroCatR uses the extract-transform-load (ETL) preprocessing module to create sky zone files and balance the workload. The matching module uses the overlapped indexing method and an in-memory reference table to improve accuracy and performance. The output of AstroCatR can be stored in CSV files or be transformed other into formats as needed. Simultaneously, the module-based software architecture ensures the flexibility and scalability of AstroCatR. We evaluated AstroCatR with actual observation data from The three Antarctic Survey Telescopes (AST3). The experiments demonstrate that AstroCatR can efficiently and flexibly reconstruct all time series data by setting relevant parameters and configuration files. Furthermore, the tool is approximately 3X faster than methods using relational database management systems at matching massive catalogues.

The CHinense Exoplanet Searching Program from Antarctica is a ground-based wide-field photometric survey using the AST3 and CSTAR telescopes located at Dome A, Antarctica. Blessed with the unparalleled observing conditions on the highest point of the Antarctic plateau, three remotely controlled, fully automatic telescopes (AST3-I, AST3-II, and CSTAR-II) carried out continuous high-precision photometric surveys through the polar nights of 2016 and 2017. During the observing seasons of 2016, a total of 26,578 light curves were obtained for stars within the area of the southern continuous viewing zone of TESS, covering an i-band magnitude range from 7.5 to 15. At m(i) = 10, photometric precision reaches similar to 2 mmag, allowing possible discoveries of sub-Jupiter-size exoplanets. Here we report 20 stellar flares with i-band energies larger than 10(34) erg detected in the 2016 data set of AST3-II, all from different sources. We model the stellar flares and calculate the durations, amplitudes, energies, and skewnesses. The flare properties and the stellar properties of their sources are presented in this work.

The location of an astronomical observatory is a key factor that affects its scientific productivity. The best astronomical sites are generally those found at high altitudes. Several such sites in western China and the Tibetan plateau are presently under development for astronomy. One of these is Ali, which at over 5000 m is one of the highest astronomical sites in the world. In order to further investigate the astronomical potential of Ali, we have installed a lunar scintillometer, for the primary purpose of profiling atmospheric turbulence. This paper describes the instrument and technique, and reports results from the first year of observations. We find that ground layer (GL) turbulence at Ali is remarkably weak and relatively thin. The median seeing, from turbulence in the range 11- 500 m above ground is 0.34 arcsec, with seeing better than 0.26 arcsec occurring 25 per cent of the time. Under median conditions, half of the GL turbulence lies below a height of 62 m. These initial results, and the high altitude and relatively low temperatures, suggest that Ali could prove to be an outstanding site for ground-based astronomy.

The original version of the chapter starting on p. 284 was revised. The grant numbers of the Joint Research Fund in Astronomy were incorrect in the acknowledgement on p. 297. The original chapter was corrected.