Present and future Chinese large telescope projects

Through out the ancient history, Chinese astronomers had made tremendous achievements. Since the main purpose of the ancient Chinese astronomy was to study the correlation between man and the universe, all the Emperors made ancient Chinese astronomy the highly regarded science throughout the history. After a brief introduction of the achievement of ancient Chinese astronomy, I describe the beginnings of modern astronomy research in China in the 20th century. Benefiting from the fast development of Chinese economy, the research in astronomy in China has made remarkable progress in recent years. The number of astronomers has doubled in the past ten years, and the number of graduate students has grown over 1300. The current budget for astronomy research is ten times larger than that ten years ago. The research covers all fields in astronomy, from galaxies to the Sun. The recent progress in both the instruments, such as the Guo Shoujing's telescope, a Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), and the theoretical research will be briefly presented. The ongoing and future projects on the space- and ground-based facilities will be described, including the Five Hundred Meter Aperture Spherical Radio Telescope (FAST), “Chang E” (Lunar mission) project, Hard X-ray Modulate Telescope (HXMT), DArk Matter Particle Explorer (DAMPE), Deep Space Solar Observatory (DSO), Chinese Antarctic Observatory (CAO), 65m steerable radio telescope, Chinese Spectral Radioheliogaph (CSRH) etc.

Observing low-frequency decimeter hydrogen radio recombination lines (RRLs) with large single-dish telescopes, such as the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in the L band, is a unique method for probing massive star formation on scales of hundreds of parsecs. This approach is particularly effective for detecting relatively weak and extended emissions from low-density gas ionized by massive stars. Deep, unbiased decimeter or centimeter RRL surveys with large single-dish telescopes can significantly enhance our understanding of the diffuse ionized gas along the Galactic plane. This, in turn, will improve our knowledge of the life cycle of matter in the interstellar medium and the dynamics of the Galaxy. In this context, we present a pilot project for such a blind L-band RRL survey targeting the Galactic plane and conducted using FAST. The results include the detection of RRL clumps and the identification of an off-arm active massive star-forming region near the Sagittarius-Carina arm. The ongoing and upcoming massive star formation in this region may be associated with the kink in the Sagittarius-Carina arm near 23$^ circ $ azimuth.

The collecting area of a radio telescope is a figure of merit of that instruments's capability. A Five hundred meter Aperture Spherical Telescope (FAST) is proposed to be built in the unique karst area of southwest China, and will act, in a sense, as a prototype for the Square Kilometer Array (SKA). It will be over twice as large as Arecibo coupled with much wider sky coverage. Some results from site surveys for such a SKA concept are briefly reported. Technically, FAST is not simply a copy of the existing Arecibo telescope but has rather a number of innovations. Firstly, the proposed main spherical reflector, by conforming to a paraboloid of revolution in real time through actuated active control, enables the realization of both wide bandwidth and full polarization capability while using standard feed design. Secondly, a feed support system which integrates optical, mechanical and electronic technologies will effectively reduce the cost of the support structure and control system. With an overall diameter of 500 m and radius of its spherical surface of 300 m, FAST will be the world's largest single dish.

In order to guarantee the usage of active reflector and achieve the highest working frequency requirement, 5GHz, in FAST, fitting accuracy of the active reflector is supposed to be analyzed. In this chapter, a novel 3 DOFs parallel mechanism, 3-PSS with constraint leg, is proposed. This mechanism can fulfill the required movement to fit a paraboloid of revolution for the active reflector. The kinematics of 3-PSS+C mechanism is studied. Based on that, the one and two-dimensional fitting accuracy are calculated and the side length

Acting as a pilot of the Square Kilometer Array (SKA), the Five hundred meter Aperture Spherical Telescope (FAST) has been proposed for construction in the unique karst area of southwest China. FAST is of Arecibo-type with rather a number of innovations, among which the active main spherical reflector shows fascinating. Furthermore, the feed cabin is supported and moved by cables controlled by computer, which avoids a heavy and expensive focal pointing system. With the effective aperture of 300 m, a large sky coverage, and a broad bandwidth (200 to 2000 MHz), possible capability up to 5 ∼8 GHz, FAST will be the world's largest single dish and perform markedly role in radio astronomy.

We present the quasar catalog from Data Releases 10 to 12 of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Quasar Survey, comprising quasars observed between 2021 September and 2024 June. We robustly identified 11,346 quasars, of which 5386 are newly discovered objects not present in the Million Quasars catalog. This release brings the total number of quasars identified by the 12 yr LAMOST survey to 67,521, of which 29,513 are newly discovered. While the absolute flux calibration for LAMOST quasar spectra from Data Releases 6 to 9 was previously performed using the Sloan Digital Sky Survey (SDSS)/PanSTARRS1 multiband photometric data, the inherent variability of quasars can affect the flux accuracy. To address this limitation, we recalibrated the LAMOST spectra using (quasi-)simultaneous photometric data from Zwicky Transient Facility, which has conducted high-cadence sky monitoring since 2018 March. Based on the recalibrated single-epoch spectra, we estimated the emission-line fluxes, continuum fluxes, and virial black hole masses. These improved spectra facilitate direct comparison with the spectra of common quasars from SDSS, enabling searches for rare quasars, such as changing-look quasars exhibiting the appearance or disappearance of broad emission lines and broad absorption line quasars. The combined dataset of photometry and multiepoch spectra will enhance the detections of active galactic nucleus–related transients, such as Bowen fluorescence flares and extreme variability quasars, thereby improving our understanding of quasar variability.

A unique wide band receiver for radio astronomy has been designed and constructed. Receivers used for radio astronomy consist of two parts, the front end cold electronics and the back end warm electronics. While the cold electronics provides for a low noise amplifier and receiver calibrations, the warm electronics provides analog signal processing that shapes and filters the signals before digitizing. The following describes the unique features of the warm electronics receiver built by Caltech for installation on China's Five hundred meter Aperture Spherical Telescope (FAST).

First feed support system, which is one of the key technologies of Five hundred meter Aperture Spherical Telescope (FAST) was discussed in this paper. A 1:30 scaled model (20 m × 20 m × 6 m) has been built to make systemic research on the feasibility of the system. The root mean square of pointing error of moving cable car was measured and the displacements of cable car within the wind speed of 8 m/s, which is the maximal wind speed of the place where the FAST will be located, were evaluated. Then the total maximal pointing error of cable car was computed. Experimental results demonstrate that the total pointing error of the cable car is less than 50 cm, the required pointing accuracy error of the system.

In the last ten years, Chinese astronomers proposed two optical and near-infrared Extremely Large Telescope (ELT) projects, one is 30m Chinese Future Giant Telescope (CFGT) the other is a 30m Ring Interferometric Telescope (RIT). The current status in the development of these two projects and their key technology research and progress are described in this paper. Both of the two plans are the preliminary projects of the National Astronomical Observatories (NAOC) of the Chinese Academy of Sciences (CAS), and finance-supported from the NAOC. The National Science Foundation of China (NSFC) also gives supports to key technology researches of the projects (such as, adaptive optics and high-resolution imaging techniques). In the final part of this paper a brief description is given on the possibility of international cooperation in the development of Chinese ELT. A review is also presented of other two ground-based Extremely Large Projects (ELP), one is Five-hundred-Meter Aperture Spherical Radio Telescope (FAST), and the other is a challenging PANDA (The Prydz bay, Amery ice shelf and Dome A Observatories) project in Antarctica.

The R&D of the Chinese 4-m ever-ambitious telescope, Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), has advanced towards a new stage, and first light is expected by the end of 2006. As one of national scientific and engineering projects the telescope will become national facility and accommodate maximum accessibility for public reach in general and for the astronomical community in particular. Thus remote or even robotic control of the telescope is put under careful exploration. With the rapid development of IT technology one of the fashions is the mobile telephone carried around by average people mainly for daily communication, and mobile notes application has become a real hit. This paper presents GSM based remote wireless application adapted to telescope control, which can be utilized for greatly enhancing LAMOST’ accessibility. The novel technique has recently been developed in LAMOST control lab.Test has demonstrated successful execution of Monitor & Control (M&C) commands for LAMOST through remote wireless mobile. The hardware and software configuration with techniques involved for reliable and secure communication is outlined in this paper too.

Stellar fundamental parameters are important in the asteroseismic study of Kepler light curves. However, the most used estimates in the Kepler Input Catalog (KIC) are not accurate enough for hot stars. Using a sample of B stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectral survey, we confirmed the systematic underestimation in the KIC effective temperature and overestimation in KIC surface gravity. The good agreement between LAMOST and other follow-up observations proved the accuracy of effective temperature and surface gravity of B stars derived from LAMOST low-resolution spectra. By searching through LAMOST data, we found four misclassified main-sequence B stars in the Kepler field, which had been previously classified as A-type variables. We present spectroscopic and detailed frequency analysis of these four stars based on LAMOST spectra and Kepler photometry.

The Phased Array Feed (PAF) is considered as one of the next generation receivers for radio telescopes, which can significantly enlarge the instantaneous Field-of-View of large aperture single dish radio telescopes and enable more flexible observing configurations. Study efforts on PAF development for radio telescopes have been made for more than two decades and have become more and more applicable. We report the development of an ambient-temperature 19 element L-band PAF system and the experimental results including its far field beam pattern and system temperature measurement, which achieve the expectations. Implementing the aperture array beam-forming method, we demonstrate a wide-field Galactic H i observations in the radio camera mode. The results indicate that this system might be applicable for strong Galactic transient detections. This system could be directly equipped to large telescopes like the Five-hundred-meter Aperture Spherical radio Telescope (FAST) and FAST array in the future.

A new kind of position control system for basic elements of sphere is introduced in the paper. Based on mechanical principle, structure analysis is made for the control system, which proved that it meets special need of the position control system of FAST (Five-hundred-meter Aperture Spherical Telescope). In addition, kinematics analysis is made for the compensation fit of the system and compensating size is calculated. Lastly, some results of experiment are given.

Stray radiation is a considerable challenge for radio telescopes, requiring careful assessment due to its effects. This is crucial when the strong background flux from side lobes significantly affects the total flux, especially for extended sources. In this study, we introduced the beam pattern of the L-band receiver on the Five-hundred-meter Aperture Spherical Telescope (FAST), covering various frequencies based on recent observations. We discovered that the main beam efficiency of all beams exceeds 90% throughout the L band frequencies, with efficiency decreasing slowly as frequency increases. Subsequently, we developed a module to mitigate stray radiation effects, incorporating it into FAST’s standard HI data reduction process, referred to as HiFAST. Our analysis shows that side lobe flux’s influence, particularly for extended sources with significant surface density gradients, necessitates detailed evaluation. Corrections for the extended M33 galaxy can reach up to 20%. Moreover, the pattern data presented here is vital for studying HI intensity maps at high redshift. The module, along with HiFAST and beam pattern data across 15 frequency bins, can be accessed at https://hifast.readthedocs.io

The positioning accuracy of optical fibers directly affects the observation efficiency of spectroscopic survey telescopes. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) adopts an optical fiber closed-loop positioning system based on a photogrammetric measurement system. A photogrammetric measurement system requires accurate identification of the optical spot position to achieve higher optical fiber positioning accuracy. However, the temperature difference within 1 day of the barrel of LAMOST will reach 40°C during the observation period. The change of air refractive index will lead to nonlinear deviation of the light propagation path of the optical spot, which will lead to the dispersion of the optical spot and cause a huge deviation in the position detection of the optical spot. To address this issue, we propose incorporating an automatic focusing system into the optical fiber closed-loop positioning system. Because each LAMOST’s fiber view camera (FVC) covers a field of view with hundreds of 320 μm-diameter optical fibers, fast and efficient focusing control for a large number of tiny optical fiber targets is highly challenging. Our solution implements a passive autofocus architecture combining an efficient image clarity evaluation method with a rapid focus search algorithm. Existing image sharpness evaluation methods are incompatible with FVC raw optical spot images, and traditional hill-climbing-based focusing algorithms require dozens of adjustments, significantly reducing efficiency. Our approach introduces an adaptive method for evaluating high-resolution optical spot image definition using the mean variance of the optical spot region, significantly reducing computational cost while improving threshold adaptability. Furthermore, we developed a focus search algorithm based on a hybrid convolutional neural network and recurrent neural network architecture. The algorithm predicts defocus distance from optical spot state sequence, achieving 95% single-shot focusing accuracy within the depth of field. It has been successfully applied to the LAMOST’s FVCs and also offers new methods for other focusing search methods based on passive autofocus for cameras.