The Multi-channel Photometric Survey Telescope (Mephisto) is a wide-field ground based telescope with a 1.6m primary mirror and 2° field of view, proposed by Yunnan University. The telescope will be capable of imaging the northern sky in three colors simultaneously and deliver a colored movie of the universe. The R-C system with lens corrector was adopted as the optical system considering of the image quality requirement, light obscuration and camera arrangement, in which three cubic splitters were adopted for the three channel beams in order to get satisfied image quality over the whole field of view. Dichroic coating on the cubic will lead to nonuniform efficiency on the focal plane due to the polarization problem and wide incident angle, which need calibration. The image quality represented in 80% encircled light energy is around 0.6arcsec. In order to keep the optimal image quality in any operational conditions, a 5-DOF mechanism was designed to actively adjust M2 mirror positions according to the wavefront sensors or by direct star psf. Now the telescope are under developing in Nanjing, expected to be installed at Lijiang observatory before the end of 2021.
The Multi-channel Photometric Survey Telescope (Mephisto) have a 1.6m primary mirror with 1.3 focal ratio, a 2degree field of view. Mephisto is capable of imaging the northern sky in three colors simultaneously. Its 0.7m secondary mirror is quite sensitive for alignment. The field dependent image quality of the misaligned Mephisto optics would be characterized as asymmetric, continuously varying and nonlinear with the misalignments. When the real-time field-PSF is measured from the astronomical images, the residual field-PSF of nominal optical design is defined as the goal of the merit function, the misaligned values of Mephisto secondary mirror can be calculated, by using the PSO (Particle swarm optimization) algorithm. The truth is field-PSF can be numerically expressed with ellipticity of the imaging stars or distribution of the ellipticity. However, for resolving the misalignment values, the stable field-PSF modes are needed, instead of random modes. PCA (Principal component analysis) algorithm is used for eliminating the random perturbations, such as turbulence.
Due to its extremely cold, dry, tenuous, and stable atmosphere, the Antarctica plateau is widely considered to be an excellent astronomical site. The long periods of uninterrupted darkness at polar sites such as Dome A provide a possibility of continuous observation for more than 3 months, which is quite suitable for time-domain astronomy. The second Antarctic Survey Telescope (AST3-2), the largest optical telescope in Antarctica so far, is a 0.5m entrance diameter large field of view optical imaging telescope which was deployed to Dome A, Antarctic in January 2015. It was used to study variable objects, such as supernova explosions and the afterglow of gamma-ray bursts, and to search for extrasolar planets. For the remoteness of the Antarctic plateau, it is designed to observe autonomously and operate remotely via satellite communication. With only 20 days attending maintenance annually, it has experienced 3 winters. It has observed for 3months in 2015 and 4 months in 2016. In the third year of 2017, the observing time of AST3-2 has covered all the polar night from March to September, the data reached to nearly 30TB with more than 200,000 exposures for searching supernovas and exoplanets. AST3-2 was also the only one telescope in the Antarctic plate that joined the optical observations of LIGO GW170817.
Except for the spectroscopic survey telescope LAMOST, there are only two 2m class general purpose telescopes for precision observation in China (2.16m in Xinglong and 2.4m in Lijiang). Chinese astronomical community unanimously agrees that a 10m class large diameter general purpose optical/infrared telescope is urgently needed in China for a wide range of scientific research. The configuration for LOT with primary aperture 12m has been selected by Chinese government for the Thirteen-five-years plan in July, 2016. The concept design introduced here has been approved by Chinese astronomical community and Chinese Academy of Sciences in Dec. 2017, and submitted into the formal funding procedure of Chinese government. For quite a long time, China will very likely have only one 10m class telescope, therefore LOT should be a general-purpose telescope including multi-foci. The Nasmyth focus, prime focus, Cassegrain focus and coudé focus have been considered or reserved. Also, LOT will closely combine with the development of new technologies, such as AO, GLAO, fiber and instrument related new technologies, to make it has powerful capability for the frontier sciences. The four-mirror Nasmyth system, optimized according to the GLAO requirements, has a f-ratio about 14 and field of view 14 arecmin with excellent image quality. Some off-axis four-mirror Nasmyth optical systems are also presented in this paper. The primary focus system has a f-ratio 2 and 1.5degree field of view with 80% light energy encircled in 0.5 arecsec, which will let LOT complementary with the coming 30m-class telescopes. A double–layer Nasmyth platforms are proposed to accommodate more instruments, such as the wide field imaging spectrograph, broad band medium resolution spectrograph, high resolution spectrograph and multi-object fiber spectrographs and so on. Not all optical systems will be constructed in the same time, which will be in stages depending on the science and funding situation.
In this paper, we present the preliminary optical system design of AST3-NIR camera, a wide-field infrared imager for 50cm Antarctic surveying telescope (AST3-3) to be deployed to Dome A, the Antarctic plateau. It is a joint project in which China is responsible for telescope hardware and control, logistics and deployment. Australia is responsible for instrument hardware design and control, and power generation. The camera uses two mosaic Leonardo detectors with 1280 x 1032 pixels each. The instrument is designed with a field of view(FOV) of 28.10 X 46.10 at the pixel scale of 1.35” per 15µm pixel. It is optimized for K dark band (2.26μm to 2.49 μm). The main challenges of this design are to produce a well-defined internal pupil stop located within cryogenic condition which reduces the thermal background and the correction of off-axis aberrations due to the large available field. Since the operating temperature of the camera could vary from -35°C to -90°C, the refocusing mechanism needs to be designed within the camera. The optical performance of the system will be demonstrated. We show the opto-mechanical error budget and compensation strategy that allows the built design to meet the optical performance.
The site testing shows that Antarctic Dome A is one of the best site on earth for astronomical observations, for wavelength ranging from visible to infrared and sub-millimeter. Continuous observation for nearly four months in polar nights makes Dome A quite suitable for time domain astronomy. In the past decade CCAA already led a series of Antarctic astronomy activities and telescope projects which will be introduced in this paper. The first generation telescope is Chinese Small Telescope Array known as CSTAR, which was composed of four identical telescopes with 145mm entrance pupil, 20 square degrees FOV and different filters, all pointing to the celestial South Point, mainly used for variable stars detection and site testing. The telescope was deployed in Dome A in Jan. 2008, and followed by automatic observations for four consecutive winters. Three Antarctic Survey Telescopes (AST3) is the second generation telescope capable of pointing and tracking in very low temperature, with 500mm entrance pupil, 8.5 square degree FOV. AST3-1 and AST3-2 were respectively mounted on Dome A in Jan. 2012 and 2015, fully remotely controlled for supernovae survey and exoplanets searching. In Aug. 2017, AST3-2 successfully detected the optical counterpart of LIGO Source GW 170817. Now AST3-3 is under development for both optical and near infrared sky survey by matching different cameras. Based on the experience of the above smaller sized optical telescopes, the 2.5m Kunlun Dark Universe Survey Telescope (KDUST) was proposed for high resolution imaging over wide field of view. Currently the KDUST proposal was submitted to the government and waiting for project review.
The Antarctic survey telescope (AST 3-3) near infrared(NIR) camera is designed to conduct the Kunlun Infrared Sky Survey which will provide a comprehensive exploration of the time varying Universe in the near infrared. It is going to be located at Dome A, on the Antarctic plateau, one of the most unique low background sites at the Kdark band (2.4μm). Carefully designed thermal emission from the telescope and the Kdark camera is very important to realize background limited operation. We setup a scattering and thermal emission model of the whole system to optimize the camera performance. An exposure time calculator was also built to predict system performance.
AST3-NIR is a new infrared camera for deployment with the AST3-3 wide-field survey telescope to Dome A on the Antarctic plateau. This project is designed to take advantage of the low Antarctic infrared sky thermal background (particularly within the Kdark near infrared atmospheric window at 2.4 μm) and the long Antarctic nights to provide high sensitivity temporal data from astronomical sources. The data collected from the Kunlun Infrared Sky Survey (KISS) will be used to conduct a range of astronomical science cases including the study of supernovae, exo-planets, variable stars, and the cosmic infrared background.
The Antarctic Survey Telescope-AST3 consists of three optical telescopes with 680mm primary mirror and 8 square degree field of view, mainly for observations of supernovas and extrasolar planets searching from Antarctic Dome A. The first two AST3 telescopes (AST3-1 and AST3-2) were successfully installed on Dome A by Chinese expedition team in Jan. 2012 and Jan. 2015 separately. Multi-anti-frost methods were designed for AST3-2 and the automatic observations are keeping on from March 2016. The best limited magnitude is 19.4m with exposure time 60s in G band. The third AST3 will have switchable interface for both optical camera and near infrared camera optimized for k dark band survey. Now the telescope is under development in NIAOT and the K-band camera is under development in AAO.
We present a new application of frame transfer Charge-Coupled Device (CCD) on measuring astronomical seeing. If a telescope is equipped with a shutterless, frame transfer CCD camera, a bright star will generate a trail during the frame transfer phase. Because the transfer is very fast, the trail is a series of short exposures (about 1 ms) of the target star. Therefore the centroid is jittery due to atmospheric turbulence, and the amplitude can be utilized to derive astronomical seeing. We present the preliminary results from STA1600FT CCD on the second Antarctic Survey Telescope (AST3) tested in China. The trail seeing moderately agrees with the simultaneous DIMM seeing.
We have successfully operated the AST3 telescope remotely as well as robotically for time-domain sky survey in 2015 and 2016. We have set up a real-time system to support the operation of the unattended telescope, monitoring the status of all instruments as well as the weather conditions. The weather tower also provides valuable information of the site at the highest plateau in Antarctica, demonstrating the extremely stable atmosphere above the ground and implying excellent seeing at Dome A.
The preliminary site testing performed since the beginning of 2008 shows that Antarctic Dome A is an excellent astronomical site. The Chinese Antarctic optical telescopes CSTAR and the first Antarctic Survey Telescope AST3-1 has been in operation on Dome A, and several Antarctic telescopes are being developed and proposed. However, the harsh environment and manpower shortage make the in-situ alignment task difficult. The study will introduce the completed alignment work of AST3 and discuss an improved align metrology based on the previous treatments of the field dependent optical aberrations, as well as its application on Antarctic Bright Star Survey Telescope BSST.
Chinese Antarctic Observatory has been listed as National large research infrastructure during twelfth five-year plan. Kunlun Dark Universe Survey Telescope, one of two major facility of Chinese Antarctic Observatory, is a 2.5-meter optic/infrared telescope and will be built at the Chinese Antarctic Kunlun Station. It is intended to take advantage of the exceptional seeing conditions, as well as the low temperature reducing background for infrared observations. KDUST will adopt an innovative optical system, which can deliver very good image quality over a 2 square degree flat field of view. All of parts of it have been designed carefully to endure the extremely harsh environment. KDUST will be perched on a 14.5-meter-high tower to lift it above the turbulence layer. In this paper, preliminary design and key technology pre-research of KDUST will be introduced.
The closed-loop correction must be carry out before observation of Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) to eliminate the low-frequency errors. A natural guide star S-H sensor in the focal plane of LAMOST is used to conduct wave-front sensing. The designed limiting magnitude of the S-H sensor is 10th magnitude, and the beacon must be located in the center of field of view, or slightly deviated from the center. The survey time of LAMOST is 2 hours before and after transit, wherefore the active optical correction should be completed within half of an hour, so it is necessary to make the wave-front sensing time as short as possible. Since the magnitude of guide star and atmospheric seeing have important effect on the efficiency of wave-front sensing, 9th magnitude or brighter stars are adopted in operation. For 9th magnitude stars, sky coverage will be about 100%, but at most of time, the beacons are not located in the center of field of view, so we propose to design a laser guide system based on Rayleigh scattering to provide a beacon whose brightness is equivalent to a 7th or 8th magnitude star and to launch the beacon in the center of field of view at any observational sky. In this paper, we describe the optical design of the implementation involved a laser system with 532nm in wavelength, beam diagnostics, a launch telescope with 350mm in diameter, and receiving system.
The AST3 project consists of three large field of view survey telescopes with 680mm primary mirror, mainly for observations of supernovas and extrasolar planets searching from Antarctic Dome A where is very likely to be the best astronomical site on earth for astronomical observations from optical wavelength to thermal infrared and beyond, according to the four years site testing works by CCAA, UNSW and PRIC. The first AST3 was mounted on Dome A in Jan. 2012 and automatically run from March to May 2012. Based on the onsite winterization performance of the first AST3, some improvements such as the usage of high resolution encoders, defrosting method, better thermal control and easier onsite assembly et al were done for the second one. The winterization observation of AST3-2 in Mohe was carried on from Nov. 2013 to Apr. 2014, where is the most northern and coldest part of China with the lowest temperature around -50°. The technical modifications and testing observation results will be given in this paper. The third AST3 will be optimized from optical to thermal infrared aiming diffraction limited imaging with K band. Thus the whole AST3 project will be a good test bench for the development of future larger aperture optical/infrared Antarctic telescopes such as the proposed 2.5m Kunlun Dark Universe Survey Telescope project.
Proc. SPIE. 8418, 6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Smart Structures, Micro- and Nano-Optical Devices, and Systems
KEYWORDS: Telescopes, Mirrors, Sensors, Resistance, Control systems, Platinum, Space telescopes, Temperature sensors, Optical instrument design, Temperature metrology
This paper focuses on a micro-temperature controller which can be used in Antarctic telescope. This controller uses integrated digital temperature sensors and platinum sensors for temperature measurement, and uses single-chip for the system control, and single-bus for signal and data information transmission, which can meet different kinds of heating. With this controller we can solve the problems about temperature of the telescope, such as there are too many temperature test pots on the telescope, the complex control of mirror defroster, and the problem of wiring in such low temperature. In this paper there are only 4 cables needed to make the connection between center computer and power supply. And the remote control and monitoring can be achieved by the center computer. It is very space less, components and energy less, and after series of tests, it can meet the temperature control need of Antarctic telescope.
The preliminary site testing carried out since the beginning of 2008 shows the Antarctic Dome A is very likely to be the
best astronomical site on earth even better than Dome C and suitable for observations ranging from optical wavelength to
infrared and sub-millimeter. After the Chinese Small Telescope Array (CSTAR) which is composed of four small fixed
telescopes with diameter of 145mm and mounted on Dome A in 2008 for site testing and variable star monitor, three
Antarctic Survey Telescopes (AST3) were proposed for observations of supernovas and extrasolar planets searching.
AST3 is composed of 3 large field of view catadioptric telescopes with 500mm entrance diameter and G, R, I filter for
each. The telescopes can point and track autonomously along with a light and foldable dome to keep the snow and icing
build up. A precise auto-focusing mechanism is designed to make the telescope work at the right focus under large
temperature difference. The control and tracking components and assembly were successfully tested at from normal
temperature down to -80 Celsius degree. Testing observations of the first AST3 showed it can deliver good and uniform
images over the field of 8 square degrees. The first telescope was successfully mounted on Dome A in Jan. 2012 and the
automatic observations were started from Mar. 2012.
The first of the trio Antarctic Survey Telescopes (AST3) has been deployed to Dome A, Antarctica in January
2012. This largest optical survey telescope in Antarctica is equipped with a 10k × 10k CCD. The huge amount of
data, limited satellite communication bandwidth, low temperature, low pressure and limited energy supply all
place challenges to the control and operation of the telescope. We have developed both the hardware and software
systems to operate the unattended telescope and carry out the survey automatically. Our systems include the
main survey control, data storage, real-time pipeline, and database, for all of which we have dealt with various
technical difficulties. These include developing customized computer systems and data storage arrays working at
the harsh environment, temperature control for the disk arrays, automatic and fast data reduction in real-time,
and building robust database system.
Proc. SPIE. 7658, 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optoelectronic Materials and Devices for Detector, Imager, Display, and Energy Conversion Technology
KEYWORDS: Observatories, Telescopes, Mirrors, Astronomy, Control systems, Domes, Astronomical telescopes, Optical instrument design, Control systems design, Temperature metrology
Preliminary site testing shows that Antarctic inland Dome A is likely to be the best astronomical observatory site on the
ground, Chinese first Antarctic astronomical equipment CSTAR has been successfully run Dome A. Three Antarctic
Schmidt Telescopes (AST3) is the next important Antarctic astronomical equipment, one of which will be mounted
Dome A. In the year of 2010, and the three will be installed Dome A finally. Because of the very low temperature and
saturation vapor pressure, and the temperature gradient changes fast near the ground layer at Dome A, the mirror is easy
to be frosted, which is one of difficulties to AST3.Indium Tin Oxide (ITO)is an N-type semiconductor material, because
it has few resistors, good light transmission, good weather resistance, small environmental impact, low cost, and it is
easy for large area coating, so it is widely used in many fields. The mirror is heated by ITO that is coated on the surface
of the mirror, the voltage on the ITO will be tuned by changing the output pulse width, and then the system achieves a
closed-loop control. The difference between the mirror temperature and ambient temperature will be maintained in an
ideal range, and this will not only ensure that the mirror surface will not get frosting, but to minimize the impact of
mirror seeing to guarantee the image quality of the telescope. The experimental results show that the temperature control
system can control the different temperature between the mirror surface and the ambient less than 2 degree in real time,
which can improve the mirror's working environment, and the overall effectiveness of the telescope's observations.
The extreme environment of Antarctic greatly benefits astronomical observations. Site testing works already show the
excellent seeing and transmission on Dome C. And the higher, colder inland plateau Dome A is widely predicted as even
better astronomical site than Dome C. Preliminary site testing carried out since the beginning of 2008 shows that Dome
A has lower boundary layer and lower precipitable water vapour. Now the automated seeing monitor is urgently needed
to quantify the site's optical character which is necessary for the telescope design and deployment. We modify the
commercial telescopes with diameter of 35cm to function as site testing DIMM and make it monitor both seeing and
isoplanatic angle at the same time automatically on Dome A at different height. Part of the processed data will be
transferred back by Iridium satellite network every day. The first DIMM will be deployed on Dome A in early 2011.
Prelimenary site testing led by Chinese Center of Antarctic Astronomy (CCAA) shows that the highest point of the
Antarctic Plateau Dome A has very clear sky, good seeing, slow wind, low boundary layer and very low precipitable
water vapour which make it the best site on earth for optical/IR and sub-mm observations. Chinese Small Telescope
ARray (CSTAR) was installed at Dome A in 2008 and have automatically observed for about 3 antarctic winters. The
three Antarctic Schmidt telescopes(AST3) with entrance pupil diameter 500mm are the second antarctic project
proposed by CCAA and the first AST are being constructed in NIAOT now which is planned to be mounted on Dome A
at the beginning of 2011. All the tracking components were tested in the low temperature chamber and an adaptive
defrosting method is designed to prevent the frost building up on the schmidt plate.
Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) is a large aperture and wide field telescope
whose image quality requirement at Xinglong station is 80% light energy within 2 arcsecond. In fact, the designed image
quality of the central field of view is diffraction limited under optical wavelength. Due to the 60m long light path and
poor natural seeing, dome seeing and other errors, the image quality is averaged about 0.5arcsecond to 1 arcsecond. We
consider deploying a low-order adaptive optics system on LAMOST to improve seeing conditions and the corresponding
image quality. Based on the sounding balloon results on Xinglong Station, we make the numerical simulation of the AO
performance and get Fried parameter, the final point spread function (PSF) characteristics of LAMOST including Strehl
ratio, full width at half- maximum (FWHM), and the residual variance.
Chinese first arrived in Antarctic Dome A in Jan. 2005 where is widely predicted to be a better astronomical site than
Dome C where have a median seeing of 0.27arcsec above 30m from the ground. This paper introduces the first Chinese
Antarctic telescope for Dome A (CSTAR) which is composed of four identical telescopes, with entrance pupil 145 mm,
20 square degree FOV and four different filters g, r, i and open band. CSTAR is mainly used for variable stars detection,
measurement of atmosphere extinction, sky background and cloud coverage. Now CSTAR has been successfully
deployed on Antarctic Dome A by the 24th Chinese expedition team in Jan. 2008. It has started automatic observation
since March 20, 2008 and will continuously observe the south area for the whole winter time. The limited magnitude
observed is about 16.5m with 20 seconds exposure time. CSTARS's success is a treasurable experience and we can
benefit a lot for our big telescope plans, including our three ongoing 500mm Antarctic Schmidt telescopes (AST3).
Since Chinese scientific expedition team first arrived Dome A in 10, Jan., 2005, meteorological data have been obtained
from this highest point of the Antarctic Plateau. It is likely that Dome A can be the best site for ground-based
astronomy. Chinese astronomy community, led by Chinese Center for Antarctic Astronomy, is part of an international
effort to survey Dome A for astronomical observations, and has built 4 small telescopes (CSTAR) which have been
installed at Dome A in 2008. We report here a more ambitious goal: three Antarctic Schmidt telescopes (AST3) with
aperture 50 cm each and the modified Schmidt system (about half shorter tube comparing with normal one) are being
constructed, and will be installed for observation at Dome A in Jan., 2010. AST3 will be used for the discovery and
exploration of astrophysical transients. This paper presents the technical configuration, design of these Schmidt
telescopes, and study on technical challenges for telescope at such a special place with extremely environment on the
An iterative deconvolution algorithm is presented in detail which utilizes regularization to combine
maximum-likelihood (ML) estimate of convolution error and several physical constraints to build error
function. The physical constraints used in this algorithm include positivity, band-limit information and the
information of multiple frames. By minimizing the combined error metric of individual ones, the object can
be expected to be recovered from the noisy data. In addition, numerical simulation of Phase Screen distorted
by atmospheric turbulence following the Kolmogorov spectrum is also made to generate the PSFs which are
used to simulate the degraded images.
We present the Gattini project: a multisite campaign to measure the optical sky properties above the two high altitude
Antarctic astronomical sites of Dome C and Dome A. The Gattini-DomeC project, part of the IRAIT site testing
campaign and ongoing since January 2006, consists of two cameras for the measurement of optical sky brightness, large
area cloud cover and auroral detection above the DomeC site, home of the French-Italian Concordia station. The cameras
are transit in nature and are virtually identical except for the nature of the lenses. The cameras have operated
successfully throughout the past two Antarctic winter seasons and here we present the first results obtained from the
returned 2006 dataset. The Gattini-DomeA project will place a similar site testing facility at the highest point on the
Antarctic plateau, Dome A, with observations commencing in 2008. The project forms a small part of a much larger
venture coordinated by the Polar Research Institute of China as part of the International Polar Year whereby an
automated site testing facility called PLATO will be traversed into the DomeA site. The status of this exciting and
ambitious project with regards to the Gattini-DomeA cameras will be presented.
Pre-HEAT is a 20 cm aperture submillimeter-wave telescope with a 660 GHz (450 micron) Schottky diode heterodyne
receiver and digital FFT spectrometer for the Plateau Observatory (PLATO) developed by the University of New South
Wales. In January 2008 it was deployed to Dome A, the summit of the Antarctic plateau, as part of a scientific traverse
led by the Polar Research Institute of China and the Chinese Academy of Sciences. Dome A may be one of the best sites
in the world for ground based Terahertz astronomy, based on the exceptionally cold, dry and stable conditions which
prevail there. Pre-HEAT is measuring the 450 micron sky opacity at Dome A and mapping the Galactic Plane in the
13CO J=6-5 line, constituting the first submillimeter measurements from Dome A. It is field-testing many of the key
technologies for its namesake -- a successor mission called HEAT: the High Elevation Antarctic Terahertz telescope.
Exciting prospects for submillimeter astronomy from Dome A and the status of Pre-HEAT will be presented.
Over a decade of site testing in Antarctica has shown that both South Pole and Dome C are exceptional sites for
astronomy, with certain atmospheric conditions superior to those at existing mid-latitude sites. However, the highest
point on the Antarctic plateau, Dome A, is expected to experience colder atmospheric temperatures, lower wind speeds,
and a turbulent boundary layer that is confined closer to the ground. The Polar Research Institute of China, who were the
first to visit the Dome A site in January 2005, plan to establish a permanently manned station there within the next
decade. As part of this process they conducted a second expedition to Dome A, arriving via overland traverse in January
2008. This traverse involved the delivery and installation of the PLATeau Observatory (PLATO). PLATO is an
automated self-powered astrophysical site testing observatory, developed by the University of New South Wales. A
number of international institutions have contributed site testing instruments measuring turbulence, optical sky
background, and sub-millimetre transparency. In addition, a set of science instruments are providing wide-field high time
resolution optical photometry and terahertz imaging of the Galaxy. We present here an overview of the PLATO system
design and instrumentation suite.
The large sky area multi-object fiber spectroscopic telescope (LAMOST) is a special reflecting Schmidt telescope with
its main optical axis on the meridian plane tilted by an angle of 25° to the horizontal. The clear aperture is 4m, working
in optical band. The light path is 60m long when working in observing mode and it will be doubled if work in auto-collimation
mode. So the image quality is affected clearly by the ground seeing and the dome seeing. In order to
improve the seeing condition of the long light path, we enclosed the spherical primary and the focus unit in a tunnel
enclosure and cooled the tunnel. This is an effective but passive method. Corresponding experiments and simulations
show the main part of the aberrations caused by the ground seeing and dome seeing is slowly changed low order items
such as tip-tilt, defocus, astigmatism, coma and spherical aberration. Thus we plan to develop the low-order AO system
based on the low-cost 37-channel OKO deformable mirror for the telescope to better the ground seeing and the dome
seeing, not aimed to reach diffraction limited image. This work is being carried on now.
We describe a large-angle survey for fast, optical transients: gamma ray bursts (GRBs), supernovae (SNe), lensed and transiting planets, AGNs and serendipitously found objects. The principal science goals are to obtain light curves for all transients and to obtain redshifts of GRBs and orphan afterglows. The array is called Xian. In conjunction with the gamma-ray satellites, ECLAIRs/SVOM and GLAST, the data will be used to study sources from z=0.1 to >6. The telescope array has 400 Schmidt telescopes, each with ~20 sq. degree focal planes and apertures of ~0.5 meters. The passively cooled, multiple CCD arrays have a total of 16000x16000 pixels, up to 13 readout channels per 1K x 4K CCD and work in TDI mode. The system provides continuous coverage of the circumpolar sky, from the Antarctic plateau, every few seconds. Images averaged over longer time intervals allow searches for the host galaxies of the detected transients, as well as for fainter, longer timescale transients. Complete, data at high time resolution are only stored for selected objects. The telescopes are fixed and use a single filter: there are few (or no) moving parts. Expected detection rates are 0.3 GRBs afterglows per day, >100 orphan afterglows per day and >0.1 blue flashes per day from Type II or Type Ib/c supernovae. On-site computers compare successive images and trigger follow-up observations of selected objects with a co-sited, well-instrumented telescope (optical, IR; spectroscopy, photometry, polarimetry), for rapid follow-up of transients. Precursor arrays with 20-100 square degrees are planned for the purpose of developing trigger software, testing observing strategies and deriving good cost estimates for a full set of telescope units.