Xiangqun Cui

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST)

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST, also called the Guo Shou Jing Telescope) is a special reflecting Schmidt telescope. LAMOST’s special design allows both a large aperture (effective aperture of 3.6 m–4.9 m) and a wide field of view (FOV) (5 ° ). It has an innovative active reflecting Schmidt configuration which continuously changes the mirror’s surface that adjusts during the observation process and combines thin deformable mirror active optics with segmented active optics. Its primary mirror (6.67 m×6.05 m) and active Schmidt mirror (5.74 m×4.40 m) are both segmented, and composed of 37 and 24 hexagonal sub-mirrors respectively. By using a parallel controllable fiber positioning technique, the focal surface of 1.75 m in diameter can accommodate 4000 optical fibers. Also, LAMOST has 16 spectrographs with 32 CCD cameras. LAMOST will be the telescope with the highest rate of spectral acquisition. As a national large scientific project, the LAMOST project was formally proposed in 1996, and approved by the Chinese government in 1997. The construction started in 2001, was completed in 2008 and passed the official acceptance in June 2009. The LAMOST pilot survey was started in October 2011 and the spectroscopic survey will launch in September 2012. Up to now, LAMOST has released more than 480 000 spectra of objects. LAMOST will make an important contribution to the study of the large-scale structure of the Universe, structure and evolution of the Galaxy, and cross-identification of multiwaveband properties in celestial objects.

Special configuration of a very large Schmidt telescope for extensive astronomical spectroscopic observation

A special reflecting Schmidt telescope is used to observe celestial objects. The telescope has an aperture of 4m, f ratio of 5, and a 5° field of view. Its optical axis is fixed and tilted 25° to the horizontal that runs from south to north. The celestial objects were observed for 1.5 h as they passed through the meridian. The shape of the reflecting Schmidt plate has to be changed with each different declination δ and in the tracking process. This is achieved with active optics. The sky area to be observed is -10° ≤ δ ≤ +90°. There are plans to place ~4000 optical fibers on the telescope focal surface that will lead to a dozen spectrographs.

Exceptional terahertz transparency and stability above Dome A, Antarctica

We present the first direct measurements of the terahertz atmospheric transmission above Dome A, the highest point on the Antarctic plateau at an elevation of 4.1 km. The best-quartile atmospheric transmission during the Austral winter is 80% at a frequency of 661 GHz (453 μm), corresponding to a precipitable water vapor column of 0.1 mm. Daily averages as low as 0.025 mm were observed. The Antarctic atmosphere is very stable, and excellent observing conditions generally persist for many days at a time. The exceptional conditions over the high Antarctic plateau open new far-infrared spectral windows to ground-based observation. These windows contain important spectral-line diagnostics of star formation and the interstellar medium which would otherwise only be accessible to airborne or space telescopes. Online material: color figures

The PLATO Dome A Site-Testing Observatory : instrumentation and first results

The PLATeau Observatory (PLATO) is an automated self-powered astrophysical observatory that was deployed to Dome A, the highest point on the Antarctic plateau, in 2008 January. PLATO consists of a suite of site-testing instruments designed to quantify the benefits of the Dome A site for astronomy, and science instruments designed to take advantage of the unique observing conditions. Instruments include CSTAR, an array of optical telescopes for transient astronomy; Gattini, an instrument to measure the optical sky brightness and cloud cover statistics; DASLE, an experiment to measure the statistics of the meteorological conditions within the near-surface layer; Pre-HEAT, a submillimeter tipping radiometer measuring the atmospheric transmission and water vapor content and performing spectral line imaging of the Galactic plane; and Snodar, an acoustic radar designed to measure turbulence within the near-surface layer. PLATO has run completely unattended and collected data throughout the winter 2008 season. Here we present a detailed description of the PLATO instrument suite and preliminary results obtained from the first season of operation.

Large-sky-area multiobject fiber spectroscopic telescope (LAMOST) and its key technology

The optical system of LAMOST is a special reflecting Schmidt system. It has an aperture of 4 m, f ratio of 5 and a 5 degree(s) field of view. The main optical axis is fixed on the meridian plane and tilted 25 degree(s) to the horizontal from south to north. The celestial objects were observed for 1.5 hours when they pass through the meridian. The reflecting Schmidt plane, MA, and the spherical mirror, MB, are segmented mirrors. MB is fixed on the foundation. The shape of the reflecting Schmidt plate has to be changed with different declination (delta) and in the tracking process. This is achieved with active optics. About 4000 optical fibers are planed to put on the focal surface. Some key technologies for LAMOST have been studied and presented in this paper: the calculation and testing method for thin mirror and segmented mirror active optics; the preliminary calculation and the experiment for active optics; the simulated calculation for optical image quality in 1.5 hours observation; a preliminary design of the alt-azimuth mounting and tracking system of MA.

Chinese Small Telescope ARray (CSTAR) for Antarctic Dome A

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. CSTARSs 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).

PHOTOMETRY OF VARIABLE STARS FROM DOME A, ANTARCTICA

Dome A on the Antarctic plateau is likely one of the best observing sites on Earth thanks to the excellent atmospheric conditions present at the site during the long polar winter night. We present high-cadence time-series aperture photometry of 10,000 stars with i < 14.5 mag located in a 23 deg(2) region centered on the south celestial pole. The photometry was obtained with one of the CSTAR telescopes during 128 days of the 2008 Antarctic winter. We used this photometric data set to derive site statistics for Dome A and to search for variable stars. Thanks to the nearly uninterrupted synoptic coverage, we found six times as many variables as previous surveys with similar magnitude limits. We detected 157 variable stars, of which 55% were unclassified, 27% were likely binaries, and 17% were likely pulsating stars. The latter category includes delta Scuti, gamma Doradus, and RR Lyrae variables. One variable may be a transiting exoplanet.

The PLATO Antarctic site testing observatory

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 First Release of the CSTAR Point Source Catalog from Dome A, Antarctica

In 2008 January the twenty-fourth Chinese expedition team successfully deployed the Chinese Small Telescope ARray (CSTAR) to Dome A, the highest point on the Antarctic plateau. CSTAR consists of four 14.5 cm optical telescopes, each with a different filter (g, r, i, and open) and has a 4.5° × 4.5° field of view (FOV). It operates robotically as part of the Plateau Observatory, PLATO, with each telescope taking an image every ~30 s throughout the year whenever it is dark. During 2008, CSTAR 1 performed almost flawlessly, acquiring more than 0.3 million i-band images for a total integration time of 1728 hr during 158 days of observations. For each image taken under good sky conditions, more than 10,000 sources down to ~16th magnitude could be detected. We performed aperture photometry on all the sources in the field to create the catalog described herein. Since CSTAR has a fixed pointing centered on the south celestial pole (decl. = -90°), all the sources within the FOV of CSTAR were monitored continuously for several months. The photometric catalog can be used for studying any variability in these sources, and for the discovery of transient sources such as supernovae, gamma-ray bursts, and minor planets.

Sky Brightness and Transparency in the i-band at Dome A, Antarctica

The i-band observing conditions at Dome A on the Antarctic plateau have been investigated using data acquired during 2008 with the Chinese Small Telescope Array. The sky brightness, variations in atmospheric transparency, cloud cover, and the presence of aurorae are obtained from these images. The median sky brightness of moonless clear nights is 20.5 mag arcsec(-2) in the SDSS i band at the south celestial pole (which includes a contribution of about 0.06 mag from diffuse Galactic light). The median over all Moon phases in the Antarctic winter is about 19.8 mag arcsec(-2). There were no thick clouds in 2008. We model contributions of the Sun and the Moon to the sky background to obtain the relationship between the sky brightness and transparency. Aurorae are identified by comparing the observed sky brightness to the sky brightness expected from this model. About 2% of the images are affected by relatively strong aurorae.