Active optics is the most difficult part in LAMOST project. Especially for the segmented reflecting Schmidt plate Ma, in which both segmented mirror active optics and thin mirror (or deformable mirror) active optics are applied. To test and optimize the thin mirror active optics of Ma, and to approach the reality of operating environment of the telescope, an outdoor experiment system has been established. This experiment system is also a ‘small LAMOST’ with one sub-mirror of the primary mirror Mb and one sub-mirror of the Schmidt plate Ma, and with full scale in spacing (40 meters) between Ma and Mb. many parts of LAMOST were tested in the experiment system except segmented mirror active optics. Especially for force actuators, thin mirror support system, friction driving of the alt-azimuth mounting and its control system, wave front test along such a long optical path. This paper presents the experiment system, research and developments, and some experiment results.

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Experiment system of LAMOST active optics

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is a quasi-meridian reflecting Schmidt telescope with a clear aperture of 4-meter, a focal length of 20-meter and a field of view of 5-degree, dedicated for spectroscopic sky survey. The telescope will be located at the Xinglong Station of National Astronomical Observatory, 
	China, as a national facility open to the astronomical community. The project was planned to be completed in 2004,with its budget of RMB 235 millions yuan (about 28 M$). 
	The project is well in progress, with various sub-systems and their parts in critical reviews or kick-out for manufacturing early or late. Here we report the current status of the project generally. Other authors in this conference will describe details for individual parts of the project.

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LAMOST project and its current status

The immediate goal of modern observational astronomy is to monitor continuously the position and brightness of all objects in the sky brighter than ∼24th magnitude. This review describes wide-field telescopes designed for this task – both existing and planned. Many systems are described for the first time (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

New designs of survey telescopes

This telescope has 30m aperture, segmented primary mirror and alt-azimuth mounting. The aspherical primary mirror with f-ratio 1.2 consists of 1122 partial annular submirrors. The optical system includes Nasmyth I and II systems,Cassegrain system, coude system and a wide field of view system. There are four Nasmyth platforms. Two Nasmyth I foci are located on the upper floor and two Nasmyth II foci are located in the lower floor. All Nasmyth I, II and Cassegrain systems use same one secondary mirror, and all are R-C systems. With adaptive optics system, several diffraction-limited observations can be operated simultaneously on Nasmyth II platforms. The wide field of view system has 20 arcmin FOV, can correct atmospheric dispersion and the low space frequency error from primary mirror and atmosphere turbulence. A special rocking chair structure is designed which can realize the horizontal axis on the front of primary mirror. The tolerances of the surface shape and position of submirrors are given. The issues about tip-tilt correction and adaptive optics are discussed. Some formulae on rotating conic surface especially used for segmented mirror are given.

http://ir.niaot.ac.cn/bitstream/114a32/378/1/Configuration%20for%20Chinese%20Future%20Giant%20Telescope.pdf

Configuration for Chinese Future Giant Telescope

We present a classification-based approach to identify quasi-stellar radio sources (quasars) in the Sloan Digital Sky Survey and evaluate its performance on a manually labeled training set. While reasonable results can already be obtained via approaches working only on photometric data, our experiments indicate that simple but problem-specific features extracted from spectroscopic data can significantly improve the classification performance. Since our approach works orthogonal to existing classification schemes used for building the spectroscopic catalogs, our classification results are well suited for a mutual assessment of the approaches' accuracies.

Detecting Quasars in Large-Scale Astronomical Surveys

This paper presents the recent progress in the optical system of LAMOST project: (1) The image quality at the edge of the field of view and the worst sky area is about 1.76 arc seconds. To improve this value, many aspherical lenses with 3 mm in diameter will be attached to some of 4000 optical fibers. With maximum 6.6 microns asphericity, these lenses could compensate the residual off-axis aberration of the optical system and obtain much better image quality, thus in any case the image quality could less than 0.6 arc seconds in diameter. (2) At the open air, an outdoor experiment program for creating the aspherical surface and accurately measuring the wave front shape of the active Schmidt correcting plate, which is with the full scale of the sub-system of the telescope, is introduced here. (3) Some further consideration and modification for the active support of each sub-mirror of the Schmidt correcting plate is discussed also in this paper. The presentation in this paper showed that the LAMOST is very likely to get much better quality even it is with a very large field of view, and its key technology - active optics is also reaching the realization.

Xiangqun Cui

Papers

Progress in LAMOST optical system

a Configuration for Chinese Future Giant Telescope (cfgt)

Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) (C)