一个新的光谱巡天望远镜方案

A NEW CONFIGURATION FOR SPECTROSCOPIC SURVEY TELESCOPE

本方案中,主镜沿东西方向长12.4米、宽4米,由多块球面子镜拼成,它能绕东西水平轴转动.利用光纤作多目标光谱观测,每个目标使用主镜上一个直径4米的通光区,由于采用大焦比4,每根光纤所需的改正器直径仅20毫米,焦面上可安置大量的改正器和光纤.观测室是不动的,顶上沿子午面开有半圆形的天窗,一个跟踪架可沿此移动,观测时四块1米×1米的安置有光纤的板放在四辆小车上沿跟踪架作跟踪运动,跟踪时间大于或等于1小时,同时观测的目标约2400个.这样的望远镜如果建成,在光谱巡天方面其威力将是世界上最强的,而望远镜本体部分的造价仅约2500万人民币.只要作一些变动,这样的方案也可用于一般的天文工作,包括高分辨工作.

In this configuration, the primary mirror is a spherical mirror with 12.4 m long in eastwest direction, 4 m wider, radius of curvature 32 m and focal length 26 m. It can rotate round the east-west level axis, consisting of 64 mirrors, with diameter 0.96m each. The celestial objects' spectra are acquired by using optical fibres. For each objeot, the diameter of useful area on the primary mirror is 4m. Each fibre is used with a corrector. Since the f-ratio is as large as 4, the diameter of the corrector is only 20 mm. Thus a large amount of correctors and fibres can be put on the focal surface and many objects can be observed simultaneously. In this configuration, the observation room is not rotatable. There is a semicircle dome window along meridian plane on the top of the observation room. A tracking frame can move along the dome window. According to the plan as a whole observing mode, this telescope will stay in each declination zone about 20 days. The primary mirror rotates and the tracking frame moves only when the declination zone changes. During observation, there are four 1 m×1 m plates, on the tracking frame, each having about 600 optical fibres and correctors, and moving for fracking. The sum of simultaneously observable objects is about 2400. For equatorial celestial object, the tracking time is about one hour. The effeciency of this telescope equal four telescope, each has 4m aperture, 1 m×1 m focal area and about 600 simultaneously observable obpects. Such a telecope will be the most powerful instrument for the spectroscopic survey in the world and the cost of it only about RMB 25 million yuan. If some modification is made, this configuration can also be used for general astronomical observation, and even high resolution observation as well. Also, in this paper an arrangement is given for offering a static focus for this configuration