摘要
本文给出了一种计算观测过程中较差大气折射引起的星象移动的方法，包括焦面最佳转动的确定．算法中除大气折射公式外，都是严格的．本文用这种方法详细计算了我国即将研制的大天区面积多目标光纤光谱望远镜（ＬＡＭＯＳＴ）中较差大气折射引起的星象移动，文中详细计算了望远镜安放在纬度４０．４°，观测天区－１０°δ＋９０°，天体过子午圈前后１．５小时，视场直径５°情况下，星象移动的结果，并得到星象的最大位移为０．８５９″，ＬＡＭＯＳＴ中光纤的直径是３．３″，光纤定位系统可不作校正．本文提出了实现焦面最佳转动的导星方法：在导星元件是ＣＣＤ的情况下，可任选一颗星来引导焦面旋转，只要使星象在ＣＣＤ靶面上作切向位移，其值等于按本文方法计算得到的值，若采用赤径、赤纬分角线方向（四个４５°方向）的星来引导旋转，也可近似地得到焦面的最佳转动．本文提出的算法和导星方法，可应用于任何天区，任意的观测时间和任何形式的焦面可旋转的望远镜．
In this paper, a method for calculating the displacement of star images caused by differential atmospheric refraction during observations is described. It includes the determination of the optimum rotation of the focal surface. All our formulas are exact except that for atmospheric refraction. The displacement of star images due to differential atmospheric refraction is calculated in detail for the Large Sky Area Multi object Fiber Spectroscopic Telescope (LAMOST) which will soon be developed in China. The latitude of the site is 40.4°, the sky area observed is -10° δ +90°, each observing duration is 1.5 hours around the time of meridian passage, and the field of view is 5°. Detailed results are listed in which the maximum displacement of star images is 0.859″. The diameter of the fiber is 3.3″ in the LAMOST. The positions of the fibers may not be adjusted during one such observation. Guiding with optimum rotation of the focal surface is suggested in this paper: If a CCD is used, the rotation of the focal surface can be guided by any appropriate star just by moving the image along the tangent in the CCD's target plane by an amount in accordance with what is calculated in this paper. Approximate optimum rotation of focal surface is obtained if the guiding star is in the direction of the angular bisector between the declination and the right ascension (four 45° directions). The algorithm and the way of guiding proposed in this paper can be used for any area of sky, any time of observation and any telescope with rotatable focal surface.
关键词
天文望远镜
大气折射
星象移动
atmospheric refraction — multi object spectrum — guiding
