FOCES - a fibre optics Cassegrain échelle spectrograph
FOCES - a fibre optics Cassegrain échelle spectrograph
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DOI：
10.1051/aas:1998231
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发表时间：
1998-06
期刊：
影响因子：
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通讯作者：
M. Pfeiffer;C. Frank;D. Baumueller;K. Fuhrmann;T. Gehren
中科院分区：
文献类型：
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作者：
M. Pfeiffer;C. Frank;D. Baumueller;K. Fuhrmann;T. Gehren
我们设计并制造了一台安装在卡拉阿尔托天文台2.2米或3.5米望远镜卡塞格伦焦点上的中阶梯光栅光谱仪FOCES。光谱图本身遵循用两个o轴抛物面镜准直的白瞳孔设计。离开31.6线/mm R2中阶梯光栅的15 cm光束重新聚焦在一个小折叠镜的附近，该小折叠镜允许精确地去除散射光。交叉色散是实现与串联棱镜安装，和光束成像与f=3的传输相机上的场集中在一个1024 2薄泰克CCD与24米像素直径。中阶梯光栅图像覆盖了380至750 nm的可见光谱区域，以70个光谱级显示，具有全光谱覆盖。光谱级在蓝色中由20个像素分隔，在红色中由10个像素分隔。最大光谱分辨率为R = 40600，2像素分辨率元件;单独由bre表示的无晕分辨率将在R = 18000时获得。用2048 × 2像素直径为15 μ m的芯片代替CCD，并考虑到减小入射狭缝宽度引起的光损失，获得了R = 65000的全2像素分辨率。上述概念使FOCES成为一种非常好的工具。在温德尔斯坦80厘米望远镜、卡拉尔阿尔托2.2米和3.5米望远镜的卡塞格伦焦点上进行的一些成功的试验装置产生了高质量的光谱，曝光时间可达60分钟。在信噪比为100标度、V = 1.2的3.5米望远镜中，1h r的极限星等仅略小于实验室试验的结果。在另一种模式下，FOCES提供了第二个携带天空背景信号的BRE，以校正非常微弱的物体光谱。该模式从额外的棱镜获得所需的更高的交叉色散，从而导致相应降低的光谱覆盖率。
We have designed and built the echelle spectro- graph FOCES fed by 100 m optical bres to be mounted at the Cassegrain focus of either the 2.2 m or the 3.5 m telescope at the Calar Alto Observatory. The spectro- graph itself follows a white-pupil design collimated with two o-axis parabolic mirrors. The 15 cm beam leaving the 31.6 lines/mm R2 echelle is refocussed in the vicin- ity of a small folding mirror which allows ecient removal of scattered light. The cross-dispersion is achieved with a tandem prism mounting, and the beam imaged with an f=3 transmission camera onto a eld centered on a 1024 2 thinned Tektronix CCD with 24 m pixel diameter. The echelle image covers the visible spectral region from 380 to 750 nm displayed in 70 spectral orders with full spectral coverage. Spectral orders are separated by 20 pixels in the blue and by 10 pixels in the red. The maximum spectral resolution is R = = = 40600 with a 2 pixel reso- lution element; unvignetted resolution as dened by the bre alone would be obtained at R = 18000. Replacing the CCD by a 2048 2 chip with 15 m pixel diameter and taking into account light losses from a reduced entrance slit width a full 2 pixel resolution ofR = 65000 is obtained. The above concept has made FOCES an extremely well-dened instrument. A number of successful test in- stallations at the Cassegrain foci of the Wendelstein 80 cm telescope, the Calar Alto 2.2 m and 3.5 m tele- scopes has produced spectra of high quality for up to 60 min exposures. The limiting magnitude for a1h r ex- posure with an S=N ratio of 100 scales to V =1 2 for a 3.5 m telescope which is only slightly less than expected from laboratory tests. In an alternative mode FOCES of- fers a second bre carrying the sky background signal to correct extremely faint object spectra. This mode obtains the required higher cross-dispersion from an additional grism resulting in a correspondingly reduced spectral cov- erage.