TEL7 Coud Feed Tower

Extending south of the 2.1-meter dome is a large shed that houses a Coudé spectrograph. This instrument is capable of dividing the spectra of stars into very fine intervals, and has been used to study the rotation of stars and to find companions. The spectrograph itself was very expensive, but because it was used less than half the time with the 2.1-meter telescope, it was decided in the 1970s

The thin cylinder to the right of the 2.1-meter building is the Coudé Tower, which houses the 0.9-meter primary mirror. The Coudé spectrograph itself is located in the large aluminum shed that extends south of the dome of the 2.1-meter telescope. Photo courtesy of National Optical Astronomy Observatory/Association of Universities for Research in Astronomy/National Science Foundation.

to build an entirely separate telescope that would feed light to it. The tall thin tower across the road from the shed houses the primary mirror, which has a diameter of 0.9 meter. The light path actually starts with a 1.5-meter flat mirror on top of the shed (inside a little enclosure that slides on rails), which reflects light to the image-forming primary mirror. The light from the primary mirror is reflected to a third small mirror on the roof of the shed, and then down into the spectrograph. Although the primary mirror is much smaller than that of the 2.1-meter telescope, in practice the Coudé feed is not much less sensitive. Although the telescope has formally been closed since February 2001, it is being used by several researchers who buy time for $195 per night from KPNO.

It was this telescope that was used to determine in the 1970s that more than half of stars like the Sun have companion stars, and now it is being used to investigate the frequency of brown dwarfs, which are bigger than planets, but not big enough to be stars. The high precision of the spectrograph has enabled astronomers to study the rotation and pulsation of stars, to better understand their lifecycles.

The 0.9-meter primary mirror can be seen inside the Coudé tower, with Baboquivari Peak in the background. This photo was taken from the roof of the Coudé spectrograph shed. Photo courtesy of National Optical Astronomy Observatory/Association of Universities for Research in Astronomy/National Science Foundation.

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