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2.1 Overview

The following table gives the basic characteristics of the instruments discussed here.

General Facts About the Spectrographs
Instrument Resolution Detector Slit Length Scale Multiplexing?

 (R=/) CCD Useful Area (arcmin) Detector Slit



'' /pixel 1'' =
4-m RC Spect 300-5000 T2KB 300x1500-1700 5.4 0.69 150m single or multi-slits
4-m CyroCam 400-600 F1KA 320x1000 4.5 0.84 150m single or multi-slits
2.1m GoldCam 300-4500 F3KC 400x2000 5.2 0.78 79m single
WIYN Hydra 700-14000 T2KC 2000x2048 fibers(FOV~~1o
~~100 fibers

In the above table the ``Useful Area" refers firstly to the number of pixels of spatial extent covered by the slit, and secondly to the number of pixels which are in focus and/or not strongly vignetted, as described below.

Each spectrograph is used typically with a specific CCD. In the case of the 4-m CryoCam and the 2.1-m GoldCam, the chip is actually built into the camera. We describe the CCD characteristics below. ``Linearity" refers to the number of electrons when the departure from linearity is 0.1%, but in point of fact, things deteriorate quickly above the listed values. The DQE curves can be found in Fig. 1.

Facts About the CCDs
Pixel Default Gain Linear(0.1%)
Instrument CCD Size Gain Read-noise #e- to
(um) (e-/ADU) RMS (e-) @65,000 ADU (e-)
4-m RC Spect T2KB 24 3.1 4.0 201,500 220,000
4-m CyroCam F1KA 15 0.8 15 52,000 150,000
2.1m GoldCam F3KC 15 1.4 8.5 91,000 80,000
WIYN Hydra T2KC 24 1.7 4.3 110,500 190,000

Our CCD controllers all now contain 16-bit A/D converters, and so the maximum digitization limit is 65,634. We see from the table above that staying with the default gain assures both good sampling of the read-noise and the use of most of the linear range of the device, with the exception of CryoCam. There the default gain is kept small to significantly decrease the read-noise contribution.


 
Figure 1:   The relative DQEs of the four CCDs used for low-to-moderate resolution spectroscopy at Kitt Peak.

next previous contents
Next: 2.2 4-m RC Spectrograph
Previous: 2 The Facts
Updated: 27Mar1998