The Coude Echelle Spectrographs

1.4 Detector Options

Sections: Available Detectors | EEV2 | MITLL3 | Tektronix | Coverage of UCLES | CCD Windows

Next: System efficiencies of UCLES | System efficiencies of UHRF | Contents | Home


Available Detectors

Two CCDs are recommended for UCLES: the EEV2 for blue observations, and the MITLL3 for red observations.

The MITLL3 is unsuitable for UHRF since it cannot be binned, so for UHRF the recommended detectors are the EEV2 for blue observations, and the Tektronix for red work. The Tektronix is also available with UCLES but is usually not recommended due to its small format and poorer efficiency.

The CCD dewars are normally refilled every ~ 8 hours. At present this is done manually by the technician, but an automatic system will be reinstituted shortly.  The large dewar bottle is refilled every 2 days.

The CCD characteristics are described in detail in the relevant web pages for the EEV, MITLL3 and Tektronix. A summary is presented here. The relative efficiencies of the CCDs are shown in Figure 1.4.1. Note that the MITLL2 is no longer available.

Figure 1.4.1. Efficiency curves of the current CCDs.

CCD Efficiency Curves

EEV2

The EEV has 2k × 4k 13.5 µm pixels. The long side is aligned along the orders. The EEV has a blue-sensitive coating, and is the preferred CCD for observations blueward of 6000Å. It suffers from strong fringing in the red, which appears to correct well using flatfields, with only a small residual. A commissioning report by Stuart Ryder is available here. Table 1.4.1 gives the characteristics of the EEV. The full chip readout  is with a window 2120 x 4096, unbinned. The readtime for 2x2 binning is also given. Data should be saved in USHORT to save disk space and time.

Table 1.4.1 Characteristics of the EEV CCD


Readout
Speed 
Readout
Noise
(e- rms) 
Gain
(e-/ADU) 
Linearity
(alpha)
(×106
Sat.
Level
(Ke-) 
Read
Rate
(µs/pix) 
Full
Chip
Read
Time
(s)
Read
Time
2x2
(s)
NONASTRO 8.2  6.8  +1.16 200  7.5  69 30
FAST 4.4  2.7 +0.59 168  11.5  105 43
NORMAL  3.4  1.3  +0.35 81  16.5 150 54
SLOW 2.7  0.32 +0.11 21 46.5  416 123

 

MITLL3

The MITLL3 has 2k × 4k 15 µm pixels. It is not possible to bin this CCD. It has the highest red sensitivity, but has a higher cosmic ray rate and no blue sensitivity. The CCD has a number of hot columns which require careful setup for UCLES to avoid important orders. By judicious adjustment of the cross disperser grating angle ECH_GAMMA, it is possible for the most part to position the worst of the hot columns in or near an inter-order gap, even with the 31.6 l/mm grating. Data should be saved in USHORT to save disk space and time. The optimum dark current of 0.3-0.4 e/pix/2000s for MITLL3 is only achieved after 2-3 days of continuous power, so for UCLES programmes with faint targets the MITLL3 should be mounted several days before the run.

Table 1.4.2 Characteristics of the MITLL3 CCD


Readout
Speed 
Readout
Noise
(e- rms) 
Gain
(e-/ADU) 
Linearity
(alpha)
(×106
Sat.
Level
(Ke-) 
Read
Rate
(µs/pix) 
Full
Chip
Read
Time
(s)
NONASTRO 5.2  4.7  -0.63 150  6.5  58
FAST 2.9  2.2  -0.15 148  10.5  108
NORMAL  2.0  1.1  +0.24  62  18  143
SLOW 1.6  0.36  +0.15  23  34  285
XTRASLOW 1.3 0.088  +0.03  6 106  924

Tektronix (Tek)

The Tek is a 1024 square thinned CCD with 24 um square pixels. This small format makes it inefficient for UCLES observations, but it can be binned, and so is useful for UHRF runs likely to be affected by the fringing of the EEV2 CCD. Typically x4 or x8 binning is used. For UCLES or UHRF the Tek should be used at 170 degrees to minimise dark current. This results in 1.0 e/pix/hr  dark current, though a higher rate has been seen within a couple of hours of power-up. Table 1.4.3  gives the basic characteristics.

Table 1.4.3 Characteristics of the Tektronix

Readout
Speed 
Readout
Noise
(e- rms) 
Gain
(e-/ADU) 
Linearity
(alpha)
(×106
Saturation
Level
(ADU) 
Readout
Time
(s) 
XTRASLOW  2.3  0.34  negl  65000  394 
SLOW  3.6  1.36  negl  65000  120 
NORMAL  4.8  2.74  -0.03  65000  75 
FAST  7.2  5.5  -0.07  65000  52 
NONASTRO  11  11  -0.14  35000  33 

Coverage of UCLES

An important point to note is that the current UCLES camera optics cannot illuminate the entire area of the large format CCDs (MITLL3 and EEV2).  MITLL3 is 61.4 x 30.7 mm and EEV2 is 55.3 x 27.6 mm. In fact the unvignetted region which can be observed is more like 38.5 x 18.8 mm (for less than 10% vignetting). The region covered at 50% vignetting is 60 x 34 mm, which is approximately the entire MITLL3 chip, and larger than the EEV2, however unless you are working in the very red the echellogram will not put any light on much of the chip.  For examples of the coverage of the EEV2 & MITLL3 CCDs see Appendix A1 for grating 31 and Appendix A2 for grating 79.

CCD Windows

CCD windows currently available in the default area (/vaxuser/sysdisk1/adamlocal/window/q0_1a/ for the Tek CCD and /vaxuser/sysdisk1/adamlocal/window/r0_0 for the EEV2 and MITLL3 CCDs) are given in Table 1.4.4. Updates to this list may be found in the UCLES Cookbook.  Custom windows can be created on request by the afternoon technician or support astronomer. Once more, note that the MITLL3 does not support on-chip binning.

Table 1.4.4: Standard CCD Windows for UCLES & UHRF
Spectrograph Detector Window name Size (X by Y pixels) Binning Comments
UCLES EEV2 EEV2_FULL 2120 x
4096
None Full CCD + 68 overscan
UCLES/
UHRF
EEV2 EEV2_CENTRE600 620 x
600
None Central 600 +
overscan - used for setup
UCLES EEV2 EEV2_SLIM 301 x
4096
None 300 pix strip
in X for setup,
no overscan
UCLES EEV2 EEV2_X2 1046 x
4096
x2 in X Full window + 20 overscan
UCLES EEV2 EEV2_X3 704 x
4096
x3 in X Full window + 
20 overscan
UHRF EEV2 EEV2_X8 261 x
4096
x8 in X Full window +
5 overscan
UCLES EEV2 EEV2_X3Y2 704 x
2048
x3 in X,
x2 in Y
Full window +
2- overscan
Useful for 
wider slit work - much faster readout
UCLES EEV2 EEV2_UCLES_X2Y2 1054 x
1748
x2 in X,
x2 in Y
Trimmed to 
match 31 obs
around 5000A.
UCLES EEV2 EEV_PLANET_BX1 2088 x
2746
None Trimmed in Y + 40 overscan
UCLES EEV2 EEV_PLANET_BX2 1044 x
2746
x2 in X Trimmed in Y
+ 20 overscan
UCLES EEV2 EEV_PLANET_SETUP 301 x
2746
None 300 strip in X
+ 1 overscan
UCLES MITLL3 MITLL_FULL 2120 x
4096
None Full CCD + 72
overscan
UCLES/
UHRF
MITLL3 MITLL_CENTRE 1044 x 1024 None Central window + 20 overscan - setup
UCLES MITLL3 MITLL_CENTRESTRIP 300 x 4096 None Used for setting up UCLES
UHRF TEKTRONIX TEK1K_DIRECT 1050 x 1024 None Full window + 26 overscan
for setup
UHRF TEKTRONIX UHRFX4 260 x 1024 x4 in X Full window + 4 overscan
UHRF TEKTRONIX UHRFX8 130 x 1024 x8 in X Full window + 2 overscan
UHRF TEKTRONIX TEK1K_DIRECT_CEN 322 x 300 None Central window, no overscan - setup



Sections: Available Detectors | Tektronix | MITLL2A | MITLL3 | CCD Windows

Next: System efficiencies of UCLES | System efficiencies of UHRF | Contents | Home



Ray Stathakis (ras@aaoepp.aao.gov.au)
Last Update: 15 November 2002