** last update: April 30 2000 **
For the past few years, some applications have used Arcon and others have used VEBs. VEBs have now been completely and permanently phased out. Thus, any information which one may have or find relative to VEBs is completely obsolete and is for reference only. It does not refer to equipment currently in use.
As a result of the conversion to Arcon, TI, GEC and Reticon CCDs have been retired and are no longer available anywhere at Cerro Tololo. Only Tektronix and Loral detectors are currently being scheduled.
This CCD was commissioned at the Schmidt telescope at CTIO during February 1995, reading through the Lower Right amplifier only, using an Arcon CCD Controller. Just recently the CCD has had the remaining three amplifiers tested, and is now working satisfactorily in "quad" mode.
For imaging at the Schmidt, the normal gain index = 2, corresponding to a DcsT = 7 microseconds. Gain is 2.3 e-/ADU with a readout noise of 3.8 e- rms (all four amplifiers are within 10% of these values) and a readout time of 40 seconds. NOTE -- the full well capacity of this CCD is around 150000 e- but linearity starts to roll off severely at only 90000 e-, corresponding to 40000 ADU. Up to this charge level linearity is excellent and differential non-linearity between amplifiers is < 0.3%. We plan to try and improve these figures even more, since we achieve < 0.1% on our two Tektronix (SITe) 2048's.
Quantum efficiency figures are approximately 18% from 3000-4600A, rising to nearly 50% at 6500A, then slowly falling to zero near 10500A. The flat response through the U and most of the B band means that transformations of U-B and B-V photometry to the standard UBV system are straightforward, while in the red the CCD is competitive with thinned CCDs, and has the advantage of not fringing. Some sensitivity figures are as follows (these are scaled from measurents made by Pat Seitzer with the Thonmson CCD -- we'll have the real figures soon).
Sensitivity for BVI filters (10th magnitude star):
Filter countrate (e-/sec) B 10900 V 24800 I 13800In a 30 second exposure the stars of the following brightness will just reach 40000 ADU (dependent on seeing, tracking, focus, so use only as a guide):
Filter magnitude B 10.5 V 11.2 I 10.7Some typical dark sky brightness values are:
Filter countrate (e-/sec/pixel) B 0.7 V 3.0 I 7.9Cosmic ray rate is 2.5 events/sq. cm./minute, fairly normal.
The defective columns are as follows (a few very small traps visible on backgrounds of a few adu are not listed):
columns rows affected type 546-547 905-1024 hot, bleeds slightly 1-904 584 391-1024 trap 587 391-1024 trap 590 391-1024 trap 612 1025-1421 blocked 748 1025-1773 trap 1334 831-1024 hot 1742 1025-1082 blocked 1788 150-1024 hot 1804-1806 1025-2048 very hot 2006 1025-1303 blockedThe pixel scale at the Schmidt telescope is 2.0 arcsec/pixel and the field size is 68 arcmin. The Newtonian secondary vignettes only slightly (correctable by flat fields) and the full field is useable. Image quality is excellent (typically 1.4-1.9 pixels fwhm depending on wavelength -- and filter quality) over the entire field.
The filter bolt holds five 4x4 inch filters. The most popular filters are UBVRI, for which the following focus values were determined recently:
Filter Focus (microns) U 190 B 250 V 230 R 265These values were measured at 15C, the focus changes by approximately -5 microns per 2C temperature change.
It is anticipated that by July the focus and filter changing will be controllable from the Arcon user interface, bringing to a completion this phase of upgrades at the Schmidt telescope, a combined effort by the University of Michigan and CTIO.
Alistair Walker & Ricardo Schmidt. 26 May 1995
The new Loral 3K CCD plus Blue Air Schmidt combination was first tested with the 4.0-m RC spectrograph during an engineering run on 15-16 February 1995. This is a thinned 3K x 1K CCD with 15 micron pixels. The CCD has a two layer AR coating and is UV flooded to maximise its QE over a wide range of wavelengths. It is flat.
All indications are that it is superior in all respects to both the Blue Air Schmidt + Reticon and the Folded Schmidt plus Tek1024. In particular we believe it to be the best choice of CCD for all the CS CCD runs in the present block of observing time.
Gain, readout noise, etc.:
The Loral 3K has two working amplifiers (lower left LL and lower right LR). However only one can be used at a time. We have set up the two video channels to have almost a factor two difference in gain, to allow the user more freedom of choice. Looking at the table below, it can be seen that LL is better optimized given that the full-well capacity is only 78000 e-. (ie LL, gain 2, gives 1.99 e/adu, 7.7 e- RON, and full well will occur at 39000 ADU). UNFORTUNATELY, the high video gain needed for LL has meant that LL suffers from some stability problems (noise bands, bias drifts) and FOR THE MOMENT, we recommend using the LR amp, at gain 4. The only advantage of gains 1,2,3 with LR is readout speed, use these gain settings only if readout time is critical for your program.
i ARCON 3.5 / Loral 3K n Full CCD d DCS ___Read_Noise___ ____1/Gain_____ __Read_Noise__ SingleRead e (us) (ADU) (e-/ADU) (e-) Time (s) x LL LR LL LR LL LR ---------------------- ---------- --------- ---------- 1 5 2.54 1.48 4.33 7.82 11.0 11.6 88.2 2 10 3.88 2.17 1.99 3.96 7.7 8.6 120.5 3 15 5.68 2.97 1.39 2.59 7.5 7.7 152.4 4 20 7.08 3.87 1.03 1.94 7.3 7.5 184.4Dark current is extremely low, 0.48 e-/pixel/hour
QE and System Efficiency:
The QE of the CCD (measured at KPNO) is: Wavelength QE (%) 3200A 78.9 3650A 73.9 4050A 73.0 5000A 86.6 6000A 93.0 7000A 93.9 8000A 73.9 9000A 41.8There has been some scepticism expressed that the QE figures below 3000A are very optimistic. We do not yet have any really definitive measurements of our own, but figures of around 30-40 % at 3500A may be nearer the truth. The below system efficiency figures assume that the KPNO QE measurements are correct.
The overall system efficiency (fraction of photons striking the primary mirror which are detected by the CCD) was measured using standard stars. Using grating KPGL1 (632 l/mm 4200A blaze) and a wide (10") spectrograph slit the measured efficiency was:
Wavelength Loral3K Reticon 3000A 2.4% 3500A 10.6% 8.0% 4000A 14.1% 9.6% 5000A 18.6% 10.4% 6000A 14.3% 8.1%The third column gives values for the Reticon #2 CCD using the same grating.
Image quality:
With a very narrow (50 mu slit which projects to 0.6666 pix), and at best focus, the measured FWHM of comparison lines is 2.3 pix. For a slit width of 150 mu (2 pix, 1.0") the best FWHM grows to ~2.6 pix, while at 225 mu (3 pix, 1.5") it is ~3.0 pix. There is slight curvature of the focal plane which results in some variation of the FWHM with position on the CCD. With the 150 mu slit the images are 3.3 pix FWHM or better over most of the chip (~4 pix in the extreme corners), while with a 225 mu slit the images are 4.5 pix or better over most of the chip (~5 pix worst case). Even the worst case images are quite symmetrical, and do not show the very broad assymmetric wings seen in out of focus images obtained with the Reticon (B A/Sch) and Tek1k (F/Sch CCDs. In general the images obtained with the Loral are much more uniform than with these other CCDs.
Gratings:
The gollowing table lists the coverage and dispersion (A/pix) obtained with the various gratings available for the R-C spectrograph. It is also valid for the Argus multiple object spectrograph.
Grating l/mm Blaze % Cover. Dispn. Notes (A) (A) (A/pix) 250 158 4000 11431 3.75 400 158 8000 11431 3.75 * 510 300 10000 5999 2.01 *# 181 316 7500 5708 1.91 kpgl2 316 4400 5708 1.91 kpgl3 527 5500 3417 1.16 420 600 8000 2981 1.02 # kpgl1 632 4200 2872 0.95 kpglf 632 8200 2872 0.95 450 632 11000 2872 0.95 kpgld 790 8500 2290 0.75 kpglf 860 11000 2101 0.68 380 1200 8000 1563 0.48 # % Littrow value: for the actual RC spectrograph configuration the effective blaze wavelength is 0.92 of the Littrow value. * This grating is silver coated and so does not reflect light below ~ 4000A # This grating is not very efficient when used in second order.Fringing:
This CCD fringes redward of about 7000A. The maximum fringe amplitude is +/-1% which occurs at a wavelength of ~8500A. The fringe spaceing is ~40 pixels. Note that the fringe amplitude for the Loral is less than that for the Reticon (+/- 3-4%). We do not yet know how well the fringes are corrected by flat fielding. The spectrograph flexes by less than 2.5 pixels or 0.06 of a fringe spacing from the zenith to +/- 5h HA. Thus dome flat fields obtained with the white spot will probably be adequate for fringe correction in many cases. Note that dome flats can be obtained at two telescope/dome positions: North 0H, +20d 40m, dome pa 218; and South 0H, -81d 00m, dome PA 039. It may help to use the flat field position according to the declination of your objects.
Nonethless, until more experience has been obtained, we recommend that users working redward of 7000A and requiring better than 1% flat fielding obtain quartz flats (using the same slit width as for the object) for each object.
Note that it is possible to switch between Ne and Quartz lamps under software control. Set the manual switch on the comparison lamp in the cage to the "Quartz position" and select Ne as the comparison lamp in setspec/instrpars. The Ne lamp will automaticaly be selected for exposures of type comp and the quartz lamp for pflats.
Gratings, Resolution & Coverage:
Gtg l/mm blaze GEC Loral A/pix Cover A/pix Cover 13 150 5000 8.4 4800 5.73 6820 11 * 158 8000 8.0 4600 5.45 6530 09 300 4000 4.21 2400 2.87 3410 32 300 6750 4.21 2400 2.87 3410 22 * 300 10000 4.21 2400 2.87 3410 58 400 8000 3.15 1800 2.15 2560 16 527 5500 2.36 1350 1.61 1920 26 600 4000 2.11 1200 1.44 1705 35 600 6750 2.11 1200 1.44 1705 56 600 11000 2.11 1200 1.44 1705 47 831 8000 1.5 860 1.02 1220 36 & 1200 7500 1.05 600 0.72 850 % Blaze is first order Littrow blaze. Effective blaze wavelength when used in the 1.5-m spectrograph is 0.89 of the Littrow value. * silver coated does not reflect light below ~4000A & Cannot be tilted far enough to be used in II order
The GEC CCD has 22 micron pixels; a slit width of 210 microns (3.8 arcsec) projects to 2 pixels. With this device there is no evidence that the resolution of the spectrograph is limited by either the camera optics or the MTF of the detector. The measured FWHM of comparison lines corresponds very closely to the projected width of the spectrograph slit down to the Nyquist sampling limit, and 2 pix FWHM resolution is routinely achieved. There is little variation of image quality with position on the chip, or with wavelength.
The Loral CCD has 15 micron, pixels and is 1.4 times longer than the GEC; a slit width of 143 microns (2.6 arcsec) projects to 2 pixels. Because of the finer sampling and larger size of this CCD it is expected that the camera optics will somewhat limit the resolution, especially at the extreme edges of the field. In addition at KPNO they have been unable to get images better than ~3 pix FWHM with their Loral chips. This has been attributed to diffusion of photoelectrons within the CCD. This effect is greatest at blue wavelengths since higher energy photons are absorbed closer to the surface of the CCD.
The following table shows the measured FWHM of arc lines obtained for a single tilt of grating 32 for a slit width 110.5 microns (2 arcsec) showing the dependance on position on the chip (and wavelength). Values are given for the center of the slit (Y=200) and at the two extreme edges (Y=130, 270).
FWHM (pix) as a function of position ==================================== Line X Y (A) (pix) (pix) 130 200 270 ==================================== 4471 112 | 3.12 2.78 2.82 4764 215 | 2.96 2.86 2.70 5015 303 | 2.89 2.69 2.70 5876 602 | 2.65 2.42 2.46 6678 879 | 2.52 2.13 2.25 6965 978 | 2.47 2.04 2.47 7384 1121 | 2.62 2.13 2.46 7635 1207 | 2.97 2.13 3.14 ====================================In general, although the lines are wider than the projected slit width, and there is some variation with position, the resolution with a slit width of 2-3 arcsec is better than or comparable to what would be obtained with the GEC CCD and the same grating.
The graph shows the FWHM as a function of slit width for spectral lines at the center of the CCD (in X and Y). Curves are shown for 3 wavelengths 3888A, 6678A and 9224A
QE:
GEC Loral 1K
3000 20 25
3500 19 48
4000 17 65
5000 22 83
6000 35 93
7000 45 91
8000 30 83
9000 14 59
10000 3 10
System efficiency:The following are the measured system efficiencies (percentage of photons striking the telescope primary mirror which are eventually detected by the CCD) for the 1.5-m spectrograph with the GEC CCD using gratings 11 and 13
GEC Loral 1K
11 13 11 13
3000 0.0 1.1 0.0 1.4
3500 0.2 1.6 0.5 4.0
4000 0.9 2.0 3.4 7.6
5000 2.2 2.7 8.3 10.2
6000 7.0 4.9 18.6 13.0
7000 6.4 3.6 12.9 7.3
8000 3.6 2.0 9.9 5.5
9000 1.5 0.7 6.3 2.9
10000 0.4 0.0 1.3 0.0
The numbers for the Loral were estimated by scaling by the ratio of the QE's
given above.Unfortunately the engineering night had heavy cirrus / thick cloud. Therefore we do not have any measurements of the absolute sensitivity. However, observations of standard stars confirm that the sensitivity peaks at approximately 6000A, where the QE curve peaks, and that there is significant sensitivity down to the atmospheric cutoff at 3000A.
RON & Dark Current:
So far only the lower left amplifier has been comissioned and the CCD is being read in single channel mode.
The following table shows the gain (e-/ADU), RON (e-), and readout time (s) for the currently available gain settings.
Arcon3.9 == Loral 1K (1200*800)
i
n Bin1x1 Maximum
d DCS Delay Read_Noise 1/Gain -> Read_Noise Read Linear
e time (ADU) (e-/ADU) (e-) Time Signal
x (us) LL UR LL UR LL UR (s) (ADU)
---- ----- ---------- --------- ---------- ---- -----
1: 1 5 3 2.5 0 4.11 0 10.3 0 25.1 21900
2: 2 7 3 2.6 0 2.87 0 7.6 0 29.1 31400
3: 3 10 3 3.6 0 2.05 0 7.2 0 35.3 43900
4: 4 14 3 4.9 0 1.42 0 6.9 0 43.4 63400
5: 5 20 3 6.7 0 0.96 6.5 0 55.6 65534
Full well (~90,000 e- is reached before the ADC saturates at the higher
gains (more e-/ADU). The Non-linearity (peak-to-peak gain variation) is
believed to be less than 2% for levels below full well / ADC saturation.Currently the dark current is very high ~15e-/pixel/hour. However, it is expected that this will be reduced to a few e-/pixel/hour by opperating the CCD in MPP mode and by running it at a lower temperature. Fringing:
The Loral 1K CCD fringes with substantial amplitude at wavelengths redward of 7500A. Press here if you really want to be horrified . The fringes run approximately perpendicular to the dispersion. The peak-to-peak amplitude and fringe spacing are given in the following table and shown in the accompanying graph:
Wavelength Amplitude Spacing (A) (%) (A) ======================================= 7500 2.5 38 7750 2.8 40 8000 4.5 40 8250 8.4 46 8500 11.3 38 8750 14.6 42 9000 16.0 54 9300 20.6 54 9500 19.6 56 9750 17.0 66 10000 11.4 50 10500 7.4 60 =======================================At least in flat field frames the fringe amplitude does not depend on slit width. Nor does it depend (to first order) on the position where the light of a particular wavelength falls.
We do not yet know how well fringing can be corrected by flat fielding techniques. Given the above amplitudes it seams likely that for wavelengths shortward of about 8000A fringing is unimportant or easily correctable. Redward of this it is likely that it will be necessary to obtain quartz flats for each object and take great care in flatfielding the data. Even then, observations requiring high S/N at wavelengths redward of 8000A may not be possible with this CCD.
Flexure:
The following table shows the displacements (pixels) due to flexure parallel and perpendicular to the dispersion as a function of Hour Angle and Declination.
Parallel to Dispersion =============================================================================== | HOUR ANGLE DEC | WEST EAST =============================================================================== +30 | 0.0h | | +0.10 ------|------------------------------------------------------------------------ 0 | 3.0h 0.0h 3.0h | | +0.35 -0.16 -0.23 ------|------------------------------------------------------------------------ -30 | 4.5h 3.0h 1.5h 0.0h 1.5h 3.0h 4.5h | | +0.75 +0.42 +0.14 0.00 -0.09 -0.10 -0.06 ------|------------------------------------------------------------------------ -60 | 5.0h 0.0h 5.0h | | +0.79 +0.13 -0.06 ------|------------------------------------------------------------------------ -90 | 0.0h | | +0.68 =============================================================================== Perpendicular to Dispersion =============================================================================== | HOUR ANGLE DEC | WEST EAST =============================================================================== +30 | 0.0h | | -0.02 ------|------------------------------------------------------------------------ 0 | 3.0h 0.0h 3.0h | | -0.66 +0.08 +0.34 ------|------------------------------------------------------------------------ -30 | 4.5h 3.0h 1.5h 0.0h 1.5h 3.0h 4.5h | | -0.75 -0.61 -0.29 0.00 +0.26 +0.34 +0.37 ------|------------------------------------------------------------------------ -60 | 5.0h 0.0h 5.0h | | -0.81 -0.10 +0.40 ------|------------------------------------------------------------------------ -90 | 0.0h | | -0.49 ===============================================================================
1. Loral 1K (1200x800) CCD dark measurements
Temperature Dark rate degK e-/hour/pix 122 4.0 130 4.5 150 11.5These measurements confirm the need to operate these CCDs at relatively low temperature (compared to SITe CCDs for instance) in order to reduce the dark rate to a satisfactory low level for spectroscopy. The rate achieved here at 120-130K is typical for Loral CCDs, but at least a factor of 8 higher than for our Loral 3K CCD, which has an exceptionally low dark rate.
Jorge Bravo & Alistair Walker, July 27 1995
The Loral 3K CCD has two operative amplifiers on the lower serial register, but only one can be read at a time due to the way that the CCD bond wires are connected (actually, aren't connected...). We have been attempting to see whether or not it is possible to increase the gain for the LL amplifier video chain, without significant penalty of read noise. If so, then this would allow a shorter pixel integration time, and hence shorter read time
This work has been successful. In the table below are the gain/read noise/readtime figures for the two amplifiers, where those for LR represent the original measurements. Most users of this CCD (4m spectroscopy) would have chosen
gain index=4, LR amplifier, 2.0 e/adu, 7.7 e RON, 3 minute readtime
Now they can choose
gain index=2, LL amplifier, 2.0 e/adu, 7.7 e RON, 2 minute readtime
which is a substantial reduction in read time. As is well-known with these CCDs, the read noise is state-of-the-art 1985...
GAIN Index SLOPE 1/G [e/ADU] RON [e] Read Time LL LR LL LR 1 5 us 4.33 8.21 11.0 12.6 88.2 sec 2 10 us 1.99 4.17 7.7 9.3 120.5 sec 3 15 us 1.39 2.74 7.9 8.6 152.4 sec 4 20 us 1.03 2.03 7.3 7.7 184.4 secRicardo Schmidt & Alistair Walker, August 8 1995
Here are gain/read noise figures for our Tek 2048 #4 CCD (Arcon 3.6), a thinned grade 0 device we have been using at CTIO since 1993. The measuremsnts were made recently in the La Serena detector Lab. No changes or adjustments were made to the system specifically for this test. The measured performance was found to be identical to that measured more than a year prior to this test.
--------------------------------------------------------------------------
DCS Time 1/G RON 1/G RON 1/G RON 1/G RON Readtime
us e/adu e e/adu e e/adu e e/adu e secs
---------------------------------------------------------------------------
3 6.45 5.70 6.73 5.99 6.39 5.68 6.26 6.31 22
5 3.93 5.30 4.03 4.73 3.81 4.49 3.83 4.57 26
7 2.80 3.86 2.86 3.56 2.72 3.82 2.71 3.80 30
10 2.00 3.15 2.00 3.09 1.92 3.20 1.89 3.28 37
15 1.29 2.77 1.36 2.89 1.27 2.75 1.27 2.79 47
20 0.97 2.49 1.01 2.54 0.96 2.54 0.95 2.63 58
40 0.49 2.26 0.50 2.19 0.48 2.37 0.47 2.27 100
---------------------------------------------------------------------------
This table shows for CCDs with (conventional) LDD on-chip amplifiers that slope
times of many microseconds are needed in order to achieve the lowest read noise.
This is, of course, a well-known result. The noise figures at long slope times
are significantly contaminated by a small amount of charge injection. If
instead the noise is measured in the overscan, values of around 2.0 e- rms
are obtained!
From the top row of the table, it is clear for short slope times that
quantization noise is expected to contribute, since the gain is several e/adu. Thus a
supplementary experiment was performed, as follows:
Video amplifier gain increased by a factor of 2.0.
1 Noise re-measured at 3uS DCS Time.
----------------------------------
DSC Time 1/G RON Read Time
us e/adu e secs
__________________________________
3 3.2 4.2 22
__________________________________
This result shows that, as suspected, quantization noise was an important contribution
at short slope times for the first series of measurements, and indeed it would be
worthwhile to repeat the experiment with even higher video gain whereby the RON
might be expected to reach ~3.5 e- rms, still at a slope time of 3 uS. We have not yet
performed this experiment.
Roger Smith & Jorge Bravo, Aug 8 1995
Ever since conversion to use with an Arcon CCD controller (Arcon 3.3) Tek 2048 #3 has been read out using only two (the upper pair) of its four operative amplifiers. This was because a bond wire was detached from its post early in the life of the CCD, during (successful) attempts to remove contamination from the CCD surface... The bond wire was expertly re-attached by Mike Lesser (U. of Arizona) a few months ago and all four amplifiers have been characterized in the CTIO detector Lab. A final check-out recently took place at the 0.9-m telescope, and the "quad" mode of operation has now officially become the default.
The gain table is appended below. The upper pair of amplifiers are slightly quieter than the lower pair, but are all very good in absolute terms. The full well is not large considering the pixel size, and is smaller for the lower half of the CCD than the upper. All three of our Tek 2048's show the same behaviour, explanations are solicited.
d dcsT ____Read_Noise_____ _____1/Gain____ __Read_Noise___ Read e (ADU) (e-/ADU) (e-) Time x (us) LL LR UL UR LL LR UL UR LL LR UL UR (s) ---- ------------------- --------------- --------------- ---- 1 5 1.09 1.2 1.02 1.09 5.0 4.8 4.8 4.8 5.4 5.4 5.0 5.4 30 2 7 1.26 1.34 1.21 1.22 3.3 3.2 3.2 3.2 4.1 4.1 3.9 3.9 34 3 10 1.62 1.75 1.46 1.47 2.5 2.4 2.4 2.4 3.8 3.9 3.6 3.6 40 4 15 2.13 2.16 1.69 1.71 1.6 1.6 1.6 1.6 3.4 3.4 2.7 2.7 50 5 20 2.57 2.83 2.10 2.08 1.2 1.1 1.1 1.1 2.8 3.0 2.3 2.4 60 Full well ~150Ke- (quad) = 32K ADU (gain 1) 50K ADU (gain 2) Full well ~225Ke- (upper) = 45K ADU (gain 1), OK for gain 2 Full well ~150Ke- (lower)Alistair Walker 31.10.95
John Filhaber designed a "field de-flattener" lens to replace the plane dewar window; this is a plano-concave lens of UV grade fused silica, with 1.0 meter radius. This was installed and tested on the February PFCCD run, and it works superbly well. We determined the power on the lens needed from focus measurements made at PF. SITe now provide a tracing of the surface profile when you purchase a 2048 from them, although care is needed as David Vaughan at KPNO has found that the profile changes (worse...) as the CCD is cooled to operating temperature.
Alistair Walker 19.2.96
GAIN e-/adu RON (e-) READ TIME (s)
INDEX LL LR UL UR LL LR UL UR (dual mode)
1 3.93 3.71 4.06 4.04 20 5.0 4.8 5.0 64
2 2.78 2.70 2.89 2.90 18 4.4 4.1 4.3 74
3 1.91 1.91 2.05 2.04 17 4.2 3.6 3.7 88
4 1.31 1.26 1.35 1.33 16 3.7 3.2 3.2 110
5 0.97 0.95 1.03 1.03 15 3.4 3.1 3.1 132
Full Well is 230 Ke- (<0.6% linearity over this whole range)
Dark rate less than 5 e-/hour
Charge Injection less than 1 e-
One adjacent pair of blocked columns
Alistair Walker & Ricardo Schmidt 17.10.96 Second piece of bad news is that our grade 0 SITe 2048 #4 has developed a noisy amplifier (upper left quadrant). Noisy means in this case 8-10 e- rms, instead of 3-4 e- rms. Apart from the noise, the amplifier is still linear, albeit with rather different bias voltages than previously. This CCD is used mostly at the 4-m. For broad band PF imaging, sky noise usually dominates the read noise so it may be advantageous to still read the CCD in quad mode, ratber than just with the lower pair.
Alistair Walker 4.11.96
So what do we have left after this attrition???
SITe 2048#3..(mostly used at the 0.9-m for direct imaging)
SITe 2048#5..(1.5-m and 4-m imaging, echelles, Fabry-Perot)
STIS 2048.....(Schmidt)
SITe 1024#2..(Some direct imaging, also Fabry-Perot)
Loral 1k.......(1.5-m spectrograph)
Lorak 3K.....(4-m RC spectrograph and ARGUS)
Alistair Walker, Ricardo Schmidt & Manuel Lazo 10.3.97
The really good news is that we have purchased a Grade 1 4-amplifier SITe
2048. This
CCD replaces SITE 2048 #4, which died. The new CCD, called SITe 2048 #6, entered
service during July, and will be used for 4-m and 1.5-m imaging, echelle spectroscopy,
and with the Fabry-Perot. It is a lovely CCD, nearly perfect cosmetically, with
four low noise amplifiers.
Alistair Walker 13.8.97
Alistair Walker 27.8.98
12. EVEN WORSE NEWS, PLUS GOOD NEWS!!!!
At the end of April the STIS 2048 CCD suffered four broken bond wires when
a screw in the dewar came detached and its associated washer ended up on the
CCD surface. The CCD was sent to Mike Lesser at the U of Arizona CCD lab.
where the wires were successfully replaced. Before it was sent off the
opportunity was taken to remove the cracked lumogen coating. The coating has
been replaced by an equivalent concoction of laser dyes by Kirk Gilmore of
Lick Observatory. He also coated a second STIS CCD, so we will have a spare.
Unfortunately (August) both these new coatings are giving trouble. One has
delaminated, and the other has many fine cracks when viewed under the microscope.
So we will not have one of these CCDs back in service for a while yet. Additionally,
it looks like we will only have two working amplifiers on each of these CCDs.
Our original CCD seesm to have suffered some damage in the accident mentioned above,
while the second CCD has a large serial trap.
13. BTC agreement renewed for 1999 Semester 1
The BTC (Big Throughput Camera) will continue at CTIO for semesters I
1999. Recent improvements include replacement CCDs for #1 and #2, a fast data
reduction machine, and miscellaneous software enhancements. For Semester II
1999 we plan to offer a clone of the NOAO 8kx8k (SITe CCDs)
mosaic imager, presently in use at KPNO on the 0.9-m and 4-m telescopes. 14. STIS CCD (ex Burrell Schmidt) Commissioned
The STIS CCD (a 2048 front-illuminated CCD made by Tektronix several years ago)
until recently used at the Burrell Schmidt on Kitt Peak, was installed
as ARCON 3.7 replacing our own STIS that suffered some trauma last year.
The new STIS has a metachrome coating to give some UV sensitivity, and
has two operative amplifiers (LL and LR). This CCD was the first to benefit
from a video chain upgrade that permitted much faster waveforms, so the
read time is only 30 seconds using 2 amps, as fast as our other 2048's
when using all 4 amps. We installed the STIS at the Schmidt since it was our
plan to take the SITe 2K#5, used there in the meanwhile, and dedicate
it to Hydra, the new 4-m MOS. Plans have changed. We'll commission
Hydra with the Loral 3K and Air Schmidt Camera, and in the long term use a
2Kx4K CCD with 15 micron pixels. So SITe 2K #5 goes back the Schmidt, and
the STIS CCD will be a spare.