Tek2K

Tek2K is a 2K optical CCD imager that provides a 13.6 arcminute field of view with 0.4 arcsecond pixels when installed on the 0.9-m telescope.

Detector Parameters (f/13.5)
Pixels 2048x2046
Pixel Scale 0.401"/pixel
Field Size 13.6'x13.6'

 

CCD Parameters

The observer can control and change several CCD parameters. These are: the CCD readout format, the binning, and the gain. To reduce the readout time, the CCD can be read out through multiple amplifiers (DUAL or QUAD mode). A single region-of-interest (ROI) can be read out, positioned at an arbitrary place on the CCD. Observers should think carefully whether they need all the field (if not, read a ROI) or the resolution (if not, bin 2x2). Even though the CCDs with QUAD readout have short read times by big-CCD standards, substantial gains in efficiency are possible by reducing the format.
 

***Table of gain values***
Index Read Noise 1/Gain Read Noise Quad Read
  LL LR UL UR LL LR UL UR LL LR UL UR Time
  (ADU) (e-/ADU) (e-) (sec)
1: 1.1 1.2 1.1 1.2 5.1 4.8 5.5 4.5 5.6 5.8 6.0 5.5 25
2: 1.5 1.6 1.5 1.6 2.6 2.5 2.7 2.5 3.9 3.9 4.0 3.9 32
3: 1.7 1.9 1.8 1.9 1.8 1.7 1.8 1.5 3.1 3.3 3.2 2.8 39
4: 2.6 2.6 2.5 2.6 1.0 1.0 1.1 1.0 2.6 2.6 2.8 2.6 53

*NOTE: A power outage that occurred on 07 March 2009 caused gain values to spike when the CCD is operated with gain index #1.  As such, the full well of the CCD is reached before digital saturation at ~ 44,000 ADU.  Non-linearity is likely a problem below this value.  We currently do not support this index setting for service observing and strongly recommend that visiting observers select another gain index.  For the remaining 3 index values, digital saturation of 65,535 (ADU) is reached before full-well capacity.  Read times are quoted for full frame quad readout with no binning. Linearity: gain increases by <0.3% over signal range. Patterns have been minimized for full frame readout at gain 1 (prior to power outage) and will be more apparent though still a minor source of noise at higher gains or when regions of interest and/or binning are used.

A raw quad-amplifier picture looks a little unusual. Each quadrant has a slightly different electrical offset (ie overscan level), and the four overscan segments are in the center of the picture. The real time display automatically removes the overscan and applies an offset to each quadrant to normalize the DC level. In addition, the real time display colors any saturated (ie 65535) pixel in red.

QUAD CCD pictures have to be trimmed and overscan-subtracted in a separate pre-processing IRAF task called quadproc (in the quad package). Note that even after the pictures are trimmed and overscan subtracted the sky levels in each quadrant will not be identical (unless the sky level is zero). This is because each of the four CCD amplifiers has a slightly different gain. After the trimming and overscan correction with quadproc, the images can be processed (bias subtraction, flatfielding) in the standard manner.
 

Data Acquisition Procedures

Please refer to the CFCCD User Manual.

Important Tip:

The data acquisition computer (ctioa4) occasionally has trouble handling simultaneous processes, resulting in ARCON crashing. It is recommended that you do not do anything (display another image, reduce data, write tapes, etc.) that uses ctioa4's CPU or accesses ctioa4's disks from another computer while an image is reading out. It is perfectly safe to do these things while the image is EXPOSING. If you want to work on your data, it is best to imcopy the raw images over to ctio36 (but not during image readout!) and do all the work there.

A night assistant is not regularly provided on the 0.9-meter telescope. A TCS software manual is available in the control room.

Domeflat exposure times (gain option #2) to reach a level of about 25,000 ADU.

Filter Exp Time
(sec)
B 180
V 100
R 110
I 120

 

Sample master bias frame A sample "master" Bias frame (quad readout) after overscan correction and trimming with quadproc (click on the image for an expanded view). The frame was created by averaging 20 individual frames (rejection option "minmax").
Sample master flat field frame A sample "master" Flatfield frame (quad readout, V filter) after overscan correction and trimming with quadproc (click on the image for an expanded view). The frame was created by median combining 10 individual frames (rejection option "avsigclip").

 

Crosstalk

When using multiple-amplifier readout, signal from one amplifier can "leak" into the signal of another. Crosstalk is an additive effect and is proportional to the signal strength in a given amplifier. In the sample frame shown below, this effect shows up as negative (white) images of bright stars in the lower left and upper right quadrants. The white images in the upper right quadrant correspond to the (black) star images of the lower left quadrant (flip the upper right quadrant left-right and up-down). We are currently working on software to correct for this effect.

crosstalk

A reduced 2048x2048 frame (quad readout)  showing examples of "crosstalk" (click on the image for an expanded view).