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CCD MANUAL FOR THE 100-INCH TELESCOPE

Table of Contents

 


1. Introduction

This manual describes how to take direct imaging data on the Las Campanas  100-inch du Pont telescope.
By December 2009, the old TEK#5 CCD camera formerly in use at the du Pont telescope has been replaced by 2 new CCD cameras.
called SITe2K and WF4K, respectively. The CCD electronics and hardware controls have been also upgraded. Both cameras have Magellan style  control electronics.
Please pass along any comments and suggestions for improving  this manual to Mark Phillips, Ian Thompson or Nidia Morrell.
 

Table 1 describes the 100-inch telescope  and Table 2 describes the two chips available for use and their performance characteristics.

Table 1. du Pont 100-inch Direct Imaging Mode
Type: Ritchey-Crétien optimized at f/7.5
Diameter of Primary: 100" (2.540 m)
Primary Focal Length: 300.0" (7.620 m)
Cassegrain Focal Length: 750.0" (19.050 m)
Nominal Plate Scale: 10.8 arcsec/mm
Field of View: 718 mm (~2.1 degrees) in diameter
Sky Shields: 2-element provides complete shielding over 10 armin diameter field and blocks 3% of beam
3-element provides complete shielding over 18 armin diameter field and blocks 11% of beam

 

 

Table 2. CCD Detectors available at the 100" telescope
Chip: SITe2k wf4k
pixel size (µm) 24.0 15.0
# pixels 20482 40642
 pixel scale (arcsec/pixel) 0.259 0.162

 Shutter timing and linearity tests have yet to be performed for these CCDs.

 

2. Taking data

 

2.1 Getting started:

Typing the 'ccd' command from any xterminal on the observer's computer (Clarity) will start the configuration GUI:

 startup

                                                                                                                      CCD startup window

In this window the observer's name has to be updated. Clicking in the CCD button will present four choices: SITe2K-1  and SITe2K-2 (same chip, but one or two amplifier readout mode) and WF4K-1 and WF4K-2 (same as previous, for the WF4K chip). The 2 amplifier readout mode is not fully operational yet and the observers are stronlgy encouraged to use only the 1 amplifier mode. It is possible to also select the number of horizontal and vertical overscan lines and columns that are stored for each CCD frame. The default (and recommended minimum) is 128 lines and columns.

Clicking "Ok"  will start the CCD Camera command window.

 

2.2 The CCD Camera GUI:

 

camera

                                                                                                                The CCD Camera GUI

Clicking on the "Options" pull-down menu, and choosing "Data_Path"  enables to define the directory where the images will be stored. If this directory does not exist, the option of creating it will be offered.

Under "Modlues" the Quick Look Tool window and the CCD status window can be started (useful to keep track of the detector's temperature).
 
ExpTime is the exposure time in seconds for the next observation. For this parameter and the ones for Loops and File# the entry window will be highlighted red after the number is typed. The value is not recorded by the program until the user hits Enter. The exposure time can be changed any time during the exposure by entering a new number and hitting Enter.

Loops Setting up a loop can be a convenient way to take flat fields or make synoptic observations.

ExpType The exposure type (saved in the fits header) can be set to "Object", "Focus", "Bias", "Dark", or "Flat". Selecting "Bias" will automaticaly set the exposure time to 0 seconds. Selecting "Dark" will disable the shutter for the exposure. Selecting "Focus" will enable a focus sequence, automatically setting the loop number to 7 (this can be changed if desired).  The focus frame will be saved under a normal filename (e.g. ccd0065.fits). In this frame, the spacing between the first and second images  will be larger than for the rest of the sequence, for easily identify the sequence order.
 

Binning can be set to 1, 2, 3 or 4 in rows and columns. Note that the readout times given below are for 1 x 1 binning.

Subrastering: It is possible to set a subraster in order to speed up readout, when the whole chip area is not needed. This is done by clicking on the button initially labelled as "Full" in the CCD Camera GUI, which will open the subraster window:

 

subraster

 

A subraster region can be defined with its central coordinates  followed by the width and height of the subraster (XcYcWH) or by its corners X1X2Y1Y2. Once the subraster has been defined, you need to click on "apppy" to activate it (the subraster limits will be shown in yellow on the Quick Look Tool window) and then "Done" to close the subraster window. The subraster can also be saved into a file, which can be later invoked and applied.

The filter list can be updated clicking on the "Edit" button.

"Start" begins an exposure. The exposure can be paused (e.g., for clouds) and resumed by toggling the "Pause" button, but observers should remember that cosmic rays are accumulating while the exposure is suspended. The progress of the exposure can be seen in the bar-graph immediately to the right of the ExpTime entry. This graph fills to the right during the exposure and as the CCD reads out the bar empties to the right.

The "Snap" button automatically sets the 4 x 4 mode, takes an exposure, and -- unlike the "start" command -- does not update the frame number at the end of the exposure. This option is meant for a quick-look before taking data, or for cleaning the chip after an "Abort" but not for science exposures.

Abort/Stop:  Exposures can be stopped or aborted. If the "Stop" button is clicked during an exposure the shutter will close and the frame read out. If the "Abort" button is clicked  during the read out the data will be dumped and the file number not updated. A wipe of the chips follows, but since the user will not generally know when it is finished, it is recommended that a short "Snap" exposure be taken to insure a clean chip before the next science frame is taken.

Exposures can be paused and resumed by toggling on the "Pause/Resume" button. This can be useful, for example, when the presence of clouds makes guiding unrealiable, The observers should be aware that, although the shutter will close during a pause, cosmic events will continue to accumulate.


For a "File" number of nnn the frame will be saved as file ccd0nnn.fits. The file number will be updated by one for all exposures except a "Snap". Note that if a frame with the same number as the current exposure already exists on the disk, it will be overwritten.

Readouts can be performed at three different speeds: Slow, Fast and Turbo. Characteristics of each mode are given in the table below, for one amplifier mode, full unbinned frames, with 128 columns and rows of overscan.

                                                                                                                             

SITe2K
SPEED GAIN NOISE (e-) READTIME (s) SATURATION (DN)
SLOW 1.05 6.0 79 >64,000
FAST 1.55 6.3 67 >63,000
TURBO 2.75 7.9 54 >55,000

 

WF4K
SPEED GAIN NOISE (e-) READTIME (s) SATURATION (DN)
SLOW 0.85         3.4            254               60,000
FAST 0.75         3.6            144               60,000
TURBO 1.4         4.8            100               45,000

 

2.3 The Quick Look Tool

From the "Modules"  pull-down menu in the CCD Camera GUI, a quick look tool can be invoked, where the succesive exposures will be automatically displayed. 

 quick_look

 

 

                                        quick look 3      quick_look_2

 

More details about the Quick Look Tool can be found at:

http://www.lco.cl/telescopes-information/magellan/instruments/imacs/user-manual/the-imacs-user-manual

 

 

Also open from the 'Modules' pull-down menu, the Dewar_Status window will provide information on the detector temperature along the observations.  

 

 

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