The SOAR Optical Imager (SOI) Cookbook

• Two windows that look like the images below should be on your screen. If they are not, then you will need to start up these windows. See the documentation on the SOI Manual for logging into the SOI data acquisition and analysis GUIs. Note that these are virtual desktops, one for taking observations and one for real time display and analysis.

  The following windows show the two Virtual Network Computing (VNC) desktops that are used with SOI:

  Figure 1: The SOI data acquisition (left) and data analysis (right) GUIs.
  
• Now it's time to check if the CCD binning and readout parameters are set properly for your observations. To check that the binning and readout are correct for your run, single click on the "GUI SETUP" button that lies above the cross-section view of SOI. The "CTIO Optical CCD Camera Setup Screen" should now open, as shown in the image on the left-hand side in Figure 2. At the top of this panel, there is the "Configuration File for NORMAL exposures". In this example, we see that the normal exposures are set for 2x2 binning with a fast readout. Thus, the images obtained with this setup have the following properties:
  1. an image with 2048x2048 pixels and a plate scale of 0.1534"/pixel,
  2. a gain of 2.0 e/ADU,
  3. a readout noise of 4.4e, and
  4. a readout time of 10.9 seconds.
  
  This is the default observing configuration for SOI. If this IS the configuration you desire for your run, click on the "Cancel" button in the upper right-hand side of the panel. If this IS NOT the desired configuration for your run, click on the file folder icon to the right of the "Configuration File for NORMAL exposures" dialog box. This opens a "File Dialog" box as seen in the image on the right-hand side of Figure 2. The "File Dialog" allows one to change the binning and the readout of SOI. The currently allowed observing modes are:
  • CCD44_fast_1x1_normal.conf,
  • CCD44_fast_2x2_normal.conf,
  • CCD44_fast_4x4_normal.conf,
  • CCD44_slow_1x1_normal.conf, and
  • CCD44_slow_2x2_normal.conf.
  Once you have selected your binning and readout modes, click the "OK" buttons in the "File Dialog" and the "CTIO Optical CCD Camera Setup Screen" windows, respectively. Please contact your support scientist or a telescope operator if you want to change the detector parameters.
  NOTE: Before any changes take effect, the Data Acquisition GUI must be stopped and re-started as discussed in the Starting and Stopping the Data Acquisition GUI section of the SOI Manual.
  Figure 2: (left) The CTIO Optical CCD Camera Setup Screen. (right) The File Dialog box to change the binning and readout parameters.
  

• After the binning and the readout have been set, it is time to set some of the parameters in the "Exposure Info" section of the data acquisition GUI, such as the Observer name and the data Path. As an NOAO/CTIO Visiting Astronomer, the Path for your data will be:

  /uyg0/simager/images/NOAO/YYYY-MM-DD.

  If this directory does not exist, open a terminal window on soaric1:9 and:

  cd /uyg0/simager/images/NOAO
  
  mkdir YYYY-MM-DD.

  This directory should be entered as the data Path in the "Exposure Info" section of the data acquisition GUI. If disk space becomes an issue during your run, please contact your support scientist so that old data can be properly deleted.
  NOTE: The default setup is to have each image displayed automatically after readout. If you do not want this default, please unclick the box in the "Exposure Info" section that controls this.
• Exposure Control: As discussed in the SOI Manual all observations with the SOAR Optical Imager are obtained through the observing GUI on soaric1:9 in the "Exposure Info" section. In this section of the GUI, you can set:
  • The observation Type (i.e., OBJECT, [DOME]FLAT, SKYFLAT, DARK, ZERO, or CALIBRATION) of the exposure;
  • The Observer name;
  • The Basename for the FITS file;
  • The Title of the FITS file;
  • The Path for the directory in which the date will be written;
  • The observer's Comment of the exposure;
  • The Sequence Number of the exposure;
  • The Exposure Time of the exposure;
  • The number of Repeats for this type of exposure; and
  • The Filter.
  Most of these fields can be edited by placing the cursor in the appropriate box and changing the text. The only exceptions to this are the observationType and the Filter boxes as shown in Figure 3. To change these two boxes, you can place the cursor on the boxes a single click. A small window will open with the current selection indicated by a black checkmark. To change the current selection, simply click on another option.

  NOTE: To change the filter you MUST click on the "FILTER MOVE" button after selecting the new filter.

  Figure 3: The SOAR Optical Imager Data Acquisition screen showing the observation Types (left) and filter selection (right) in the Exposure Info section.

• Take a test exposure, specifying that you want to take a "zero" frame. Once the exposure is taken and read out, check to see if the file has been written to the proper data directory. If you are in the nominal 2x2 fast read-out mode, the data should be written in about 10sec. You can check the

  /uyg0/simager/images/NOAO/YYYY-MM-DD

  directory to make sure that the file has the proper dimensions using the IRAF imheader task. Once the zero frame is read out, does is look like this? If the zero looks OK, you should check that it has the correct image size in IRAF. In normal 2x2 binning, each amplifier should be 563x2048 pixels.
• If your first zero image looks OK, then you are set to go ahead with your calibrations. Take more zeros by incrementing the number of Repeats to your desired value. After you have completed your zero sequence, ask the telescope operator to point SOAR at the white spot and turn on the flat field lamps. Take as many dome flats through each filter, using the exposure times given to you by the telescope operators. These times have been determined to allow you to obtain a peak of ~20000 counts. If the standard dome flat exposure times produce fewer than 20000 counts, then the dome lamps may be misaligned or a bulb may have burned out. Please ask observer support to check the dome lamps if this is the case.
• Observer support will open the dome before sunset to clear the air out of the dome. Right after sunset, prepare to take twilight sky flats. The telescope should be pointing a couple of hours to the east. Take 1-second "test" exposures, starting with the filter that you expect will require the brightest illumination, until the peak counts drop to ~25000. Take successive sky flat exposures, asking the telescope operator to move the telescope between exposures. Increase the integration time as needed to maintain your count rates.
• Once it is too dark to take twilight sky flats, ask the telescope operators to move to a bright star to zero point the telescope and tune the optics.
• Telescope focus procedure: The Calibration Wavefront Sensor (CWFS) is used to tune SOAR's Adaptive Primary and Secondary mirrors in order to achieve the best possible images. It was built for SOAR by Adaptive Optics Associates of Cambridge, Massachusetts and is based on their Wavescope laboratory measurement device. The CWFS is mounted at the center (90 degree) bent Cassegrain port on the elevation ring.

  The CWFS is a Shack-Hartman type wavefront sensor in which a microlens array is used to divide the telescope pupil into approximately 530 sub apertures (thus over sampling the spacing of the primary mirror actuators by slightly more than a factor of two). Each microlens produces a spot, the position of which is recorded using an Apogee AP6E Thermo-electrically cooled CCD camera. By comparing the position of the spots from a star, with those from a calibration source that projects a perfect spherical wavefront, it is possible to measure the slope of the wavefront across each sub aperture, and thus reconstruct the shape of the wavefront. The CWFS is capable of obtaining accurate wavefront measurement using stars as faint as R=12 in a 60 second exposure.

  The control software for the SOAR Active Optics System (AOS) uses the CWFS measurements to compute the force required on each of the 117 Primary mirror actuators, and the position of the Secondary mirror, needed to correct the wavefront to have the ideal form. In normal operation the AOS is controlled via a lookup table containing the optimum parameters for the Primary and Secondary as a function of Zenith distance, and Temperature. The CWFS is used to populate this table by taking measurements of stars at various positions over the sky during engineering time. However, when the very best possible images are required it is also possible to tweak the parameters of the AOS by using the CWFS to measure a star near the science target, at a cost of about 10 min overhead.

  The telescope operators will tune the mirror at the beginning of each night. It is generally recommended to ask the telescope operators to re-tune the mirror after the first 1-2 hours of observing and after large slews. Occasionally check your science data using the IRAF imexamine task. If the FWHM of the stellar profiles are worse than the sight seeing and/or the stellar images are elongated, then it is probably time to re-tune the mirror. The telescope operators will let you know if this advisable, depending on the seeing and other environmental factors. The SOAR Optical Imager should have the same best focus as the CWFS.

• The two CCDs in the SOI are mounted with their long sides parallel and spaced 102 pixels apart, resulting in a 7.8" gap between the individual CCD images. The gap can be filled by taking dithered images. We recommend taking at least 3 images with 10" steps to produce a complete combined image with no gap.

This page was last updated on 01 September 2008 by SDP.
Please send comments or questions to spoints@ctio.noao.edu.