Calypso Lunar Observing Instructions

Bruce Truax
May 23, 2008

Introduction

Arlin Crotts (Columbia University) and Gerald Cecil (University of North Carolina) have developed a lunar observing program for Calypso called Lucky Imaging. This program uses a high speed CCD camera from Andor Corporation mounted in the position of the WFCam guide camera. A variety of color filters are used for the observations with each filter cell containing the appropriate color filter plus a selected ND filter in order to allow exposure times in of approximately 0.1s. These exposure times are fast enough to freeze the atmostpheric turbulence. The observer then instructs the camera controller to acquire 5 to 8 sets of 1,000 images on each target. Once the data is aquired it is shipped (on a hard disk) to Gerald who then runs it through software which selects the sharpest images and aligns and stacks those images to form a final, high resolution, low noise image. The name Lucky Imaging comes from the fact that only the best images with almost perfect seeing (the lucky ones) are selected for analysis.

Calypso can be switched from normal observing to Lucky Imaging in less than 1 hour. The switch involves removing the normal guide camera and installing the Andor camera + filter, lugging the Andor camera control computer up to the observing level and connecting it to the camera and the network and testing the camera function. Switching back is also about 1 hour of work.

Observing the moon does require some special software to generate the pointing and tracking information. Russell Owen provided Calypso with a Python script which generates the required TCC commands to point and track objects on the moon based on their lunar longitude and latitude. These commands need to be given directly to the TCC, bypassing the TOI. This is a relatively simple operation involving multiple windows and cutting and pasting operations but once you get proficient at the procedure it is quite efficient.

This document provides instructions on how to change over the telescope for Lucky Imaging, how to connect to the Andor camera computer and how to tell Calypso to track objects on the lunar surface.

Configuring Calypso for Lucky Imaging

Installation

  1. Turn off instrument power on the main control panel in the electronics room at the base of the pier
  2. Disconnect the signal cable from the Guide Camera

  3. Remove the Guide camera by loosening the two screws shown in the following image and slide the camera up and out of the mount.

  4. Remove the lens tube from the guide camera. To do this you must first back out the four locking screws shown in the photo and then unscrew the lens tube from the guide camera. Count the number of turns required to unscrew the lens tube! You will need to reinstall the tube with the same number of turns to get the focus correct!
  5. Measure the distance from the flange on the lens tube to the bottom of the Focus Reference label. Record this number and remove the label.
  6. Screw the T-mount to C-mount adapter onto the lens tube and screw the Andor camera onto the adapter
  7. Install the first filter set into the lens tube

  8. Install the Andor camera on the telescope. Slide the lens tube down as far as it will go into the mount.
  9. Strap Andor power supply to the dewar as shown and plug the AC power cable into the supply

  10. Connect the power cable and the USB cable to the camera

  11. Secure the unused guide camera cables to the WFCam so that they do not inhibit the rotation of the camera
  12. Place the Andor control computer (PC- ugh!) and monitor on the diamond plate below the secondary truss. Connect the network, power, and USB cables.

Removal

In the best Bentley service manual tradition - Removal is the reverse of the installation procedure. Actually there is one exception, the Focus Reference label needs to be re-installed on the lens tube. Print a new Focus Reference label using the label printer which is located in the library on the top of the bookshelves. Position the label so that its bottom edge is located at the same position recorded in step 5 above. When you slide the lens tube back into the mount on the WFCam position it so that the bottom of the label just touches the mount.

Tracking the Moon

  1. Start up telescope and set it to use the WFCam.
  2. Slew to a known object and take an image with the WFCam. Make sure that the object appears centered in the main camera. (If it does not then there is a pointing problem with the telescope which needs to be resolved before observing, such problems are NOT related to the Andor camera.)
  3. Halt telescope axes
  4. Select "TCC Commands…" from the Engineering menu

  5. Issue the command SET INSTRUMENT=ANDOR

  6. Slew to the bright object, it should be in the field.
  7. Select the "Telescope Focus…" option from the "Observe" menu

  8. Set focus to -335

  9. Fine Adjust focus while watching live image (it may be necessary to find a dimmer start depending on which filter is being used)
  10. Open an XTERM and ssh into saturn.
  11. Navigate to /Shared Items/Calypso Documents/Lunar Observing Program/lunar_pointer 2/
  12. Enter the command ./moon_pos_calypso.py FEATURE_NAME where FEATURE_NAME is the name of the feature you wish to observe (i.e. TYCHO)
  13. At the end of the resulting output there will be two lines which start with TCC
    tcc track 283.333820, -26.291222/distance=0.00268635 geo /keep=bore
    tcc offset arc 0.0, 0.0, 0.000136923, 0.000021975, 4718274959.00 /computed
    Ignore the TCC and copy the rest of the first line. Open the TCC command window in the TOI and paste the command into the text field and press send.

    This will send the telescope to the object. Next copy the OFFSET command and paste it into the TCC command window and send it. The first command sends the telescope to the object and the second command sets the proper drift rate.
That is all there is to it.

Offsets

We have tried using offset commands to nudge the pointing direction while performing lunar tracking and found that none of the offset commands work properly. It does not seem to be possible to offset and maintain the proper drift rate. If it is necessary to offset the telescope you are advised to compute the new coordinates on the moon and enter a new feature with those coordinates in the "features.dat" file located in the directory with the Python script.

Advanced tracking hint

Rather than pasting the track and offset commands into the TCC Command dialog window I found it much quicker to issue the commands directly to the TCC. To do this, open another XTERM window and log into charon as user TCC. Once logged in start a TCC session using the command TELRUN. Once you have this separate session running it is possible to paste the track and offset commands directly into this window. It saves a few mouse clicks.