FAT-CATThe Field Acquisition Telescope for the Coude Auxiliary Telescope, FAT-CAT, is a wide field CCD camera mounted at the top of the focusing mechanism for the CAT secondary mirror and is used as a finder for the CAT. In its current configuration it consists of an Opticstar DS-335C CCD camera coupled to a 180 mm f/2.8 Nikkor lens with a plate scale of 3.95 arcsec/pixel and an effective field of view of 135 arcmin x 101 arcmin. The camera is connected to a computer named fatcatpc that resides on a shelf near the MOS via a USB cable. The camera software is run remotely using a VNC environment. To use FAT-CAT follow these instructions:
- Open an xterm on catpc and type vncviewer fatcatpc (use the standard VNC password)
- Click the start button within MS-Windows XP on fatcatpc and select the program Nebulosity
- Click the maximize button in the upper right corner of the Nebulosity program
- Click the camera button and select Opticstar DS-335C from the pull-down menu
- Click the advanced button and check the box for 2x2 binning
- Set the exposure time to a value between 3s and 18s
- Set the number of exposures to 1
- To set the camera in live video mode click the green play button in the StarView. If StarView has been close reselect the camera (select no camera then the DS-355C again).
- To take an image without saving it click the preview button
- To take an image and save it type a name for the image and click the capture button
The current Hamilton boresight is (1110, 674) for 1x1 binning, (563, 340) for 2x2 binning, or (280,170) for 4x4 binning. Click for larger image.
At the start of the night center a star on the slit and start guiding then capture an image making a note of the (row,column) coordinates of the star. Move the cursor to the location of the star on the image and right click the mouse to mark this position. To use FAT-CAT to find your way when you are lost follow these instructions:
- Acquire an image as per the instructions above
- Mark the position of the target star (using a finder chart as a guide)
- Using the compass on the CAT guider image as a guide mark a third point on the image such that the three points form a right triangle with the adjacent sides parallel to the compass directions.
- Select the measure distance option from the image menu and enter the plate scale (7.91 arcsec/pixel) and the program will compute the lengths of the 3 sides of the triangle formed by the three points you previously selected. Referring again to the CAT guider compass you can now compute the offsets in RA and DEC that will put the target close to the slit of the spectrograph. If the target star is still not visible on the CAT guider take another exposure and repeat the above steps. (You may have got the signs of the offsets wrong!)
Known USB issues: When you first start up the Nebulosity program and select the camera if you are greeted with a popup window saying "Cannot Init Camera" then close the program and go upstairs and unplug the USB cable coming from the camera from the USB extension cable and then reconnect the two cables. Do not unplug the USB cable from the computer!
- If you change the binning in the "Advanced" options, you won't see it until the next image is taken.
- If you use 1x1 binning the image is large and you'll have to use the scroll bars to see all parts of the image (in particular the coordinates where the CAT boresight is set).
- You may also use the Frame and Focus function for acquiring
stars (in fact this may be the preferred mode). If you start the
Frame and Focus mode, right click on the image to remove the large
white target cross hairs. Then right click on the appropriate pixel to
get the red crosshair to mark the boresight:
bin 1x1: (1110, 674)
bin 2x2: (563,340)
bin 4x4: (280,170)
Please Abort the Frame and Focus function at the end of the night to stop the constant readout of the detector.