Ultra-fast imaging camera mounted at Cass exposing in 3 bands simultaneously through two dichroics, with a 5x5 arcmin field. It has Peltier-cooled chips (so no need for LN2). It is fed with cool water by a chiller placed on the observing floor close to one arm of the mounting fork of the telescope. This chiller is connected to the instrument with two long pipes which hang from cass and are long enough to allow telescope movements in DEC and rotator position (commissioned May 2002).

REMEMBER TO CHECK THE PIPES TO THE COOLER ARE CLEAR TO MOVE AND AWAY FROM WHERE THE TELESCOPE WILL ROTATE!

For more information see Vik Dhillon's Ultracam Page TCS:

• USER> STATION CASS
• USER> INSTRUMENT ULTRACAM
• USER> AGSELECT CASSE
• Zeroset Rot, AZ and ALT
• USER> CAL LAST
• USER> FOCUS 98.0 (2012 value)

Telescope focus: determined on the detector by the Ultracam team. 98.0 is a good starting point, but they might want to adjust it to increase the S/N, by trial and error.

Autoguider: Use the standard uDAS autoguider for CASS with AUTOFOCUS 2400 (2012 value). Run from UDASDEV2 (whtdas18) with 'obssys 1', 'startobssys' and 'startag AG6' followed by 'option 4'. GSS2 is used for finding guide stars, with instrument configuration Ultracam.

TV: The TV is not used for acquisition, this is done on the detector. AGCOMP mirror is used only for direct viewing, finding the rotator center and performing calibrate, i.e. it is not used for general observing.

Agmirror: for observing do:

SYS> agmirror out

Determine rotator center: Use direct viewer (AGCOMP) and TV camera.

Calibrate procedure: Calibrate is done on the rotator center and with the rotator stopped (ROT MOUNT xxx) using the direct view TV.

Determine aperture offset: There is no need for defining an aperture.

Typically objects are followed for several hours at a time without any breaks, and often on the following nights too. Standards may be done just after evening sky flats.

Sky flats: Sky flats may be done at the start and end of the night and can begin around 20 minutes after sunset (this might vary). The observer does the sky flats, using an ICL-script to dither in a spiral pattern. To run the script, do in the observing system prompt in the scripts directory:

SYS>spiral.csh

The script can be terminated by ctrl-c any time.

Acquisition: PLEASE REMEMBER to check the rotator limit because often one target is observed for many hours. Acquisition is done through the camera itself, as it is a fast-reading device for high time resolution observations. Typically offsets of a few arcsecs are needed to place the target where it is required on the detector. Guiding can begin as soon as observers are happy with the acquisition.

XY HANDSET movements are as expected:

       +------+
       |  ^   |
       |  |   |
       |  |   |
       |      |
+------+------+------+
|      |      |      |
|      |  |   |      |
|  <-- |  |   | -->  |
|      |  v   |      |
+------+------+------+

Guiding: It is likely that targets will be observed again on subsequent nights and it might be desirable to return the target to the same pixel on the detector. If this is the case, note the Sky PA, telescope offsets (only if large, and approximate is fine), autoguider r and theta, and x,y guiding coordinates from the TCS. To go back to the same position do:

• USER> gocat target
• USER> rot sky XXX
• offset telescope as before (only very approximately, since the guide star will pull the telescope back into exactly the right position).
• SYS> prag r theta
• Finally, when everything is in position, do
  USER> auto on x y
  and wait for the guiding errors to decrease to normal before starting observing.

The data are numbers of images (up to 2 Gb) stored in a single data file on dedicated Ultracam machines, so the runs do not appear on ING logs.