Aligning the Secondary Mirror on UKIRT (WFCAM)

WFCAM Secondary Tilt Alignment
Wavefront Sensing with WFCAM

Aligning the Secondary Mirror on UKIRT (Cassegrain)

To do this you must use the wavefront sensor with the dome, dvs and mirror covers closed and the dome lights on.

Log onto KIKI as curve and run the engineering version of the curve acquisition software by typing

  > curve_eng

This will open up the curve epics display, as shown below. With the epics window set to “eng”, the data will be written in fits format to an engineering directory, /ukirtdata/raw/eng/curve/UTdate/.

Make sure the eng/ directory is highlighted in the epics display, and set the focus to 0.00

Use a short exposure time (1 second is good) and take an image. A typical image should look something like the following. This gaia display is zoomed by 6-8x:

Note: this is also an ideal time to focus the WFS. The secondary image should be sharply in focus.

The central circle is an image of the hole in the secondary mirror and this should aligned within a fraction of a pixel of the four rectangular images at the top, bottom and sides of the image. If it is not, you must realign the secondary by adjusting the WE beam and NS beam of the hexapod controls in the MCU engineering interface epics screen. This adjusts the hexapod and this realigns the secondary mirror. The MCU engineering interface epics screen is run by typing:

  > dm topend.dl

and select the MCU engineering interface, which looks like the following:

Once the image is perfectly central, the secondary primary configuration file must be updated, in order to make the changes permanent. The configuration file can be found in the directory /jac_sw/itsroot/install/configs/ and is called secondary.cfg>. Before modifying this file, make a copy of it as so as to keep a record of previous settings. Copy it as follows:

  > cp secondary.cfg secondary_{UTdate}.cfg

and replace the information in parentheses with the current UT date.

The secondary.cfg file looks like the following text file. You only want to adjust the East-west and North-south beam positions.

# Secondary mirror support system model

# Z7 – East-west coma setpoint
mcu:EWcollim:coma = -150;

# Z8 – North-south coma setpoint
mcu:NScollim:coma = 1400;

# East-west beam position
mcu:EWcollim:beam = -30;

# North-south beam position
mcu:NScollim:beam = 45;

The coma setpoints are determined by wavefront sensor analysis. DO NOT CHANGE THESE.

After you have made an edit type:

  > cvs commit -m "{message about the reason for the change}" {filename}

and then the changes are permanently saved. You should replace the things in the parentheses with the actual reason for making the changes and the configuration filename (i.e. secondary.cfg).