LUCI User`s Manual Download

LUCIFER User Manual
Issue 1.3
CIFER detector with the telescope elevation axis (up-down on LUCIFER) and perpendicular to this (left-right on LUCIFER). A list of pointing stars is available at the telescope in
the IRTC notebook, and the corresponding stars are in a catalog on the LUCIFER computer
TargetsCoord/ The stars to use are named WT10 * or ACT*
4. Take a 2.0 second exposure with LUCIFER. At this point you can iterate this step, allowing
the telescope operator to manually correct any gross focus errors until that is not the dominant
collimation error, then
5. Ask the telescope operator for the current values of IE and CA. Also measure the approximate
centroid of star on the LUCIFER image (xstar , ystar )
6. Calculate the offset needed to move the star to the projected mechanical rotator center, currently
at pixel (xref , yref )=(1014,1043) as follows:
CAnew = CAold + 0.12 × (xref − xstar )
IEnew = IEold + 0.12 × (yref − ystar )
Please note that this reference position may change slightly after each new installation of the
instrument at the telescope. Current values will always be available in the LUCIFER image
headers in the keywords CRPIX1 (xref ) and CRPIX2 (yref )
7. Ask the telescope operator to implement these new values of IE and CA
8. Take another 2.0 second exposure to verify that the pointing star is indeed placed at the reference
coordinates to within a few pixels
There is currently no user-friendly tool to perform this simple operation.
Monitor the guide star offset from the wfs on the acquisition images during subsequent presets. Whenever the guide star is more than halfway to the edge of the acquisition image you should consider
repeating the above pointing correction procedure outlined above. Please keep in mind that the more
out of thermal equilibrium the telescope is, the more often this will need to be repeated. On wellequilibrated stable nights you may only need to do this correction once after the beginning of the
Collimation Once the pointing has been corrected, the guide stars should be within the capture
range of the acquisition, guiding, and wavefront sensing (AGw) system that will be used to correct
any remaining collimation errors in the telescope and maintain collimation throughout the night. Any
large focus offset at the start of the night should be manually removed by the telescope operator
during the initial pointing correction (above). This will deliver an image to the AGw that can be
guided on while the wfs collimates the telescope.
You may select any star for this initial collimation, including an off-axis guide star at your first science
target. If the telescope is far out of collimation at the beginning of the night, or the seeing is poor
(> 2 arcsec), a brighter star (R 10 − 12m ) would be useful until the point where it is saturating
the guider or wavefront sensor. A list of Persson infrared standards is available at the telescope
in the IRTC notebook, and the corresponding stars are in a catalog on the LUCIFER computer
TargetsCoord/PerssonStds The stars to use are named BS91*. These are well-distributed
over the sky, so one should be reasonably near your first science target.
Once the telescope is collimated, meaning that the rms wavefront error has converged to something
below 400nm, the collimation model will normally keep you close to decent collimation even on large
slews of the telescope. Difficulties can be found on nights with very poor seeing (>3 arcsec), very
low winds (<2 m/s), or large temperature swings. The poor seeing affects collimation because the
entrance aperture to the wfs is three arcsec in diameter, so poor seeing makes it difficult to find the
centroids in each subaperture. Conversely, very good seeing should yield rms wavefront errors well