LUCIFER - Suggestions for Successful Observation Preparation

Generic Suggestions
  • When in doubt, read the manual, website, and wiki!
  • Still not sure? Email us at ScienceOps@lbto.org, we are here to help!

Visualization tools
  • Olga's perl script for guide star selection/visualization: LUCIguidestars.tar.gz
  • Steve's perl script for checking LUCI scripts found here

Scripts
  • Verify your long slit specifications, they have changed! See the current LUCIFER mask list
  • For spectroscopy acquisition and science data, set FLEXURE_COMP to ON (not needed for imaging)
    Mar 2012: FLEXURE_COMP = ON in spectroscopic scripts
  • Be sure to include an ARCHIVE section in all scripts
  • If the ARCHIVE section is missing in scripts, data will be marked with the defaults in the RMGUI

An example ARCHIVE section for scripts is given below. Note that extra spaces used for indentation and readability in this example are ignored by the LUCIFER script processing engine.
[START_ARCHIVE_INFORMATION]
   PARTNER   = LBTO         # OSURC, LBTB, INAF, AZ, CALIBRATION, or any space-free comma-separated combination
   PI_NAME   = DThompson
   PROP_ID   = MyFavObj_123
               [END_ARCHIVE_INFORMATION] 

The PI_NAME and PROP_ID are arbitrary strings left for the user to define. They can include comma-separated values but no spaces. These can be used to group together sets of related data in the archive by investigator or by project.

Flexure considerations
Over a 360-degree rotation and a 90-degree change in elevation LUCI flexes up to ~20 pixels range. If you consider the maximum rate of flexure and limit image motion to below an assumed limit of 0.5pix image movement during an exposure:

  N3.75 N1.80
Exp Time Elevation Elevation
10 min 60deg 75deg
5 min 75deg 82deg
3 min _ 85deg
2 min 85deg _

From our expericence, 10min is the maximum recommended exposure time. An elevation of 85deg will be anyway the limit due to stability of the grating tilt. Thus, for the most used mode - spectroscopy with N1.80 camera - there is no severe restriction for observing. Using a 1arcsec slit, the maximum loss in resolution <=10% for any elevation under 75deg within 10min exposure. For programs using a slit width <=0.5arcsec and eventually the N3.75 camera, the maximum exp. time should be reduced if the limiting resolution is important.

MOS Mask Design
The LMS software does not automatically place slits over the alignment sources. You must explicitly request this when designing your masks. Having some source visible in a slit or small box once you have completed the alignment gives you a visual confirmation that the alignment was accurate. There are a couple of ways to approach this. One is to cut small boxes at the position of two or more alignment stars (two arcsec square boxes are frequently used). These will then (mostly) dither out of the boxes when you run the spectroscopic scripts. The other method is to select two or more sources that are visible in a short exposure and place slits on them. To have maximum confidence of your alignment it is best to place these sources at the extremes of the field of view.

Finding Charts
Good finding charts can significantly reduce the overhead of mask or slit alignment on sky. The closer your finding chart matches what is actually seen at the telescope, the easier it is for the observers. In particular, your FCs should match:

  • LUCIFER's field of view is 4x4 arcmin
  • LUCIFER's orientation is north-up and east-right
  • A 60s exposure reaches Ks~17mag even in poor seeing

To the extent that it is difficult to match these suggestions, at least be sure to clearly mark scale and orientation of your FC. Note also that finding charts based on optical data (e.g. the DSS) are often difficult to use because the relative brightness of blue and red stars can change significantly between the optical and infrared bands. Finding charts based on Hubble Deep Field data are are close to useless as the thousands of sources are hard to match to a LUCIFER image showing only five source!

Guide Stars
The recommendation is to use guide stars of 13 < Mag < 16.5 in the R band. Brighter stars can saturate in good seeing. It would be a good idea to include at least in the project README file an alternative guide star that could be substituted for the one in your script.

OFFSETS
  • For spectroscopy, always use RELATIVE offsets (ABSOLUTE offsets undo your alignment!)
  • Blind offsets should be given as REL/RADEC offsets after the ACQUISITION command
  • An exposure is taken AND saved (using the requested DIT/NDIT/NEXPO) 2 w

-- DavidThompson - 12 Oct 2010
Topic attachments
I Attachment Action Size Date Who Comment
LUCIguidestars.tar.gzgz LUCIguidestars.tar.gz manage 3 K 06 Dec 2010 - 21:28 DavidThompson Perl script for guide star selection
Topic revision: r6 - 22 Feb 2012, DavidThompson
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