European Southern Observatory New Technology Telescope

General :
Observations :
Operations :

Image Quality

THIS PAGE IS OBSOLETE - SCHEDULED FOR DESTRUCTION - see http://www.ls.eso.org/lasilla/sciops/esoonly/operations/astro/imageQuality.html

1 The Observations you need

For the 3 instruments, templates are already done: you just have to choose your object, if possible an isolated star. The templates take 36 images of the same object to map the detector. At the end you have an array of 36 positions (36 fits files). The templates are on kila, nttt account in the directory Imagery_Quality/<inst>/ and they are named Image_Quality_<inst>.obx.

NB: for SOFI we have a problem, because when we use a normal template the telescope has not stopped when the exposition begins... so we have two solutions: 1- take the 36 images manually 2- do a template with several seconds between the mouvement of the telescope and the exposition.

2 The reduction of the data

To reduce the data you have to use different methods depending on which instrument you are working with.

SOFI : in drl5 as guest (+Love4*S), you have an iraf script named imagequality.cl that simply substracts the median sky and divides by flat. (so you need flats !!!). The script needs as input a list of the raw data (liste*.lis), some flats and it asks to you the prefix you want to give to the reduced files (ex: LF_J). The final files must be called LF_J_001.fits to LF_J_036.fits.

EMMI:

SUSI:

3 The determination of the image quality

Now you have to use the python program imagequal_3.0.py to extracte the star, calculate the ellipticity and plot some graphs.
imagequal_3.0.py needs as input:

• liste.txt:
  example of liste.txt:

First column: directory where the reduced images are
Second column: name of the list of all the fits files
Third column: instrument/configuration : SUSI - EMMI - LARGE - SMALL - FE _ SO (the last 4 choices are for SOFI)
Fourth column: the prefix for the final files <prefix>

• plot_mac.x: the executable file of the plot_mac.f program. A fortran/Smongo program who plots the final results.BE sure that the plot_mac.x is already compile on the machine you are working on: problems of uniformity of the machines in La Silla, the librairies are not updated.......... so work on drl5.
  The python porgram reads inside the list file the name of all the fits files and do an extraction of all the objects in the field with SEXTRACTOR. The extraction parameters are in default.sex (they can be modified). For each file, a sex*.cat file is created with all the positions encountered by SEXTRACTOR.
  imagequal_3.0.py selects inside each sex*.cat file THE position that corresponds to the number of the file and the predefined position (where the star you are looking for should be according to the template). The numerotation of the files from 001 to 036 is really important to do the link between the fits file and the position of the star.A file smongo.dat is created with the needed parameters for the 36 files : ximage, yimage, A, B, rotational angle.
  When the extraction is done, imagequal_3.0.py calls plot_mac.x to plot the final graph : there are 3 options 1- xterm 2-printer 3-ps file. It's important to know which option is wanted because the plot cannot be repeated whitout star again the complete procedure.

At the end you have a <prefix>.dat file and <prefix>.ps file.

All the reduction part and analyse part must be done on drl5 for the moment !!!!!!!!!!!!!!!!!! You can find eerything in the directory :
Image_Quality/

To start the python program, just enter %> python imagequal_3.0.py

Send comments to: NTT Webmasters <nttweb@www.ls.eso.org> Last Update: October , 2001 (Billeres Malvina)