| gmosinfo (October2004) | gemini.gmos | gmosinfo (October2004) |
The tasks are designed to provide a fairly complete and flexible reduction for the purpose of assessing data quality at the time of observation. Real-time reductions may not be optimal for a particular science application. The GMOS package scripts can be optimized for a particular application using the hidden parameters to achieve the best possible results.
The tasks produce logfiles of the performed processing steps. The name of the logfile may be set in each individual task, or at the package level by setting gmos.logfile.
The tasks add header keywords to the output images. These header keywords contain information about the performed processing steps and the values of the critical parameters that were used.
All GMOS images are written as multi-extension FITS (MEF) files. Raw data can have up to six unnamed extensions. For full frame read-outs the number of pixel extensions match the number of amplifiers used. Thus, the images have either three or six pixel extensions. Most science observations will be done using the amplifiers with the lowest noise and therefore have three pixel extensions. Most of the header information is written to the primary header unit (PHU) which is extension [0].
After being processed with GPREPARE, GMOS data extensions will be named as defined by the parameters and several additional header keywords will be added. The default is to name the pixel extensions using the keywords EXTNAME and EXTVER:
Extension in raw image EXTNAME EXTVER
[0]
[1] SCI 1
[2] SCI 2
[3] SCI 3
etc.
The named extensions can be accessed as, e.g., gmosimage[SCI,1], gmosimage[SCI,2], gmosimage[SCI,3] etc.
Additional information and ways to handle MEF files can be found in:
GMOS data can be binned in both axis. The header keyword CCDSUM in each pixel extension shows the type of binning. The region on the detector that is read can be changed to any section on the array. The region read out is contained in the keyword DETSEC in the pixel extensions. The content of DETSEC refers to unbinned pixels.
Each amplifier has its own bias level, gain value, and read out noise (RON), therefore, the count levels of each extension will not match when these are in units of ADU. To match the count levels between each CCD, the images can be bias subtracted and multiplied by the gains. This is incorporated in the reduction tasks described in GMOSINFOIMAG, GMOSINFOSPEC, and GMOSINFOIFU.
The tasks in the GMOS package will eventually all support variance and data quality planes. Currently this functionality has not been tested, though the flag fl_vardq to calculated these planes are present in most of the tasks. It is recommended to use all tasks with fl_vardq=no.
There are four display buffer sizes, imtgmos, imtgmos2, imtgmos4, and imtgmos8, available to display the GMOS images. The display task GDISPLAY requires that one of these buffer sizes is used. The buffer size to use is set by setting the IRAF parameter stdimage, e.g.
set stdimage=imtgmos
The sizes of the buffers are as follows
Name Size Notes
----------------------------------------------------------
imtgmos 6400x4644 Full size display of unbinned full
frame images from GMOS
imtgmos2 3200x2322 Full size display of full frame
images from GMOS binned 2x2
imtgmos4 1600x1161 Full size display of full frame
images from GMOS binned 4x4
imtgmos8 800x581 Full size display of full frame
images from GMOS binned 8x8
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It is recommended to use imtype="fits". This is set automatically when loading the GEMINI package.
Abbreviation Explanations
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GMOS Gemini Multi-Object Spectrograph
IFU Integral field unit
MDF Mask defintion file (a binary FITS table)
MEF Multi-extension FITS
MOS Multi-object spectroscopy
PHU Primary header unit (extension [0] of a MEF file)
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The tasks in the GMOS package have been tested with up to three extension MEF files.
The tasks in the GMOS package are designed to operate on MEF FITS images that have been processed using GPREPARE. GPREPARE will not run on data from instruments other than GMOS. The GMOS tasks will not run on simple FITS files.
Input image names should in general not contain directory paths as not all tasks have been tested in this mode.