Science Operations

Quick Reduce


The mods_quickreduce software is an IDL-based quick reduction tool which outputs sky-subtracted, wavelength-calibrated spectra. It available from all partner accounts on the mountain obsN workstations, both the older obs2,3,4 and the new 64-bit OS machines, robs, obs5 and obs6. Currently, the quick reduction pipeline can only be used to look at MODS1 data.

To run the quick reduce software:

  1. Open IDL in a directory in which you have write permission and which contains the MODS file you wish to process. It is recommended that you create a UT-date subdirectory under /scratch on obs2,3,4 (/scratch is local to each machine) or in a similarly named directory under your home directory on obs5, obs6 and robs. If you wish to reduce a multi-object spectrum, you must also copy the mms file to this directory. To open IDL, use:

    modsidl on obs5, obs6 and robs
    or just idl on obs2, obs3 and obs4.

  2. Run:

    mods_quickreduce, ’<filename>’, [options]

There are two main options one can use.

  1. Add the option to use the wavelength calibration /calwave in the modsIDL library. This option is necessary and valid only for longslit spectra.
  2. Add the option apertures=[1] to only reduce slit aperture number 1, which for the segmented long-slits, refers to the central slit segment (see the cartoon below). You could also do apertures=[1,2] to reduce slits 1 & 2 or any other combination of valid slits.

For most long-slit spectroscopy where the target is in the central slit segment, the following command syntax is all that is needed:    

>>mods_quickreduce, ‘mods1C.YYYYMMDD.NNNN.fits’, /calwave, apertures=[1]

NOTE: If you are looking at a MOS field you also need the mms file in the directory.  The sky subtraction may have trouble if there are objects on the edges of the apertures.

The output of mods_quickreduce is a x2d file which can be viewed using dispMODSx2d.


Once the file is processed, the processed image can be viewed outside of IDL the resultant x2d file:

dispMODSx2d <filename>

Some of the options in dispMODSx2d are:

  1. To change the scaling, put the cursor on the image and type “s”. Then the low and high values you want, separated by a space “ “ . This is confusing as the current values are displayed within parenthesis and separated by a comma, i.e. (min,max), but this is not correct syntax for input.
  2. The output *_x2d.fits file, for long-slit mode at least, has 6 extensions:

    0 = OTF

    1 = sky subtracted

    2 = variance

    3 = sky

    4 = wavelength image

    5 = slit mask

    6 = Slit BinTable

    You can view it in ds9, but then you lose the wavelength scale.

  3. Long-Slit segments are numbered from top to bottom: