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Creating Object Definition Files (ODFs)

Creating Object Definition Files (ODFs)

Once all object priorities and slit angles have been set, you are ready to create mask file(s). This step will allow you to create a minimal ODF for each mask required for the current FITS image. The software has the ability to select objects based on their priority to optimally place the slits in the mask. The following steps outline how to create the mask: 

  1. Click on the "Design Mask" button in the catalog window. This will bring up a pop-up window similar to the window shown below.
  2. Input mask design parameters
    • GMMPS now remembers previous settings for each instrument.
    • Central wavelength defaults to 600 for GMOS-N and GMOS-S. For F2 central wavelength is determined by your grating and filter selections, and is not editable in the design masks window.
    • Select grating and filter from the pull down menu, if a different grating and filter are desired.
      • Not all filters are available at both GMOS-N and GMOS-S, refer to the filter lists for details.
      • For Flamingos-2 only certain grating / filter combinations are recognized by GMMPS. ODFs can still be created using unrecognized combinations, but the calculated spectra will have length = detector size.
    • Select 'Slit Expansion' mode. Slit expansion “on” will expand slits after selection to maximize the amount of sky covered by the mask.
    • To simultaneously create more than one mask for the field, the "Number of Masks" parameter may be changed. Adjust the slider position adjacent to this parameter to increase/decrease the number of masks requested.
  3. Click on "Make … Mask Files" when satisfied with the mask design parameters.
  4. Confirm overwrite or choose new name.
    • If you have already attempted to create a mask for the current image, the program will warn you that the mask name already exists and that it wishes to overwrite this file. If you do not wish to overwrite the old mask name, either click on "Enter New Filename" or "Browse for New File Name". Clicking on the "Browse..." button also allows you to enter a new filename.
  5. Verify mask creation.
    • When the masks are designed, the mask design pop-up window shown below will not contain information about how the objects are sorted into the masks. If you find that you have too few high priority objects for the number of masks you have, you can go back to the catalog window and change the priorities, however be sure to close all mask making windows first.
[Mask design window]


Some points to note:

  • The information in the mask design window tells you the number of objects selected for each mask sorted by priority. In the example, two masks were requested and thus two ODF FITS files were created: mask_OTODF1.fits and mask_OTODF2.fits for Mask 1 and Mask 2, respectively. These files will contain the information about which objects were selected for each mask. In the window shown above, the files are referred to by the matching *cat names.
  • If the OT catalog did not have a slitsize_y column then the slit length will be set to 5 arcseconds. Otherwise the slit length is taken from the values of slitsize_y for each object in the table. You can use IRAF to creae the slitsize_y and any other optional columns.
  • The position of the slit is taken from the values listed in the catalog columns and converted to pixel position using x_ccd + slitpos_x and y_ccd + slitpos_y.
  • The length of the spectra for each slit is determined by the selection of filter, grating and bandwidth combination. Pre-defined calculations determine the expected first order spectrum length. The spectrum length is stated at the bottom of the window (visible after scrolling down).
  • If multiple masks are created, each mask will preferentially include the maximum possible number of Priority 1 objects with lower priority objects filling any spare spaces. The following mask will not include any objects used in the prior masks, except for acquisition objects, which will be included in all masks.
  • If any priority changes are required, close all mask making windows first, otherwise any changes made in the catalog window are not recognized by the already-open mask making windows.


Last update June 5, 2013; Mischa Schirmer and Bryan Miller
In original form February 10, 2003; Dione Scheltus