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Designing Nod and Shuffle Masks
Selecting or Creating a Band Definition File
The Nod & Shuffle mode and the definition of micro-shuffling and band-shuffling are described on the Nod & Shuffle pages. The terms from those pages will be used in the description below. Also note that Nod and Shuffle masks can only be created for GMOS mask files --- Flamingos-2 does not support N&S masks.
N&S band definition are stored in .bands files associated with one Object Table catalog and zero or more Object Definition File catalogs. To enter N&S mode click the “Design N&S Mask” in an open GMOS OT catalog window. A dialog window will open, prompting you to select or create a band definition file. This dialog window lists all band definition files associated with this OT catalog, as well as the special tmp.bands definition file. Bandfiles associated with other OT files will not be displayed.
The tmp.bands file is not associated with any single OT file, and in fact may not even exist when it appears in the bandfile selection dialog. It is a common temporary file that can be used when the user does not want to create a dedicated bandfile for this OT, if it does not exist it is created when selected from the band file list.
Setting the Nod & Shuffle specific parameters
The following parameters need to be set:
- Select "Microshuffle Mode" or "Band Shuffling Mode"
- For "Microshuffle Mode",
- Set "Slitlen (arcsec)" to the slit length in arcseconds you require;
- The nod amount is defined only in the Observing Tool, not in the mask making software. The mask making software will design the masks with the objects centered in the slits.
Set “Shuffle Amt (arcsec)” or
“Shuffle Amt (arcsec)” to a value greater than or equal to your
slit length—these two fields will automatically update relative
to one another. Note down what the shuffle amount is in unbinned
pixels - you need this for your Phase II preparations using the
- For "Band Shuffling Mode",
- Set "Band Size (unbinned pix)". Default gives one band of slits at the center of the array in the y-direction.
- Set "Shuffle amt (unbinned pix)" or “Shuffle amt (arcsec)” to an amount greater than or equal to "Band Size (unbinned pix)". Changing either Shuffle Amt field will automatically update the equivalent value in the other respective field. Note down what the shuffle amount is in unbinned pixels - you need this for your Phase II preparations using the Observing Tool.
- Click "Recalculate Bands" to see where the bands fall. The storage areas where you cannot place slits are shown as red-hatched areas, while the areas where slits can be placed have yellow rectangles around them (see figure below).
- Adjust the offset of the bands in the Y-direction, using the "Bands y Offset" as needed. To see the effect, click "Recalculate Bands"
- When the Nod & Shuffle specific parameters have been set, click "Design N & S Mask files". This brings up the usual mask design window that allows you to select the grating, filter and wavelength. From here, proceed as for other masks.
Some important points:
- In "Microshuffle Mode":
- The shuffle amount should be greater than or equal to the slit length.
- The nod in slit amount is defined only in the Observing Tool, not in the mask making software.
- In "Band Shuffling Mode":
- The shuffle amount (unbinned pixels) should be the same value as the band size.
- When the shuffle amount (arcsec) is altered, the shuffle amount (unbinned pixels) is automatically changed to correspond with the band size.
- The nod amount is defined only in the Observing Tool, not in the mask making software. You can either nod in the slits or nod off to sky.
Last update June 5, 2013; Mischa Schirmer and Bryan Miller