XMOS -- The MOS Slitlet Defining Tool

Table of Content

Starting with the MOS Mask Tool

Given below is a recipe for defining slitlets starting with an image  (EFOSC_Image.#.fits ):

The MOS mask definition tool is basically a panel which provides an interface between the user and MIDAS. Apart from the MOS mask definition tool (click on link to see the panel) 2 other windows are opened, a MIDAS display window and a MIDAS message window where the commands and their output are reflected.

MOS Mask Tool Menu Options

Listed below are the various menu options available and a brief description of the same. After that will follow a continuation of the recipe for defining the slitlets.

Making a mask -- Using the MOS mask tool

  • Select a valid punch tool option --  Note this has to be the first operation after opening the tool and cannot be changed while working on a mask.
  • Load an image using either the Fits->Load and R90 .....  option to select FITS files or File->Load *.bdf  to load midas files that have been rotated before (not recommended!)
  • You may change the values for the parameters listed below and then click on Update Midas on the panel:
  • Change the display intensity cuts Tools->Cuts  to something sensible.
  • There are 4 possible slitlet defining operations. First select Options->slit length and then Slit->object/cursor option:
  • Some of the commonly used functions include:
  • Finally after everything is done:
  • Some Considerations

    The 3 reference stars

    Slits to the right of centre will yield a spectrum which covers a range blueward of a central slit while those to the left will cover redder wavelengths.

    There is no spatial restriction on the location of targets on the CCD other than for the reference stars. However if you are using the narrowest punch be prepared to lose 1 or 2 objects close to the margins of the CCD especially if your reference star locations are less than perfect.