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A Beginner's Guide to MMS

This guide describes the basics of how to design a mask for MODS at LBT. A more complete guide to all of the functionality of MMS is provided in the excellent LMS User's Manual. A description of the key differences between LMS and MMS is provided on the MMS Homepage.


The current version of MMS is available from the MMS Homepage. Gunzip the file and extract the tarball into some convenient directory (we'll call this directory DIR from now on). Type:


If you are using a shell other than bash, this command may not work. If it does not, try:

setenv MMSROOT DIR/mms_v160

where DIR is the name of the directory to which you saved the original file. Now open mms_v160/bin/mms.sh in your favorite editing program. Change line 61 to the directory in which MMS is installed (DIR/mms_v160). Change line 63 to your home directory ($HOME) or wherever you want the mask files to be saved. MMS is now installed!


Now run the mms.sh shell script (make sure that the file is executable; if it is not, type chmod +x mms.sh). To do this, type


If you are not using the bash shell, type:

bash mms.sh


Most masks are designed based on fits image data with a high-quality WCS solution (at least in a relative sense, absolute WCS precision is less important). Click on Open in the File menu to open an image. Note that by default the image is assumed to be in the .mms/PREP/ directory. It is convenient to place images in that directory, rather than navigate to another location. Note that alignment stars (see below) should be selected from this same image.

Once the image loads, it is often useful to reset the scaling to better see faint objects. The scale parameters are set with numbers in the Low: and High: entry boxes on the left side of the Skycat window.

An alternative to an input image is to use a local catalog with coordinates for the objects. Click on Local Catalogs in the Data-Servers menu and chose Load from file to select a local catalog. By default this catalog is assumed to be in the .mms/PREP/ directory. This catalog needs to be in Skycat format.

Finally, one can also use image data from various public sources. In the Data-Servers menu, mouse over the Image Servers sub-menu and pick your favorite sky survey. If you don't have a favorite sky survey, Digitized Sky (Version II) at ESO or ... at STScI is a good choice, depending on your geographical location. Type in the right ascension, declination, and equinox and click Get Image.

For any of these options, after the image or catalog loads click on the Init Mask from the MODS menu. The white box that appears is the MODS field of view.


First make sure that the slits you will be placing are the correct size. To select the size, find the Config / Layout sub-menu under the MODS menu and pick the length and width of the slits under the appropriate sub-sub-menus. Note that the default is a 1x10 arcsec slit and this is a reasonable choice.

Before you begin to place slits, it is worthwhile to identify the alignment stars and guide star(s) you will use, particularly if your field is at high galactic latitude. The details of how to select these stars are provided in the next subsection below. It may be advantageous to select these objects first.

You can now place slits by clicking on the targets you want to observe. The Center Slit option on the Config / Layout submenu may also be helpful. The slit will appear as a rectangle and MMS will draw a band into which the spectrum of the target will fall. Note that you will not be able to place slits with overlapping bands. If you used an input catalog, rather than an image, the Auto-Slit option in the MODS menu is a quick way to place slits on the targets.

If you wish to delete a slit, click the middle button in the region directly to the left of the slit. MMS will ask if you are sure you want to delete the slit before doing so. To zoom in and out, use the big Z and small z buttons in the bottom left.


You need to select at least one guide star so that the telescope can properly track your targets. Click on the MODS menu and mouse over the Guide Stars sub-menu. Click add. MMS will draw a red box on the image; this is the region that the guide probe can see. Try to pick guide stars outside of the MODS field of view.

To pick a guide star, click Pick object in the Enter Object pop-up window. Find a nice star in the image and click on it. Then click Enter in the Enter Object window. To pick more guide stars, repeat this process, although only one is necessary. When you are finished, close the guide stars window.

Next pick alignment stars to properly register the mask with the sky. In MODS, unlike in LUCI, the alignment stars are simply square 4x4 arcsec slits. To start, first change the slit width and slit length to 4 arcsec. Then follow the same procedure you used to place slits on objects to mark the alignments stars. A good magnitude range is r = 15 to 18 mag. Such stars are very easy to see in a short acquisition exposure, yet are unlikely to saturate. Given that we are in the early stages of mask alignment with MODS, we presently recommend a minimum of 5 alignment stars distributed around the edge of the field.


Once you have finished placing the slits, selected alignment stars, and have chosen at least one guide star, click on the ProjectName option on the Config / Layout sub-menu to name the mask. Then click on the Save mods button in the MODS menu to save the mask. Note that the software will complain that no reference objects were selected. Simply ignore these error messages and click on OK as they are not relevant to MODS masks. The gbr and mms files will be saved in $HOME/.mms/SET/. (The .mms folder may be in a different location depending on where you set the path to in line 63 of mms.sh.

Return to: [ MMS Home | LBTO | MODS at LBTO ]

Updated: 2011 March 24 [pm]