The Ohio State University
College of Mathematical & Physical Sciences
Department of Astronomy
MMS User's Manual
Mask Design Software for MODS
- Differences between MMS and LMS
- How to Submit Masks
- Change Control
MMS (MODS Mask Simulator) is a mask design software package for the
MODS instrument. MMS is a modified version of the LMS (LUCI Mask Simulator)
software suitable for MODS. Potential users of MMS are strongly encouraged to
become familiar with the excellent LMS User's Manual
before beginning to work with MMS. This MMS manual assumes familiarity with
LMS and only describes the key Differences between LMS and
Joe Antognini has written a Beginner's
Guide to MMS with a basic introduction to use of the software. Please note
that this does not describe all of the capabilities of MMS, which are
provided in the LMS manual.
The current version of MMS is available here:
MMS is written in Tcl/Tk and has been tested on both linux and MacOS operating
systems. The version available here includes a linux binary for version 2.7.3
of ESO's SkyCat Tool.
Users of MacOS and other operating systems will need to download the
SkyCat binary appropriate to their operating system. MMS has been tested with
skycat version 3.1.2 for MacOS. The main web
page for SkyCat at ESO is here:
The .tgz file above will unpack into a subdirectory containing
all of the code. The path to this code should then be set to the
environment variable MMSROOT, e.g.
- The ESO SkyCat Tool
One can then run the software with the command:
- setenv MMSROOT $HOME/mms_v160
MMS has a MODS pull-down menu with similar options to the
LUCIFER pull-down menu for LMS. Once an image or catalog
has been loaded, the Init Mask option will draw an outline
of the MODS field, which is shown and described below.
- bash $MMSROOT/bin/mms.sh
Field of View
The figure above shows a screen shot of MMS immediately after Init
Mask has been selected (click on the image for a larger version).
The outlines are similar to those for LMS.
The large, blue rectangle is the 3k by 8k detector footprint. The
white square marks the 6' by 6' field for imaging and multi-object
spectroscopy. The five squares along the top of the field are reference
boxes that may be used in future versions of the mask alignment software,
although at present they are not used. The red rectangle in the upper left
corner is the location of the Mask ID number. MODS Mask ID numbers begin with
the number '5' to distinguish them from LUCI masks, which start with a '9.'
MODS masks may be used in either red-only, blue-only, or dual-channel
mode and there is a choice of either a grating or prism in either
channel. These choices do not matter at present, as MMS does not
presently calculate the dispersed wavelength range on the detector
for different disperser and filter combinations. In the future we
plan to include the footprint of slits in the dispersion direction.
This will be particularly valuable for the prism modes, as their short
footprint on the detector will allow placement of multiple slits
(tiers) in the dispersion direction.
Slits, Alignment Boxes and Reference Stars
Slits are assigned to objects in a similar manner to LMS. The
Config/Layout submenu under the MODS menu has a
range of length and width options. The default is an 0.6" by 10" slit.
Note that the instrument produces the best image quality in a 4.5' diameter
circle centered on the field. Outside of this region the resolution and
width of the spectrum will be somewhat degraded.
A significant difference from LMS is that mask alignment is accomplished
with alignment stars and there must be alignment boxes in the mask
at the location of these stars. Alignment boxes are simply implemented
as 4" by 4" slits. Before selecting alignment stars, set the slit width and
slit length to these values in the Config/Layout submenu. The
figure above shows an example of 2 alignment boxes in the upper left
corner of the field (click on the image for a larger version)
and two 0.6" by 10" slits. Note that the length of the two boxes is specified
The alignment stars should not be selected as reference stars in MMS. The reference star category is used by LUCI for mask alignment, but the MODS alignment software (modsAlign) does not use them. In fact, if the alignment stars are labeled as reference stars, it may be quite difficult to place a box on them.
We recommend a minimum of 3-4 alignment stars with r = 15-18 mag and that
these stars be relatively uniformly distributed within the central 5'
In principle only two stars are necessary to align a mask, but in practive
issues such as poor astrometric solutions, saturated stars, proper motions
that have not been corrected, poor placement of the stars (e.g. all in the
same quadrant), uncertain stellarity, and bad pixels/columns may impact one
or more stars. Five stars, all separated from each other by a few arcminutes,
is even better if you are not an expert or do not have complete confidence in
your astrometric catalog. Extra stars allow the observers freedom to eliminate
one or more problematic stars, if necessary. Note that the alignment stars
should be selected from catalogs (or images) with the same astrometric
solution as the targets.
The alignment stars should be in the magnitude range r = 15-18 mag to
avoid saturation in a short acquisition image, yet bright enough to yield a
precise centroid measurement.
The stars should be within the central 5' diameter because the delivered
image quality degrades outside of this region and it becomes progressively
more difficult to centroid properly, and thus calculate the correct rotation
and translation offsets. Stars outside a 5.6' diameter circle suffer such
significant aberrations that they should not be used for alignment.
A final suggestion: If you have extra space on your mask, and your targets
are quite faint (fainter than about 22 mag), consider placing a few extra
slits on brighter objects. These may provide valuable, additional checks on
the quality of the mask alignment at the telescope.
Guide Star Selection
Guide stars should be 12-15 mag, stars as faint as 16 mag may work
under dark sky conditions and in good seeing. The guide star selection process
is identical to LMS, although the patrol field geometry is different. Select
the add option under
the Guide Stars submenu. This will draw the guide star patrol
field, as shown in the figure above (click on the image for a larger
version). The patrol field is 5' by 4.5' and extends into the science
field such that the top of the patrol field is at the center of the field of
MMS produces three output files. The rootname of these files has the
format: mods.N.name where N is some integer and
name is the Project Name (if specified). These output files
These files are written by default to the $HOME/.mms/SET/
The postscript file contains a drawing of the mask design and is useful
to have at the telescope to check against the as-built mask.
The MMS file contains detailed information about the mask design,
including the mask center, position angle, Mask ID, and information
about each slit, alignment box, and guide star. This file is also useful to
have at the telescope, as it is used for mask alignment.
The Gerber file contains a description of the mask for the laser cutting
machine. It is essentially identical to the postscript file, although it
also contains the Mask ID. One viewer for Gerber files is
Send the Gerber (.gbr) and mms (.mms) files to your Partner Coordinator.
The Partner Coordinator will then ship all of these files to
firstname.lastname@example.org. More information is available on the
Science Operations Homepage.
- mods.N.name.epsf: encapsulated postscript
- mods.N.name.mms: ascii text file
- mods.N.name.gbr: Gerber file
- Current version: v1.6-20110825
- Fixed what may be a mac-specific bug in menus.tcl
- Previous version: v1.6-20110714
- Fixed bug with tilted slits, changed rootname of output files to just 'mods'
- Previous version: v1.6-20110221
- Initial, development version. While this version has been
used to successfully construct masks, it does not include all available
instrument modes. Specifically, it does not allow multiple tiers of slits
in the prism modes.
We are very grateful to the LUCI team for supplying the LMS code.
The LMS code is based on the ESO FIMS code.
- MODS Webpage at LBTO
- LMS User's Manual
- LUCI Webpage at LBTO
- LBTO Science Operations Homepage
- The ESO SkyCat Tool
- gerbv A Gerber (RS-274X) viewer
Return to: [
MODS at LBTO
Updated: 2011 November 28 [pm]