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OMS User's Manual

Mask Design Software for OSMOS

[OMS Screen Shot]


Differences between OMS and LMS
How to Submit Masks
Change Control


OMS (OSMOS Mask Simulator) is a mask design software package for the OSMOS instrument. OMS is a modified version of the LMS (LUCI Mask Simulator) software for OSMOS. Potential users of OMS are strongly encouraged to become familiar with the excellent LMS User's Manual before beginning to work with OMS. This OMS manual assumes familiarity with LMS and only describes the key Differences between LMS and OMS.

Joe Antognini has written a Beginner's Guide to MMS with a basic introduction to use of the MMS software. OMS and MMS are nearly identical, so this guide should also be useful for first-time OMS users. Please note that this does not describe all of the capabilities of OMS (or MMS), which are only described in the LMS manual.


The current version of OMS is available here:
OMS 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. OMS has been tested with skycat version 3.1.2 for MacOS. The main web page for SkyCat at ESO is here:
The ESO SkyCat Tool
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 OMSROOT, e.g.
setenv OMSROOT $HOME/oms_v160
One can then run the software with the command:
bash $OMSROOT/bin/oms.sh

Differences between OMS and LMS

OMS has a OSMOS 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.

Field of View

[OMS Screen Shot]

The figure above shows a screen shot of OMS 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 detector footprint. The white square marks the 18.5' by 18.5' field for imaging and multi-object spectroscopy. The square at the top of the field is a reference box 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. OSMOS Mask ID numbers begin with the number '5' to distinguish them from LUCI masks, which start with a '9.'

Rotator Angle

Masks may be designed for the range of position angles allowed by the telescope instrument rotator. Please see the MDM Hiltner Rotator Guide for these limits. OSMOS is usually installed such that the access hatches (e.g. for slit mask installation) are facing East (toward the garage door) when the telescope instrument rotator is at 0 degrees. At this orientation the slit PA and telescope rotator angle are equivalent. This also corresponds to the TEL.ROT.OFFANGLE keyword in the .oms file.

Instrument Configuration

The choice of instrument configuration does not matter at present, as OMS does not 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 OSMOS menu has a range of length and width options. The default is an 1" by 10" slit.

[OMS Alignment Boxes]

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 5" by 5" 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 1" by 10" slits. Note that the length of the two boxes is specified as 4.00" (because this image is from a MODS mask, not an OSMOS mask).

We recommend a minimum of 5 alignment stars and that these stars be distributed in the 4x1k ROI (approximately the central 18' by 4' region). This will lead to the best solution for the rotation and translation in the fewest iterations at the telescope, as well as minimize readout time for the acquisition images. The alignment stars should also be selected from catalogs (or images) with the same astrometric solution as the targets. Finally, the alignment stars should be in the magnitude range r = 14-16 mag to avoid saturation in a short acquisition image, yet bright enough to obtain a precise centroid measurement.

We recommend that observers avoid placing slits on the East side of the field when using the Medium Blue VPH grism. This is because the East side corresponds to the outer or blue slit option and only fairly blue light will be dispersed onto the detector. See the section on Wavelength Calibration in the manual for further details.

Guide Star Selection

[OMS Guide Star Selection]

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). This patrol field is presently not correct. Please simply plan to identify a suitable guide star at the telescope.

Output Files

OMS produces three output files. The rootname of these files has the format: osmos.N.name where N is some integer and name is the Project Name (if specified). These output files are:

osmos.N.name.epsf: encapsulated postscript
osmos.N.name.oms: ascii text file
osmos.N.name.gbr: Gerber file
These files are written by default to the $HOME/.oms/SET/ directory. The postscript file contains a drawing of the mask design and may be useful to have at the telescope to check against the as-built mask. The OMS 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 the best reference to the mask design, as this is the file used to cut the mask. One viewer for Gerber files is gerbv.

How to Submit Masks

Send the Gerber (.gbr) and oms (.oms) files to Paul Martini, who will then arrange to have the masks cut and shipped to MDM in advance of your run.

Change Control

Current version: v1.7-20130218
Minor change in plate scale
Previous version: v1.6-20111008
Minor modifications to maintain similarity to MMS
Previous version: v1.6-20110607
Minor modifications to allow slit placement all the way to the edge of the field.
Previous versions: v1.6-20110525:
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 mode.


OSMOS Home Page
MDM Observatory
MMS Home Page
MODS Webpage at LBTO
LMS User's Manual
LUCI Webpage at LBTO
The ESO SkyCat Tool
gerbv A Gerber (RS-274X) viewer


We are very grateful to the LUCI team for supplying the LMS code. The LMS code is based on the ESO FIMS code.

Return to: [ OSMOS Home Page | MDM Observatory | MODS at LBTO ]

Updated: 2012 March 2 [pm]