The Ohio State University
College of Mathematical & Physical Sciences
Department of Astronomy
OMS User's Manual
Mask Design Software for OSMOS
- 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
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 .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.
- The ESO SkyCat Tool
One can then run the software with the command:
- setenv OMSROOT $HOME/oms_v160
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.
- bash $OMSROOT/bin/oms.sh
Field of View
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.'
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.
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.
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
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.
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
These files are written by default to the $HOME/.oms/SET/
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
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.
- osmos.N.name.epsf: encapsulated postscript
- osmos.N.name.oms: ascii text file
- osmos.N.name.gbr: Gerber file
- Current 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.
We are very grateful to the LUCI team for supplying the LMS code.
The LMS code is based on the ESO FIMS code.
- 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
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Updated: 2012 March 2 [pm]