The Ohio State University
College of Mathematical & Physical Sciences
Department of Astronomy

MMS User's Manual

Mask Design Software for MODS

Introduction

Installation

Differences between MMS and LMS

Introduction

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 MMS.

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.

Installation

The current version of MMS is available here:

MMS-v1.6-20110825.tgz

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 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 MMSROOT, e.g.

setenv MMSROOT $HOME/mms_v160

One can then run the software with the command:

bash $MMSROOT/bin/mms.sh

Differences between MMS and LMS

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.

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.'

Instrument Configuration

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 as 4.00".

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' diameter. 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 view.

Output Files

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 are:

mods.N.name.epsf: encapsulated postscript

mods.N.name.mms: ascii text file

mods.N.name.gbr: Gerber file

These files are written by default to the $HOME/.mms/SET/ directory. 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 gerbv.

How to Submit Masks

Send the Gerber (.gbr) and mms (.mms) files to your Partner Coordinator. The Partner Coordinator will then ship all of these files to slitmasks@lbto.org. More information is available on the LBTO Science Operations Homepage.

Change Control

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.