MODS Slit Masks
Contents
- Overview
- Mask Design and Manufacture
- Standard Facility Slit Masks
MODS has a 24-position slit mask storage cassette that can be loaded by
instrument support personnel during the afternoon. There are three
types of slit masks:
- Standard Facility Slit Masks
- These are imaging stops, segmented long slits, and calibration masks that
are always available in each MODS instrument. They are stored in the first
9 slots in the mask stroage cassettes, and may not be removed except under
unusual circumstances.
- User-Designed Slit Masks
- Each MODS may hold up to 15 custom user-designed slit masks per night.
MODS observers create these masks using the MMS
program and submit them a couple of weeks in advance of their observing run to
LBTO for cutting and transport to the telescope.
- Instrument Testing Masks
- These are custom masks used during instrument testing and evaluation
in the lab and on the telescope. They include 2D and 1D pinhole grids,
ghost image masks, back-looking test patterns, and special mask frames
used for optical alignment. Some are available in matched pairs, others
as one copy shared between instruments.
The MODS Mask Simulator (MMS) program is
provided to design custom slit masks. It is a modified version of the
LMS program for LUCI, and works much the same way as LMS. The MMS webpage describes the differences between
LMS and MMS, otherwise we follow the LMS manual. One day in the future
these two programs will merge into a single, unified mask design program
for LUCI and MODS.
MMS creates 3 files:
- MMS File (.mms)
- ASCII text file describes the mask. It is used by the data reduction and
script generation tools.
- Gerber file (.gbr)
- This is the file used by the laser cutting machine to actually
make the mask.
- PostScript file (.epsf)
- An encapsulated postscript file that shows your mask design.
Instructions for submitting masks for manufacture are given in the
MMS manual.
Slit masks are laser machined in spherical mask blanks made of
150-micron thick electroformed NiColoy®, a
proprietary electro-deposited Nickel-Cobalt alloy produced by the mask
blank vendor, NiCoForm, Inc. of
Rochester, NY.
The blanks are then mounted in special handling cells and transported to
the LBT where they are then loaded into the mask cassette by observatory
instrument support personnel before your observing run.
The first 9 slots in each MODS slit mask cassette are reserved for the
standard facility slit masks. A table of the masks is given below. The
links are to PDF and Gerber files for the masks.
| Position |
MaskID1 |
Description |
Files |
| 1 |
DarkMask |
Dark Mask (uncut mask shell)2 |
n/a |
| 2 |
Imaging |
6x6-arcminute Direct-Imaging Field Stop3 |
n/a |
| 3 |
LS5x60x0.3 |
0.3-arcsec Segmented long-slit4 |
PDF |
Gerber |
| 4 |
LS5x60x0.6 |
0.6-arcsec Segmented long-slit |
PDF |
Gerber |
| 5 |
LS5x60x0.8 |
0.8-arcsec Segmented long-slit |
PDF |
Gerber |
| 6 |
LS5x60x1.0 |
1.0-arcsec Segmented long-slit |
PDF |
Gerber |
| 7 |
LS5x60x1.2 |
1.2-arcsec Segmented long-slit |
PDF |
Gerber |
| 8 |
LS60x5 |
60x5-arcsec spectrophotometric "fat slit" |
PDF |
Gerber |
| 9 |
SieveMask |
0.3-arcsec Pinhole Sieve Mask (focus & geometric calibration) |
PDF |
Gerber |
Notes
- MaskID is the name used to select the mask in MODS observing
scripts (e.g., "slitmask ls5x60x0.6").
MaskIDs are case-insensitive and have no spaces in them. It is
stored in the MASKNAME keyword in image FITS headers.
- The dark mask is used to block the view out of the
instrument/telescope focal plane to measure internal scattered light,
and to provide protection for the post-slit field lens when the
instrument is put to sleep.
- The imaging field-stop mask ensures proper baffling at the edges of
the full science field of view.
- Long-slit masks are segmented long-slits composed of a line of five
(5) 60-arcsec long slits separated by 3-arcsec wide struts (with slit
centers at 0, ±63, and ±126-arcsec from the nominal science field
center). This strut is required to ensure the structural integrity of
the spherical mask shells over their 190mm length so that the slit maintains
its shape in 3 dimensions. The PDF files above will let you view each of the
segmented long-slit masks.
Return to: [
MODS Project Page |
OSU LBT Page |
OSU Astronomy Home Page
]
Updated: 2011 May 4
[rwp]
