Science Operations

Masks

Facility Masks

Each MODS reserves the first 12 mask slots for the standard facility slit masks which includes imaging stops, segmented long slits, and calibration masks that are always available in each MODS instrument. MODS1 and MODS2 are nearly identical, although MODS1 contains a DarkMask in slot1, while this slot contains the 0.6 arcsec long slit in MODS2 due to slot 5 not being usable.  The gerber files (input files for the Mask Manufacturing Unit, see below) are also included for the standard facility masks.  To view them you will need an application that can open gerber files, such as Cuprum (free version available).

Position MODS1 MaskID MODS1 Description MODS1 Partner MODS2 MaskID MODS2 Description MODS2 Partner
1 DarkMask Blank mask for a dark block Facility LS5x60x0.6 (Gerber) 0.6-arcsec segmented long-slit Facility
2 SieveMask (Gerber) Pinhole imaging sieve Nr3 Facility SieveMask (Gerber) Pinhole imaging sieve Nr3 Facility
3 Imaging Empty frame for imaging stop Facility Imaging Empty frame for imaging stop Facility
4 LS5x60x0.3 (Gerber) 0.3-arcsec segmented long-slit Facility LS5x60x0.3 (Gerber) 0.3-arcsec segmented long-slit Facility
5 LS5x60x0.6 (Gerber) 0.6-arcsec segmented long-slit Facility  NOT USABLE NOT USABLE
6 LS5x60x0.8 (Gerber) 0.8-arcsec segmented long-slit Facility LS5x60x0.8 (Gerber) 0.8-arcsec segmented long-slit Facility
7 LS5x60x1.0 (Gerber) 1.0-arcsec segmented long-slit Facility LS5x60x1.0 (Gerber) 1.0-arcsec segmented long-slit Facility
8 LS5x60x1.2 (Gerber) 1.2-arcsec segmented long-slit Facility LS5x60x1.2 (Gerber) 1.2-arcsec segmented long-slit Facility
9 LS60x5 (Gerber) 5.0-arcsec spectrophotometric long-slit Facility LS60x5 (Gerber) 5.0-arcsec spectrophotometric long-slit Facility
10 PinholeSlit Pinhole Slit Facility PinholeSlit Pinhole Slit Facility
11 Pointing Mask MODS Pointing Mask (40″) Facility Pointing Mask MODS Pointing Mask (40″) Facility
12 LS5x60x2.4 (Gerber) 2.4-arcsec segmented long-slit Facility LS5x60x2.4 (Gerber) 2.4-arcsec segmented long-slit Facility

Installed Custom Masks

The remaining 12 mask slots are available for custom-designed mask from our users, and are inserted and removed according to demand.  Below are the currently installed masks.

Position MODS1 MaskID MODS1 Description MODS1 Partner MODS2 MaskID MODS2 Description MODS2 Partner
13 531956 mods.3.g20d25ep2.mms LBTO 531956 mods.3.g20d25ep2.mms LBTO
14 Do Not Use Do Not Use Empty Position Empty
15 531713 mods.2.g00d25ep.mms LBTO 531713 mods.2.g00d25ep.mms LBTO
16 Pointing Mask MODS Pointing Mask (108″) LBTO Pointing Mask MODS Pointing mask (108″) LBTO
17 532732 mods.4.g04d25ep.mms LBTO 532732 mods.4.g04d25ep.mms LBTO
18 515404 mods.37.r06d80ep.mms LBTO 515404 mods.37.r06d80ep.mms LBTO
19 Do Not Use Do Not Use Empty Position Empty
20 585146 mods.25.kopo2.mms INAF 585146 mods.25.kopo2.mms INAF
21 Empty Position Empty Empty Position Empty
22 Empty Position Empty Empty Position Empty
23 Empty Position Empty Empty Position Empty
24 Empty Position Empty Empty Position Empty

Mask table updated: Oct 24, 2024

Masks scheduled to be installed in the near future are listed (requires VPN access):
http://wiki.lbto.org/bin/view/Instrumentation/FutureMODSMOSMasks

Mask Properties and Slit Tolerances

Masks are 230 ± 0.1 mm square to cover a 6 arcmin field of view. The mask curvature contains a 1040mm spherical radius which results in a 12.8mm sag from the center of the mask to the corner. This curvature is so they follow the curved telescope focal plane.

The best image quality is in the 4.5 arcmin diameter circle centered on the field. Outside this central region, the resolution and width of the spectrum will be somewhat degraded. The substrates that form the masks are electroformed on a spherical mandrel with NiColoy, which is a proprietary Nickel-Cobalt alloy used by NiCoForm with a nominal thickness of ~150 microns.

The properties and tolerances of the spectroscopic slits or apertures are summarized below:

 

Width 0.15-1.2mm
Length <10mm (typ)
Orientation ±30°
Shape Arbitrary polygon or circle
Width Tolerance ±15um
Position Tolerance ±15um
Edge Roughness ±1.8um RMS over 180um

Masks are often designed with slits packed way too close together, either in the vertical direction, or sometimes in both vertical and horizontal directions. As a rule of thumb, please keep any space between slits (and reference stars) to about 1.8 millimeters (about 3”). If slits are too close, there is a risk of losing the bridge between them, which creates a very oddly shaped slits. If a user is unsure, please contact us (or have the PI contact us) prior to the deadline.

Mask Manufacturing and Laser Cutting

LBTO has a dedicated universal laser cutting workstation (Mask Manufacturing Unit aka MMU), which has been since installed at the University Research Instrumentation Center (URIC) located at the University of Arizona.


The GERBER file is converted to machine code (.pgm file) for the Mask Manufacturing Unit where the blank mask substrate is cut.

Mask Installation

Masks are installed in the instruments internal cassette upon request.

Mask exchanges for MODS are part of daily operations and can be performed for masks on hand on short notice, unlike LUCI which are scheduled well in advance.

A database listing all cut previously cut masks kept on site is available here, for users who desire to use previously cut masks and wish to check the availability.