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GMOS Mask Design Checks
This document is based on the procedures used by Gemini Staff to check GMOS MOS masks submitted by users. The document describes, step by step, the mask checking procedures.
- Before checking the masks
- Checking the masks
- Post-checking tasks
Before you start to check the masks
Standard naming convention for submitted masks
PIs have to use a standard naming convention when they submit the masks. This is to avoid confusion as to which mask name is associated with the ODF. The submitted masks should have the following naming convention: G(N/S)YYYYSQPPP-XX_ODF.fits (N/S indicates North or South). Here the YYYY is the year, S the semester, PPP is the program number and XX is the mask number (e.g. GS2007BQ038-01_ODF.fits). If the naming conventions are not the standard, then ask the PIs to remove the masks from the Observing Tool (OT) and re-submit them with the correct names. Note that the root names with the numbers (e.g. GS2007BQ038-01) correspond to the names of the masks that are added to the field “Custom Mask MDF’’ in the GMOS static component in the OT Phase 2. An example of a set of masks submitted with the wrong names is given in Figure 1.
Pre-imaging distribution for mask design checks
The pre-images required to check the masks are provided by the Gemini Staff. The processed images are uploaded using the OT file attachment facility.
Downloading the pre-images and the ODF files
PIs use the OT file attachment facility to upload the ODF fits files. Download the ODF fits files and the pre-images into your local computer using the Fetch button in the "File Attachment’’ window (see the example below). To download the fits files, the OT will ask for your NGO password. Verify that the PIs supplied the names of the pre-images used to create the ODF files. In the example below (Fig. 1), the name of the pre-imaging is inserted in the Description field in the File Attachment window. However, the description could be inserted also in a Note inside OT Phase 2 program.
Figure 1: File attachment window with the details about the submitted files (could be ODF fits files or finding chart). Note that in this example, the mask names are not the standard name. The Description Field shows the name of the pre-images used to generate the masks. The description could be also presented as a Note in the OT Phase 2 program.
Starting the Gemini Mask Making Software (gmmps)
To check the mask design, you have to install the gmmps program. Here we will assume that gmmps is installed in your computer and is working properly. Start gmmps. Go to File --> Open and load the distributed pre-imaging. Select the HDU 2 in the FITS HDU window (see Figure 2). You can adjust the intensity levels by using View --> Cut Levels. A 98% level should work fine in most of the cases (you can see in detail the bright and the faint objects).
Figure 2: Portion of the gmmps main window with the FITS HDUs (1) window.
For ODF fits file. Go to GMOS-MMS --> Convert ODF fits to catalog --> Convert ODF fits to Cat. File….…, and load the ODF fits file. A new window will be displayed (see Figure 3). This window contains information about the targets, i.e. ID, RA, DEC, XCCD, YCCD, slitpos_x, slitpos_y slitsize_x, slitsize_y, slittilt, MAG, priority, slittype, etc... The figure below shows the main parameters listed in the ODF fits file. Objects with priority "0’’ are the alignment stars (always in the first rows). The size of the alignment boxes are 2 x 2 arcsec and is constant. The slit width is given by the column "slitsize_x’’ (in the example is 0.75 arcsec) and the slit length is given by the column "slitsize_y’’ (arcsecs).
Figure 3: Window containing all the column of the designed mask (ODF). The column slitsize_x contains the slit width (in this example 0.75”). The alignment stars have slitsize_x, slitsize_y 2x2 arcsec and have priority 0.
Click Plot Slits to draw the slits over the image. Display the location of GMOS CCD gaps by clicking on Plot GMOS Gaps (see Fig. 3). The figure below (Fig. 4) shows the object slits (white and yellow), the alignment stars (cyan) and the GMOS gaps (blue) plotted over a GMOS image. The red rectangle indicates the mask area. No objects will be cut outside this area.
Figure 4: Object slits (white and yellow) with the alignment stars (cyan) , CCD gaps (blue) and the mask area plotted over the pre-imaging. This is the visualization used to check the masks.
Object Slits (science targets)
For tilted slits, slit tilt must be within 45 < tilt < -45 deg.
Nod & Shuffle masks
N&S MOS mask design requires special attention. There are two shuffling modes that you one choose from when observing with Nod & Shuffle: 1) Band-shuffling; 2) Micro-shuffling. Here we describe the two modes and show how to check the N&S MOS mask design.
Check that all the slits have the same length
Check that the minimum space between slits has at least the same length as the slit.
Figure 11: Example of a micro-shuffling mask (slit length of 2”).
gm> tprint maskname-01_ODF.fits prparam+ prdata-
With this command you will list the header parameters inside the masks. An example is given below.
Checking the Masks
You should not expect to find any problems with the mask design if the PI followed the mask design instructions. However, if you see any of the problems listed below, immediately contact the PI and request they design a new mask(s).