MDP Manual

2024.3.28 Ver.1.1 Kentaro Aoki

2002.3.27 Ver.0.9 Yoshihiko Saito

2002.4.3 Ver.0.9e Youichi Ohyama
2002.12.31 Ver.1.0e Youichi Ohyama (for tilt slit version)
 

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0. Introduction

This document describes the usage of the MDP program.

1. Preparation

1.0 Software requirement

• IDL5.4 or later
• IDL software and data files provided by the FOCAS team
  • Mask Design Program (wmdp3.pro)
  • FOCAS Image Processing Program (bigimage.pro)
  • Mask design parameter file (DATA/*{MIT}{SITe}*.dat for MIT and SITe chip data. Now we are using MIT chips.)
  • See here for more detail.
• FITS images of the target field
  • Normally images taken with FOCAS (pre-images) are used as a base of the mask design. Any filters can be used for the pre-imaging.

1.1 Preparing the images

A pair of two images is obtained per single exposure since two 2Kx4K CCDs (hereafter, chip1 and chip2) are simultaneously read out to form 4Kx4K image. One need to use a n accurately combined "big" image for the mask design, and is made in the following way.

1. Type "idlde" on your computer where IDL is installed. (idlde = IDL Developing Environment)

2. Type "bigimage" within the command-line box at the bottom of the IDLDE window, and then press <return> key.

3. Choose the appropriate bigimage options on the check-button window:

4. Within the window "Input Distortion Data File", select an appropriate distortion data file. Currently use the data file for MIT chip (*MIT*.dat).

5. Just click "OK" in the "dialog_input" window.

6. In "Objects" window, input two filenames for chip1 and chip2 in selection box as "<chip1_filename>,<chip2_filename>", or select two files at once by dragging the mouse.

7. Input a output filename in "Output File Name" window.

8. Wait for a while for image processing (~5-10 min.).

See here for more detail of the bigimage software.

Notes

• You need to select "distortion correction" in all cases. Only after correcting the distortion, you can change the center position of the mask for more flexible designing.
• Since only the target "positions" are essential in designing the masks, only rough image reduction (even just overscan subtraction) will give a good result in most cases. However, if your targets are faint, you must take care of the proper data reduction.
• Overscan correction is always performed even with the "Bias subtraction" option. Never choose "bias subtraction" and "overscan subtraction" options at a same time.
• Never select "CCD -> Sky coordinate transformation" option to make images for MDP since MDP do the design in the CCD coordinates.
• When you perform your own data reduction, take care not to change the geometry of the images. For example, never remove the overscan region. This would cause the wrong combined images since the "bigimage" software assumes the original image dimension.

1.2 Target selection

Choose your targets on the combined image. It is better to think about the priority of your targets at this step since some objects might need to be removed due to slit-overlapping etc.

Find CCD coordinates of your targets on the combined (chip 1+2) images:

• Use your favorite FITS image viewer (e.g., SAOimage, ds9, Skycat) to find out the object coordinates.
  • In Skycat, "Pick Object" procedure might be useful to find the coordinates.
• Use "Sextractor" program for automatic target extraction. Then use a simple AWK program to convert the format of the sextractor output file (cat) to the MDP format. A sample AWK program is provided with the FOCAS data reduction package.
• Any other ways of the target selection can be used. Do it in your favorite way.

Make your input file for the MDP program. This file contains information of your targets and their slit shape. Note, however, this file is not always required: You can design all slits interactively within the MDP.

• Mask design file (*.mdp) is a simple ASCII file specifying object coordinates (x, y in pixel unit), slit width, length, and the slit position angle.
• Priorities of the slits are also specified in this file which will be used (if you wish) in the automatic slit rejection procedure within the MDP.
• Format of the MDP file:

• One object per line, and number of lines equals to the number of slits + holes.
• PA is defined in the CCD coordinates (not in the SKY coordinates) and is expressed in degree whose positive/negative direction is in a normal geometry (counter-clockwise). For example, PA=0 for normal slit (perpendicular to the dispersion axis), and 45 degree for the tilted slit whose right side is raised by 45 degree in the MDP.
• In case of the tilted slit, the slit width means the slit width projected into the dispersion direction (to keep the effective velocity resolution to the same for all slits with various tilt angle), and the slit length means the projected length on the X coordinate. Be careful.
• Although PA for the alignment holes has no meaning, explicitly specify "0" in the file for consistency. Also, you need to specify two diameters for the alignment stars.
• Slit/Hole shape is specified by "B" for box=slit or "C" for circular=alignment hole.
• Alignment holes can be added within the MDP, and you do not have to specify the alignment holes in *.mdp file.
• All remaining characters after the end of the shape determination (B or C) are regarded as a comment. Comments can be reviewed within the MDP while editing the mask, and might be useful in deciding which slits to be chosen.
• Priority can be used when doing automatic slit rejection within the MDP. See below for the detail.
  • Smaller number means higher priority.
  • Priority of alignment holes added within the MDP is zero (0), i.e., higher priority than newly added slits.
  • Priority of slits added within the MDP is three (3), i.e., lower priority than that for alignment stars.
  • If you do not want to perform automatic slit rejection, set all priorities to one (1) in *.mdp file.

2. MDP start-up

1. Type "idlde" in your computer.

2. Type "wmdp3" (mdp version 3 using widget) within the command line box at the bottom of IDLDE, and press <return>. A window with several buttons show up.

3: Click on "*MIT*.dat". Within the window "Input Distortion Data File", select an appropriate distortion parameter file.

Currently use the data file for MIT chip (DATA/*MIT*.dat).

4: Click on "badpixel.dat". Within the window "Input CCD Bad Pixel Table*, select an appropriate bad pixel file ("currently badpixlst.dat").

5. Select "File/Read FITS image" from a pull-down menu, and select a combined FITS image in "Input Bigimage" window. A FITS image will show up.

6. Select "File/Read MDP file", and select a MDP file you created as shown above in "Input MDP file" window.

If you do not have a MDP file, just push "Cancel" button for interactive mask design for all slits. In this case, one dummy slit will be set.

7. Select "Option/Grism select", and select an appropriate grism-order sorting filter combination in "Grism Selection" window.

8. Click on "Redraw" or "Draw Slit" buttons to see the image and the slits.

9. Now you are ready to start editing the masks.

2.1 Explanation of the Main MDP window

A) Pull-down menus

File: Tasks for file I/O
Option: Grism selection, Set parameters for slits used in adding slits interactively within the MDP, etc.
Special menu: Tasks for data reduction software. Out of service in version 3.
Print: Print out menu: Out of service in version 3.

B) Main window

Your FITS big-image is shown in the CCD coordinates (i.e., CCD pixel coordinates), not in the sky coordinates (NSEW).
Wavelength is in vertical direction. (upper = bluer, lower = redder)

Items shown:

Main FITS image display (entire view of the image at reduced size)
Slit marker (small elongated rectangle on targets)
Spectra marker (long rectangle elongated vertically)
0th-order light marker (small rectangle at upper side of the slit. No 0th-order light in a certain combination of the grism used. optional)
Slit ID number (small number just right of the slit pointers: optional)
FOV circle (large circle showing the available area for MOS design: optional)
CCD Chip position (large square showing the available CCD chip area: available when FOV circle option is chosen)
Gap between chips (a long rectangle elongated vertically showing the insensitive area just right of the FOV center: optional)
Bad columns (some narrow vertical lines. There are several bad columns in the chip 1, and one in the chip 2. Note that only big (worse) bad columns are shown.)


C) Mode selection switches

Object pick-up mode (apply Gaussian fitting on the image around the clicked position, or simply adopt the clicked position as a final position)
FOV circle display switch
Slit ID display switch

D) Zoom image display

Display for zoomed (non-reduced) FITS image around the selected region for slit review. This display is also used for object selection by mouse.

E) Buttons for controlling the image display

Display intensity adjustment, image redraw button, etc.

F) Buttons for slit editing

Buttons for editing slits and alignment holes.

G) Information panel

Panel showing default slit parameters used when adding slits within the MDP, and current mouse positions.

3. Mask Design

In the followings, detailed procedures on how to design the mask interactively is described.

We recommend to design your masks following the order as we show below. Of course, you may repeat any tasks until you are satisfied with your design.

You may want to adjust the intensity scale of the FITS image display to see faint targets. In this case, push "Change Intensity Scale" button, and input new MIN and MAX cut-off levels for the image display. This setting is for both the main and sub (zoom) windows.

3.2 Set the mask center position

Set the center coordinates of the mask. Sometimes you may want to shift the mask FOV center position for optimal slit distributions within a mask, e.g., to avoid any spectra fall out of the CCD or on the insensitive gap between the chips and to maximize the number of slits.

You can change the mask center position later if you wish.

If you change the FOV center position, then the RA, DEC coordinates for the MOS pointing in the observing nights also need to be modified accordingly. You need to submit a list of new RA, DEC coordinates together with mask design files (see below) at the end of the mask design.

Note: currently the FITS WCS coordinates of the bigimage do not work correctly. Please check the coordinates carefully.

Operation

1. Click a "Draw FOV" button. (Sometimes you need to click it twice.)
2. Input center coordinates (X, Y in pixel) of the FOV in Xcen and Ycen boxes. You do not have to change the radius of the FOV since it is set to the 6 arcmin FOV by default. This option is only for experts.

3.3 Design of alignment holes

Tips for designing the alignment holes

• Choose at least four (4) stars within the FOV.Try to locate alignment stars evenly over the FOV, i.e., locate two stars per chip, two stars at upper half and other two at lower half of the chips. See the following illustrations.
• Avoid locating stars closer to the FOV edge or near the CCD gap. [Our experience shows that it is more dangerous to place them around the CCD gap.] There might be a chance for them to be out of the observable area due to telescope pointing error, etc.
• To avoid damages of the alignment hole/star images due to bad columns, create the holes well away from the bad columns.
• Choose more than four (4) stars if possible in case of some unexpected troubles such as comic rays or bad columns of CCDs hitting some alignment stars/holes.
• Try placing alignment holes isolated. If holes are located at very close to the adjacent holes/slits, MOS pointing software may easily fail to detect them  automatically. Place a hole 2" (which is a typical hole diameter) or more away from its nearest hole/slit. If you can not do so, put a hole anyway there.
  

Example of BAD alignment hole distribution Only one star on the left chip and no stars at upper half of the chips.

Example of GOOD alignment hole distribution Stars are distributing over entire FOV evenly.

Operation

1. Push "Add Alignment Hole" button.
2. Click on the alignment star in a main image display for choosing the region around the star.
3. Click again on the alignment star in a zoom image display. Position of the alignment star is determined by Gaussian fitting with the initial guess of the clicked position.

• Selected star is displayed at the center of the zoom display as well as a small square (not a circle) if the fitting was successfully done.
• "Click-object" mode is not available for the alignment star since Gaussian fitting is required for better accuracy.

3.4 Design of slits

3.4.1 Add slits interactively

1. Select [Option]-[Change Default Parameters] from the top menu bar, and input "Default Slit Width" and "Default Slit Length" in arcsec unit in a "Parameter setting" window. Both length and width of each slit can be modified after locating the slits. The PA of the slits will be fixed to 0 here, but you may change it later.
2. Select a mode for the target selection at upper left of the MDP window. You may choose "pick-object" mode in which Gaussian fitting is used to find the object coordinates, or "click-point" mode in which mouse click position itself is used as the object coordinates. (If you are familiar with the skycat FITS viewer, you may understand why we call the Gaussian fitting as the Pick-object mode. "Pick-object" mode is suitable for point or compact sources, and "click-object" mode is for diffuse and extended sources.
3. Push "Add slit by click" button.
4. Click on the object on the main image display.
5. Region around the clicked position is shown on the zoom image display, and click on the target again on the zoom display. In "pick-object" mode, Gaussian fitting is performed around the clicked position, and the detected source is shown at the center of the zoom display as well as the rectangles for the calculated slit position.
6. In "click point" mode, click on your favorite position on the zoom display, and the image is re-displayed around the clicked position.
7. Regions occupied by the spectrum will be shown as an elongated rectangle both on the zoom and the main window.

3.4.2 Check/modify the slit/hole parameters.

There are four ways to check /modify the slit/hole parameters.

1. Click the region of your interest on the main image display, and the zoom image around the selected region is shown in the zoom image display.
2. Push "Show nearest slit" button and click on the image near your interest slit on the main image display. Nearest slit is found automatically, and the zoom image around the slit is shown in the zoom image display. A small pop-up window shows the slit information as well as the slit ID selected
3. Push "Show slit (ID)" button and then input the slit ID number shown beside the slit (this ID is shown only when the "show slit ID" switch is selected). The zoom image around the selected slit is shown in zoom image window. A small pop-up window shows the slit information as well as the slit ID selected.
4. Push "Show Slit List" button to make a slit list which displays all slit information as well as comments (if any). Radio buttons at the left of each slit ID number can be used to activate/delete slits/holes. Deleted slits/holes can be re-activated from this slit list later if you wish.

3.4.3 Slit overlap check

• Push "Slit overlap check" button to find out any slits where slits/holes overlapping is detected. The results are shown on a pop-up window.
• If the slit priorities are specified within the *.mdp file, slits with lower priority are automatically rejected when slit overlapping is detected.

3.4.4 Adjusting the slit length

Manual operation

1. Push "Change Slit Params" button and click near the slit you want to modify on the main image display. The nearest slit is automatically selected.
2. Input the new slit coordinates (X coordinates of the left and right side of the slit) and/or slit width/angle in the new popup window.
3. Push "redraw" button to see the updated slit design

Automatic operation

Automatic slit expansion can be applied to fill in the available space near the slit. MDP searches for any available space toward right from each slit, and expand the right edge of the slit to just left of the next slit. You can set the separation between the slits in "default parameter set" window (from the top menu bar).

Select [Option]-[Auto Slit Expansion] from the top menu bar.

Important

You can NOT undo this operation. Save the *.mdp file before applying the automatic expansion.

3.4.5 Deleting slits/holes

Case 1:

1. Push "Del Nearest Slit" button.
2. Click the region around the slit you want to delete on the main image display. The nearest slit is automatically selected, and deleted.
3. Push "Redraw" button to see the updated slit design.

Case 2

1. Push "Display Slit ID" button to see slit IDs on the image.
2. Push "Show Slit List" button. A slit list will show up.
3. Disable the slits you want to delete by clicking on the radio button just left of the slit. Then press "accept" button at the bottom of the list.
4. Push "Redraw" button to see the updated slit design.

3.5. Saving the results

3.5.1 Save *.mdp file

3.5.2 Save *.sbr file

Note

3.6 Quitting the MDP

3.7 Other notes

3.7.1 Dummy slit (0th slit)

3.7.2 Coordinate system convention

3.7.3 Care for extremely out-of-FOV slits

Slits far out of the FOV may cause some serious troubles in the slit cutting machine. Check your *.mdp file or *.sbr file before submitting them to the observatory. Check the warning message when saving the *.sbr file.

4. Take a snapshot image of MDP

5. Submitting the results

• *.mdp file
• *.sbr file
• snapshot image of MDP display
• X, Y coordinates (pixel) of the FOV center
  
• Fits images used for mask design.

6. Acknowledgment