IDP3 for SPITZER

IDP3 now has a special menu for functions that will mainly interest people using SPITZER data. It is also capable of loading data in the MIPS format.

On this page:


The downloaded version of idp3 has all the SPITZER options available. If your version does not automatically have the "SPITZER" Menu at the top right of the Main Display Page, you will need to edit your "idp3_preferences" file. Set the parameter "dospitzer=1".

You will still need the libraries described on the Set up Page.

Loading MIPS Files

Unmosaicked MIPS data has to be handled a bit differently because there can be several images per fits file. Each "observation" is one fits file, with the first extension used for header information and the other extensions are different images taken during that observation.

Here is a test 24 micron data file: idp3_test.24.fits.

On the Main Display Window, go to File/Load Mips. Choose "idp3_test.24.fits". Put in "*" to select all of the images, and hit "Enter".
You will see the star in 14 different pixel locations (2 images overlap with previous ones.)
Use Images/Align by WCS on the Main Display Window to align the star by the world coordinate system.

Aligning MIPS Data

For an even more precise alignment, you will need to realign by centroids.
The first thing you will need is a Region of Interest. So on the Main Display Window click and drag a square around the star, and the ROI Window will appear.

Turn off all of the images except the Reference Image.
Select the mouse mode to be Radial Profile. Click in the center of the star and drag the circle out until the star is surrounded. The Radial Profile Widget should appear. Next you will need to

Repeat until the position of the center stops changing.

Now turn all the images back on. In the ROI Window use Plot/ReAlign by Centroids.

If you would like to save a fits file of the Median,Sigma Clipped Median or a Sigma CLipped Mean of the 16 images of star, go to the Images Menu on the Main Display Window and pick the option you would like. You will be prompted for the name of the fits file that will be written.

Getting PSF's for MIPS

When the images were ReAligned by Centroids the text file "idp3_test.24_tinytim.lis" was written. This file contains a list of the original x-y coordinates of the centroid for all of the 16 images and the name that will corespond to each of the PSF's in those location. For example, "idp3_test.24_01_psf" will go with the image of the star that is in extension 1.

You can now load this list into STINYTIM to create PSF's at each of the locations on the detector that correspond to the centroids of the images of the star. You will get 16 PSF's named "idp3_test.24_01_psf" and so on.
For this example, you can download the PSF's here: idp3_test_psf.fits.tar.gz.

NOTE:For version 2.6, you will need to change the values in the Edit SPITZER Parameters menu to match the example shown below.

If the original 16 images are still being displayed, remove them by going to the File/Delete Images menu on the Main Display Page. At the bottom of the Delete Images Window, chose Mark All then Delete.

On the Main Display Window, go to the SPITZER menu and chose Load PSFs. Then chose the same file that was put into STINYTIM, "idp3_test.24_tinytim.lis". This will load both the original idp3_test.24.fits along with the PSF's created by STINYTIM. The original images will also be subsampled to match the resolution of the PSF's. In this case, by a factor of 4. This can be changed by selecting File/Edit Preferences on the Main Display Window. At the bottom of the Edit Preferences Window, chose SPITZER Parameters. The "Zoom Factor" is the resampling factor.

The PSF's will be automatically subtracted, and the first pair will be displayed. (This is loading 32 images, so it will take some time.) Once you are satisfied with the alignment of all of the pairs, you can turn all of them ON on the Show Images Window. Then on the Main Display Window, chose SPITZER/Align MIPS. This will align all of the images of the star and the PSF's.

To save this work to a file, go to SPITZER/PSF Subtract and Median. You will then be prompted for the name of the fits file where this image will be saved.

NOTE:If you have your own PSF that corrisponds to the star, simply edit the "filename_tinytim.lis" file to have the name of your file corresponding to the proper x-y coordinates. Also change the parameters in the Edit SPITZER Parameters menu. (See below)

WCS Centroids

If the stars that you would like to line up have the same World Coordinates, there is now an easier way to align them.
The ROI Plot Menu now has two new options: Ref-WCS Centroids and Ind-WCS Centroids. Both of these work in basically the same way, but there are some differences. "Ref-WCS Centroids" assumes that the reference point (ie. CRPIX and CDMATRIX) are for all of the images are the same as those for the Reference Image. The CRVAL's can be different for each image, so the RA and DEC of the CRPIX can be different. The "Ind-WCS Centroids" does not assume that the reference point and the World Coordinate information are the same for each image , so it will find the location of the star with respect to the reference points on the individual images. This is what you want to use if there is any rotation of the field of view or if the CRPIX and CD-Matrix are different.

The steps are as follows:

  1. Turn off all images except for the Reference Image.
  2. With the mouse in Radial Profile mode, click on the center of the star and drag outward, to make a circle that encompasses the star.
  3. Fit the FWHM by pushing the Calc FWHM button.
  4. Choose which method of centroiding you would like to do and then push the Centroid button.
  5. Repeat steps 3 and 4 until the FWHM stops changing.
  6. Turn on all of the images that you would like to align.
  7. On the ROI Widget, select Plot/Ref-WCS Centroids OR Plot/Ind-WCS Centroids . This will find a centroid on the star in all of the "ON" images that are at the same World Coordinates as the star in the Reference Image.
  8. Now align the stars by using Plot/Align by Centroids. All of the images should line up.
SPITZER Preferences

To find this window, on the Main Display Window choose File/Edit Preferences and at the bottom of that wiget choose SPITZER Parameters.

The Zoom Factor (Science Images) will determin the amount of subsampling done to the original image so that the resolution will match the PSF.

The next three options go with the Radial Profile of the images of the star. The Target Radius should be located just outside the Airy Ring. The inner and outer radii will form an annulus of pure background. So the Background Inner Radius should be out a bit from the Target Radius, and the Background Outer Radiusshould be still larger than that.

The PSF Radius uses the subsampled scale. To have the same aperture as the Target Radius for the star, the PSF Radius should be equal to (Zoom Factor) times the (Target Radius). So in this example, a Zoom Factor of 4 times a Target Radius of 5 yields a PSF Radius of 20.

The XCenter and YCenter give the location of where TINYTIM has made the PSF. This will also be on the subsampled scale. TINYTIM will make the PSF close to the center of the array. In this example the original array is 128 by 128. So with a Zoom Factor of 4, the new scale is 512 by 512 which has a center at (256,256). As you can see the PSF X and YCenter are close to that, but not exactly. The exact numbers were obtained by finding the centroid of the PSF. This will be the same for every PSF generated by TINYTIM at the Zoom Factor of 4. It will change only if the Zoom Factor is changed.

If you would like to try using the star with the debris disk in the MIPS format to do the exercises on the Example Page, you can get that version here: souce_mips.fits

If you have any questions or comments about this page, please feel free to email Myra Blaylock at blaylock@as.arizona.edu.