70 µm PSF Characterization

Principal: Karl Stapelfeldt
Deputy: Dean Hines, Jane Morisson
Data Monkey(s):
Priority: Desired
Downlink Priority: Normal
Analysis Time: One month
Last Updated:

Objective

Measure the field dependence of the MIPS 70 µm point spread function, using both blue and red astronomical sources, and for both the default and fine image scales.

Description

We will observe two sources with two known, but different colors. One will be a normal star with a Rayleigh-Jeans spectrum; the other will be a bright asteroid. Observations will be done with IERs in a mode similar to MIPS photometry. In default scale, each source will be observed on a grid of 5 columns by 5 rows, spread over the square FOV. Columns 2 and 4 will match exactly the positions of the source in the standard photometry AOT. Columns 1, 3, and 5 will be at non-standard positions near the left, center, and right parts of the FOV - going no closer than 3 pixels to the edge of the detector FOV. These three columns will NOT duplicate the source positions from photometry, instead they need to go closer to the edge of the FOV. Overall, this will give a grid of 25 positions over the field of view:

       -------------------------
       | *         *         * |      Approximate distribution of
       |                       |
       | *    *    *    *    * |        25 source positions to be
       |      *         *      |
       | *    *    *    *    * |       used in 70 µm default
       |      *         *      |       
       | *    *    *    *    * |       scale PSF characterization
       |                       |
       | *         *         * |
       -------------------------

AT EACH OF THESE 25 POSITIONS, WE OBSERVE THE STAR 64 TIMES over an 8x8 grid stepped by 1/8 pixel. To avoid latency effects on the image, we will observe the target at five dither PSF positions in a column, then return to the first position but offset by 1/8 pixel, repeat all 5 observations in a column, etc until all 8 subpixel steps have occurred. We then move to the next column, and do all 5 FOV positions for each of the 8 subpixel offsets. After going through all 5 columns in the FOV, completing 8x1/8 pixel vertical scans for each, we move back to column 1 offset by 1/8 pixel in the cross-scan direction, and repeat everything; come back to column 1 offset by another 1/8 pixel, etc until all 8 subpixel columns have been sampled. In fine scale, each source will be observed on a grid of 5 columns by 4 rows, spread over the square FOV. Columns 2 and 4 will match exactly the positions of the source in the standard photometry AOT. Columns 1, 3, and 5 will be at non-standard positions near the left, center, and right parts of the FOV - going no closer than 6 pixels to the edge of the detector FOV. These three columns will NOT duplicate the source positions from fine scale photometry, instead they need to go closer to the edge of the FOV. Overall, this will give a grid of 20 positions over the field of view:

       -----------------
       | *     *     * |      Approximate distribution of
       |               |       20 source positions        
       | *  *  *  *  * |       used in 70 µm fine
       |    *     *    |       scale PSF characterization
       | *  *  *  *  * |
       |    *     *    |
       | *     *     * |
       -----------------

AT EACH OF THESE 20 POSITIONS, WE OBSERVE THE STAR 64 TIMES over an 8x8 grid stepped by 1/8 pixel. To avoid latency effects on the image, we will observe the target at three dither PSF positions in a column, then return to the first position but offset by 1/8 pixel, repeat all 4 observations in a column, etc until all 8 subpixel steps have occurred. We then move to the next column, and do all 4 FOV positions for each of the 8 subpixel offsets. After going through all 5 columns in the FOV, completing 8x1/8 pixel vertical scans for each, we move back to column 1 offset by 1/8 pixel in the cross-scan direction, and repeat everything; come back to column 1 offset by another 1/8 pixel, etc until all 8 subpixel columns have been sampled.