24 µm PSF Characterization

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

Objective

Measure the field dependence of the MIPS 24 µm point spread function, for both blue and red astronomical sources.

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. Each source will be observed on a grid of 5 columns by 7 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 10 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 35 positions over the field of view: 

       -------------------------
       | *         *         * |
       |                       |       Approximate distribution of
       | *         *         * |
       |      *         *      |
       | *    *    *    *    * |         35 source positions to be
       |      *         *      |
       | *    *    *    *    * |    
       |      *         *      |       used in 24 µm PSF characterization
       | *    *    *    *    * |
       |      *         *      |
       | *         *         * |
       |                       |
       | *         *         * |
       -------------------------
AT EACH OF THESE 35 POSITIONS, WE OBSERVE THE STAR 64 TIMES over an 8x8 grid stepped by 1/8 pixel. To avoid latency effects on the imageIn each column, we observe the target at seven dither PSF positions, then move the scan mirror up by 1/8 pixel, and repeat 7 more times. We then move to the next column, and do all 7 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.

Data Collected

A huge amount of photometry-like data will be acquired: 35x64 3 sec exposures.

Data Reformatting Requirements

Array Data Desired:

24 µm only

Data Reformatting Option:

Special Instructions:
Preference is for multiple extended fits files. Each would contain 35 DCEs, one for each field position. There would be 64 such files, one for each 0.125,0.125 subpixel offset.

Task Dependencies

Calibration Dependencies

Output and Deliverable Products

MIPS data will be reduced by the task lead, and made available to a consulting optical expert. Deliverables will be sets of Zernicke polynomial coefficients for different positions in the 24 micron field of view.

Data Analysis

Optical consultant will fit the PSF images with models to derive field-dependent aberrations in the 24 µm optical train.

Software Requirements

Actions Following Analysis

Written report will be generated on PSF properties of the camera. Results to be supplied to SSC and observer teams concerned with accurate source extractions.

Failure Modes and Responses

Stable and repeatable telescope pointing is needed to properly subsample the PSF. Program might have to be repeated if significant pointing drifts take place.

Additional Notes

Consulting agreement being finalized with John Krist (STScI) to serve as optical data analyst