IOC Task Cookbook:
24 Micron Spectral Leak Check

Principal: Karl Stapelfeldt
Deputy: Marcia Rieke
Data Monkey(s):
Priority: Necessary
Downlink Priority: Normal
Analysis Time: 1 week
Last Updated:

Objective

Measure high spatial frequency PSF structure indicative of short wavelength spectral leaks in the MIPS 24 micron filter

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 wil be a bright red AGN or asteroid. Each source will be observed using multiple dithers in a pattern similar to that used for MIPS photometry. This 14 position pattern will then be repeated a total of 8 times, each with an offset of 1/8 pixel in the scan mirror direction. The resulting dataset will subsample the PSF by a factor of 8 in one dimension, which should yield sensitivity to spatial structure in the PSF due to transmisison at wavelengths as short as 3 microns. Detector latency requires that we do NOT simply observe the target and then shift 1/8 pixel; by observing all the standard dither positions, at least 20 sec should elapse before the source is observed again near its latent image. Since spacecraft slews will produce pointing jitter equal to the 1/8 pixel sampling goal, we elect to use an IER which observes a single column of 7 dither positions placed by the scan mirror motion, and then complete all 8 subpixel repeats; then move the spacecraft to the second column of photometry dither positions in a similar way.

Data Collected

The data collected will be similar to a standard photometry AOR, except that only a single column of dither positions will be executed in a cycle. 3 sec exposures will be used. The result will be images 14 field positions taken with 1/8 pixel substepping, or a total of 112 frames.

Data Reformatting Requirements

Array Data Desired:

24 µm

Data Reformatting Option:

Special Instructions:
Preference is for multiple extended fits files. Each would contain 7 DCEs comprising a single column of dithers from the MIPS photometry frame table. There would be 8 such files from one column (each offset by 1/8 pixel), and aonther 8 from the second column.

Task Dependencies

Calibration Dependencies

Output and Deliverable Products

The outputs will be one-dimensional power spectra of the blue source and red source PSF structure. These will be compared to each other, and power spectra of TinyTIM simulations, to measure or place limits on the filter transmission at wavelengths between 5-20 microns.

Data Analysis

For each of the two source types, a subsampled PSF will be built up at each of the 14 dither positions. These will be collapsed into 1 dimension and fourier transformed. The same analysis will be performed on idealized SIRTF TinyTIM PSFs which lack red leaks.

Software Requirements

Actions Following Analysis

An instrument status note will be written for the SSC webpages.

Failure Modes and Responses

If the AGN target is surrounded by extended structure, this would render the red source measurements useless. A new AGN would need to be selected and the observation repeated.

Additional Notes