IOC Task Cookbook:
70 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 70 micron filters

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 AGN. Each source will be observed using multiple dithers in a pattern similar to that used for MIPS photometry. At the default image scale, the 10 position pattern will then be repeated a total of 8 times, each with an offset of 1/8 pixel in the scan mirror direction; at fine scale, the 8 position pattern will likewise be repeated 8 times. The resulting datasets 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 10 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 10 sec should elapse before the source is observed again near its latent image. Since spacecraft slews will produce pointing jitter equal, we elect to use an IER which observes a single column of 5(4) 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. The above procedure will be employed both for coarse and fine scales.

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 10 field positions taken with 1/8 pixel substepping, or a total of 80 frames in default scale; and 8 field positions taken with 1/8 pixel substepping, or a total of 48 frames in fine scale.

Data Reformatting Requirements

Array Data Desired:

70 µm

Data Reformatting Option:

Special Instructions:
Preference is for multiple extended fits files. Each would contain 5/3 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 10-30 microns.

Data Analysis

For each of the two source types, a subsampled PSF will be built up at each of the 10/8 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 spectral leaks. The movement of the PSF core across pixel boundaries is the key discriminant of a spectral leak: In the absence of leaks, the energy in the core should move slowly across the pixel boundary as the scan mirror makes 1/8 pixel steps.

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 not dominated by a single central point source, this would render the red source measurements useless. A new AGN would need to be selected and the observation repeated.

Additional Notes