Ultimate Scattered Light Levels, 70 um

Principal: Karl Gordon
Deputy: James Muzerolle
Data Monkey(s):
Priority: Normal
Downlink Priority: Normal
Analysis Time: 48 hours
Last Updated:

Objective

This task will measure two effects of scattered line for the 70 µm. One, the amount of light scattered into the FOV when the array is pointing towards the dark position(s). Two, the amount of light scattered into the FOV from a star located off the array near the edge of the FOV.

Description

Part 1: The importance of scattered light in the dark measurements of the MIPS 70 µm array can be measured by pointing SIRTF towards a very bright extended region while performing the standard 70 µm dark measurements. Usually, the dark measurements are taken while SIRTF points at a dark region of the sky. By pointing at a bright region, the amount of scatterd light will be measured by differencing the results of this task with those obtained from the standard dark task.

Part 2: Scattered light due to bright sources located just off the edge of the array FOV can be measured by placing a very bright point source near the edge of the FOV and taking standard DCEs. This task will search for reflections in the detector plan which cause glints to be seen when bright stars are beyond, but near the edge of the FOV (ie., in the projected FOV, but not in the detector FOV). A glint is a brightness (probably sharper than the PSF) which appears only at specific off-FOV positions of the bright star. Such glints are possible because the lyot stop is larger than the 70 µm array FOV. This test will be done only for the coarse scale as similar glints will exist for both the coarse and fine scales.

A bright star will be placed so that it is 42 (radial extent of the airy ring in the 70 µm PSF) arcsec off the edge of the array FOV for the standard photometry AOR. The fact that the standard photometry AOR puts the star 61.5 arcsec (crossscan) and 69 arcsec (scan) from the center of the array is needed to do this task properly.

The bright star choosen in TY Dra with a 60 µm IRAS flux of 7.55 Jy (a 100 µm flux of 2.48 Jy and a 24 µm flux of 43.9 Jy). TY Dra is in the CVZ.

Data Collected

The part 1 dataset will be the standard 70 µm dark IER, except pointing towards a very bright region of the sky.

The part 2 dataset generated for this task is a standard AOR

Data Reformatting Requirements

Array Data Desired:

70 µm

Data Reformatting Option:

Special Instructions:

Task Dependencies

Calibration Dependencies

Output and Deliverable Products

The first output of this task is are a measurement (or upper limit) on the scattered light level in the 70 µm dark position.

The second output of this task is the location of any glints near the edge of the 70 µn;m array FOV.

Data Analysis

All the datasets will be run through mips_sloper & mips_caler. The resulting images will be examined for glint artifacts. Any glints found will be noted and the locations where the source was when the glints appeared will be listed. IDL will be used for this purpose (general purpose image viewer).

Software Requirements

Actions Following Analysis

The level of the scattered light at the dark position will put limits on where SIRTF should be pointed when performing routine dark calibrations.

If glints are found then the observer handbook will need to be updated.

Failure Modes and Responses

If this task fails, the reason of the failure needs to be determined and corrected. This task would then need to be rerun.

Additional Notes