PSF Reconstruction: Part IThe PSF “Core”

• Primary Goal: Derive PSFs for point source detection and PSF fitting photometry.

• Secondary Goal: Derive PSFs to use in point source subtraction - can reduce signal from PSF by a factor of 1000 or more.

Data Set

• IOC task IRAC 500 in Campaign R

• Imaged 7th magnitude IRAC standard p73.0324, a 7.2 mag K0III star

• Used HDR mode since there will be some saturation in Bands 1 and 2.

• Observed stars at 25 positions on the array, with a 4x4 grid of dithers at each position spaced by 1.5”

• 16 AORs resulting in 800 images per band

Distribution of Pointings(for Channel 2)

Data Reduction:1st iteration1. PSFs are found and a centroid is measured in each

image.

2. The data for each of the 25 position is separated. Typically there are sixteen 0.6 sec and 10.4 sec frames per position.

3. A 51x51 pixel region centered on the PSF is extracted.

4. For each of the 25 positions, the data are drizzled onto a grid with 0.3” pixels with a drop size of 0.5. Uses Richard Hook’s drizzle library linked to IDL.

Position Sampling

Combining 0.6 and 12 sec Frames

Variations in the PSF(for Channel 1)

Lower Left Upper Right

Data Reduction: Iteration II(work in progress)

1. Take PSF derived from interation 1.

2. Derive new centering using a least square fit of PSF with each image.

3. Compare drizzled PSF with each image to detect cosmic rays and reject.

4. Recombine with drizzle.

Dynamic Range in Channel 1

Log

1e-55e-5

1e-4

Finishing1. Finish cosmic ray rejection and re-centering.

2. Produce next generation in all four channels.

3. Test in Source Extractor.

4. Re-run with cleaner data.

5. Try other reconstruction techniques (Fourier??)