Simulated WISE PSFs incorporating geometric distortion during SUTR

Introduction

Scan-averaged PSFs in WISE are expected to suffer somewhat from the effects of geometric distortion over the focal plane as the scan mirror moves. This effect has been investigated for Band 1 by Eisenhardt (2006), using a Code V simulation of the WISE PSF shape. The latter was shifted according to a set of values in a distortion trajectories file, and summed after applying a set of weights appropriate to the "sample up the ramp" (SUTR) procedure. For the 9 scan mirror positions, the SUTR weights used were: -4,-3,-2,-1,0,1,2,3,4. As it happens, the latter values were incorrect for Band 1; they were actually the Bands 3 and 4 values.

Procedure

I have produced a set of simulated PSFs for all 4 bands using the same prescription as Eisenhardt (2006), which involved shifting and adding the Code V PSFs ("prf_out_2_3band#.dat", where # = 1,2,3,4) generated by Larson (2005).

The following set of SUTR weights were used:

Bands 1 and 2: 0, -7, -5, -3, -1, 1, 3, 5, 7

Bands 3 and 4: -4, -3, -2, -1, 0, 1, 2, 3, 4

For each band, the PSFs were centered at 3x3 grids of focal plane locations, based on the two configurations in the distortion trajectories file. Both configurations involve equally spaced focal plane positions in the following arrangement:

FP7 FP8 FP9

FP2 FP1 FP3

FP4 FP5 FP6

In Configuration 1, the spacing is 0.392 deg, so that the PSF center locations extend out to the edges of the focal plane. In Configuration 2, the spacing is 0.196 deg, i.e. the off-center locations go halfway out to the edges of the focal plane.

PSF Set

The PSFs are presented as FITS files, labeled by band, configuration and focal-plane position, using the naming convention: "psf_bandB_configC_fpN.fits", where B = 1,...4, C = 1 or 2, and N = 1,...9.

Each FITS header includes the keywords XFP and YFP which indicate the focal-plane coordinates (in pixel units; 1,...1024) of the PSF center.

Configuration 1:

Band 1: FP1 FP2 FP3 FP4 FP5 FP6 FP7 FP8 FP9

Band 2: FP1 FP2 FP3 FP4 FP5 FP6 FP7 FP8 FP9

Band 3: FP1 FP2 FP3 FP4 FP5 FP6 FP7 FP8 FP9

Band 4: FP1 FP2 FP3 FP4 FP5 FP6 FP7 FP8 FP9

Configuration 2:

Band 1: FP1 FP2 FP3 FP4 FP5 FP6 FP7 FP8 FP9

Band 2: FP1 FP2 FP3 FP4 FP5 FP6 FP7 FP8 FP9

Band 3: FP1 FP2 FP3 FP4 FP5 FP6 FP7 FP8 FP9

Band 4: FP1 FP2 FP3 FP4 FP5 FP6 FP7 FP8 FP9

Tar gzip file containing all 72 PSFs:

sutr_psfs.tar.gz

Note:

In generating the PSFs it was assumed that the DeltaXIM_PIX and DeltaYIM_PIX in P. Eisenhardt's distortion trajectories file correspond to image motion in the AXIS1 and AXIS2 directions, respectively, in the FITS files.