Single-exposure WPHot-derived vs Flux-weighted centroid source positions (NEOWISER - v7.5)

Below we summarize differences between the positions of (mostly compact/point-) sources derived from PSF-fit photometry and then independently derived using flux-weighted centroids in the x-y system of single exposure frames. The goal is to explore the accuracy of the PSF positioning for profile-fitting. This is coupled to the accuracy of the astrometric/distortion calibration since WPHot (mdex) positions are first natively derived and refined on the sky, and then mapped to the x-y system for comparison with the image-derived centroids. The offsets quoted in the figures below represent trimmed medians with uncertainties derived from half the 84^th - 16^th percentile range per-axis divided by √N.

Here are the frame and source filters used:

  * > 35 deg from the moon,
  * |glat| > 15 deg,
  * |elat| < 84 deg,
  * saadist > 5 deg
  * no smeared frames (by eye)
  * w1mpro>=8.1  &  w1mpro<=15  &  w1rchi2>=0.3  &  w1rchi2<=2  &  w1snr>=5
  * w2mpro>=7.0  &  w2mpro<=14  &  w2rchi2>=0.3  &  w2rchi2<=2  &  w2snr>=5

Figure 1a - W1 CRYO PSFs and 3-parameter SFPREx. Click to enlarge.	Figure 1b - W1 NEW (neowiser) PSFs and 10-parameter SFPREx. Click to enlarge.
Figure 1c - W2 CRYO PSFs and 3-parameter SFPREx. Click to enlarge.	Figure 1d - W2 NEW (neowiser) PSFs and 10-parameter SFPREx. Click to enlarge.