WFC3/IR Geometric Distortion - Time Evolution of Linear Terms w.r.t. Gaia DR3

TL;DR

This study analyzes the stability of WFC3/IR geometric distortion over 16 years using Gaia DR3 data, finding no significant linear evolution but noting periods of increased uncertainty linked to instrument jitter.

Contribution

It provides a comprehensive assessment of the temporal stability of WFC3/IR geometric distortion terms relative to Gaia DR3, highlighting the importance of ongoing calibration for high-precision astrometry.

Findings

No significant linear evolution in rotation, skew, or scale offsets over 16 years.

Periods of increased uncertainty in offsets correspond with instrument jitter from 2018 to 2021.

External telescope pointing inaccuracies dominate shift offset variations.

Abstract

We examine the relative offsets of the linear terms in the geometric distortion between WFC3/IR and the Gaia DR3 catalog using the Mikulski Archive for Space Telescopes (MAST) pipeline WFC3/IR to Gaia DR3 alignment solutions to assess temporal stability over the lifetime of the WFC3 instrument (2009-2024). We find a period of increased uncertainty and offsets in the rotation term between 2018 and 2021, as seen in a previous analysis of WFC3/UVIS linear geometric distortion (O'Connor et al., 2024), corresponding with a period of increased jitter. We find a similar pattern of increased uncertainty between 2018 and 2021 in the skew offsets to Gaia DR3, as well. We find no significant linear temporal evolution in the rotation, skew, or scale offsets between the WFC3/IR IDCTAB distortion solution and Gaia DR3 over the 16-year lifetime of the WFC3 instrument; however, we do see temporal evolution in the shift offsets (the difference -in pixels- between the IDCTAB and Gaia WCS positions), which are dominated by telescope pointing inaccuracy external to the WFC3/IR geometric distortion solution. For observers requiring high-precision astrometry, we continue to recommend that observers verify or improve image alignment using the tweakreg routine.