16588

The standard astrometric catalog in the field of globular cluster Omega Cen has been used to examine the geometric distortion of WFC3 UVIS and IR as function of wavelength in multicycle calibration programs over last 11 years of WFC3 on HST board. All observations from these programs have been reduced and provided the multi-wavelength geometric distortion in UVIS and IR detector. The derived geometric distortion coefficients implemented in the IDCTAB format are used in the HST pipe-line to correct for a virgul7% distortion in WFC3-UVIS and IR images down to <1%. Additional to multi-wavelength WFC3 geometric distortion comma all observations of Omega Cen taken through F606W and F160W UVIS and IR filters respectively during the last 11 years (all together 12 epochs) were used to look for time dependency of UVIS and IR geometric distortion and the effect of the scale change due to the thermal breathing. The results of the stability WFC3 geometric distortion published in WFC3-ISR-2015-02 (Kozhurina-Platais and Anderson comma 2015) comma WFC3-ISR-2019-09 (Martlin comma Kozhurina-Platais) comma have show that the UVIS geometric distortion is stable over 10 years on-orbit within 0.05 pixels or 2 mas in UVIS. The results of WFC3-IR published in WFC3-ISR-09-19 (M. McKay comma Kozhurina-Platais comma et al) have show that the IR geometric distorion is stable over 10 years on orbits within 0.1 pixel or 2 mas. The same observations were used to examinate the WFC3-UVIS and IR photometric changes with time ( WFC3-ISR-2020-05 comma Kozhurina-Platais comma Bagget). The purpose of this calibration proposal is to continue the monitor of the WFC3 geometric distortion stability of over time. The observations of Omega Cen through the UVIS F606W filter and the F160W IR filter will be used to derive the skew and scale terms of the geometric distortion and look for any secular changes over time.