Temporal Pointing Variations of The Solar Dynamics Observatory's HMI and AIA Instruments on Sub-Weekly Time Scales

Achieving sub-arcsecond co-registration across varying time-lines of multi-wavelength and instrument images is not trivial, and requires accurate characterization of instrument pointing jitter. In this work we have investigated internal pointing errors, on daily and yearly time-scales, occurring across the \textit{Solar Dynamics Observatory}'s (SDO) {\it Atmospheric Imaging Assembly} (AIA) and { \it Helioseismic Magnetic Imager} (HMI). Using cross-correlation techniques on AIA 1700\,Å passband and HMI line-of-sight (LOS) magnetograms, from three years of observational image pairs at approximately three day intervals, internal pointing errors are quantified. Pointing variations of $\pm$\,0.26$\arcsec$ (jitter limited) and $\pm$\,0.50$\arcsec$ in the solar East-West ($x$) and North-South ($y$) directions, respectively, are measured. AIA observations of the Venus June 2012 transit are used to measure existing coalignment offsets in all passbands. We find AIA passband pointing variations are $< ΔX_{CO} >$\,$=$\, 1.10$\arcsec$\,$\pm$\,1.41$\arcsec$ and $< ΔY_{CO} >$\,$=$\, 1.25$\arcsec$\,$\pm$\,1.24$\arcsec$, when aligned to HMI's nominal image center, referred to herein as the CutOut technique (CO). Minimal long-term pointing variations found between limb and correlation derived pointings provide evidence that image center positions provided by the instrument teams achieve single pixel accuracy on time-scales below their characterization. However, daily AIA passband pointing variations of $\lesssim$\,1.18$\arcsec$ indicate autonomous sub-arcsecond co-registration is not yet fully achievable.

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