There is significant flexure between the position of the slit and the guiding camera during a target visit. The flexure can introduce flexion of as much as 0.2-0.3 arcsec during two hours.
In 2019 we obtained engineering observations to characterize, measure, and modelled this flexure.
Procedure:
Calculate the RA and DEC of the slit center on each slit viewing camera image (scam). We can use astrometry.net for this. This software can be installed locally.
Calculate the RA and DEC of the guider camera center pixel
Correlate in time the scam and guider images.
Calculate the distance from the scam slit center and the optical guider center in mm (deltaX and DeltaY).
Extract the physical drive angle (ROTPPOSN) from each scam image
Create a table with the following data:
UT time | Scam image | Guider image | Delta X(mm) | Delta Y (mm) | ROTTPOSN |
Generate plots of Delta X and Delta Y vs ROTPPOSN
Model the change of DeltaX and DeltaY vs ROTTPOSN
Coordinate with Shui to format the model so that it can be used by Magiq