Implement proper motion

[nicholasjannsen]

I open this issue on behalf of Magali as she pointed it out.

Since the PIC (>= 2.1.0.1) now only include proper motion estimates (at least for tPIC stars), it was raised if it would be possible to implement the proper motion of stars.

This could implemented as an extra file input with the columns (time [s], pmRA [deg], pmDec [deg]) which simply updates the previous exposure (RA(t+1), Dec(t+1)) value for each star. To be consistent with the way PlatoSim defined multiple variable source files injected into a field of stars, we should define a properMotionFile.txt being equivalent to a variableSourceFile.txt and for each source in the catalogue (requested a proper motion change (since one would probably only add this to stars with a high proper motion), we define a file for each source with the columns (time [s], pmRA [deg], pmDec [deg]). The good thing about proper motions is that we do not need to save a 2-yr duration and 25-s cadence file (of typically ~300Mb storage), we just need to define two time points and PlatoSim can make a linear interpolation between the two proper motion points.

[JorisDeRidder]

Could you elaborate how this feature could be useful, i.e. what its use case would be?

[nicholasjannsen]

I think it generally very useful since your star light will leak out of the mask over time for high proper motion targets. For magali, the usefulness is to test the PSF photometry algorithm as the centroid is one of the key parameters in the fit. I don't see this issue as high priority, but it good to have on the list so we also keep track of what PlatoSim also "can't do" yet.