[AstroPy] proper motion and parallax

[gonghang.naoc]

Hi evryone,
I have a series of  images for a single target.  So a series of positions
can be got.
How to get  proper motion and parallax? The two values are coupled,
right?  So I have to fit them simutaneously.  The apparent orbit of a
nearby star should be a Cycloid, (parallax makes circular motion and pm
makes uniform rectilinear motion), right?
I am totally a layman. Or simplely, is thee any pythonic modules which can
derive pm and parallax?

Thank you.
best
hang
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