This procedure is used to fit
pairs to individual nights.
The list of nights is derived from the ones currently loaded, and they
are re-loaded (load_interferometry) despite the overhead in order
to allow data sets of the same night to be combined.
Initial estimates for
are obtained from
the orbital elements. The results are written to file fitnights.psn,
including fitted synthesized beam widths. This file is in the standard
astrometry format and can be read back into AMOEBA.