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.