For adaptive
optics and phase referencing for interferometry to work at their best, a bright
point source as reference object is required within the isoplanetic patch of
the science object. Given the small size of the isoplanetic patch, the number
of reference objects for PRIMA around a science object is restricted. This work
package uses the following approach: first select a reference object, followed
by looking for science objects within the isoplanetic patch of that reference
object. (Richichi et al., 2001).