Fields 7-9 provide details of the position of the secondary component(s) with respect to the position of the reference component identified by the first digit of field 2, and thus provide a concise summary of the geometry of the system. For separations smaller than 10 arcsec, these relative positions are taken from the CCDM and thus from the IDS. For separations larger than 10 arcsec, the position angle and separation were deduced from the data on each component (for these systems, the relative positions are thus consistent with the absolute positions of the components).
For several thousand double systems, the relative position and
proper motion of the secondary components were computed (Brosche &
Sinachopoulos 1986, 1988a, 1988b), using all available observations
communicated by C.E. Worley from the USNO double star data base.