Multiple Stars in the Field

Brian D. Mason & William I. Hartkopf
US Naval Observatory, Washington (USA)

When examining the statistics of multiple stars in the field, 
especially coming from visual binary star point of view, 
several problems present themselves. First, and most 
importantly, is distinguishing between physical multiples and
optical pairs. Establishing physicality is not a simple 
"binary" response as there are degrees of certainty. We 
discuss some of the reasons for caring about non-physical
pairs, as well as the tools for establishing or more 
correctly identifying apparent kinematic properties which 
hopefully result in dynamic solutions. The Washington Double 
Star Catalog, the Visual Orbit Catalog, and the US Naval 
Observatory speckle program are used as examples in many of 
these cases. The magnum opus for a global characterization of
these systems is the Washington Multiplicity Catalog (WMC). 
Selected as a catalog and a method to "develop a simple, 
unambiguous, flexible, and computer friendly designation 
scheme for stellar companions (including planets)" at a 
multi-commission meeting in Manchester (GA24). This was 
re-affirmed at Special Session 3 in Sydney (GA25) by 
Commissions 5, 8, 26, 42, 45 and the Working Group on 
Interferometry when a sample (1/2 hour band) WMC was produced.
An all-sky WMC is in progress the binary sources utilized in 
its construction and the implications resulting from it with 
regards to multiple stars in the field are discussed.