The Binary Mode of Star Formation

Hans Zinnecker 
Astrophys. Inst. Potsdam

Observations over the past decade have shown that most young stars are 
born in binary or multiple systems.  The binary mode of star formation 
seems to be the rule rather than the exception.  This has important 
implications for our understanding of the Initial Mass Function,
the star formation history, and the formation of planetary systems,
some of which will be discussed in this talk.

After a brief historical introduction, we will review our current knowledge 
about the binary nature of young stars (frequency as a function of mass, 
distributions of mass ratios and separations, dependence on star formation 
environment, proto-binary systems).  Then we will demonstrate the astrophysical 
potential of young binaries (e.g. deriving dynamical masses, testing 
pre-Main Sequence tracks, constraining the fragmentation process).
We will also raise the subject how to synthesize the galactic field star 
population mix using young vs. old binary statistics.  Finally we will 
take a look at the future of young binary star research, with a view to the 
forthcoming facilities (Keck, VLT, and LBT interferometers, as well as ALMA 
and SMA).