Stars show a marked tendency to be in systems of different multiplicity, ranging from simple binaries and triples to globular clusters with several 10,000's of stars. The formation and evolution of multiple systems remains a challenging part of astrophysics, and the contributions in this book report on the significant progress that had been made in this research field in the last years. The reader will find a variety of research topics addressed, such as the dynamical evolution in multiple stars, the effects of the environment on multiple system parameters, stellar evolution within multiple stars, multiplicity of massive stars, pre-main sequence and intermediate mass stars, multiplicity of low-mass stars from embedded protostars to open clusters, and brown dwarfs and extrasolar planets in multiples. This book presents the proceedings of the ESO Workshop on Multiple Stars across the H-R Diagram held in the summer of 2005.

Zusammenfassung
The ESO workshop Multiple Stars across the H-R Diagram was held in Garching on 1215, July 2005. The topics included observations of multiple stars from ground and space, dynamical and stellar evolution in multiple systems, e?ects of the environment on multiplicity, formation and early e- lution of multiple stars, and special components of multiple stars (chemically peculiar stars, blue stragglers, brown dwarfs, etc.). Stars show a marked tendency to be in systems of di?erent multiplicity, 7 ranging from simple binaries and triples to globular clusters with N?10 . Modern observations give a frequency of binary and multiple stars in the Galactic ?eld of up to 70%, and between 5% and 20% of these systems are at least triple. There is evidence that the degree of multiplicity increases with primary mass. Many known multiple systems are too wide to have s- ni?cant physical interaction between their components. However, tidal and N-body dynamical interactions are important even in relatively wide s- tems and probably lead to the shrinkage of inner orbits. This sets the stage for spectacular evolutionary processes such as Roche-lobe over?ow, me- ers, supernovae, formation of special components, etc. Only recently did we realize that some of these processes require at least three stars. Theformationofmultiplesystemsremainsadi?cultandchallengingpart of astrophysics, although it has been addressed at the Workshop only brie?y.

Inhalt

Evolutionary Processes in Multiple Systems.- Dynamics and Stability of Triple Stars.- Multiple Stars: Physics vs. Dynamics.- Gliese 225.2: An Old (Stable?) Quadruplet.- Multiple Stars: Designation, Catalogues, Statistics.- Radial-velocity Studies of Certain Multiple Systems.- Spectral Disentangling Applied to Triple Systems: RV Crt.- Evidence for Rapid Variability in the Multiple System 68 u Her.- DG Leo: A Triple System with a Surprising Variety of Physical Phenomena.- A Spectroscopic Study of HD 208905.- The Suspected Binarity of the Nearby Flare Star Gl 424.- The Ecology of Dense Star Clusters with Binaries.- The Formation of Multiple Stars.- Population of Dynamically Formed Triples in Dense Stellar Systems.- Interferometric Studies of Multiple Stars.- Interferometric Orbits of New Hipparcos Binaries.- New Facts about ? Velorum: Fewer but Larger Components.- Speckle Interferometry of Two Low-mass Triple Systems in the Solar Neighbourhood.- Tertiary Companions to Close Spectroscopic Binaries.- Spectroscopic Subcomponents in Visual Double Stars: The Most Probable Values of their Physical and Orbital Parameters.Application to the System WDS 14404+2159.- Multiple Stars in the Field.- Multiplicity of Chemically Peculiar Stars.- Multiplicity of Contact Binary Stars.- Extrasolar Planets in Double and Multiple Stellar Systems.- Homogeneous Comparison of Directly Detected Planet Candidates: GQ Lup, 2M1207, AB Pic.- Searching for Planets Around Stars in Wide Binaries.- Multiplicity at the Very Low Mass End of the H-R Diagram.- Spectroscopic Companions of Very Young Brown Dwarfs.- The Observed Multiplicity of Low-mass Stars: From Embedded Protostars to Open Clusters.- High-order Multiplicity of PMS Stars: Results from a VLT/NACO Survey.- Accretion onto Binary YSOs Through Gapfrom Their Circum-binary Disk.- The Nearest Pre-Main Sequence Multiple Stars.- A Study of the Young Quadruple System AO Vel with a ZAMS Eclipsing BpSi Primary and PMS Companions.- Multiplicity of Massive Stars.- The Triple System ?1 Orionis A in the Heart of the Orion Trapezium Cluster.- The Primordial Binary Population in OB Associations.- Multiplicity of Early-type Stars in the Field: Progress Report.- Search for Low-mass Companions to X-ray Emitting A-type Stars.