Stellar Multiplicity – a historical review

Stellar Multiplicity - a historical review

Many, if not most stars, live in binary or multiple systems, and studies of stellar multiplicity have a long and fascinating history. starting in earnest more than 200 years ago, with the catalogs of the Herschels (father and son) and the Struves (father and son). Later in the 20h century the story continues with the visual double star surveys by Burnham and Aitken, and others, followed by Curtis & Campell’s first spectroscopic binary star catalog (1905) at Lick Observatory. I will highlight in passing the discovery of the Doppler effect (Doppler 1842) and the interstellar medium (Hartmann 1904) which involved spectroscopic binary star observations. The classic books of Aitken (1935) and Batten (1973) used to be the bible of binary and multiple stars, The radial velocity work of Abt & Levy (1976) and Duquennoy & Mayor (1991) on a volume limited sample of solar-type binary systems (and their statistics) had a major impact to revive the interest in binary stars and their formation. Another relatively recent spark was the first catalog of hierarchical multiple systems by Tokovinin (1997). The most recent study of the multiplicity of a complete sample of all field stars in the solar neighborhood (within 25pc) is the paper by Raghanvan et al. (2010).

I will try to review these milestones and the significance of the improved and more complete observational data, based on the advent of modern techniques like speckle interferometry and adaptive optics plus VLTI and recently adding astrometry results from GAIA. I will discuss old and new binary field star statistics (companion frequency, mass ratios, orbital lperiods, etc) and their implications for the theory of star formation. One of the conclusions is that stellar multiplicity is a strong function of Main Sequence stellar mass or spectral type.

I will also discuss recent observational results on the binary characteristics of young stars, both low mass and high mass stars, and ideas on the orgin of stellar multiplictiy in general. I will draw upon review papers from the binary star IAU Symp No. 200 published 25 years ago, of which I was the organizer and chief editor, as well as from Ann. Rev. A & A publications and from several Protostars & Planets review articles since.

I will end with future questions and challenges, such as the origin of the Trapezium stars in the Orion Nebula and how to find exo-planets in multiple stellar systems such as the hierarchical triple system alpha Centauri.

Sebastián López
Coordinador de Coloquios
DAS/UChile  – slopez@das.uchile.cl