Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-10-26
Astronomy and Astrophysics
Astrophysics
PhD thesis, University of Amsterdam, 2006 (very low resolution). Full-resolution PDF available at http://dare.uva.nl/en/record
Scientific paper
Observations over the last decade have indicated that a large fraction of the stars are part of a binary or multiple system. For our understanding of star formation it is therefore of crucial importance to characterise the outcome of the star forming process in terms of binary parameters. This thesis describes the recovery of the primordial binary population in the nearby OB association Sco OB2. The current binary population in Sco OB2 is first recovered using two adaptive optics surveys (ADONIS, NAOS-CONICA), a literature study, and a detailed analysis of the selection effects of visual, spectroscopic, and astrometric binary surveys. Our results indicate a binary fraction close to 100%. The mass ratio distribution (among A/B primaries) has the form f(q) = q^-0.4, while random pairing is excluded. The semi-major axis distribution has the form f(log a) = constant. Due to its youth and low stellar density, the current binary population of Sco OB2 is very similar to its primordial binary population. Our study further indicates a small brown dwarf companion frequency and a small substellar-to-stellar companion frequency among A and B type stars. These properties, often referred to as the brown dwarf desert, are a natural result of the mass ratio distribution in Sco OB2. The embryo ejection scenario is not necessary to explain observations. The brown dwarf desert may be ascribed to an excess of planetary companions, rather than by a lack of brown dwarf companions.
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