Rolf Chini : Stellar Multiplicity across the Mass Spectrum
The talk will review the latest results from our multiplicity studies on three flux- and/or volume-limited samples of 250 O, 540 B
and 500 F, G, and early K stars, i.e. for a mass range from 0.8 to 80 solar masses. Our data – mainly obtained at the observatory
near Cerro Armazones – comprise several thousand high-resolution (R ~ 50.000) spectra and indicate that more than 80 per cent
of stars with masses above 16 Mʘ form close binary systems while this fraction drops to 20 per cent for stars of 3 Mʘ. It is likely
that this apparent decrease is an observational artifact caused by an increasing mass ratio M2/M1 with decreasing primary mass.
This is corroborated by our results from the FGK stars, where we find a solid increase of the fraction of binary and higher level
systems as a function of the primary mass suggesting that the single-star fraction may already converge to zero at the transition to
the A stars. We also find new eclipsing O star binaries by means of optical multi-epoch photometric monitoring. Multi-epoch
infrared imaging of nearby FGK stars reveals a substantial fraction of common proper motion companions turning a number of
bona fide spectroscopic binaries into higher-level systems. Eventually results from a Lucky Imaging study with a spatial
resolution of 0.1” are presented. Summarizing our results we raise the question whether stars are born as singles.
Instituto de Astronomia
Viernes 15 de Noviembre 2013