Physical properties of seven binary and higher-order multiple OB systems

Analyses of multi-epoch, high-resolution ( R ~ 50 000) optical spectra of seven early-type systems provided various important new insights with respect to their multiplicity. First determinations of orbital periods were made for HD 92206 C (2\hbox{$.\!\!^{\rm d}$}022), HD 112244 (27\hbox{$.\!\!^{\rm d}$}665), HD 164438 (10\hbox{$.\!\!^{\rm d}$}25), HD 123056 A (~1314 d) and HD 123056 B ( -1 , which coincides with the radial velocity of the cluster NGC 6530. This fact, together with its distance, suggests the cluster membership of HD 164816. The OB system HD 318015 (V1082 Sco) belongs to the rare class of eclipsing binaries with a supergiant primary (B0.5/0.7). Our combined orbital and light-curve analysis suggests that the secondary resembles an O9.5 III star. Our results for a limited sample corroborate the findings that many O stars are actually massive multiple systems.