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

Analyses of multi-epoch, high-resolution (R similar to 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(d).022), HD 112244 (27(d).665), HD 164438 (10(d).25), HD 123056 A (similar to 1314 d) and HD 123056 B (< 2 d); the orbital period of HD 318015 could be improved (23(d).445975). Concerning multiplicity, a third component was discovered for HD 92206 C by means of He I line profiles. For HD 93146 A, which was hitherto assumed to be SB1, lines of a secondary component could be discerned. HD 123056 turns out to be a multiple system consisting of a high-mass component A (approximate to O8.5) displaying a broad He II 5411 angstrom feature with variable radial velocity, and of an inner pair B (approximate to B0) with double He I lines. The binary HD 164816 was revisited and some of its system parameters were improved. In particular, we determined its systemic velocity to be 7 km s(-1), which coincides with the radial velocity of the cluster NGC6530. 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.