ICCD SPECKLE OBSERVATIONS OF BINARY STARS - XIX - AN ASTROMETRIC SPECTROSCOPIC SURVEY OF O-STARS/

We present the results of a speckle interferometric survey made with t he CHARA speckle camera and 4 m-class telescopes of Galactic O-type st ars with V < 8. We can detect with the speckle camera binaries in the angular separation range 0''.035 < rho < 1''.5 with Delta m < 3, and w e have discovered 15 binaries among 227 O-type systems. We combined ou r results on visual binaries with measurements of wider pairs from the Washington Double Star Catalog and fainter pairs from the Hipparcos C atalogue, and we made a literature survey of the spectroscopic binarie s among the sample. We then investigated the overall binary frequency of the sample and the orbital characteristics of the known binaries. B inaries are common among O stars in clusters and associations (>59% ha ve a visual or spectroscopic companion) but less so among field and es pecially runaway stars. There are many triple systems among the speckl e binaries, and we discuss their possible role in the ejection of star s from clusters. The period distribution of the binaries is bimodal in log P, but we suggest that binaries with periods of years and decades may eventually be found to fill the gap. The mass ratio distribution of the visual binaries increases toward lower mass ratios, but low mas s ratio companions are rare among close, spectroscopic binaries (proba bly because of the difficulty of spectroscopic detection rather than a real deficit). We present distributions of the eccentricity and longi tude of periastron for spectroscopic binaries with elliptical orbits, and we find strong evidence of a bias in the longitude of periastron d istribution (the ''Barr effect''), which is probably caused by line di stortions introduced by circumstellar gas.