The OB stellar associations in the Large Magellanic Cloud.

Results are presented of a photometric investigation of 96 of the 122 catalogued OB stellar associations in the Large Magellanic Cloud. Photographic photometry in two colors (B and V) of 4661 stars is used to construct color-magnitude diagrams and luminosity functions of the associations. Standard stars in the associations were measured photoelectrically in three colors (U, B, and V) for the purpose of calibrating the iris photometry, and permitted the determination of the interstellar reddening in or near many of the associations. An effort was made to measure stars which were in the catalogs of Ardeberg et al., Fehrenbach and Duflot, and Sanduleak. This made it possible to distinguish galactic foreground stars from true Large Cloud members among the brightest stars, and to study the relationship between spectral type and position in the color-maguitude diagrams of the associations. Many known variable stars were also measured. In general it is found that the brightest stars in the associations are the G-type supergiants. Along the main sequence the brightest stars are B and A supergiants and often emission stars such as Of or Be stars. As found by Westerlund the WoIf-Rayet stars usually occur at the tip of the main sequence. Sbme of the color-magnitude diagrams show groups of evolved blue supergiants above the tip of the main sequence. The number of red supergiants drops sharply above M = -6.6, and when red variables occur they are usually the brightest and reddest stars on the red-supergiant branch. Subject headings: associations - luminous stars - Magellanic Clouds