The System of Stellar Associations of the Large Magellanic Cloud

From a study of the 122 recognized stellar 0 associations in the Large Magellanic Cloud it is found that the mean diameter is 78 pc, similar to the mean diameter of stellar associations recognized in the solar neigh- borhood. The mean number of stars with absolute visual magnitudes brighter than about -4 per 102 projected square parsecs in the associations is 19, while the mean total population of such stars is 18 per stellar association. Both of these figures are somewhat larger than the populations and the population densities of such stars in stellar associations near the sun. There is a considerable spread in the densities of bright stars in the LMC's associations, but a general over-all correlation exists between the size of the asso- ciation and the total number of stars. Fifteen "star clouds" are recognized and these have a mean diameter of 225 pc, with total populations averaging 32 stars brighter than Mv = -4.2. in dimensions these objects are more similar to the objects studied in M31 by van den Bergh than are the majority of the stellar associa- tions in the LMC or our Galaxy. There is, however, no obvious discontinuity between the characteristics of the two kinds of objects. The radial distribution of the associations is shown in Fig. 2. it appears to be considerably steeper than the radial distribution of stars or H I in the LMC. Sixteen of the associations contain clusters that are probably coexistent physically, only a few of which might be superimposed by chance on the association. These clusters seem to be similar to the nuclei found in some stellar associations of our Galaxy. A total of 96 of the 122 recognized stellar associations contain H II regions. The Ha fluxes of these H II regions are related to the mean stellar densities of the associations.