SIMBAD references

Three LMC stellar aggregates and two LMC stellar complexes located inside the constellations Shapley I, IV, IX, and X have been examined in order to study their morphology and properties. Star counts were performed on excellent quality film copies of direct plates taken with the 1.2m U.K. Schmidt telescope. They have been used for deriving isodensity contour mapping of the four studied regions. Low dispersion objective prism plates taken with the same telescope were also used to classify the spectra of the stars down to M_V∼0.0mag. Combination of the two sets of data was used to define the boundaries of these regions, their age, the density and the spatial distribution of their OB stars. It is therefore found that the bright and massive OB type stars are the predominant stellar component of the four studied regions. They are embedded in a fainter and less massive stellar component within the boundaries of a region, revealed by the isopleths, where the limiting detection magnitude is down to M_V∼1.5mag. Thus it appears that the stellar content of the complexes and aggregates is made not only by the stars as massive as ∼40M_☉, but they also contain lower mass stars, at least ∼3M_☉. The spatial distribution of early type stars (down to M_V∼0.0mag) shows a gradient which reveals a region coinciding with the one, defined by the isopleths, where fainter stars are also located. For the near future, we plan to study whether the gradient of the radial distribution of the early type stars represents the mass distribution of the molecular cloud from which these stellar structures are formed, or it is due to sequential star formation process and/or expansion because of the high stellar winds of the very massive stars.