THE LMC STELLAR COMPLEXES IN LUMINOSITY SLICES - STAR-FORMATION INDICATORS

An approach towards the investigation of the star formation mechanisms in galaxies can be achieved through the search of stellar complexes a nd the determination of their properties. A method has been developed for the detection of stellar complexes and the derivation of their fun damental properties in the LMC. Photographic plates taken with the 1.2 m U.K. Schmidt Telescope have been digitized by the APM and SuperCosm os machines to produce homogeneous data for extended regions. Star cou nts have been performed for extended areas in selected luminosity slic es and colours (U, HeII, R filters). Isodensity contours have been use d to identify the various structures with enhanced stellar number dens ity (3 sigma above the mean background density). About 50 large stella r groupings have been revealed showing: 1) hierarchical structure, whe re the smallest are found within the large ones. 2) their size distrib ution has peaks at 250+/-50 pc (aggregates) and 600+/-50 pc (complexes ), there are also a few cases with size 1200+/-50 pc (supercomplexes). 3) there is evidence that at the fainter magnitudes these structures are aligned to a general trend whereas at the most bright end (B 1, O spectral types) they become more clumpy and symmetrical in shape. The relationship between the above complexes' properties and the various s cenarios of star formation are discussed.