1997A&A...328..167B

The youngest stellar populations of a 'J'-shaped region inside the supergiant shell (SGS) LMC4 have been analysed with CCD photometry in B, V passbands. This region consists of 2 coherent strips, one from the east to the west reaching about 400 pc across the OB superassociation LH77 and another extending about 850 pc from south to north. The standard photometric methods yield 25 colour-magnitude diagrams (CMDs) which were used for age determination of the youngest star population by isochrone fitting. The resultant ages lie in the range from 9 Myr to 16 Myr without correlation with the distance to the LMC4 centre. We therefore conclude that there must have been one triggering event for star formation inside this great LMC SGS with a diameter of 1.4kpc. We construct the luminosity function and the mass function of five regions consisting of 5 fields to ensure that projection effects don't mask the results. The slopes lie in the expected range (γ∈[0.22;0.41] and {GAMMA}∈[-1.3;-2.4] respectively). The greatest values of the slope occur in the north, which is caused by the absence of a young, number-dominating star population. We have calculated the rate with which supernovae (SNe) have exploded in LMC4, based on the finding that all stars are essentially coeval. A total of 5-7x10³ supernovae has dumped the energy of 10^54.5erg over the past 10Myr into LMC4, in fact enough to tear the original star-forming cloud apart in the time span between 5 and 8 Myr after the starformation burst. We conclude that LMC4 can have been formed without a contribution from stochastic self-propagating star formation (SSPSF), although the ring of young associations and HII regions around the edge have been triggered by the events inside LMC4.