A LARGE SUPERSHELL H-II REGION COMPLEX IN THE LARGE MAGELLANIC CLOUD AND THE INTERSTELLAR ENVIRONMENT OF SN-1987A

Optical narrow-bandpass imagery taken in the light of [O III], lambda-5007, reveals an unusually large, almost-equal-to 1 kpc, H II region complex in the LMC. This complex shows diffuse [O III] emission engulfing the 30 Doradus nebulosities and significant portions of Shapley's Constellation II, located to the west. The recent supernova, SN 1987A, also appears to have occurred inside this large ionized gas complex. Similar imagery acquired in the optical continuum at 4215 angstrom shows an even grander structure, a large dust ring, enclosing most of the diffuse [O III] emission. The dimensions of this structure, 1.5 x 2.0 kpc, are larger than the well-known supershell (LMC 4) enclosing Shapley's Constellation III. The dust ring likely delineates the periphery of a supershell structure and encompasses at least 830 OB stars with M(v) brighter than -4.2. Simple theoretical modelling suggests that the EUV radiation from these massive stars ionize the H II region complex, while their winds have served as the driving mechanism for the expansion of the dust ring supershell. The expansion of this supershell may have triggered the recent star formation activity in 30 Doradus. The implications for the recent IUE observations of SN 1987A and the ambient interstellar environment of SN 1987A are also discussed.