HST study of the LMC compact star-forming region N83B

High resolution imaging with the Hubble Space Telescope has uncovered the thus far hidden stellar content and the nebular features of the high excitation compact H ii region N83B in the Large Magellanic Cloud (LMC). We discover that the H ii region is powered by the most recent massive starburst in the OB association LH 5 and the burst has created about 20 blue stars spread over ~ 30'' on the sky (7.5 pc). Globally N83B displays a turbulent environment typical of newborn massive star formation sites. It contains an impressive ridge, likely created by a shock and a cavity with an estimated age of only ~ 30 000 yr, sculpted in the ionized gas by the powerful winds of massive stars. The observations bring to light two compact H ii blobs, N83B-1 and N83B-2, and a small arc-nebula, N83B-3, lying inside the larger H ii region. N83B-1, only ~ 2''.8 (0.7 pc) across, is the brightest and most excited part of N83B. It harbors the presumably hottest star of the burst and is also strongly affected by dust with an extinction of A_V=2.5 mag. The second blob, N83B-2, is even more compact, with a size of only ~ 1'' (0.3 pc). All three features are formed in the border zone between the molecular cloud and the ionized gas possibly in a sequential process triggered by the ionization front of an older H ii region. Our HST imaging presents an interesting and rare opportunity to observe details in the morphology of star formation on very small spatial scales in the LMC which are in agreement with the concept of the fractal structure of molecular star-forming clouds. A scenario which supports hierarchical massive star formation in the LMC OB association LH 5 is presented. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.