UIT AND OPTICAL IMAGERY OF LARGE MAGELLANIC CLOUD ASSOCIATIONS LH-52 AND LH-53 - AGES AND INITIAL MASS FUNCTION SLOPES

A 40' field including the stellar associations LH 52 and LH 53 and the supernova remnant N49 in the Large Magellanic Cloud was observed by the Ultraviolet Imaging Telescope (UIT) during the Astro-1 Space Shuttle mission in 1990 December. The image in the 162 nm bandpass is discussed together with groundbased BV data on subfields containing LH 52 and LH 53. Point-spread function photometry in the 162 nm, B, and V bands is presented in the form of color-magnitude diagrams and two-color diagrams, which are compared with stellar models. The far-ultraviolet extinction curve of the dust in LH 52 is unusually steep for the LMC. The most probable age of both associations is similar to 10 Myr, which constrains the scenario for the evolution of the supergiant H alpha shell LMC 4 by stochastic self-propagated star formation. The initial mass function (IMF) slope for LH 52 is Gamma approximate to -1, in agreement with previous work, and the slope for LH 53, which is less densely populated, is Gamma approximate to -2. A similar relationship between surface density of stars and IMF slope is reported for a UIT held near 30 Dor. The ultraviolet morphology of N49, which is contained in LH 53, is dominated by two bright features that straddle an X-ray bright spot, consistent with an encounter between the blast wave and a cloud. The estimated age of similar to 10 Myr for LH 53 implies an initial mass of similar to 20 M. for the N49 progenitor star.