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 t he Ultraviolet Imaging Telescope (UIT) during the Astro-1 Space Shuttl e mission in 1990 December. The image in the 162 nm bandpass is discus sed together with groundbased BV data on subfields containing LH 52 an d LH 53. Point-spread function photometry in the 162 nm, B, and V band s is presented in the form of color-magnitude diagrams and two-color d iagrams, which are compared with stellar models. The far-ultraviolet e xtinction curve of the dust in LH 52 is unusually steep for the LMC. T he most probable age of both associations is similar to 10 Myr, which constrains the scenario for the evolution of the supergiant H alpha sh ell LMC 4 by stochastic self-propagated star formation. The initial ma ss function (IMF) slope for LH 52 is Gamma approximate to -1, in agree ment with previous work, and the slope for LH 53, which is less densel y populated, is Gamma approximate to -2. A similar relationship betwee n surface density of stars and IMF slope is reported for a UIT held ne ar 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.