THE ASTROPHYSICAL JOURNAL, 446:622-636, 1995 June 20

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

      ROBERT S. HILL, K.-P. CHENG, RALPH C. BOHLIN, ROBERT W. O'CONNELL,
          MORTON S. ROBERTS, ANDREW M. SMITH, AND THEODORE P. STECHER


                                   ABSTRACT

        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 ground-based 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 ~10
     Myr, which constrains the scenario for the evolution of the supergiant
     Halpha shell LMC 4 by stochastic self-propagated star formation.  The
     initial mass function (IMF) slope for LH 52 is Gamma ~ -1, in
     agreement with previous work, and the slope for LH 53, which is less
     densely populated, is Gamma ~ -2.  A similar relationship between
     surface density of stars and IMF slope is reported for a UIT field
     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 ~10 Myr for LH 53 implies an initial
     mass of ~20 Msun for the N49 progenitor star.

     Subject headings: dust, extinction -- Magellanic Clouds -- open
                       clusters and associations: individual (LH 52, LH 53)
                       -- stars: luminosity function, mass function -- 
                       ultraviolet: stars