Precision Photometry at the LMC Center: Simulating Post-COSTAR HST Observations

We intend to use the restored HST to study age structure and chemical evolution of the stellar population at the center of the LMC. To obtain the necessary observational parameters, Stromgren photometry is planned using the Planetary Camera. To study the reduction techniques needed, a set of simulated PC images have been made. The stellar density in the images is based on an extrapolated luminosity function and show a high degree of crowding. Two of the generally available photometric software packages, ROMAFOT and DAOPHOT, have been used to analyse the images. Results show that the photometric accuracy reached with these packages is not enough for high precision photometry in this configuration. We show that the two major contributors to theerrors are undersampling and the unusual shape of the point spread function. Adaptation of locally developed software is currently in progress to deal with these problems.