BLUE STARS IN THE CENTER OF THE S0 GALAXY NGC-5102

The S0 galaxy NGC 5102 has been observed with the Faint Object Camera on-hoard the Hubble Space Telescope. Individual blue stars have been r esolved in the central region and measured photometrically through the F175W and F342w filters. The limits of detection and completeness are not uniform over the field observed because the unresolved galaxy lig ht increases toward the center. Comparison of integrated light with pr evious IUE observations and study of the light profiles determined fro m the FOC images confirm the blue color gradient inward. The F175w-F34 2w color is found to get bluer from 1.'' 4 (21 pc) to 0.'' 4 (6 pc) bu t the gradient does not continue in the nucleus. There is no evidence for a central core. The resolved blue stars are slightly more concentr ated toward the center than the integrated light distribution. In the m(175) vs. m(175-342) plane the stars are at positions where either yo ung stars or P-AGB stars may be expected. Although neither interpretat ion is certain, several arguments suggest that the majority of the res olved stars are young and belong to the last generation of a star form ation episode that ended similar to 15 Myr ago. According to spectral evolution models. the IUE ultraviolet spectrum is best reproduced if t his star Formation episode started 500-800 Myr ago.