1997A&A...326..528D

The S0 galaxy NGC 5102 has been observed with the Faint Object Camera on-board the Hubble Space Telescope. Individual blue stars have been resolved 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 light increases toward the center. Comparison of integrated light with previous IUE observations and study of the light profiles determined from the FOC images confirm the blue color gradient inward. The F175w-F342w color is found to get bluer from 1.4" (21pc) to 0.4" (6pc) but the gradient does not continue in the nucleus. There is no evidence for a central core. The resolved blue stars are slightly more concentrated toward the center than the integrated light distribution. In the m₁₇₅ vs. m₁₇₅-m₃₄₂ plane the stars are at positions where either young stars or P-AGB stars may be expected. Although neither interpretation is certain, several arguments suggest that the majority of the resolved stars are young and belong to the last generation of a star formation episode that ended ∼15Myr ago. According to spectral evolution models, the IUE ultraviolet spectrum is best reproduced if this star formation episode started 500-800Myr ago.