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Astron. Astrophys. 326, 528-536 (1997)

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5. Conclusion

A number of blue stars have been resolved within [FORMULA] 3" from the center of NGC 5102, using the FOC with the F175W and F342W filters on board the Hubble Space Telescope. The main findings are.

- The angular resolution of the HST confirms and extends the previous ground-based result of a blue color gradient in the central region of the galaxy. The m175m342 color gradient gets stronger at galactocentric distances smaller than 1:004 (21 pc) with the UV color decreasing from 0.0 to 0.5 at 0:004 (6 pc). This gradient does not continue in the nucleus which has a color similar to that found at a few arcsec in the inner bulge. The light profiles through both filters rise steeply at the resolution limit and show no evidence of a core.

- The resolved stars follow approximately the integrated light distribution with an indication that the stars are slightly more concentrated. There is no significant clustering and the stars do not seem to be confined to a disk.

- In the m175 vs. m175m342 color-magnitude diagram most of the resolved stars lie at positions where they may be interpreted either as young stars or as P-AGB stars. Both interpretations have difficulties. From the overall distribution in the color-magnitude diagram it seems more likely that the majority of the stars are young and can be explained as the result of a star formation episode that ended some 15 Myr ago.

- If the latter interpretation is correct, spectral evolutionary models show that this star formation episode began 500-800 Myr ago.

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© European Southern Observatory (ESO) 1997

Online publication: October 15, 1997