Photometric study of the double cluster h & chi Persei

We present uvby beta CCD photometry of the central region of the double clu ster h & chi Persei. We identify approximate to 350 stars, of which 214 wer e not included in Oosterhof's catalogue. Our magnitude limit V = 16.5 allow s us to reach early F spectral type and obtain very accurate fits to the ZA MS. We derive reddening values of E(b-y) = 0.44 +/- 0.02 for h Persei and E (b-y) = 0.39 +/- 0.05 for chi Persei. From the ZAMS fitting, we derive dist ance moduli V-0-M-V = 11.66 +/- 0.20 and V-0-M-V = 11.56 +/- 0.20 for h and chi Persei respectively. These values are perfectly compatible with both c lusters being placed at the same distance and having identical reddenings. The shift in the main-sequence turnoff and isochrone fitting, however, show that there is a significant age difference between both clusters, with the bulk of stars in h Persei being older than chi Persei. There is, however, a significant population of stars in h Persei which are younger than chi Pe rsei. All this argues for at least three different epochs of star formation , corresponding approximately to log t = 7.0; 7.15 and 7.3**.