Photometric study of the double cluster & Persei^*,**

Dpto. de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Aptdo. de Correos 99, 03080, Alicante, Spain

Corresponding author: A. Marco, amparo@astronomia.disc.ua.es

Received: 20 July 2000
Accepted: 28 January 2001

Abstract

We present CCD photometry of the central region of the double cluster h & χ Persei. We identify ≈350 stars, of which 214 were not included in Oosterhof's catalogue. Our magnitude limit allows us to reach early F spectral type and obtain very accurate fits to the ZAMS. We derive reddening values of for h Persei and for χ Persei. From the ZAMS fitting, we derive distance moduli and for h and χ Persei respectively. These values are perfectly compatible with both clusters 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 χ Persei. There is, however, a significant population of stars in h Persei which are younger than χ Persei. All this argues for at least three different epochs of star formation, corresponding approximately to and 7.3.