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, firstname.lastname@example.org
Accepted: 28 January 2001
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.
Key words: techniques: photometric / Galaxy: open clusters and associations: individual: h Persei, χ Persei / stars: evolution / emission-line, Be / formation
Based on observations obtained with the Jacobus Kapteyn Telescope operated on the island of La Palma by the Isaac Newton Group, in the Spanish Observatorio Roque de los Muchachos of the Instituto de Astrofísica de Canarias.
© ESO, 2001