SCYON Abstract

Received on May 14 2001

Photometric study of the double cluster h & chi Persei

Authors	Amparo Marco and Guillermo Bernabeu
Affiliation	Departamento de Fisica, Ingenieria de Sistemas y Teoria de la Señal Universidad de Alicante, Apdo 99, E-03080, Alicante, Spain
Accepted by	Astronomy & Astrophysics
Contact	amparo@astronomia.disc.ua.es
URL
Links	h Persei (NGC 869) \| chi Persei (NGC 884)

Abstract

We present uvby ß CCD photometry of the central region of the double cluster h & chi Persei. We identify 350 stars, of which 214 were not included in Oosterhof's catalogue. Our magnitude limit V=16.5 allows us to reach early F spectral type and obtain very accurate fits to the ZAMS. 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 distance moduli Vo-Mv=11.66 ± 0.20 and Vo-Mv=11.56 ± 0.20 for h & chi 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 chi Persei. There is, however, a significant population of stars in h Persei which are younger than chi Persei. All this argues for at least three different epochs of star formation, corresponding approximately to log t=7.0, 7.15 and 7.30.