UBV RI CCD photometric study of the open clusters Basel 4 and NGC 7067

Abstract

In this paper we present UBV RI CCD photometry in the region of two young open star clusters Basel 4 and NGC 7067 for the first time. Our sample consists of ~4000 stars down to V ~21 mag. Stellar surface density profile indicates that radii of Basel 4 and NGC 7067 are about 1.8 and 3.0 arcmin respectively. The (U-B) versus (B-V) diagrams indicate that the metallicity of NGC 7067 is solar while that of Basel 4 is Z~0.008. We estimate the mean value of E(B-V) = 0.45 ± 0.05 and 0.75 ± 0.05 mag for Basel 4 and NGC 7067, respectively. The analysis of 2MASS JHK data in combination with the optical data in both the clusters yields E(J-K) = 0.30 ± 0.20 mag and E(V-K) = 1.60 ± 0.20 mag for Basel 4 while E(J-K) = 0.40 ± 0.20 mag and E(V-K) = 2.10 ± 0.20 mag for NGC 7067. Furthermore, colour excess diagrams show a normal interstellar extinction law towards both the clusters. Using the intrinsic colour-magnitude diagrams of the cluster members, we estimated the distances of the clusters as 3.0 ± 0.2 and 3.6 ± 0.2 kpc for Basel 4 and NGC 7067, respectively. By fitting the proper metallicity isochrones to the bright cluster members we estimated the age of the clusters as 200 ± 50 and 100 ± 25 Myr for Basel 4 and NGC 7067, respectively. The mass function slopes that are derived by applying the corrections of field star contamination and data incompleteness are 1.55 ± 0.25 and 1.68 ± 0.47 for Basel 4 and NGC 7067, respectively. The values of the mass function slope are thus not very different from Salpeter's value. Mass segregation is observed in both the clusters, which may be caused by the dynamical evolution or the imprint of star formation processes or both.