A deep UBVRI CCD photometric study of the open clusters Tr1 and Be 11

Abstract

We present deep UBVRI charge-coupled device (CCD) photometry for the young open star clusters Tr1 and Be11. The CCD data for Be11 are obtained for the first time. The sample consists of ~1500 stars reaching down to V~ 21 mag. Analysis of the radial distribution of the stellar surface density indicates that radius values for Tr1 and Be11 are 2.3 and 1.5 pc, respectively. The interstellar extinction across the face of the imaged clusters region seems to be non-uniform with a mean value of E(B-V) = 0.60 +/- 0.05 and 0.95 +/- 0.05 mag for Tr1 and Be11, respectively. A random positional variation of E(B-V) is present in both the clusters. In the cluster Be11, the reason for the random positional variation may be the apparent association of the HII region (S 213). The 2MASS JHK data in combination with the optical data in the cluster Be11 yield E(J-K) = 0.40 +/- 0.20 mag and E(V-K) = 2.20 +/- 0.20 mag. Colour excess diagrams indicate a normal interstellar extinction law in the direction of the cluster Be11. The distances to Tr1 and Be11 are estimated as 2.6 +/- 0.10 and 2.2 +/- 0.10 kpc, respectively, while the theoretical stellar evolutionary isochrones fitted to the bright cluster members indicate that the clusters Tr1 and Be11 are 40 +/- 10 and 110 +/- 10 Myr old, respectively. The mass functions corrected for both field star contamination and data incompleteness are derived for both clusters. The slopes 1.50 +/- 0.40 and 1.22 +/- 0.24 for Tr1 and Be11, respectively, are in agreement with the Salpeter value. Observed mass segregations in both clusters may be the result of dynamical evolutions or the imprint of star formation processes or both.