UBVI CCD Photometry of Berkeley 55 Open Cluster

Abstract

Fundamental astrophysical parameters have been derived for Be 55 open cluster based on UBVI CCD photometric data, observed with the AZT-22 1.5m telescope at Maidanak Astronomical Observatory in Uzbekistan. The mean reddening is obtained as E(B-V)=1.77+-0.10 mag from early type members. The zero age main sequence fitting in the Q(VA)- Q0 diagrams indicates the distance modulus, (V0 - MV)=12.4+-0.20 mag (d=3.02+-0.28 kpc). This photometric distance is consistent with the distances of Gaia EDR3 (d=3.09+-0.16 kpc) and period-luminosity relation (d=2.78+-0.32 kpc) of its Cepheid S5 within the uncertainties. This distance also locates the cluster near the Perseus spiral arm. The Geneva isochrone fittings to the Hertzsprung-Russell diagram and observational colourmagnitude diagrams derive turn-off age, 85+-13 Myr, by taking care five red supergiants/bright giants. The possible inconsistences on the locations of the bright giants with the rotating/non-rotating isochrones may be due to both the age spread of stars in young open clusters and the diversity in rotational velocities.