CCD UBVRI photometry of NGC 6811
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We present the results of CCD UBVRI observations of the open cluster NGC 6811 obtained on 18th July 2012 with the 1 m telescope at the TÜBİTAK National Observatory (TUG). Using these photometric results, we determine the structural and astrophysical parameters of the cluster. The mean photometric uncertainties are better than 0.02 mag in the V magnitude and B−V, V−R, and V−I colour indices to about 0.03 mag for U−B among stars brighter than magnitude V=18. Cluster member stars were separated from the field stars using the Galaxia model of Sharma et al. (2011) together with other techniques. The core radius of the cluster is found to be r c =3.60 arcmin. The astrophysical parameters were determined simultaneously via Bayesian statistics using the colour-magnitude diagrams V versus B−V, V versus V−I, V versus V−R, and V versus R−I of the cluster. The resulting most likely parameters were further confirmed using independent methods, removing any possible degeneracies. The colour excess, distance modulus, metallicity and the age of the cluster are determined simultaneously as E(B−V)=0.05±0.01 mag, μ=10.06±0.08 mag, [M/H]=−0.10±0.01 dex and t=1.00±0.05 Gyr, respectively. Distances of five red clump stars which were found to be members of the cluster further confirm our distance estimation.
KeywordsGalaxy: open cluster and associations: individual: NGC 6811 Stars: Hertzsprung Russell (HR) diagram
We appreciate the referee for his/her valuable comments and suggestions. This work has been supported in part by the Scientific and Technological Research Council (TÜBİTAK) 113F201 and 113F270. We thank to TÜBİTAK for a partial support in using T100 telescope with project number 12BT100-324. EP acknowledge support by the SoMoPro II programme (3SGA5916). It was also supported by the grants GP14-26115P, 7AMB14AT015, the financial contributions of the Austrian Agency for International Cooperation in Education and Research (BG-03/2013 and CZ-09/2014). This research has made use of the WEBDA, SIMBAD, and NASA’s Astrophysics Data System Bibliographic Services.