BVRI photometry of NGC 3231, NGC 7055, and NGC 7127⋆
1 Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlarska 2, 611 37 Brno, Czech Republic
2 Rozhen National Astronomical Observatory, Institute of Astronomy of the Bulgarian Academy of Sciences, PO Box 136, 4700 Smolyan, Bulgaria
3 Sandvretens Observatory, Linnégatan 5A, 75332 Uppsala, Sweden
Received: 16 November 2011
Accepted: 22 April 2012
Context. Open clusters are often used as tracers for the formation and evolution of the Milky Way. But they can also be used to study distinct “local stellar populations” and all kind of stellar groups. All these studies crucially depend on their unambiguous detection and classification separating them from the fore- and background field population.
Aims. Still more than one third of the catalogued galactic open clusters are unstudied to date. We have chosen three northern open cluster fields, namely NGC 3231, NGC 7055, and NGC 7127 which have been never studied before to shed more light on their true nature.
Methods. We present Johnson-Cousins BVRI photometry down to V ≈ 19 mag. After the transformation to the standard systems, colour–magnitude diagrams were generated. These diagrams were used to fit solar abundant isochrones to determine the distance modulus, reddening and apparent age of the main sequences.
Results. As reported before, a significant plate-dependent distortion of the UCAC3 compared to the PPMXL within all three star fields was found. No correlation of this distortion with the apparent magnitude of the objects was detected. From the analysis of the colour–magnitude diagrams and the available proper motions we conclude that NGC 7055 and NGC 7127 are young, real, open clusters with ages of about 10 and 100 Myr, respectively. They are located in a distance of about 3300 as well as 5700 pc from the Sun. NGC 3231, on the other hand, is probably a high galactic latitude open cluster remnant.
Key words: open clusters and associations: general / open clusters and associations: individual: NGC 3231 / open clusters and associations: individual: NGC 7055 / open clusters and associations: individual: NGC 7127
The complete tables with the photometric measurements are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/542/A68
© ESO, 2012