First CCD $UBVI$ photometric analysis of four moderately young open clusters in the third galactic quadrant

PIATTI, ANDRÉ E.; CLARIA, J.J.; AHUMADA, A.V.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2010 vol. 408 p. 1147 - 1167

0035-8711

We present CCD photometry in the Johnson UBV and Kron–Cousins I systems down to V ∼22.0 for the open clusters NGC 2311, Trumpler 6, NGC 2432 and BH 54 and their surroundingfields. Trumpler 6 and BH 54 have never been studied before and so we provide, for the firsttime, estimates of their fundamental parameters. We obtained colour–magnitude diagrams(CMDs) and colour–colour diagrams cleaned from field star contamination by statisticallysubtracting stars in terms of spatial density, magnitude and colour distributions. Cluster angularradii were estimated from star counts in appropriate-sized boxes distributed throughout theentire observed fields. Using the cleaned CMDs and colour–colour diagrams, we applied soundphotometric membership criteria to discriminate cluster members from interloper field stars.The interstellar extinction across the cluster fields derived from the 100-μm dust emissionfull-sky maps can be considered uniform within the quoted uncertainties. The E(B − V) andE(V − I) colour excesses and the apparent distance moduli of the clusters were estimated fromthe fit of the zero-age main-sequence to the colour–colour diagrams and CMDs, respectively.Cluster ages were determined from the comparison of the four clusters’ CMDs with solarmetallicity theoretical isochrones of the Geneva group. All the clusters were found to bemoderately young objects, their ages ranging between 60 and 250 Myr.