CCD ${U\!B\!V\!(R\!I)}_{KC}$ photometry of NGC 2323 and NGC 2539 open clusters

Abstract

The open clusters NGC 2323 and NGC 2539 have been analysed using CCD $U\!B\!V\!(R\!I)_{KC}$ photometric data, observed at the San Pedro Mártir Observatory. Cluster memberships have been determined with the proper motion and parallax measures from the GaiaDR2 astrometric data release. Photometric metal and heavy element abundances have been obtained as $([M/H],\;Z) = (-0.10,~0.012)$ (NGC 2323) and $(-0.31,\;0.007)$ (NGC 2539) from the $\delta (U$–B) technique in the two-colour diagrams, which are used to select the appropriate PARSEC isochrones. The estimated reddening of NGC 2323 is $E(B-V)=0.23\pm 0.04$ using 11 early type stars. For NGC 2539, we find $E(B-V)= 0.02\pm 0.06$. For $(B-V)$ colour, distance moduli and distances for NGC 2323 and NGC 2539 are derived as $(V_{0}-M_V, d\ \mathrm{(pc)}) = (10.00\pm 0.10, 1000\pm 50)$ and $(V_{0}-M_V, d \mathrm{(pc)}) = (10.00\pm 0.04, 1000\pm 20)$, respectively. The median GaiaDR2 distance $d=1000\pm 140$ pc ($\varpi =0.998\pm 0.136$ mas) for the likely members of NGC 2323 is in concordance with its four-colour photometric distances 910–1000 pc. For NGC 2539, its GaiaDR2 distance $d=1330\pm 250$ pc ($\varpi =0.751\pm 0.139$ mas) is close to its four-colour photometric distances, 1000 pc. Fitting the PARSEC isochrones to the colour magnitude diagrams (CMDs) gives an old age, $890\pm 110$ Myr, for NGC 2539. Whereas NGC 2323 has an intermediate age, $200\pm 50$ Myr. One red clump/red giant candidate (BD-12 2380) in the CMDs of NGC 2539 has been confirmed as a member in terms of the distances $d_{I} =950\pm 50$ pc and $d_{V}=910\pm 90$ pc of VI filters within the uncertainties, as compared to the distance $1000\pm 20$ pc of NGC 2539. This giant’s GaiaDR2 distance ($d=1200\pm 70$ pc) is not close to these photometric distances.