UBV(RI)_C photometry of the open clusters Be 15, Be 80, and NGC 2192

TL;DR

This study presents CCD UBV(RI)_C photometry of three open clusters, deriving their fundamental parameters such as reddening, distance, age, and metallicity, and highlights the variable interstellar extinction in Be 80.

Contribution

It provides new photometric data and detailed parameter estimations for Be 15, Be 80, and NGC 2192, including evidence of variable extinction and metallicity for NGC 2192.

Findings

Reddening values determined for all three clusters.

Evidence of variable extinction across Be 80.

Consistent fit for NGC 2192's reddening and metallicity.

Abstract

The three open clusters Be 15, Be 80, and NGC 2192 have been observed using CCD UBV(RI)_C photometry at the San Pedro M\'artir Observatory, M\'exico within the framework of our open-cluster survey. The fundamental parameters of interstellar reddening, distance, and age have been derived, and also the metallicity for NGC 2192 (solar metallicity has been assumed for the other two). By shifting the colours of Schmidt-Kaler in the (U-B, B-V) two-colour diagram along the appropriate reddening vector, the interstellar reddenings have been derived as E(B-V)=0.23+/-0.03 mag for Be 15, 1.31+/-0.05 for Be 80, and 0.16+/-0.03 for NGC 2192. Evidence is shown for a variable interstellar extinction across the cluster Be 80. For NGC 2192 a nicely consistent fit is obtained for both the interstellar reddening and the metallicity ([Fe/H]=-0.31) using simultaneously the F-type and red-clump stars. By fitting isochrones to the observed sequences of these three clusters in various colour-magnitude diagrams of different colour indices, (B-V, V-I, or V-R) the averages of distance moduli and heliocentric distances ((V-M_V)_o (mag); d(pc)) are the following: (10.74+/-0.01; 1202) for Be 15, (10.75+/-0.01; 1413) for Be 80, and (12.7+/-0.01; 3467) for NGC 2192, and the averages of the inferred best ages (log(age); age (Gyr)) are (8.6+/-0.05; 0.4) for Be 80, and (9.15+/-0.05; 1.4) for NGC 2192; for Be 15 there are two distinct possibilities for the age fit, depending on the membership of three brighter stars, (9.35 or 9.95+/-0.05; 2.2 or 8.9). The need for spectroscopic observations in Be 15 is emphasized to select between alternate reddening and age solutions, and for deeper UBV observations in Be 80 to study in greater detail the variable interstellar, or intracluster, reddening across this cluster.