Seven-color Vilnius photometry of the open cluster NGC 752

TL;DR

This study presents new seven-color Vilnius photometry for stars in NGC 752, determining cluster parameters like distance, reddening, metallicity, and age, and analyzing binary star influence on these measurements.

Contribution

It provides the first detailed seven-color photometric analysis of NGC 752, including refined cluster parameters and binary star population assessment using isochrone fitting.

Findings

Distance modulus (m-M)=8.38 from individual stars

Reddening E(Y-V)=0.027, E(B-V)=0.034

Photometric metallicity [Fe/H]=-0.14 for main-sequence stars

Abstract

New photoelectric seven-color observations in the Vilnius system are presented for 65 stars in the region of the open cluster NGC 752. Based on individual stars with accurate photometric classifications, we determine the apparent distance modulus (m-M)=8.38 and the mean reddening to the cluster E(Y-V)=0.027, or E(B-V)=0.034. The mean photometric metallicity for the main-sequence stars, [Fe/H]=-0.14, is found to be slightly lower than that derived for the red clump giants, [Fe/H]=-0.08. This difference suggests that red giants in later evolutionary phases may not have zero-age surface values of [Fe/H]. We made use of the least-squares minimization techniques to fit the Padova theoretical isochrones to the CMD, when the binary star population is taken into account. By varying the distance modulus, metallicity and age, the best match has been found between the seven magnitudes and colors of the observed stars and those of model binaries, which gives the distance modulus by 0.2 mag smaller than that derived from individual stars, i.e., (m-M)=8.18, a closely similar metallicity ([Fe/H]=-0.12), and age of 1.6 Gyr. With these results, the fraction of photometric binaries among the main-sequence stars is ~40%.