Photometry of the Four Anti-Galactocentric Old Open Clusters: Czernik 30, Berkeley 34, Berkeley 75, and Berkeley 76

TL;DR

This study analyzes four old open clusters in the Milky Way's anti-Galactocentric direction, determining their physical parameters and examining the Galactic metallicity gradient using combined data from multiple sources.

Contribution

It provides new detailed parameters for four old open clusters and investigates the Galactic radial metallicity distribution, including evidence for a possible discontinuity.

Findings

Four old open clusters are 2-3 Gyr old and 6-8 kpc from the Sun.

The metallicity gradient for the Galaxy is approximately -0.052 dex/kpc.

A broken linear fit suggests a flatter metallicity gradient beyond 12 kpc.

Abstract

We present a BVI photometric study of four old open clusters (OCs) in the Milky Way Galaxy, Czernik 30, Berkeley 34, Berkeley 75, and Berkeley 76 using the observation data obtained with the SMARTS 1.0 m telescope at the CTIO, Chile. These four OCs are located at the anti-Galactocentric direction and in the Galactic plane. We determine the fundamental physical parameters for the four OCs, such as age, metallicity, distance modulus, and color excess, using red clump and PARSEC isochrone fitting methods after finding center and size of the four OCs. These four old OCs are 2-3 Gyr old and 6 - 8 kpc away from the Sun. The metallicity ([Fe/H]) values of the four OCs are between -0.6 and 0.0 dex. We combine data for these four OCs with those for old OCs from five literatures resulting in 236 objects to investigate Galactic radial metallicity distribution. The gradient of a single linear fit for this Galactocentric [Fe/H] distribution is -0.052 +/- 0.004 dex/kpc. If we assume the existence of a discontinuity in this radial metallicity distribution, the gradient at Galactocentric radius < 12 kpc is -0.070 +/- 0.006 dex/kpc, while that at the outer part is -0.016 +/- 0.010 which is flatter than that of the inner part. Although there are not many sample clusters at the outer part, the broken linear fit seems to better follow the observation data.