UBVI CCD Photometry of the Open Cluster NGC 4609 and Hogg 15

TL;DR

This study provides new UBVI CCD photometry for the open clusters NGC 4609 and Hogg 15, determining their fundamental parameters, age, reddening, and mass function, with implications for cluster membership of WR 47.

Contribution

First CCD photometry data for NGC 4609 is presented, along with detailed analysis of cluster parameters and mass functions for both clusters.

Findings

NGC 4609 has E(B-V)=0.37, distance modulus=10.60, age ~50 million years.

Hogg 15 has E(B-V)=1.13, distance modulus=12.50, age <=4 million years.

Mass function slopes are approximately -1.2 for NGC 4609 and -0.95 for Hogg 15.

Abstract

UBVI CCD photometry is obtained for the open clusters NGC 4609 and Hogg 15 in Crux. For NGC 4609, CCD data are presented for the first time. From new photometry we derive the reddening, distance modulus and age of each cluster - NGC 4609 : E(B-V) = 0.37 +/- 0.03, V_0 - M_V = 10.60 +/- 0.08, log tau = 7.7 +/- 0.1; Hogg 15 : E(B-V) = 1.13 +/- 0.11, V_0 - M_V = 12.50 +/- 0.15, log tau <= 6.6. The young age of Hogg 15 strongly implies that WR 47 is a member of the cluster. We have also determined the mass function of these clusters and have obtained a normal slope (Gamma = -1.2 +/- 0.3) for NGC 4609 and a somewhat shallow slope (Gamma = -0.95 +/- 0.5) for Hogg 15.