Deep Hubble Space Telescope Imaging of Globular Clusters Towards the Galactic Bulge: Observations, Data Reduction and Color-Magnitude Diagrams

TL;DR

This study uses Hubble Space Telescope imaging to produce detailed color-magnitude diagrams of 16 globular clusters near the Galactic bulge, overcoming previous observational challenges due to extinction.

Contribution

It provides high-resolution photometric data and CMDs for poorly studied clusters, along with optimized data reduction methods and a comparative analysis of observational strategies.

Findings

Deep CMDs of 16 globular clusters are presented.

Data reduction strategies improve photometric accuracy.

Comparison fields help distinguish cluster features from background.

Abstract

The Galactic globular clusters (GGCs) located towards the Galactic bulge have generally been excluded from large-scale photometric GGC surveys due to severe total and differential extinction. Here, we present an overview of a Hubble Space Telescope program designed to obtain deep, high spatial resolution multiband imaging of 16 poorly studied GGCs located towards the inner Galactic bulge and disk. In this first paper of a series resulting from these observations, we give an overview of target cluster selection, observations and data reduction procedures for optimizing the resulting photometric catalogs. Artificial star tests are used to compare the respective advantages of different data reduction strategies in terms of photometric and astrometric precision and photometric incompleteness. We present the resulting color-magnitude diagrams (CMDs) of all target clusters in several color-magnitude planes, along with CMDs of comparison fields from parallel observations. For each target cluster, we summarize existing studies, and discuss their CMDs qualitatively in the context of these results.