UV Properties of Galactic Globular Clusters with GALEX I. The Color-Magnitude Diagrams

TL;DR

This study provides the largest homogeneous UV photometric dataset of 44 Galactic globular clusters, revealing diverse horizontal branch morphologies and identifying various post-He burning stellar populations.

Contribution

It offers a comprehensive UV color-magnitude diagram analysis of globular clusters, including a catalog of post-He burning star candidates, enhancing understanding of stellar evolution in these clusters.

Findings

Diverse horizontal branch morphologies observed

Identification of blue stragglers and post-He burning stars

Established UV loci for post-core He burning stars

Abstract

We present GALEX data for 44 Galactic globular clusters obtained during 3 GALEX observing cycles between 2004 and 2008. This is the largest homogeneous data set on the UV photometric properties of Galactic globular clusters ever collected. The sample selection and photometric analysis are discussed, and color-magnitude diagrams are presented. The blue and intermediate-blue horizontal branch is the dominant feature of the UV color-magnitude diagrams of old Galactic globular clusters. Our sample is large enough to display the remarkable variety of horizontal branch shapes found in old stellar populations. Other stellar types that are obviously detected are blue stragglers and post core-He burning stars. The main features of UV color-magnitude diagrams of Galactic globular clusters are briefly discussed. We establish the locus of post-core He burning stars in the UV color-magnitude diagram and present a catalog of candidate AGB-manqu \'e, post early-AGB, and post-AGB stars within our cluster sample.