Cataclysmic Variables and Other Compact Binaries in the Globular Cluster NGC 362: Candidates from Chandra and HST

TL;DR

This study combines Chandra X-ray and HST optical data to identify and analyze compact binaries, such as cataclysmic variables, in the core of globular cluster NGC 362, revealing a significant population of these sources.

Contribution

It demonstrates the effectiveness of combined X-ray and optical imaging in detecting and characterizing compact binary populations in dense globular cluster cores, especially in crowded fields.

Findings

Detected 100 X-ray sources in NGC 362, mostly likely cluster members.

Identified an excess of Hα-emitting objects associated with X-ray sources.

Suggested most sources are cataclysmic variables, with a candidate quiescent low-mass X-ray binary.

Abstract

Highly sensitive and precise X-ray imaging from Chandra, combined with the superb spatial resolution of HST optical images, dramatically enhances our empirical understanding of compact binaries such as cataclysmic variables and low mass X-ray binaries, their progeny, and other stellar X-ray source populations deep into the cores of globular clusters. Our Chandra X-ray images of the globular cluster NGC 362 reveal 100 X-ray sources, the bulk of which are likely cluster members. Using HST color-magnitude and color-color diagrams, we quantitatively consider the optical content of the NGC 362 Chandra X-ray error circles, especially to assess and identify the compact binary population in this condensed-core globular cluster. Despite residual significant crowding in both X-rays and optical, we identify an excess population of H{\alpha}-emitting objects that is statistically associated with the Chandra X-ray sources. The X-ray and optical characteristics suggest that these are mainly cataclysmic variables, but we also identify a candidate quiescent low mass X-ray binary. A potentially interesting and largely unanticipated use of observations such as these may be to help constrain the macroscopic dynamic state of globular clusters.