Searching for exotic object companions in the dense core of NGC 362. A multi-wavelength and multi-epoch photometric analysis

Ettorre, G, Dalessandro, E, Pallanca, C, Cadelano, M, Kumawat, G, Heinke, CO, Kamann, S, Libralato, M, Lugger, PM, Cohn, HN and Dreizler, S (2025) Searching for exotic object companions in the dense core of NGC 362. A multi-wavelength and multi-epoch photometric analysis. Astronomy & Astrophysics, 697. pp. 1-22. ISSN 0004-6361

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Abstract

The dense cores of globular clusters (GCs) are efficient environments for the production of exotic stellar populations, including millisecond pulsars (MSPs), low-mass X-ray binaries (LMXBs), and cataclysmic variables (CVs). Most of these objects likely form through two- and three-body interactions and are useful tracers of the cluster's dynamical evolution. In this work, we explore the exotic object population in the galactic GC NGC 362, searching for the optical counterpart of 33 X-ray sources identified within $1 from the cluster centre. To this end, we exploited a large Hubble Space Telescope dataset obtained in eight different epochs and covering a wavelength range from the near UV to the optical I band. To identify the most promising counterparts, we followed a multi-step analysis based on four main ingredients, namely, positional coincidence, position in the colour-magnitude diagrams, Hα excess, and photometric variability. In addition, we complemented the photometric analysis with spectroscopic information coming from the analysis of MUSE radial velocity curves. Thanks to this multi-diagnostic approach, we were able to identify 28 high-confidence optical counterparts, including several candidate MSPs, active binaries, and CVs. The most intriguing counterparts include a candidate black widow system, an eclipsing binary blue straggler, and a system in outburst, potentially representing either an LMXB or a nova eruption from a CV. The candidate MSPs proposed in this work will contribute to ongoing radio analyses with MeerKAT for the identification and detailed study of MSPs in NGC 362.

Item Type:	Article
Uncontrolled Keywords:	5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	EDP Sciences
Date of acceptance:	28 March 2025
Date of first compliant Open Access:	21 May 2025
Date Deposited:	21 May 2025 08:42
Last Modified:	21 May 2025 09:00
DOI or ID number:	10.1051/0004-6361/202553776
URI:	https://researchonline.ljmu.ac.uk/id/eprint/26393

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