The X-ray emissivity of low-density stellar populations. Issue 4 (24th January 2020)

• Record Type: Journal Article
• Authors: Heinke, C O; Ivanov, M G; Koch, E W; Andrews, R; Chomiuk, L; Cohn, H N; Crothers, S; de Boer, T; Ivanova, N; Kong, A K H; Leigh, N W C; Lugger, P M; Nelson, L; Parr, C J; Rosolowsky, E W; Ruiter, A J; Sarazin, C L; Shaw, A W; Sivakoff, G R; van den Berg, M
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 492:Issue 4(2020)
• Page Start: 5684
• Page End: 5708
• Publication Date: 2020-01-24
• Subjects: binaries: general -- globular clusters: general -- open clusters and associations: general -- galaxies: stellar content -- X-rays: binaries; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa194
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: The dynamical production of low-mass X-ray binaries and brighter cataclysmic variables (CVs) in dense globular clusters is well-established. We investigate how the X-ray emissivity of fainter X-ray binaries (principally CVs and coronally active binaries) varies between different environments. We compile calculations (largely from the literature) of the X-ray emissivity of old stellar populations, including open and globular clusters and several galaxies. We investigate three literature claims of unusual X-ray sources in low-density stellar populations. We show that a suggested quiescent neutron star in the open cluster NGC 6819 is a foreground M dwarf. We show that the suggested diffuse X-ray emission from an old nova shell in the globular cluster NGC 6366 is actually a background galaxy cluster. And we show that a suggested population of quiescent X-ray binaries in the Sculptor Dwarf Galaxy is mostly (perhaps entirely) background galaxies. We find that above densities of 10 4 M⊙ pc −3, the X-ray emissivity of globular clusters increases, due to dynamical production of X-ray emitting systems. Below this density, globular clusters have lower X-ray emissivity than the other populations, and we do not see a strong dependence of X-ray emissivity due to density effects. We find significant correlations between X-ray emissivity and binary fraction, metallicity, and density. Sampling these fits via bootstrap techniques gives less significant correlations, but confirms the effect of metallicity on low-density populations, and that of density on the full globular cluster sample.