Mon. Not. R. Astron. Soc., 492, 5684-5708 (2020/March-2)
The X-ray emissivity of low-density stellar populations.
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. and VAN DEN BERG M.
Abstract (from CDS):
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 104 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.
© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
binaries: general - globular clusters: general - open clusters and associations: general - galaxies: stellar content - X-rays: binaries
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