2023/11/11 by Rebecca G. Martin, P. A. Charles, Martin, Rebecca G. +1 · 1 citation
Earth and Planetary Sciences · Engineering · Physics and Astronomy · #Astrophysical Phenomena and Observations #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #High-pressure geophysics and materials #Mechanics and Biomechanics Studies
paper · pdf · doi:10.48550/arxiv.2311.06442
openalex publication_date 2023/11/11 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Superorbital periods that are observed in the brightness of Be/X-ray binaries may be driven by a misaligned and precessing Be star disc. We examine how the precessing disc model explains the superorbital variation of (i) the magnitude of the observed X-ray outbursts and (ii) the observed colour. With hydrodynamical simulations we show that the magnitude of the average accretion rate on to the neutron star, and therefore the X-ray outbursts, can vary by over an order of magnitude over the superorbital period for Be star spin-orbit misalignments \gtrsim 70^∘ as a result of weak tidal truncation. Most Be/X-ray binaries are redder at optical maximum when the disc is viewed closest to face-on since the disc adds a large red component to the emission. However, A0538-66 is redder at optical minimum. This opposite behaviour requires an edge-on disc at optical minimum and a radially narrow disc such that it does not add a large red signature when viewed face-on. For A0538-66, the misalignment of the disc to the binary orbit must be about 70-80^∘ and the inclination of the binary orbit to the line of sight must be similarly high, although restricted to <75^∘ by the absence of X-ray eclipses.