{
  "id": "2311.06442",
  "version": "v1",
  "published": "2023-11-11T00:19:17.000Z",
  "updated": "2023-11-11T00:19:17.000Z",
  "title": "Disc precession in Be/X-ray binaries drives superorbital variations of outbursts and colour",
  "authors": [
    "Rebecca G. Martin",
    "Philip A. Charles"
  ],
  "comment": "Accepted for publication in MNRAS",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "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 $\\gtrsim 70^\\circ$ 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 $70-80^\\circ$ and the inclination of the binary orbit to the line of sight must be similarly high, although restricted to $<75^\\circ$ by the absence of X-ray eclipses.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2023-11-11T00:19:17.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "be/x-ray binaries drives superorbital variations",
      "disc precession",
      "binary orbit",
      "x-ray outbursts",
      "superorbital period"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}