{
  "id": "2001.00716",
  "version": "v1",
  "published": "2020-01-03T04:20:16.000Z",
  "updated": "2020-01-03T04:20:16.000Z",
  "title": "The chemical composition of the accretion disk and donor star in Ultra Compact X-ray Binaries: A comprehensive X-ray analysis",
  "authors": [
    "Filippos Koliopanos",
    "Mathias Peault",
    "Georgios Vasilopoulos",
    "Natalie Webb"
  ],
  "comment": "submitted to MNRAS, comments and suggestions encouraged and appreciated. 17 pages 21 figures",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "We have analyzed the X-ray spectra of all known Ultra Compact X-ray Binaries (UCXBs), with the purpose of constraining the chemical composition of their accretion disk and donor star. Our investigation was focused on the presence (or absence) of the Fe K${\\alpha}$ emission line, which was used as the probe of chemical composition of the disk, based on previously established theoretical predictions for the reflection of X-ray radiation off the surface of C/O-rich or He-rich accretion disks in UCXBs. We have contrasted the results of our spectral analysis to the history of type I X-ray bursts from these systems, which can also indicate donor star composition. We found that UCXBs with prominent and persistent iron K${\\alpha}$ emission also featured repeat bursting activity. On the other hand, the UCXBs for which no iron line was detected, appear to have few or no type I X-ray bursts detected over more than a decade of monitoring. Based on Monte Carlo simulations, demonstrating a strong correlation between the Fe K${\\alpha}$ line strength and the abundance of C and O in the accretion disk material and given the expected correlation between the H/He abundance and the recurrence rate of type I X-ray bursts, we propose that there is a considerable likelihood that UCXBs with persistent iron emission have He-rich donors, while those that do not, likely have C/O or O/Ne/Mg-rich donors. Our results strongly advocate for the development of more sophisticated simulations of X-ray reflection from hydrogen-poor accretion disks.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-01-03T04:20:16.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "ultra compact x-ray binaries",
      "accretion disk",
      "donor star",
      "chemical composition",
      "comprehensive x-ray analysis"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 17,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}