{
  "abstract": "We present new observations of a candidate O-type donor star in a high-mass X-ray binary (HMXB) in M33. The candidate donor star is spatially coincident with a hard X-ray point source. The star’s optical magnitude and colors are consistent with what is expected for a massive star. The four-band optical/UV spectral energy distribution (SED) of the donor star is well fit by an O-giant model with an effective temperature of ∼43 kK, mass of 75 + 9 − 0.3 M ⊙ , and surface gravity of log( g ) of ∼3.8. We present four epochs of optical spectroscopy of the donor star taken with the Keck/DEIMOS spectrograph over the course of approximately one year. Features in the star’s spectrum are consistent with an O-type star. The star’s spectrum exhibits a strong H α emission line during all epochs of observation with a variable line profile. We measure the star’s radial velocity for each epoch, which we use to fit for a systemic velocity. We find that the systemic velocity is offset from the local gas velocity from H I measurements, suggesting that the system has a peculiar velocity relative to the local gas. We observe a radial velocity shift in the He I absorption lines that is consistent with motion within a binary system.",
  "abstract_shown": true,
  "affiliations": [
    "California State University Los Angeles",
    "Leibniz-Institut für Astrophysik Potsdam",
    "Space Telescope Science Institute",
    "Johns Hopkins University",
    "University of California Santa Cruz",
    "University of Washington",
    "California Institute of Technology",
    "University of Utah"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 11,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Margaret Lazzarini",
      "orcid": "0000-0003-3252-352X"
    },
    {
      "affs": [
        1
      ],
      "name": "Lara Cullinane",
      "orcid": "0000-0001-8536-0547"
    },
    {
      "affs": [
        2,
        3
      ],
      "name": "Karoline Gilbert",
      "orcid": "0000-0003-0394-8377"
    },
    {
      "affs": [
        4
      ],
      "name": "Puragra Guhathakurta",
      "orcid": "0000-0001-8867-4234"
    },
    {
      "affs": [
        5
      ],
      "name": "Kyros Hinton",
      "orcid": "0000-0002-0206-1208"
    },
    {
      "affs": [
        6
      ],
      "name": "Daniel Stern",
      "orcid": "0000-0003-2686-9241"
    },
    {
      "affs": [
        7
      ],
      "name": "O. Grace Telford",
      "orcid": "0000-0003-4122-7749"
    },
    {
      "affs": [
        5
      ],
      "name": "Tobin M. Wainer",
      "orcid": "0000-0001-6320-2230"
    },
    {
      "affs": [
        5
      ],
      "name": "Benjamin F. Williams",
      "orcid": "0000-0002-7502-0597"
    },
    {
      "affs": [
        0
      ],
      "name": "Robert Alexander"
    },
    {
      "affs": [
        0
      ],
      "name": "Ernesto Ramirez"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/5psb9nw9m2fwm.bib",
  "cited_by": 0,
  "doi": "10.3847/1538-4357/ae9fef",
  "fulltext_url": null,
  "id": "5psb9nw9m2fwm",
  "issns": [
    "0004-637X",
    "1538-4357"
  ],
  "landing_url": "https://iopscience.iop.org/article/10.3847/1538-4357/ae9fef",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "3103|Stellar, planetary, and galactic studies"
    ]
  ],
  "openalex": "W7213431215",
  "pdf_url": "https://iopscience.iop.org/article/10.3847/1538-4357/ae9fef/pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-06",
  "publisher": "American Astronomical Society",
  "ris": "https://research.draconitic.com/paper/5psb9nw9m2fwm.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:11Z",
      "native_id": "10.3847/1538-4357/ae9fef",
      "source": "crossref",
      "url": "https://iopscience.iop.org/article/10.3847/1538-4357/ae9fef"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "openalex:3103|Stellar, planetary, and galactic studies",
      "subfield": "stellar"
    }
  ],
  "title": "Optical Spectroscopy of a Candidate O-star X-Ray Binary in M33",
  "title_text": "Optical Spectroscopy of a Candidate O-star X-Ray Binary in M33",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:18:11Z",
  "url": "https://research.draconitic.com/paper/5psb9nw9m2fwm",
  "venue": "The Astrophysical Journal",
  "versions": [
    {
      "doi": "10.48550/arxiv.2609.16174",
      "pid": "bt2bdbdeav0sr",
      "relation": "preprint",
      "title": "Optical Spectroscopy of a Candidate O-Star X-ray Binary in M33",
      "venue": "arXiv"
    }
  ]
}