{
  "abstract": "We present discovery of SMASH J004005$-$733351, an intermediate-mass stripped helium star in the Small Magellanic Cloud with a dark companion. The system was identified in a new optical color-selected survey for stripped stars and confirmed through spectroscopic follow-up. We measure an orbital period of $P_{\\rm orb}=19.95\\pm 0.002$ hours and a radial-velocity semi-amplitude of $K=91.7 ^{+3.2}_{-3.1}\\,{\\rm km\\,s^{-1}}$. Simultaneous modeling of the optical spectrum and ultraviolet-to-optical spectral energy distribution yields a stripped star evolutionary mass $M_{\\rm stripped} = 3.84 \\pm 0.54\\,M_\\odot$, temperature $T_{\\rm eff} = 68.3 \\pm 6.4$ kK, surface gravity $\\log g= 4.76 \\pm 0.12$, luminosity $\\log(L/L_\\odot)= 4.28 \\pm 0.13$, radius $R= 0.99 \\pm 0.09\\,R_\\odot$, and an unusually high surface hydrogen abundance of $X_{\\rm H, s}=0.63 \\pm 0.04$. The companion is undetected spectroscopically, and the orbital solution and stripped-star evolutionary mass imply a minimum companion mass of $M_2 \\gtrsim 1.2\\,M_\\odot$. The absence of photometric variability from irradiation rules out a main-sequence companion. The companion is most likely a neutron star (NS), although a massive white dwarf or low-mass stripped star cannot be fully excluded. Binary evolution models predict that the stripped star will refill its Roche lobe after core helium exhaustion, likely producing a stripped or ultra-stripped supernova and ultimately a double NS binary if the system survives. SMASH J004005$-$733351 is among the first known stripped stars with a compact object companion. The system provides a new empirical benchmark for the late stages of binary interaction that lead to (ultra-)stripped supernovae and double NS binaries.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.36050",
  "author_total": 12,
  "authors": [
    {
      "name": "Lisa Blomberg"
    },
    {
      "name": "Kareem El-Badry"
    },
    {
      "name": "Peter Senchyna"
    },
    {
      "name": "Ylva Götberg"
    },
    {
      "name": "Bethany Ludwig"
    },
    {
      "name": "Maria R. Drout"
    },
    {
      "name": "Ana Bonaca"
    },
    {
      "name": "Warren R. Brown"
    },
    {
      "name": "Tim Cunningham"
    },
    {
      "name": "Brenna Mockler"
    },
    {
      "name": "Przemek Mroz"
    },
    {
      "name": "Andrzej Udalski"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/71f3k0trwg3j5.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.36050",
  "fulltext_url": null,
  "id": "71f3k0trwg3j5",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.36050",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.SR"
    ],
    [
      "openalex",
      "3103|Stellar, planetary, and galactic studies"
    ]
  ],
  "openalex": "W7224090767",
  "pdf_url": "https://arxiv.org/pdf/2610.36050",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-26",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/71f3k0trwg3j5.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:35:50Z",
      "native_id": "2610.36050",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.36050"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.SR",
      "subfield": "stellar"
    }
  ],
  "title": "An intermediate-mass stripped star with a dark companion in the Small Magellanic Cloud",
  "title_text": "An intermediate-mass stripped star with a dark companion in the Small Magellanic Cloud",
  "type": "preprint",
  "updated_at": "2026-10-30T12:35:50Z",
  "url": "https://research.draconitic.com/paper/71f3k0trwg3j5",
  "venue": "arXiv",
  "versions": []
}