{
  "id": "2401.12429",
  "version": "v1",
  "published": "2024-01-23T01:34:12.000Z",
  "updated": "2024-01-23T01:34:12.000Z",
  "title": "A new route to massive hot subdwarfs: common envelope ejection from asymptotic giant branch stars",
  "authors": [
    "Zhenwei Li",
    "Yangyang Zhang",
    "Hailiang Chen",
    "Hongwei Ge",
    "Dengkai Jiang",
    "Jiangdan Li",
    "Xuefei Chen",
    "Zhanwen Han"
  ],
  "comment": "9 pages, 5 figures, accepted for publication in ApJ",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "The hot subdwarf O/B stars (sdO/Bs) are known as extreme horizontal branch stars, which is of great importance in stellar evolution theory. The sdO/Bs are generally thought to have a helium-burning core and a thin hydrogen envelope $(M_{\\rm env }<0.02M_\\odot)$. In the canonical binary evolution scenario, sdO/Bs are considered to be the stripped cores of red giants. However, such a scenario cannot explain the recently discovered sdO/B binary, SMSS J1920, where the strong Ca H$\\&$K lines in the spectrum are found. It suggests that this binary is likely originated from the recent ejection of common envelope (CE). In this {work}, we proposed a new formation channel of massive sdO/Bs, namely sdO/Bs produced from a CE ejection process with an asymptotic giant branch (AGB) star (hereafter AGB CE channel). We constructed the evolutionary model of sdO/Bs and successfully explained most of the important observed parameters of the sdO/B star in SMSS J1920, including the evolutionary age, sdO/B mass, effective temperature, surface gravity and surface helium abundance. The minimum sdO/B mass produced from the AGB CE channel is about $0.48M_\\odot$. The evolutionary tracks in $\\log T_{\\rm eff}-\\log g$ plane {may explain a fraction of the observational samples} with high-$\\log T_{\\rm eff}$ and low-$\\log g$. Considering wind mass-loss of sdO/Bs, the model could produce helium-rich hot subdwarfs with $\\log (n_{\\rm He}/n_{\\rm H})\\gtrsim-1$.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2024-01-23T01:34:12.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "asymptotic giant branch stars",
      "common envelope ejection",
      "massive hot subdwarfs",
      "agb ce channel",
      "sdo/b mass"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 9,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}