{
  "id": "1104.4786",
  "version": "v1",
  "published": "2011-04-25T20:00:01.000Z",
  "updated": "2011-04-25T20:00:01.000Z",
  "title": "Chandra X-ray spectroscopy of the very early O supergiant HD 93129A: constraints on wind shocks and the mass-loss rate",
  "authors": [
    "David H. Cohen",
    "Marc Gagné",
    "Maurice A. Leutenegger",
    "James P. MacArthur",
    "Emma E. Wollman",
    "Jon O. Sundqvist",
    "Alex W. Fullerton",
    "Stanley P. Owocki"
  ],
  "comment": "Accepted for publication in Monthly Notices of the Royal Astronomical Society. 12 pages, 10 figures (incl. 5 color)",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "We present analysis of both the resolved X-ray emission line profiles and the broadband X-ray spectrum of the O2 If* star HD 93129A, measured with the Chandra HETGS. This star is among the earliest and most massive stars in the Galaxy, and provides a test of the embedded wind shock scenario in a very dense and powerful wind. A major new result is that continuum absorption by the dense wind is the primary cause of the hardness of the observed X-ray spectrum, while intrinsically hard emission from colliding wind shocks contributes less than 10% of the X-ray flux. We find results consistent with the predictions of numerical simulations of the line-driving instability, including line broadening indicating an onset radius of X-ray emission of several tenths Rstar. Helium-like forbidden-to-intercombination line ratios are consistent with this onset radius, and inconsistent with being formed in a wind-collision interface with the star's closest visual companion at a distance of ~100 AU. The broadband X-ray spectrum is fit with a dominant emission temperature of just kT = 0.6 keV along with significant wind absorption. The broadband wind absorption and the line profiles provide two independent measurements of the wind mass-loss rate: Mdot = 5.2_{-1.5}^{+1.8} \\times 10^{-6} Msun/yr and Mdot = 6.8_{-2.2}^{+2.8} \\times 10^{-6} Msun/yr, respectively. This is the first consistent modeling of the X-ray line profile shapes and broadband X-ray spectral energy distribution in a massive star, and represents a reduction of a factor of 3 to 4 compared to the standard H-alpha mass-loss rate that assumes a smooth wind.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2011-04-25T20:00:01.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "mass-loss rate",
      "wind shock",
      "supergiant hd 93129a",
      "chandra x-ray spectroscopy",
      "x-ray emission line profiles"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1111/j.1365-2966.2011.18952.x",
      "journal": "Monthly Notices of the Royal Astronomical Society",
      "year": 2011,
      "month": "Aug",
      "volume": 415,
      "number": 4,
      "pages": 3354
    },
    "note": {
      "typesetting": "TeX",
      "pages": 12,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 897220,
      "adsabs": "2011MNRAS.415.3354C"
    }
  }
}