{
  "id": "astro-ph/9803127",
  "version": "v1",
  "published": "1998-03-11T12:13:49.000Z",
  "updated": "1998-03-11T12:13:49.000Z",
  "title": "Fe II emission lines in the UV spectrum of Sirius-A and Vega",
  "authors": [
    "M. van Noort",
    "T. Lanz",
    "H. J. G. L. M. Lamers",
    "R. L. Kurucz",
    "R. Ferlet",
    "G. Hebrard",
    "A. Vidal-Madjar"
  ],
  "comment": "14 pages including 11 figures; accepted for publication in Astronomy & Astrophysics",
  "journal": "Astronomy & Astrophysics, 334, 633-645 (1998)",
  "categories": [
    "astro-ph"
  ],
  "abstract": "We present high-quality HST/GHRS spectra in the Hydrogen L alpha spectral region of Vega and Sirius-A. Thanks to the signal-to-noise ratio achieved in these observations and to the similarity of the two spectra, we found clear evidence of emission features in the low flux region, 1190-1222 A. These emission lines can be attributed unambiguously to Fe II and Cr II transitions. In this spectral range, silicon lines are observed in absorption. We built a series of non-LTE model atmospheres with different, prescribed temperature stratification in the upper atmosphere and treating Fe II with various degrees of sophistication in non-LTE. Emission lines are produced by the combined effect of the Schuster mechanism and radiative interlocking, and can be explained without the presence of a chromosphere. Silicon absorption lines and the L alpha profile set constraints on the presence of a chromosphere, excluding a strong temperature rise in layers deeper than tau_R ~ 10^{-4}.",
  "revisions": [
    {
      "version": "v1",
      "updated": "1998-03-11T12:13:49.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "emission lines",
      "uv spectrum",
      "strong temperature rise",
      "alpha spectral region",
      "alpha profile set constraints"
    ],
    "tags": [
      "journal article"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 14,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 488692
    }
  }
}