{
  "id": "0901.3991",
  "version": "v1",
  "published": "2009-01-26T12:56:15.000Z",
  "updated": "2009-01-26T12:56:15.000Z",
  "title": "Optical spectroscopy and photometry of SAX J1808.4-3658 in outburst",
  "authors": [
    "P. Elebert",
    "M. T. Reynolds",
    "P. J. Callanan",
    "D. J. Hurley",
    "G. Ramsay",
    "F. Lewis",
    "D. M. Russell",
    "B. Nord",
    "S. R. Kane",
    "D. L. DePoy",
    "P. Hakala"
  ],
  "comment": "12 pages, 10 figures; Accepted for publication in MNRAS",
  "doi": "10.1111/j.1365-2966.2009.14562.x",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "We present phase resolved optical spectroscopy and photometry of V4580 Sagittarii, the optical counterpart to the accretion powered millisecond pulsar SAX J1808.4-3658, obtained during the 2008 September/October outburst. Doppler tomography of the N III 4640.64 Bowen blend emission line reveals a focused spot of emission at a location consistent with the secondary star. The velocity of this emission occurs at 324 +/- 15 km/s; applying a \"K-correction\", we find the velocity of the secondary star projected onto the line of sight to be 370 +/- 40 km/s. Based on existing pulse timing measurements, this constrains the mass ratio of the system to be 0.044^{+0.005}_{-0.004}, and the mass function for the pulsar to be 0.44^{+0.16}_{-0.13} Msun. Combining this mass function with various inclination estimates from other authors, we find no evidence to suggest that the neutron star in SAX J1808.4-3658 is more massive than the canonical value of 1.4 Msun. Our optical light curves exhibit a possible superhump modulation, expected for a system with such a low mass ratio. The equivalent width of the Ca II H and K interstellar absorption lines suggest that the distance to the source is ~2.5 kpc. This is consistent with previous distance estimates based on type-I X-ray bursts which assume cosmic abundances of hydrogen, but lower than more recent estimates which assume helium-rich bursts.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2009-01-26T12:56:15.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "optical spectroscopy",
      "photometry",
      "mass function",
      "accretion powered millisecond pulsar sax",
      "powered millisecond pulsar sax j1808"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "publisher": "Wiley-Blackwell",
      "journal": "Monthly Notices of the Royal Astronomical Society",
      "year": 2009,
      "month": "May",
      "volume": 395,
      "number": 2,
      "pages": 884
    },
    "note": {
      "typesetting": "TeX",
      "pages": 12,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 811805,
      "adsabs": "2009MNRAS.395..884E"
    }
  }
}