Optical spectroscopy and photometry of SAX J1808.4-3658 in outburst

P. Elebert, M. T. Reynolds, P. J. Callanan, D. J. Hurley, G. Ramsay, F. Lewis, Dave Russell, B. Nord, S. R. Kane, D. L. Depoy, P. Hakala

    Research output: Contribution to journalArticle

    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 λ4640.64 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 -1; applying a 'K-correction', we find the velocity of the secondary star projected on to the line of sight to be 370 ± 40 km s -1. 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 M . 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 M . 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.

    Original languageEnglish (US)
    Pages (from-to)884-894
    Number of pages11
    JournalMonthly Notices of the Royal Astronomical Society
    Volume395
    Issue number2
    DOIs
    StatePublished - May 1 2009

    Fingerprint

    outburst
    photometry
    spectroscopy
    mass ratios
    pulsars
    bursts
    estimates
    stars
    line of sight
    neutron stars
    light curve
    inclination
    tomography
    helium
    time measurement
    modulation
    accretion
    hydrogen
    pulses
    x rays

    Keywords

    • Accretion, accretion discs
    • Binaries: close
    • Pulsars: individual: SAX J1808.4-3658
    • Stars: individual: V4580 Sagittarii
    • Stars: neutron
    • X-rays: binaries

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

    Cite this

    Elebert, P., Reynolds, M. T., Callanan, P. J., Hurley, D. J., Ramsay, G., Lewis, F., ... Hakala, P. (2009). Optical spectroscopy and photometry of SAX J1808.4-3658 in outburst. Monthly Notices of the Royal Astronomical Society, 395(2), 884-894. https://doi.org/10.1111/j.1365-2966.2009.14562.x

    Optical spectroscopy and photometry of SAX J1808.4-3658 in outburst. / Elebert, P.; Reynolds, M. T.; Callanan, P. J.; Hurley, D. J.; Ramsay, G.; Lewis, F.; Russell, Dave; Nord, B.; Kane, S. R.; Depoy, D. L.; Hakala, P.

    In: Monthly Notices of the Royal Astronomical Society, Vol. 395, No. 2, 01.05.2009, p. 884-894.

    Research output: Contribution to journalArticle

    Elebert, P, Reynolds, MT, Callanan, PJ, Hurley, DJ, Ramsay, G, Lewis, F, Russell, D, Nord, B, Kane, SR, Depoy, DL & Hakala, P 2009, 'Optical spectroscopy and photometry of SAX J1808.4-3658 in outburst', Monthly Notices of the Royal Astronomical Society, vol. 395, no. 2, pp. 884-894. https://doi.org/10.1111/j.1365-2966.2009.14562.x
    Elebert, P. ; Reynolds, M. T. ; Callanan, P. J. ; Hurley, D. J. ; Ramsay, G. ; Lewis, F. ; Russell, Dave ; Nord, B. ; Kane, S. R. ; Depoy, D. L. ; Hakala, P. / Optical spectroscopy and photometry of SAX J1808.4-3658 in outburst. In: Monthly Notices of the Royal Astronomical Society. 2009 ; Vol. 395, No. 2. pp. 884-894.
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    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 λ4640.64 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 -1; applying a 'K-correction', we find the velocity of the secondary star projected on to the line of sight to be 370 ± 40 km s -1. 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 M ⊙. 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 M ⊙. 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.",
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    T1 - Optical spectroscopy and photometry of SAX J1808.4-3658 in outburst

    AU - Elebert, P.

    AU - Reynolds, M. T.

    AU - Callanan, P. J.

    AU - Hurley, D. J.

    AU - Ramsay, G.

    AU - Lewis, F.

    AU - Russell, Dave

    AU - Nord, B.

    AU - Kane, S. R.

    AU - Depoy, D. L.

    AU - Hakala, P.

    PY - 2009/5/1

    Y1 - 2009/5/1

    N2 - 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 λ4640.64 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 -1; applying a 'K-correction', we find the velocity of the secondary star projected on to the line of sight to be 370 ± 40 km s -1. 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 M ⊙. 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 M ⊙. 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.

    AB - 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 λ4640.64 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 -1; applying a 'K-correction', we find the velocity of the secondary star projected on to the line of sight to be 370 ± 40 km s -1. 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 M ⊙. 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 M ⊙. 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.

    KW - Accretion, accretion discs

    KW - Binaries: close

    KW - Pulsars: individual: SAX J1808.4-3658

    KW - Stars: individual: V4580 Sagittarii

    KW - Stars: neutron

    KW - X-rays: binaries

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    DO - 10.1111/j.1365-2966.2009.14562.x

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    EP - 894

    JO - Monthly Notices of the Royal Astronomical Society

    JF - Monthly Notices of the Royal Astronomical Society

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