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 language | English (US) |
|---|---|
| Pages (from-to) | 884-894 |
| Number of pages | 11 |
| Journal | Monthly Notices of the Royal Astronomical Society |
| Volume | 395 |
| Issue number | 2 |
| DOIs | |
| State | Published - May 1 2009 |
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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
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 journal › Article
}
TY - JOUR
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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U2 - 10.1111/j.1365-2966.2009.14562.x
DO - 10.1111/j.1365-2966.2009.14562.x
M3 - Article
VL - 395
SP - 884
EP - 894
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 2
ER -