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

被引:88
作者
Elebert, P. [1 ]
Reynolds, M. T. [2 ]
Callanan, P. J. [1 ]
Hurley, D. J. [1 ]
Ramsay, G. [3 ]
Lewis, F. [4 ,5 ,6 ]
Russell, D. M. [7 ]
Nord, B. [8 ]
Kane, S. R. [9 ]
DePoy, D. L. [10 ]
Hakala, P. [11 ]
机构
[1] Univ Coll Cork, Dept Phys, Cork, Ireland
[2] Univ Michigan, Dept Astron, Ann Arbor, MI 48109 USA
[3] Armagh Observ, Armagh BT61 9DG, North Ireland
[4] Cardiff Univ, Faulkes Telescope Project, Sch Phys & Astron, Cardiff CF24 3AA, S Glam, Wales
[5] Open Univ, Dept Phys & Astron, Milton Keynes MK7 6AA, Bucks, England
[6] Las Cumbres Observ Global Telescope, Goleta, CA 93117 USA
[7] Astron Inst Anton Pannekoek, NL-1098 SJ Amsterdam, Netherlands
[8] Univ Michigan, Dept Phys, Ann Arbor, MI 48109 USA
[9] CALTECH, NASA Exoplanet Sci Inst, Pasadena, CA 91125 USA
[10] Texas A&M Univ, Dept Phys, College Stn, TX 77843 USA
[11] Univ Turku, Tuorla Observ, FIN-21500 Piikkio, Finland
基金
爱尔兰科学基金会;
关键词
accretion; accretion discs; binaries: close; stars: individual: V4580 Sagittarii; stars: neutron; pulsars: individual: SAX J1808.4-3658; X-rays: binaries; DIFFUSE INTERSTELLAR BANDS; ACTIVE RADIO PULSAR; X-RAY BINARIES; MILLISECOND PULSAR; ACCRETION DISCS; NEUTRON-STAR; LIGHT-CURVE; QUIESCENCE; COUNTERPART; SUPERHUMPS;
D O I
10.1111/j.1365-2966.2009.14562.x
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
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 NIII lambda 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(-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(-0.004)(+0.005), and the mass function for the pulsar to be 0.44(-0.13)(+0.16)M(circle dot). 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 1.4M(circle dot). Our optical light curves exhibit a possible superhump modulation, expected for a system with such a low mass ratio. The equivalent width of the CaII H and K interstellar absorption lines suggest that the distance to the source is similar to 2.5 kpc. This is consistent with previous distance estimates based on type-IX-ray bursts which assume cosmic abundances of hydrogen, but lower than more recent estimates which assume helium-rich bursts.
引用
收藏
页码:884 / 894
页数:11
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