2005/07/08 by A. K. F. Val Baker, Baker, A. K. F. Val, A. J. Norton +3 · 1 citation
Decision Sciences · Earth and Planetary Sciences · Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics (astro-ph) #FOS: Physical sciences #High-pressure geophysics and materials #Scientific Measurement and Uncertainty Evaluation #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0507206
Accepted for publication by A&A. 4 Figures & Table 2 will only appear in the on-line version
arxiv created 2005/07/08 · openalex publication_date 2005/07/08 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We present new optical spectroscopy of the eclipsing binary pulsar Sk 160/SMC X-1. From the He I absorption lines, taking heating corrections into account, we determine the radial velocity semi-amplitude of Sk 160 to be 21.8 +/- 1.8 km/s. Assuming Sk 160 fills its Roche-lobe, the inclination angle of the system is i=65.3 deg +/- 1.3 deg and in this case we obtain upper limits for the mass of the neutron star as Mx = 1.21 +/- 0.10 Msolar and for Sk 160 as Mo= 16.6 +/- 0.4 Msolar. However if we assume that the inclination angle is i=90 deg, then the ratio of the radius of Sk 160 to the radius of its Roche-lobe is beta = 0.79 +/- 0.02, and the lower limits for the masses of the two stars are Mx = 0.91 +/- 0.08 Msolar and Mo = 12.5 +/- 0.1 Msolar. We also show that the HeII 4686A emission line tracks the motion of the neutron star, but with a radial velocity amplitude somewhat less than that of the neutron star itself. We suggest that this emission may arise from a hotspot where material accreting via Roche lobe overflow impacts the outer edge of an accretion disc.