Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005a%26a...441..685v&link_type=abstract
Astronomy and Astrophysics, Volume 441, Issue 2, October II 2005, pp.685-688
Astronomy and Astrophysics
Astrophysics
8
Binaries: Close, Stars: Neutron, Stars: Individual: Smc X-1, Stars: Individual: Sk 160, Stars: Fundamental Parameters
Scientific paper
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-1. Assuming Sk 160 fills its Roche-lobe, the inclination angle of the system is i=65.3° ± 1.3° and in this case we obtain upper limits for the mass of the neutron star as M_x= 1.21 ± 0.10 M&sun; and for Sk 160 as M_o= 16.6 ± 0.4 M&sun;. However if we assume that the inclination angle is i=90°, then the ratio of the radius of Sk 160 to the radius of its Roche-lobe is β = 0.79 ± 0.02, and the lower limits for the masses of the two stars are M_x= 0.91 ± 0.08 M&sun; and M_o= 12.5 ± 0.1 M&sun;. We also show that the He II 4686 Å 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.
Norton Andrew J.
Quaintrell Hannah
Val Baker K. F. A.
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