The Open UniversitySkip to content

The mass of the neutron star in SMC X-1

Val Baker, A.K.F.; Norton, A.J. and Quaintrell, H. (2005). The mass of the neutron star in SMC X-1. Astronomy and Astrophysics, 441(2) pp. 685–688.

Full text available as:
PDF (Version of Record) - Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader
Download (218Kb) | Preview
DOI (Digital Object Identifier) Link:
Google Scholar: Look up in Google Scholar


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⊙ and for Sk 160 as M_o= 16.6 ± 0.4 M⊙. 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 beta = 0.79 ± 0.02, and the lower limits for the masses of the two stars are M_x= 0.91 ± 0.08 M⊙ and M_o= 12.5 ± 0.1 M⊙. 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.

Item Type: Journal Article
ISSN: 1432-0746
Extra Information: Article published by EDP Sciences and available at or
Keywords: binaries; close stars; neutron stars; individual; SMC X-1 stars; Sk 160; stars; fundamental parameters
Academic Unit/Department: ?? scie-phya ??
Science > Physical Sciences
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 4694
Depositing User: Users 6827 not found.
Date Deposited: 10 Jul 2006
Last Modified: 08 Sep 2012 21:43
Share this page:

Actions (login may be required)

View Item
Report issue / request change

Policies | Disclaimer

© The Open University   + 44 (0)870 333 4340