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 & Astrophysics, 441(2) pp. 685–688.

DOI: https://doi.org/10.1051/0004-6361:20053074

Abstract

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 β = 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.

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About

• Item ORO ID
• 4694
• Item Type
• Journal Item
• ISSN
• 1432-0746
• Keywords
• binaries; close stars; neutron stars; SMC X-1 stars; Sk 160; fundamental parameters
• Academic Unit or School
• Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
  Faculty of Science, Technology, Engineering and Mathematics (STEM)
• Copyright Holders
• © 2005 ESO
• Depositing User
• Users 6827 not found.