The mass of the neutron star in SMC X-1

A. K. F. Val Baker; A. J. Norton; H. Quaintrell

doi:10.1051/0004-6361:20053074

Home

All issues

Volume 441 / No 2 (October II 2005)

A&A, 441 2 (2005) 685-688

Abstract

Free Access

Issue		A&A Volume 441, Number 2, October II 2005


Page(s)		685 - 688
Section		Stellar structure and evolution
DOI		https://doi.org/10.1051/0004-6361:20053074
Published online		19 September 2005

A&A 441, 685-688 (2005)

Research Note

The mass of the neutron star in SMC X-1

A. K. F. Val Baker, A. J. Norton and H. Quaintrell

Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK e-mail: [a.k.f.val-baker;a.j.norton]@open.ac.uk

Received: 16 March 2005
Accepted: 1 July 2005

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 $21.8 \pm 1.8$ km s^-1. Assuming Sk 160 fills its Roche-lobe, the inclination angle of the system is $i=65.3^{\circ} \pm 1.3^{\circ}$ and in this case we obtain upper limits for the mass of the neutron star as $M_{\rm x}= 1.21 \pm 0.10$ $M_{\odot}$ and for Sk 160 as $M_{\rm o}= 16.6 \pm 0.4$ $M_{\odot}$ . However if we assume that the inclination angle is $i=90^{\circ}$ , then the ratio of the radius of Sk 160 to the radius of its Roche-lobe is $\beta = 0.79 \pm 0.02$ , and the lower limits for the masses of the two stars are $M_{\rm x}= 0.91 \pm 0.08$ $M_{\odot}$ and $M_{\rm o}= 12.5 \pm 0.1$ $M_{\odot}$ . 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. 

Key words: binaries: close / stars: neutron / stars: individual: SMC X-1 / stars: individual: Sk 160 / stars: fundamental parameters

© ESO, 2005

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.