Journal Article

On the mass of the neutron star in Cyg X-2

J. Casares, J. I. González Hernández, G. Israelian and R. Rebolo

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 401, issue 4, pages 2517-2520
Published in print February 2010 | ISSN: 0035-8711
Published online January 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.15828.x
On the mass of the neutron star in Cyg X-2

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We present new high-resolution spectroscopy of the low-mass X-ray binary Cyg X-2, which enables us to refine the orbital solution and rotational broadening of the donor star. In contrast with Elebert et al., we find a good agreement with results reported in Casares et al. We measure P= 9.84450 ± 0.00019 d, K2= 86.5 ± 1.2 km s−1 and V sin i= 33.7 ± 0.9 km s−1. These values imply q=M2/M1= 0.34 ± 0.02 and M1= 1.71 ± 0.21 M (for ). Therefore, the neutron star in Cyg X-2 can be more massive than canonical. We also find no evidence for irradiation effects in our radial velocity curve which could explain the discrepancy between Elebert et al.'s and our K2 values.

Keywords: accretion, accretion discs; binaries: close; stars: individual: Cygnus X-2; X-rays: binaries

Journal Article.  2925 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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