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arXiv · 0910.4496

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

J. Casares·J. I. Gonzalez Hernandez·G. Israelian·R. Rebolo
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Abstract

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 (2009) we find a good agreement with results reported in Casares et al. (1998). We measure $P=9.84450\pm0.00019$ day, $K_2=86.5\pm1.2$ km s$^{-1}$ and $V \sin i=33.7\pm0.9$ km s$^{-1}$. These values imply $q=M_{2}/M_{1}=0.34 \pm 0.02$ and $M_{1}=1.71\pm 0.21$ M$_{\odot}$ (for $i=62.5 \pm 4^{\circ}$). 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 $K_2$ values.

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J. Casares, J. I. Gonzalez Hernandez, G. Israelian, R. Rebolo. 2009-10-23. On the mass of the neutron star in Cyg X-2. https://doi.org/10.1111/j.1365-2966.2009.15828.x

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