On the mass of the neutron star in Cyg X-2
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 kms-1 and V sini = 33
Casares, J. et al.
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2010