2010MNRAS.401.2517C

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 and V sini = 33.7±0.9 km/s. These values imply q = M₂/M₁= 0.34±0.02 and M₁= 1.71±0.21M_☉(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 K₂values.