2009MNRAS.399.1534C

Intermediate-resolution (0.5-1 Å) optical spectroscopy of the cataclysmic variable (CV) SY Cnc reveals the spectrum of the donor star. Our data enable us to resolve the orbital motion of the donor and provide a new orbital solution, binary mass ratio and spectral classification. We find that the donor star has spectral-type G8±2 V and orbits the white dwarf with P = 0.3823753 ±0.0000003 d, K₂= 88.0±2.9 km/s and V sini = 75.5 ±6.5 km/s. Our values are significantly different from previous works and lead to q = M₂/M₁= 1.18±0.14. This is one of the highest mass ratios known in a CV and is very robust, because it is based on resolving the rotational broadening over a large number of metallic absorption lines. The donor could be a slightly evolved main sequence or descendant from a massive star which underwent an episode of thermal time-scale mass transfer.