SY Cancri, a case for unstable mass transfer?

TL;DR

This study provides new spectroscopic measurements of SY Cancri, revealing a high mass ratio and suggesting the donor star may be evolved, which supports the idea of unstable mass transfer in this cataclysmic variable.

Contribution

The paper offers the first detailed orbital solution and spectral classification of SY Cnc's donor star, highlighting a high mass ratio indicative of potential unstable mass transfer.

Findings

Donor star is spectral type G8+-2 V.

Orbital period is approximately 0.3824 days.

Mass ratio q=1.18+-0.14, one of the highest in CVs.

Abstract

Intermediate resolution (0.5-1 Angs) optical spectroscopy of the cataclysmic variable 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 day, K2=88.0 +-2.9 km/s and V sin i=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-timescale mass transfer.