Multiwavelength observations of V479 Andromedae: a close compact binary with an identity crisis

Aims. We conducted a multi-wavelength study to unveil the properties of the extremely long-period cataclysmic variable V479 And. Methods. We performed series of observations, including moderate to high spectral resolution optical spectrophotometry, X-ray observations with Swift, linear polarimetry, and near-IR photometry. Results. This binary system is a low-inclination ∼17◦ system with a 0.594093(4) day orbital period. The absorption line complex in the spectra indicate a G8–K0 spectral type for the donor star, which has departed from the zero-age main sequence. This implies a distance to the object of about 4 kpc. The primary is probably a massive 1.1–1.4 M magnetic white dwarf, accreting matter at a rate Ṁ > 10−10 M yr−1. This rate can be achieved if the donor star fills its corresponding Roche lobe, but there is little observational evidence for a mass-transfer stream in this system. An alternative explanation is a stellar wind from the donor star, although such a high rate mass loss is not anticipated from a subgiant. If the strongly magnetic white dwarf in V479 And is confirmed by future observations, the system would be the polar with the longest observed orbital period. We also discuss the evolutionary state of V479 And.