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

TL;DR

This study presents a comprehensive multi-wavelength analysis of V479 Andromedae, revealing it as a potentially unique long-period polar binary with a magnetic white dwarf and a subgiant donor, challenging existing models of such systems.

Contribution

The paper provides the first detailed multi-wavelength characterization of V479 And, suggesting it may be the longest-period polar with a magnetic white dwarf, and discusses its unusual evolutionary state.

Findings

V479 And has a 0.594-day orbital period and a G8--K0 donor star.

The white dwarf is likely a massive magnetic white dwarf with a high accretion rate.

The system may be a polar with the longest observed orbital period.

Abstract

We conducted a multi-wavelength study to unveil the properties of the extremely long-period cataclysmic variable V479 And. We performed series of observations, including moderate to high spectral resolution optical spectrophotometry, X-ray observations with Swift, linear polarimetry and near-IR photometry. This binary system is a low-inclination ~ 17^o 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 Msun magnetic white dwarf, accreting matter at a rate M(dot) > 10^-10 Msun/ yr. 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 the polar with the longest observed orbital period. We also discuss the evolutionary state of V479 And.