The Curious Case of V CVn

Abstract

Decades of observations on the star V Canum Venaticorum (V CVn) have revealed an unusual inverse relationship between its linear polarization and light curves (sometimes with a lead/lag time between them) and an almost constant polarization position angle. One theory proposed to explain this behaviour is the existence of a bow shock driven by a spherically symmetric time-varying dusty wind from the star, which is assumed to vary due to radial pulsations. To test this hypothesis, this study uses a new framework developed in \textsc{ZEUS3D}, a multiphysics magnetohydrodynamics code. The results of this work show that when a time-varying stellar wind is at its maximum brightness, the polarization signal is at a minimum due to the wind structure and a dense, symmetric shell that forms around the star. Conversely, when the brightness is at a minimum, the symmetric shell around the star is much less dense, and the polarization is instead dominated by the asymmetric bow shock structure, causing the polarization signal to attain a maximum value. Numerically reproducing the observed inverse relationship between the polarization and light curve provides a strong theoretical argument that a variable stellar wind bow shock is the solution to the curious case of V CVn.