Modeling the Photometric Variability of Alpha$^2$ CVn with a Dynamical Magnetosphere

TL;DR

This paper models the photometric variability of the magnetic star Alpha$^2$ CVn using a simplified dynamical magnetosphere and magnetic dipole, providing insights into its surface and ultraviolet variability.

Contribution

It introduces a dynamical magnetosphere model with a tilted, offset magnetic dipole to explain Alpha$^2$ CVn's variability, challenging the traditional diffusion explanation.

Findings

The dipole model reproduces the observed TESS variability.

The model aligns with the magnetic surface map from previous studies.

Ultraviolet variability is consistent with reddening models.

Abstract

Alpha$^2$ Canum Venaticorum (AM CVn) is a strongly magnetic star with peculiar chemical signatures and periodic variability that have been long attributed to the diffusion of magnetic elements through the photosphere, leading to chemical spots across the stellar surface. However, recent studies of other magnetic hot stars are consistent with magnetospheric clouds above the surface. Here we take a renewed approach to modeling AM CVn with a simplified dynamical magnetosphere (DM) and a tilted, offset magnetic dipole to reproduce its Transiting Exoplanet Survey Satellite (TESS) variability. Our dipole model also reproduces well the magnetic surface map of AM CVn from Silvester, Kochukhov, & Wade (2014). Its ultraviolet variability, from IUE archival spectra, is also consistent with traditional reddening models. We further discuss the implications of a magnetosphere on other observable quantities from the system to conclude that it is unlikely to be present in AM CVn.