Modelling the photometric variability of magnetic massive stars with the Analytical Dynamical Magnetosphere model

TL;DR

This study models the photometric variability of magnetic O-type stars using the Analytical Dynamical Magnetosphere model to interpret phase-dependent occultations and compare predictions with observations.

Contribution

It introduces a simple, effective method to synthesize light curves from magnetosphere density structures and validates it against observed data of Of?p stars.

Findings

The ADM model accurately reproduces observed light curves of HD 191612.

Magnetic field properties inferred are consistent with observational constraints.

Parameter space study reveals key factors influencing photometric variability.

Abstract

In this paper, we investigate the photometric variability of magnetic O-type stars. Such stars possess oblique, predominantly dipolar magnetic fields that confine their winds roughly axisymmetrically about the magnetic equator, thus forming a magnetosphere. We interpret their photometric variability as phase-dependent magnetospheric occultations. For massive star winds dominated by electron scattering opacity in the optical and NIR, we can compute synthetic light curves from simply knowing the magnetosphere's mass density distribution. We exploit the newly-developed Analytical Dynamical Magnetosphere model (ADM) in order to obtain the predicted circumstellar density structures of magnetic O-type stars. The simplicity in our light curve synthesis model allows us to readily conduct a parameter space study. For validation purposes, we first apply our algorithm to HD 191612, the prototypical Of?p star. Next, we attempt to model the photometric variability of the Of?p-type stars identified in the Magellanic Clouds using OGLE photometry. We evaluate the compatibility of the ADM predictions with the observed photometric variations, and discuss the magnetic field properties that are implied by our modelling.