Polarimetric observations of $\sigma$ Orionis E

Abstract

Some massive stars possess strong magnetic fields that confine plasma in the circumstellar environment. These \textit{magnetospheres} have been studied spectroscopically, photometrically and, more recently, interferometrically. Here we report on the first firm detection of a magnetosphere in continuum linear polarization, as a result of monitoring of $\sigma$\,Ori\,E at the Pico dos Dias Observatory. {The non-zero intrinsic polarization indicates an asymmetric structure, whose minor elongation axis is oriented $150\fdg0$ east of the celestial north.} A modulation of the polarization was observed, with a period of half of the rotation period, which supports the theoretical prediction of the presence of two diametrally opposed, co-rotating blobs of gas. A phase lag of -0.085 was detected between the polarization minimum and the primary minimum of the light curve, suggestive of a complex shape of the plasma clouds. We present a preliminary analysis of the data with the Rigidly Rotating Magnetosphere model, which could not reproduce simultaneously the photometric and polarimetric data. A toy model comprising two spherical co-rotating blobs {joined by a thin disk} proved more successful in reproducing the polarization modulation. {With this model we were able to determine that the total scattering mass of the thin disk is similar to the mass of the blobs ($2M_{\mathrm{b}}/M_{\mathrm{d}}=1.2$) and that the blobs are rotating counterclockwise on the plane of the sky.} This result shows that polarimetry can provide a diagnostic of the geometry of clouds, which will serve as an important constraint for {improving} the Rigidly Rotating Magnetosphere model.

5 pages, 4 figures, accepted for The Astrophysical Journal Letters

References in corpus (2)

• Achernar: Rapid Polarization Variability as Evidence of Photospheric and Circumstellar Activity
• Variations of the high-level Balmer line spectrum of the helium-strong star Sigma Orionis E

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• The MiMeS Survey of Magnetism in Massive Stars: Introduction and overview
• The Magnetic Early B-type Stars IV: Breakout or Leakage? H$\alpha$ emission as a diagnostic of plasma transport in centrifugal magnetospheres
• MOST Observations of sigma Ori E: Challenging the Centrifugal Breakout Narrative
• How the breakout-limited mass in B-star centrifugal magnetospheres controls their circumstellar H-alpha emission
• The surface magnetic field and chemical abundance distributions of the B2V helium-strong star HD184927
• Diffusion-plus-drift models for the mass leakage from centrifugal magnetospheres of magnetic hot-stars
• Characterizing the Rigidly Rotating Magnetosphere Stars HD 345439 and HD 23478
• Characterizing the magnetic field and spectral variability of the rigidly rotating magnetosphere star HD345439
• Photometric signatures of corotating magnetospheres of hot stars governed by higher-order magnetic multipoles
• Ultraviolet Spectropolarimetric Diagnostics of Hot Star Magnetospheres
• Ultraviolet Spectropolarimetry With Polstar: Using Polstar to test Magnetospheric Mass-loss Quenching
• Photometric properties and stellar parameters of the rapidly rotating magnetic early-B star HD 345439
• Untangling magnetic massive star properties with linear polarization variability and the Analytic Dynamical Magnetosphere model
• MOBSTER -- VII. Using light curves to infer magnetic and rotational properties of stars with centrifugal magnetospheres