POLARIMETRIC OBSERVATIONS OF sigma ORIONIS E

Author(s)

Carciofi, A. C. ^[1] ; Faes, D. M. ^[1] ; Townsend, R. H. D. ^[2] ; Bjorkman, J. E. ^[3]

Affiliation

^[1] Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfericas, BR-05508900 Sao Paulo - Brazil

^[2] Univ Wisconsin, Dept Astron, Madison, WI 53706 - USA

^[3] Univ Toledo, Dept Phys & Astron, Ritter Observ, Toledo, OH 43606 - USA

• Document type: Journal article
• Source: Astrophysical Journal Letters; v. 766, n. 1 MAR 20 2013.
• Web of Science Citations: 11

Abstract

Some massive stars possess strong magnetic fields that confine plasma in the circumstellar environment. These 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 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 degrees.0 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, corotating 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 corotating 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(b)/M-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. (AU)

• FAPESP's process: 10/19029-0 - 3D radiative transfer models: bridging theory and observations
• Grantee: Alex Cavaliéri Carciofi
• Support type: Regular Research Grants
• FAPESP's process: 09/54006-4 - A computer cluster for the Astronomy Department of the University of São Paulo Institute of Astronomy, Geophysics and Atmospheric Sciences and for the Cruzeiro do Sul University Astrophysics Center
• Grantee: Elisabete Maria de Gouveia Dal Pino
• Support type: Multi-user Equipment Program
• FAPESP's process: 10/19060-5 - An interferometric view on hot star disks
• Grantee: Daniel Moser Faes
• Support type: Scholarships in Brazil - Doctorate