Magnetically aligned dust and SiO maser polarization in the envelope of the red supergiant VY CMa

Abstract

We use Atacama Large Millimeter/submillimeter Array Band 5 science verification observations of the red supergiant VY CMa to study the polarization of SiO thermal/masers lines and dust continuum at ~1.7 mm wavelength. We analyse both linear and circular polarization and derive the magnetic field strength and structure, assuming the polarization of the lines originates from the Zeeman effect, and that of the dust originates from aligned dust grains. We also discuss other effects that could give rise to the observed polarization. We detect, for the first time, significant polarization (~3%) of the circumstellar dust emission at millimeter wavelengths. The polarization is uniform with an electric vector position angle of $\sim 8^{\circ }$. Varying levels of linear polarization are detected for the J=4-3 28SiO v=0, 1, 2, and 29SiO v=0, 1 lines, with the strongest polarization fraction of ~30% found for the 29SiO v=1 maser. The linear polarization vectors rotate with velocity, consistent with earlier observations. We also find significant (up to ~1%) circular polarization in several lines, consistent with previous measurements. We conclude that the detection is robust against calibration and regular instrumental errors, although we cannot yet fully rule out non-standard instrumental effects. Emission from magnetically aligned grains is the most likely origin of the observed continuum polarization. This implies that the dust is embedded in a magnetic field >13 mG. The maser line polarization traces the magnetic field structure. The magnetic field in the gas and dust is consistent with an approximately toroidal field configuration, but only higher angular resolution observations will be able to reveal more detailed field structure. If the circular polarization is due to Zeeman splitting, it indicates a magnetic field strength of ~1-3 Gauss, consistent with previous maser observations.

12 pages, 9 figures, accepted for publication in Astronomy and Astrophysics

References in corpus (14)

• Radiative torques: Analytical Model and Basic Properties
• Too little radiation pressure on dust in the winds of oxygen-rich AGB stars
• A close halo of large transparent grains around extreme red giant stars
• Radiative transfer with POLARIS: I. Analysis of magnetic fields through synthetic dust continuum polarization measurements
• Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles I. Theoretical model -- Mass-loss history unravelled in VY CMa
• Atmospheric dynamics and the mass loss process in red supergiant stars
• The 3D Morphology of VY Canis Majoris. I The Kinematics of the Ejecta
• ALMA sub-mm maser and dust distribution of VY Canis Majoris
• ALMA Observations of Anisotropic Dust Mass-loss in the Inner Circumstellar Environment of the Red Supergiant VY Canis Majoris
• Interferometric mapping of magnetic fields: The ALMA view of the massive star forming clump W43-MM1
• The 3D Morphology of VY Canis Majoris II: Polarimetry and the Line-of-Sight Distribution of the Ejecta
• Non-Zeeman Circular Polarization of Molecular Maser Spectral Lines
• Simultaneous VLBA polarimetric observations of the v=$\{$1,2$\}$ J=1-0 and v=1, J=2-1 SiO maser emission toward VY CMa II: component-level polarization analysis
• Simultaneous 183 GHz H2O Maser and SiO Observations Towards Evolved Stars Using APEX SEPIA Band 5

Cited by in corpus (26)

• ALMA observations of polarization from dust scattering in the IM Lup protoplanetary disk
• Review of Zeeman Effect Observations of Regions of Star Formation
• Stringent limits on the magnetic field strength in the disc of TW Hya: ALMA observations of CN polarisation
• Core collapse supernovae as Cosmic Ray sources
• Episodic Gaseous Outflows and Mass Loss from Red Supergiants
• Magnetic field at a jet base: extreme Faraday rotation in 3C 273 revealed by ALMA
• High-resolution observations of gas and dust around Mira using ALMA and SPHERE/ZIMPOL
• The Mass-Loss History of the Red Hypergiant VY CMa
• The Unexpected Spectrum of the Innermost Ejecta of the Red Hypergiant VY CMa
• On massive dust clumps in the envelope of the red supergiant VY Canis Majoris
• Low Level Carbon Monoxide Line Polarization in two Protoplanetary Disks: HD 142527 and IM Lup
• PORTAL--three-dimensional polarized (sub)millimeter line radiative transfer
• Discovery of Molecular Line Polarization in the Disk of TW Hya
• Characterizing maser polarization: effects of saturation, anisotropic pumping and hyperfine structure
• Magnetic Field Structure of Orion Source I
• History of two mass loss processes in VY CMa. Fast outflows carving older ejecta
• Thermal Emission in the Southwest Clump of VY CMa
• Mapping circumstellar magnetic fields of late-type evolved stars with the Goldreich-Kylafis effect: CARMA observations at $\lambda 1.3$ mm of R Crt and R Leo
• Asymmetric shocks in $\chi$ Cyg observed with linear spectropolarimetry
• ALMA reveals the coherence of the magnetic field geometry in OH 231.8+4.2
• Tracing the large-scale magnetic field morphology in protoplanetary disks using molecular line polarization
• Polarisation of molecular lines in the circumstellar envelope of the post-Asymptotic Giant Branch star OH 17.7-2.0
• SiO maser polarization and magnetic field in evolved cool stars
• The Red and Yellow Hypergiants
• Studies of Evolved Stars in the Next Decade: EAO Submillimetre Futures White Paper Series, 2019
• Molecular line polarisation from the circumstellar envelopes of Asymptotic Giant Branch stars