Polarization of thermal molecular lines in the envelope of IK Tauri
Journal article, 2012

Molecular line polarization is a unique source of information about the magnetic fields and anisotropies in the circumstellar envelopes of evolved stars. Here we present the first detection of thermal CO(J = 2 -> 1) and SiO(J = 5 -> 4, nu = 0) polarization, in the envelope of the asymptotic giant branch star IK Tau. The observed polarization direction does not match predictions for circumstellar envelope polarization induced only by an anisotropic radiation field. Assuming that the polarization is purely due to the Goldreich-Kylafis effect, the linear polarization direction is defined by the magnetic field as even the small Zeeman splitting of CO and SiO dominates the molecular collisional and spontaneous emission rates. The polarization was mapped using the Submillimeter Array (SMA) and is predominantly north-south. There is close agreement between the CO and SiO observations, even though the CO polarization arises in the circumstellar envelope at similar to 800 AU and the SiO polarization at less than or similar to 250 AU. If the polarization indeed traces the magnetic field, we can thus conclude that it maintains a large-scale structure throughout the circumstellar envelope. We propose that the magnetic field, oriented either east-west or north-south is responsible for the east-west elongation of the CO distribution and asymmetries in the dust envelope. In the future, the Atacama Large Millimeter/submillimeter Array will be able to map the magnetic field using CO polarization for a large number of evolved stars.

circumstellar envelopes

magnetic-field direction

stars

frequencies

polarization

sio masers

agb

magnetic fields

emission

submillimeter:

stars: AGB and post-AGB

radio

clouds

Author

Wouter Vlemmings

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

S. Ramstedt

University of Bonn

R. Rao

Academia Sinica

Matthias Maercker

University of Bonn

European Southern Observatory (ESO)

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 540 Article Number: L3 - L3

Subject Categories

Astronomy, Astrophysics and Cosmology

DOI

10.1051/0004-6361/201218897

More information

Latest update

4/4/2018 1