Query : 2012A&A...540L...3V

2012A&A...540L...3V - Astronomy and Astrophysics, volume 540, L3-3 (2012/4-1)

Polarization of thermal molecular lines in the envelope of IK Tauri.


Abstract (from CDS):

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, ν=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 ∼800AU and the SiO polarization at ≲250AU. 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.

Abstract Copyright:

Journal keyword(s): stars: AGB and post-AGB - magnetic fields - polarization - submillimeter: stars

Simbad objects: 5

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Number of rows : 5
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
1 V* IK Tau Mi* 03 53 28.8924743304 +11 24 21.895183368 16.99 17.03 13.39 7.29 3.20 M7-11 600 0
2 QSO B0420-0127 QSO 04 23 15.8007747432 -01 20 33.063518580   17.50 17.00 16.28   ~ 1128 3
3 IRC +10216 C* 09 47 57.40632 +13 16 43.5648     10.96     C9,5e 2240 0
4 V* VX Sgr s*r 18 08 04.0442790744 -22 13 26.600899044 11.72 9.41 6.52 3.90 2.11 M8.5Ia 577 0
5 3C 454.3 Bla 22 53 57.7480438728 +16 08 53.561508864   16.57 16.10 15.22   ~ 2664 2

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