1. Polarization in Interferometry Greg Taylor
What is polarized light?
What fun science can be done with polarimetry?
How do interferometers measure polarization?
How do you calibrate and image in full polarization?
Greg Taylor, Synthesis Imaging School, 18 June 2002

2. Greg Taylor, Synthesis Imaging School, 18 June 2002

3. Greg Taylor, Synthesis Imaging School, 18 June 2002
What is Polarized Light?
Light is oscillating electric and magnetic fields
Polarization is labeled by the shape of the trace of the tip of the E vector
Each polarization has an orthogonal state
Incoherent light can contain many polarization states
Stokes Parameters describe partially polarized light
I = RR + LL
Q = RL + LR
U = i(LR – RL)
V = LL - RR
For circular feeds
Alternate representation:
pol. angle (EVPA) f = 0.5 atan (U/Q)
polarized intensity p = sqrt(Q2 + U2)
fractional linear m = p / I
fractional circular v = |V | / I
Greg Taylor, Synthesis Imaging School, 18 June 2002

4. Greg Taylor, Synthesis Imaging School, 18 June 2002
8.4 GHz
E-Vectors
Laing (1996)
3 kpc
Greg Taylor, Synthesis Imaging School, 18 June 2002

5. Greg Taylor, Synthesis Imaging School, 18 June 2002
Perley & Carilli (1996)
Cygnus A
B-Vectors
8.5 GHz
10 kpc
Greg Taylor, Synthesis Imaging School, 18 June 2002

6. Greg Taylor, Synthesis Imaging School, 18 June 2002
Attridge et al 1999
VLBA @ 5 GHz
Greg Taylor, Synthesis Imaging School, 18 June 2002

7. Greg Taylor, Synthesis Imaging School, 18 June 2002

8. Greg Taylor, Synthesis Imaging School, 18 June 2002
R Aquirrii
Stellar SiO Masers
Boboltz et al 1998
43 GHz
Greg Taylor, Synthesis Imaging School, 18 June 2002

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10. Greg Taylor, Synthesis Imaging School, 18 June 2002
GHz
Greg Taylor, Synthesis Imaging School, 18 June 2002

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12. Greg Taylor, Synthesis Imaging School, 18 June 2002
See Review of “Cluster Magnetic Fields” by Carilli & Taylor 2002 (ARA&A)
Greg Taylor, Synthesis Imaging School, 18 June 2002

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15. Greg Taylor, Synthesis Imaging School, 18 June 2002
Parallactic Angle
Greg Taylor, Synthesis Imaging School, 18 June 2002

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25. Greg Taylor, Synthesis Imaging School, 18 June 2002
Bad D-term solution
Good D-term solution
Greg Taylor, Synthesis Imaging School, 18 June 2002

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27. Greg Taylor, Synthesis Imaging School, 18 June 2002
Compact Symmetric
Objects (CSOs)
8.4 GHz
Peck & Taylor (2001)
Greg Taylor, Synthesis Imaging School, 18 June 2002

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Practical VLBI
polarization angle
calibration
Greg Taylor, Synthesis Imaging School, 18 June 2002

30. Greg Taylor, Synthesis Imaging School, 18 June 2002
1) Find a Calibrator
Greg Taylor, Synthesis Imaging School, 18 June 2002

31. Greg Taylor, Synthesis Imaging School, 18 June 2002
2) Estimate
f_VLA
Greg Taylor, Synthesis Imaging School, 18 June 2002

32. Greg Taylor, Synthesis Imaging School, 18 June 2002
3) Sum Q and U over
VLBA image.
4) Compute
f_VLBA = 0.5 atan (U/Q)
5) Rotate VLBA data by
(f_VLA – f_VLBA)
Greg Taylor, Synthesis Imaging School, 18 June 2002

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36. Greg Taylor, Synthesis Imaging School, 18 June 2002
Greg Taylor, Synthesis Imaging School, 18 June 2002

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