Greg Taylor, Synthesis Imaging School, 18 June 2002

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Polarization in InterferometryGreg 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

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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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

Alternate representation:

• pol. angle (EVPA) = 0.5 atan (U/Q)• polarized intensity p = sqrt(Q2 + U2)• fractional linear m = p / I• fractional circular v = |V | / I

I = RR + LLQ = RL + LRU = i(LR – RL)V = LL - RR

For circular feeds

Greg Taylor, Synthesis Imaging School, 18 June 2002

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3C 31VLA @ 8.4 GHz

E-VectorsLaing (1996)

3 kpc

Greg Taylor, Synthesis Imaging School, 18 June 2002

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Cygnus AB-VectorsVLA @ 8.5 GHz

Perley & Carilli (1996)

10 kpc

Greg Taylor, Synthesis Imaging School, 18 June 2002

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Attridge et al 1999

VLBA @ 5 GHz

1055+018

Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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R Aquirrii

Stellar SiO MasersBoboltz et al 1998

VLBA @ 43 GHz

Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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15 12 8 GHz

Taylor (1998)

Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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See Review of “Cluster Magnetic Fields” by Carilli & Taylor 2002 (ARA&A)

Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Parallactic Angle

Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Bad D-term solution Good D-term solution

Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Compact Symmetric

Objects (CSOs)

VLBA @ 8.4 GHz

Peck & Taylor (2001)

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Practical VLBIpolarization anglecalibration

Greg Taylor, Synthesis Imaging School, 18 June 2002

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1) Find a Calibrator

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2) Estimate _VLA

Greg Taylor, Synthesis Imaging School, 18 June 2002

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2200+4203) Sum Q and U over VLBA image.

4) Compute VLBA = 0.5 atan (U/Q)

5) Rotate VLBA data by (_VLA – _VLBA)

Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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Greg Taylor, Synthesis Imaging School, 18 June 2002

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