Polarization in Interferometry Greg Taylor

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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?

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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
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

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3C 31 VLA _at_ 8.4 GHz E-Vectors Laing (1996)
3 kpc
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Perley Carilli (1996)
Cygnus A B-Vectors VLA _at_ 8.5 GHz
10 kpc
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1055018
Attridge et al 1999 VLBA _at_ 5 GHz
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R Aquirrii Stellar SiO Masers Boboltz et al
1998 VLBA _at_ 43 GHz
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Taylor (1998)
15 12 8 GHz
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See Review of Cluster Magnetic Fields by
Carilli Taylor 2002 (ARAA)
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Parallactic Angle
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Bad D-term solution
Good D-term solution
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Compact Symmetric Objects (CSOs) VLBA _at_ 8.4
GHz Peck Taylor (2001)
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Practical VLBI polarization angle calibration
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1) Find a Calibrator
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2) Estimate f_VLA
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2200420
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)
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