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Astronomical PolarimetryAstronomical PolarimetryOptical and NIR applicationsOptical and NIR applications

Antonio Pereyra

Observatório Nacional (ON)Rio de Janeiro - Brazil

LNA site

LNA site

LNA site

Polarimetry at LNAPolarimetry at LNA

• Instrument: IAGPOL– Polarimetric module

– Operations modes:• Imaging:

– Point sources

– Extended sources

– Optical (w/ CCDs)

– NIR (w/ CamIV)

• Spectropolarimetry– w/ EIFU (Integral

Field Unit)

Retarder(λ/2 or λ/4)

Analyser(Savart / Polaroid)

Filters(Clear, U,B,V,R,I)

Optical axis

Wheel axis

Detector(CCD, NIR – J,H,K)

IAGPOL - Optical System

V

U

Q

I

S

S

S

S

S

4

3

2

1

Measuring the PolarizationMeasuring the PolarizationStokes parameters:

Measuring the PolarizationMeasuring the Polarization

)(tan

100

/

/

12

1

22

QU

UQP

IUU

IQQ

Linear polarization:

U’(x100)

P

2θ

Q’(x100)

Transmitted intensity through waveplate /2 + Savart:

Ni +

Ni –

iiii

iii UQ

NN

NNz 4sin4cos

I’(i) = ½ [I ± Q cos 4i ± U sin 4i ]

II’

Measuring the PolarizationMeasuring the Polarization

Example: Crowded fieldExample: Crowded field

Modulation (Modulation (waveplatewaveplate++SavartSavart))

HD110984 (optical polarized standard)

Z

PR=(5.670.01)%@91.3°(Tapia 88’)

P = (Q’ 2 + U’ 2)½ 100θ = ½ tan-1 (U’/Q’)

ApplicationsApplications

Interstellar MediumInterstellar Medium

Unpolarized light from background star

Aligned grain w/ angular momentum // B

B

Linear polarized light

Musca Dark CloudMusca Dark Cloud

Feitzinger & Stüve 84

MDC2.5°x2.5°DSS

Pereyra &Magalhães 00

B ~ perpendicular to the longest axis of MDC

Results support models of collapse along B

Pereyra &Magalhães 00

B ~ perpendicular to the longest axis of MDC

Results support models of collapse along B

Pereyra &Magalhães 00

B ~ perpendicular to the longest axis of MDC

Results support models of collapse along B

2 %

2MASS (H)DDS (optical)

IRAS 12322-7023

9’x9’

Pereyra & Magalhães 05

Optical vs NIROptical vs NIR

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