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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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