Preliminary Design of the
Spectropolarimeter for Arago
Martin Pertenaïs1,2
Coralie Neiner1 (PI), Laurent Parès2, Jean-Michel Reess1, Pernelle Bernardi1, Frans Snik3, Gerard van Harten3
1Paris
Observatory (FR)
2IRAP-CNRS, University of Toulouse (FR)
3Leiden Observatory, Leiden Univsersity (NL)
Punta Leona
2nd
December 2014
1
François Arago
1811 : Arago discovered rotary polarization experimentally (Quartz)
Polarimetry was born !!
2
Scientific goals
• What is the life cycle of matter ? (star formation, evolution and death)




ISM Characterization
Young (PMS) stars in accretion
All kinds of stars (Massive stars, Solar-like stars…)
Late stages of evolution (Supergiants, supernovae,…)
• How do stars impact the formation of planets and the emergence of life?
 Star-Planet interactions (stellar wind, magnetic interaction,…)
 Space weather (irradiation of the planet by the star,…)
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Specifications
Specification
Requirement
Spectral range
[119 nm ; 888 nm]
UV Resolution
25 000
Visible Resolution
35 000
S/N
100
Typical exp. time
30 min (OBA stars, V=7)
1h (FGK stars, V=7)
Target Magnitude
V=3-10
Vrad accuracy
1 km.s-1 (in absolute)
0.1 km.s-1 (for magnetic fields measurement)
Polarization accuracy
10-3
4
Instrument Scheme
5
Telescope
Spec. :
- SNR 100
- V=7 Star
- 30 min exposure time
 1.3m diameter
Cassegrain telescope
F/13
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Instrument Scheme
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Polarimeter
Aim : create a polychromatic polarimetric modulator
•
4 MgF2 stacked wave plates with fast-axis angle and thicknesses:
(a1,d1), (a2,d2),(a3,d3),(a4,d4)
•
Optimization on these 8 variables
•
The stack of the 4 plates takes 6 different angular positions (0°,30°,60°,90°,120° et 150°)
d1
a1
d2
a2
d3
a3
d4
a4
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Polarimeter
Aim : create a polychromatic polarimetric modulator
•
Definition of a demodulation matrix D such as:
•
The extraction efficiencies of the Stokes parameters *:
Sin=D.Iout
−1/2
𝑛
2
𝐷𝑖𝑗
𝜖𝑖 = 𝑛
𝑗=1
1
•
The optimal efficiency for Q, U and V is
•
The extraction is achromatized and not the retardance of the plates!
3
≈57.7%
* Optimum modulation and demodulation matrices for solar polarimetry, JC del Toro Inista and Collados (2000)
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Polarimeter
10
Instrument Scheme
11
Spectrograph
12
Instrument Scheme
Classical CCD
detector (13µm
pixel pitch)
MCP Detectors
(20µm pixel pitch)
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To take home
• High-resolution spectropolarimetry
• Precise Full Stokes (IQUV) measurement
• From FUV (119 nm) to NIR (888 nm)
• Exciting science !
Thank you for your attention !
Contacts : martin.pertenais@irap.omp.eu
coralie.neiner@obspm.fr
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15
Thank you for
your attention !
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SNR figures
T=9790 K
Mag = 10
Exposure Time = 30min
SNR
SNR
T=16000 K
Mag = 7
Exposure Time = 30min
Wavelength (nm)
Wavelength (nm)
Considering an optical transmission in the UV of 3% and 10% in the VIS,
and a quantum efficiency in the UV of 35% and 70% in the visible
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Spectral band
Visible
[390-890] nm
UV
[119-320] nm
UV
[119-320] nm
UV
[119-320] nm
Minimum
SNR
Magnitude V
Spectral type
Maximum exposure time [min]
100
7
all
30
100
7
OBA
30
100
7
FGK
60
100
10
Chromospheric emission lines
of M dwarfs
60
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Birefringence MgF2
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Focal planes
Frame size 120 x 14 mm
UV
100 mm
Visible :
Frame size 30 x 30 mm
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Back-up polarimeter
x
x
2x


x

6 tan(x ) n( )
𝐼𝑜𝑢𝑡
= 0,5(𝐼 + 𝑄 cos Φ𝑐𝑜𝑠2𝜃 + 𝑠𝑖𝑛Φsin2θ
+ Ucos2Φsin2θ
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