Spectropolarimtrie Multiraies Frdric Paletou

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Spectropolarimetry at THÉMIS
Frédéric Paletou Guillaume Molodij
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THÉMIS
VTT
Latitude 2818 N Longitude 1630
W Altitude 2456 m
GCT
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THÉMIS an overview

• The telescope polarimeter
• The transfer optics
• The spectrographs detectors

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A unique design!
Ritchey-Chrétien pointing directly _at_ the Sun
Polarimeter location
With a 90 cm diameter light collector, THÉMIS is
the 2nd largest solar telescope worldwide
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Polarization Analysis

• The polarimeter is located _at_ the telescopes (F1)
  Cassegrain focus

THÉMIS IS A POLARIZATION FREE SOLAR TELESCOPE
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The Polarimeter

• Consists in 2 achromatic quarter wave plates
  which can be independently rotated over a 45
  range, 22.5 stepwise followed by a calcite
  beam-splitter

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The Quarter Wave Plates

• Cristalline QWPs consisting in a pair of Quartz
  MgF2 elementary plates (by Optique J. Fichou,
  France)

Phase degrees
Wavelength Å
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The Transfer Optics

• Re-imaging (f/63)
• Derotating
• Corrections of chromatisms

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The Spectrographs
2 in serie

• 1 predisperser (to choose from)
• 79 grooves mm-1 (63º)
• 150 grooves mm-1 (2º)
• 1200 grooves mm-1 (45º)
• 1 echelle grating
• 79 grooves mm-1 (63º)

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Transfer optics to the detectors

• Thomson TH7863
• 12 bits
• 384x288 pixels
• FW 8x105 e-
• Tnum 236 ms

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Active Regions Magnetometry
B//
Courtesy Dr N. Meunier, OMP Tarbes (November 25,
2000)
NiI line _at_ 676.8 nm. The total FOV is 136x110
and the average seeing was about 0.6 during the
scan period
Icontinuum
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Weak Polarization Signals
The enigmatic linear polari-zation of the D2 line
of NaI (measured at ? 0.15). F. Paletou G.
Molodij (April 7, 2000)
Resonance polarization of the SrI _at_ 460.7 nm line
at the northern limb (and depolariz- ation in the
nearby FeI line). J. Trujillo Bueno et al. (May
29, 2000)
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THÉMIS/MTR mode in figures

• Full-Stokes spectropolarimetry in 6 spectral
  domains simultaneously, across a 260 nm range
  (THEMIS bandpass is 450-900 nm)
• High spatial spectral resolution (0.5)
  resolving power 300000
• Vector magnetometry 2x2 scans in 10 mn (with
  a 300 ms exposure time per frame)
• Beam exchange for all the Stokes parameters
• 400-700 nm 600-900 nm achromatic quarter wave
  plates available

New in 2001!