SpectropolarimetrySpectropolarimetryat THÉMISat THÉMIS

Frédéric Paletou & Guillaume MolodijFrédéric Paletou & Guillaume Molodij

THÉMISVTT

GCT• Latitude : 28°18’ N• Longitude : 16°30’ W• Altitude : 2456 m

THÉMIS:THÉMIS:an overviewan overview

• The telescope & polarimeter

• The transfer optics

• The spectrographs & detectors

PolarimeterPolarimeterlocationlocation

A “unique”A “unique”design!design!

Ritchey-Chrétien pointing directly@ the Sun

With a 90 cm diameter light collector, THÉMIS is the 2nd

largest solar telescope worldwide

Polarization AnalysisPolarization Analysis

The polarimeter is located @ the telescope’s (F1) Cassegrain focus

THÉMIS IS A “POLARIZATION FREE” SOLAR TELESCOPE

M7

M6

M5

M4

F1

TELESCOPE

TRANSFEROPTICS

Entrance window

Secondary mirror

Primary mirror

Polarisation analyserExit window

Focusingtelescope

Tilting mirror

The PolarimeterThe 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

The Quarter Wave PlatesThe Quarter Wave Plates• Cristalline QWPs consisting in a pair of [Quartz + MgF2]

elementary plates (by Optique J. Fichou, France)Phase [degrees]

Wavelength [Å]

The Transfer OpticsThe Transfer Optics

M7

M6

M5

M4

M3

F1

M8 M9

Echelle grating

TRANSFEROPTICS

Primary mirrorExit window

Focusingtelescope

Fieldrotator

F2 Focus

Tilting mirror

Polarisation analyser

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

chromatisms

The SpectrographsThe Spectrographs

• 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)

2 in serie:2 in serie:

M7

M3

SP1 MTR

DPSM

IPM

IPM

M8 M9

M6

M7

M10

M11

Echelle grating

OPTICStelescope

Fieldrotator

CCD 3

F2 Focus

CCD 1

CCD 2

Echellespectrograph

Predisperserspectrograph

MS

DP

tra

nsf

er

optic

s

Transfer Transfer optics optics to the to the

detectorsdetectors

• Thomson TH7863Thomson TH7863

• 12 bits12 bits

• 384x288 pixels384x288 pixels

• FW = 8x10FW = 8x1055 e e--

• TTnumnum = 236 ms = 236 ms

Active Regions MagnetometryActive Regions Magnetometry

IIcontinuumcontinuum

BB////

Courtesy Dr N. Meunier, OMP Tarbes (November 25, 2000)

NiI line @ 676.8 nm. The total FOV is 136”x110” and the average seeing was about 0.6” during the scan period

Weak Polarization SignalsWeak 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 @ 460.7 nm line at the northern limb (and depolariz-ation in the nearby FeI line).

J. Trujillo Bueno et al. (May 29, 2000)

THÉMIS/MTR mode in figuresTHÉMIS/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: 2’x2’ 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!