1. Spectropolarimetry at THÉMIS Frédéric Paletou & Guillaume Molodij

2. THÉMIS VTT GCT Latitude : 28°18’ N Longitude : 16°30’ W Altitude : 2456 m

3. THÉMIS: an overview The telescope & polarimeter The transfer optics The spectrographs & detectors

4. Polarimeterlocation A “unique” design! Ritchey-Chrétien pointing directly @ the Sun With a 90 cm diameter light collector, THÉMIS is the 2nd largest solar telescope worldwide

5. Polarization Analysis The polarimeter is located @ the telescope’s (F1) Cassegrain focus THÉMIS IS A “POLARIZATION FREE” SOLAR TELESCOPE

6. 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

7. The Quarter Wave Plates Cristalline QWPs consisting in a pair of [Quartz + MgF 2 ] elementary plates (by Optique J. Fichou, France) Phase [degrees] Wavelength [Å]

8. The Transfer Optics Re-imaging (f/63) Derotating Corrections of chromatisms

9. The 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:

10. Transfer optics to the detectors Thomson TH7863 Thomson TH7863 12 bits 12 bits 384x288 pixels 384x288 pixels FW = 8x10 5 e - FW = 8x10 5 e - T num = 236 ms T num = 236 ms

11. Active Regions Magnetometry I continuum B // 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

12. Weak Polarization Signals The enigmatic linear polari- zation of the D 2 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)

13. 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: 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!