Spectropolarimetry at THÉMIS Frédéric Paletou & Guillaume Molodij

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

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

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

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

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

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]

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

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:

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

Active Regions Magnetometry I continuum B // Courtesy Dr N. Meunier, OMP Tarbes (November 25, 2000) NiI nm. The total FOV is 136”x110” and the average seeing was about 0.6” during the scan period

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 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 figures Full-Stokes spectropolarimetry in 6 spectral domains simultaneously, across a 260 nm range (THEMIS bandpass is ~ nm) High spatial & spectral resolution (0.5”) & resolving power ~ Vector magnetometry: 2’x2’ scans in ~ 10 mn (with a 300 ms exposure time per frame) Beam exchange for all the Stokes parameters nm & nm achromatic quarter wave plates available New in 2001!