Thinkshop12

Non-LTE Inversion of Spectropolarimetric and Spectroscopic Observations of a Filament on 11 September 2014 at the VTT

Pavol Schwartz (Astronomical Institute of Slovak Academy of Sciences)

Abstract. A filament in the active region NOAA 12159 (at solar disk coordinates [x,y] = [225,-440] arcsec) was observed with the Vacuum Tower Telescope at Tenerife on 11 September 2014. Full-Stokes spectropolarimetric observations of the HeI IR triplet at a wavelength around 10830 A and of the SiI 10827 A line were acquired using the VTT Echelle spectrograph together with the Tenerife Infrared Polarimeter (TIP). Additional simultaneous spectroscopic observations in the CaII 8542 A line were also obtained with the Echelle spectrograph. With the TESOS Fabry-Perot interferometer, the filament was observed in H_alpha in intensity mode with a field-of-view of 25 x 25 arcsec (136 wavelength points within the range 6561 — 6564 A). Magnetic structure and properties of the photospheric plasma in the vicinity of the filament were inferred from the SiI 10827 A line with the Stokes Inversion using Response function code (SIR; Ruiz Cobo & del Toro Iniesta 1992, Bellot Rubio 2003). From the HeI Stokes profiles a horizontal magnetic field of around 160 G was inferred in the filament using the Hanle Zeeman Light inversion code (HAZEL; Asensio Ramos, Trujillo Bueno and Landi Degl’Innocenti 2008). Although the filament showed no activity in the CaII 8542 A absorption profiles (no central emission, no high velocities), it has a structure typical for an active filament composed of thin and long fluxtubes where plasma can flow along the magnetic field lines inside the fluxtubes. Thus, for diagnostics of the filament plasma, observed H_alpha profiles are simulated using a simple isothermal and isobaric two-dimensional non-LTE model with two finite dimensions — vertical and across the fluxtube. The velocity of the plasma flows is also taken into account in the model because it can cause a Doppler brightening in the observed profiles. The line-of-sight (LOS) component of the flow velocity is estimated from the asymmetry of the H_alpha profiles. Assuming the flows are parallel to the magnetic field in the fluxtube, the LOS component is then projected onto a velocity vector according to the direction of the vector magnetic field inferred from the HAZEL inversions.

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