Non-LTE inversion of spectropolarimetric and spectroscopic observations of a filament on 11 September 2014 at the VTT

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 in the HeI IR triplet at a wavelength around 10830 Å and the SiI 10827 Å line were performed using the Echelle spectrograph together with the Tenerife Infrared Polarimeter (TIP). Additional spectroscopic observations in the CaII 8542 Å line were obtained with the 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 Å). Magnetic structure and properties of the photospheric plasma in the vicinity of the filament were inferred from the SiI 10827 Å line using 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).
The filament showed no activity in the CaII 8542 Å absorption profiles (no central emission, no high velocities). Therefore it was possible to use the 2D non-LTE model of a quiescent filament to simulate the H_alpha profiles obtained from TESOS to diagnose the filament hydrogen plasma. In this non-LTE model, the same magneto-hydrostatic structure of Kippenhahn-Schlueter type was used as in the non-LTE 2D prominence model of Heinzel and Anzer (2001).