Non-LTE inversion of spectropolarimetric and spectroscopic observations of a small active-region filament observed at the VTT
Astro. Inst., Slovak Acad. of Sci.; AIP Potsdam; Astro. Ins., Acad. of Sci. of the Czech Rep.
Main category
Natural Sciences (Astrophysics and Astrononmy)
An active-region 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 Å and of the SiI 10827 Å line were acquired using the VTT Echelle spectrograph together with the Tenerife Infrared Polarimeter (TIP I). Additional simultaneous spectroscopic observations in the CaII 8542 Å line were also obtained with the Echelle spectrograph. With the TESOS Fabry-Pérot interferometer, the filament was observed in Ha in intensity mode with a field-of-view of 25 x 25 arcsec (136 wavelength points within the range 6561 – 6564 Å). The filament shows a structure typical for an active filament composed of thin and long fluxtubes with plasma flowing along the magnetic field lines inside these fluxtubes. Thus, for diagnostics of the filament plasma, observed Ha 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. Assuming the flows are parallel to the magnetic field lines in the fluxtube, the LOS component is then projected onto a velocity vector according to the direction of the vector magnetic field that we were trying to obtain from inversions using the HAZEL inversion code (Asensio Ramos, 2008).
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