Imaging spectropolarimetry of the He I 1083 nanometer line in a flaring solar active region

Abstract

Slit spectra, simultaneously measuring left and right circular polarization of the solar spectrum at 1082.9 +/- 0.4 nm, were taken using the National Solar Observatory (NSO) Vacuum Tower Telescope (VTT) at Sacramento Peak with a 128 x 128 pixel HgCdTe IR camera. By moving the slit the solar active region NOAA 7629 was scanned with a cadence of 246 s from 1724 to 1902 UT on 1993 December 6. The region was in the decay phase of a C9.7 flare. Intensity, velocity and longitudinal magnetic field in both the Si I (photospheric) and He I (chromospheric) lines are computed from fits to the line profiles in left and right polarizations. Analysis of these quantities show: (1) He I line emission in three decaying flare kernels, (2) Zeeman splitting of the He I emission measuring the longitudinal magnetic field inside the flare kernels; (3) dark He I active region filaments avoid strong longitudinal chromospheric magnetic field, and an active filament (with a transverse speed of 9 km/s) produces fluctuations in the strength of the longitudinal magnetic fields, and (4) bipolar moving magnetic features (MMFs) and emerging active region bipoles (EARBs) are observed at photospheric but not chromospheric heights.