HEI10830Å in Solar Active Regions and its Correlat with Chromospheric Lines

Abstract

During the August 1993 International EFR Campaign, five active regions, which were at different phases of development, were observed at the German Vacuum Tower Telescope in Tenerife. We took filtergrams in Hα, in Call K232, and in green continuum, simultaneously with HeI 10830A spectra over the target active regions. Spectroscopic quantities, such as equivalent widths, line widths, Doppler shifts, residual intensities etc. of HeI 10830A, were derived and mutual correlations among them were studied. Our main results are as follows. (1) The HeI 10830A absorption line is strong in plage areas and in Hα filaments. In fibril area of active regions, HeI 10830A shows only weak absorption, not different from that in quiet regions. (2) Except in active region filament areas, the equivalent width of HeI 10830A is well correlated with the brightness of K232. Plage and enhanced network seen in Call K232 are associated with enhanced absorption in HeI 10830A. On the other hand, Hα on-band brightnesses show less correlation with HeI 10830A than Call K232. This result is new and gives a clue to the helium excitation mechanism in the solar atmosphere. (3) Doppler-shifted streaks were frequently found in HeI 10830A spectra. They were found both in association with the arch filaments of emerging flux regions and in plage area. Correlation analysis showed that, in plage areas, downflows are dominant in the regions where HeI 10830A absorption is strong. This finding in HeI 10830A is consistent with the characteristics of the Civ line (Klimchuk, 1987).