An Investigation of IR Triplet He I 10830 Å Profiles in Active Regions and the Quiet Chromosphere

Abstract

This paper gives a description of the technique and equipment used to make solar observations in the near IR region with a coronagraph. Examination of active-region spectra in the neighborhood of the He 110830 Å line confirm that the the line is enhanced in sunspot umbrae. The line profiles of umbrae and faculae differ qualitatively. Flares show a decrease in the line depth in comparison to faculae, and in flare kernels the line undergoes an emission reversal. Simultaneous observations of spectra of chromospheric spicules at two heights above the solar surface reveal that the half-width of the 10830 line increases with height.

An Investigation of IR Triplet He I 10830 Å Profiles in Active Regions and the Quiet Chromosphere

“…As is evident from Table I, the He I 10830 line is indeed present in the sunspot umbra, and its depth is increased in comparison to the quiet photosphere, for which r = 98%. Fay et al (1972) obtained residuals, r, of 0.83 and 0.72 for sunspots with fractional hemispheric areas, 5, of 70 χ 10" 6 and 100 χ 10~6 respectively. Comparing our values of 0.95 and 0.94 for S = 35 x 10~6 and S = 50 χ 10"" 6 , one is justified in believing that the dependence of r on the sunspot umbral area found by Fay et al (1972) is real.…”

“…Fay et al (1972) obtained residuals, r, of 0.83 and 0.72 for sunspots with fractional hemispheric areas, 5, of 70 χ 10" 6 and 100 χ 10~6 respectively. Comparing our values of 0.95 and 0.94 for S = 35 x 10~6 and S = 50 χ 10"" 6 , one is justified in believing that the dependence of r on the sunspot umbral area found by Fay et al (1972) is real. The asymmetry of the He I 10830 profile, caused by its triplet character, is less in a sunspot umbra than in plage.…”

“…Because of the low level of instrumental stray light in the coronagraph, we considered it possible to address the effect of image blurring by itself upon the profiles, using the method suggested by Stepanov (1957). Results of observations and analysis of two sunspots are presented in Table I (Borodina and Papushev, 1979). Indices s and pi stand for the sunspot umbra and plage respectively, the other symbols being standard.…”

“…The observing program was aimed at a study of the behavior of the He I 10830 triplet in different features on both the solar limb and disk. In this case we tried to take advantage of the fact that rather stringent requirements on light scattering are satisfied for the optical elements in the coronagraph; the instrumental scattered light is less than 0.5% (Nikolsky and Sazanov, 1967). With this instrument we obtained spectra of the He I 10830 line in sunspot umbrae and in chromospheric spicules and flares.…”