Measurement of the profile of solar He I resonance lines

Abstract

The profile of the helium resonance line at λ 584 Å from the full solar disk has been investigated through analysis of data obtained by sounding rockets flown in 1977 and in 1980. The instrument, a helium‐filled spectrometer, made use of a curve‐of‐growth technique. In the analysis, the solar He I line profile was represented by a Gaussian distribution. Between 6.5 and 13% of the Gaussian core area was found to be missing due to self‐reversal. Data from our 1980 experiment gave a line width of 101 ± 10 mÅ (full width at half maximum). The 1977 line width, obtained with less experimental reliability, was 128 ± 20 mÅ (full width at half maximum). Results obtained in a similar experiment in 1974, corrected for background radiation and for solar line self‐reversal, gave a revised 1974 line width of 103 mÅ (full width at half maximum). While the measured line width did vary, a comparison of the 1974, 1977, and 1980 data showed no consistent relationship between the measured widths and solar activity. An observation of the solar He I 537‐Å emissions during the 1980 sounding rocket flight provided a measurement of that line width, giving a value of 148 ± 27 mÅ (full width at half maximum).