Spectral characteristics of HeI 10830 A line in the quiet chromosphere

Abstract

We describe preliminary results of the observation of the HeI 10830 AD line in the quiet chromosphere in 1986 and 1987 with the newly installed Reticon system on the solar spectrograph of Purple Mountain Observatory. We found: (1) The HeI 10830 A line has an emission maximum outside the solar limb. The maximum intensity in 1987 was definitely greater than the maximum in 1986. (2) The maximum intensity was roughly proportional to the line half-width. (3) The line half-width in coronal hole regions wasclearly smaller than in non-hole regions and was independent of the emission intensity. (4) The line half-width before the emission maximum is basically a constant, mostly with a tendency of increasing outward, the height at which the change begins depends on the optical thickness. (6) The emission maximum only correlates positively with the monthly smoothed sunspot number and there is no trace of it correlating with the 1–8 A X-ray flux or the intensity of the coronal green line above the observed point. We also give preliminary results of fitting our calculated theoretical profiles to the observed profile. The uniform model cannot give a good fit; a simple two-layer model not only greatly improved the fit, it also gave a reasonable absorption profile for solar disk observation. There seems no need for assuming a 20 km/s horizontal turbulence field, as many authors have done.