Calculation of the broadening of HeI 10830إ for a solar limb flare

In this paper the Doppler and Stark broadening mechanisms of HeI 10830Å are discussed and various broadening parameters calculated. The following conclusions are drawn: compared to the Doppler effect, the action of radiative damping on the broadening of HeI 10830Å can be neglected. For the generally acknowledged value of electron density of flares (Ne = 3.2 x 1013cm−3), none of the damping terms can produce any discernible broadening. Up to Ne = 1015cm−3, none of the various types of damping can effect an increase in the half-width of the line center, and the maximum increase is of the order of 10−3Å. Therefore, the broadening at the line center may always be thought to be Doppler broadening. When Ne > 1014 cm−3, Stark broadening, especially the Stark broadening of electrons, plays the chief role in the broadening of HeI 10830Å. If the wings of the Stark-broadened profile are to be 2–3 times larger than those of the purely Doppler-broadened profile, then the half-width of damping broadening should be comparable to ΔλD. If the observed profile of the limb flare of 1989 is interpreted as Stark broadening, then the electron density would be as high as 1017 cm−3. The collisional damping (γ3) with helium atoms causes clearly different amounts of broadening on the components I12 and I3: the effect is one order of magnitude higher on I12 than on I3. But our observation shows that the wing extensions of I12 and I3 are basically the same, so it is impossible that our observed profile is produced by γ3.