THE HE I D3 LINE IN G AND K STARS.

Abstract

High-resolution spectra have been obtained of 18 late-type stars in order to search for He I λ5876. This feature is present in main-sequence stars that are known to have active chromospheres, and the line widths, depths, and the ratio λ10830/λ5876 in integrated starlight are similar to what is measured in solar plages. The line λ5876 is also present, with an equivalent width of 35 mÅ, in the RS CVn star λ And. In the remaining giants and supergiants in the present sample, the ratio λ10830/λ5876 is apparently much larger than it is in either solar plages or active dwarfs, and the conditions under which the helium triplet lines are formed may be very different in highly luminous stars. Theoretical analyses of the line-formation process indicate coronal emission may not be the dominant factor in determining the helium level populations in main-sequence stars.