FABRY-PEROT OBSERVATIONS OF HELIUM-10830 ANGSTROM EMISSION AT MILLSTONE HILL

The He(23S) triplet at 10830 Angstrom is observed using a Fabry-Perot interferometer optimized for the near infrared. These observations, ma de at the zenith at the Millstone Hill Optical Facility during evening twilight, are the first to resolve the individual members of the heli um triplet from the surrounding OH(5-2) lines. The introduction of an aeronomically unique germanium detector Note ef at, [1993] was crucial to this achievement. The instrument is configured with a spectral res olution of 1/2 the helium line width at 1000 degrees K, assuring that the line widths accurately reflect the velocity distribution of metast able helium. Although the intensities observed are within a factor of two of helium 10830 Angstrom intensities observed by [Tinsley, 1968, T insley & Christensen et. al, 1971], the observed temperatures are diff erent from the expected behavior of a neutral species in the upper-the rmosphere during twilight.