8446-Angstrom observations of neutral oxygen with the Spatial Heterodyne Spectrometer at Millstone Hill

Abstract

Neutral oxygen (O I) is a dominant species between about 250 and 500 km in the thermosphere. A complete thermospheric model requires measurements of the species density ([O]) to incorporate into forward models. One way to measure [O] is to detect Bowen fluorescence at triplet 8446 Å. Bowen fluorescence is generated when thermospheric oxygen absorbs Solar Lyman-β and de-excites through a path eventually leading to 8446 emission. This emission must be distinguished from the brighter 8446 emission caused by photoelectron (PE) impact, which can be done by measuring the intensity ratio between two branches of the 8446 triplet. An instrument to measure Mid-latitude Bowen fluorescence has been installed at Millstone Hill Observatory. The instrument is a Spatial Heterodyne Spectrometer (SHS), a novel type of Fourier transform spectrometer. This SHS was first used to observe Na Fraunhofer lines from dayglow at 589 nm, and then observed the 8446 region in an oxygen spectrum tube. Modifications to the system will allow it to observe 8446 emissions from the evening sky.