First light for the Bowen fluorescence spatial heterodyne spectrometer at Millstone Hill Observatory

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 844.6 nm. Bowen fluorescence is generated when thermospheric oxygen absorbs Solar Lyman-β and de-excites through a path eventually leading to 844.6 nm emission. This emission must be distinguished from the brighter 844.6 nm emission caused by photoelectron (PE) impact, which can be done by measuring the intensity ratio between two branches of the 844.6 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 is to be turned to the 844.6 region. With simple readjustments, it can also be reset for other visible and near IR wavelengths.