First Performance Results of a New Field-Widened Spatial Heterodyne Spectrometer for Geocoronal Hα Research

<p> A new, high-resolution &filig;eld-widened spatial heterodyne spectrometer (FW-SHS) designed to observe geocoronal Balmer &alpha; (H&alpha;, 6563 &Aring;) emission was installed at Pine Bluff Observatory (PBO) near Madison, Wisconsin. FW-SHS observations were compared with an already well-characterized dual-etalon Fabry-Perot Interferometer (PBO FPI) optimized for H&alpha;, also at PBO. The FW-SHS is a robust Fourier transform instrument that combines a large throughput advantage with high spectral resolution and a relatively long spectral baseline (~10 times that of the PBO FPI) in a compact, versatile instrument with no moving parts.Coincident H&alpha; observations by FW-SHS and PBO FPI were obtained over similar integration times, resolving powers (~67,000 and 80,000 at H&alpha;) and &filig;elds of view (1.8&deg; and 1.4&deg;, respectively). First light FW-SHS observations of H&alpha; intensity and temperature (Doppler width) versus viewing geometry (shadow altitude) show excellent relative agreement with the geocoronal observations previously obtained at PBO by FPI. The FW-SHS has a 640 km/s (14 &Aring;) spectral band pass and is capable of determining geocoronal H&alpha; Doppler shifts on the order of 100 m/s with a temporal resolution on the order of minutes. These characteristics make the FW-SHS well suited for spectroscopic studies of relatively faint (~12&ndash;2 R), diffuse-source geocoronal H&alpha; emission from Earthˈs upper thermosphere and exosphere and the interstellar medium in our Galaxy. Current and future FW-SHS observations extend long-term geocoronal hydrogen observation data sets already spanning three solar minima. This paper describes the FW-SHS &filig;rst light performance and H&alpha; observational results collected from observing nights across 2013 and 2014.</p>