First performance results of a new field-widened spatial heterodyne spectrometer for geocoronal H[alpha] research

A new, high-resolution field-widened spatial heterodyne spectrometer (FW-SHS) designed to observe geocoronal Balmer [alpha] (H[alpha], 6563Å) 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 fields of view (1.8° and 1.4°, 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 640km/s (14Å) spectral band pass and is capable of determining geocoronal H[alpha] Doppler shifts on the order of 100m/s with a temporal resolution on the order of minutes. These characteristics make the FW-SHS well suited for spectroscopic studies of relatively faint (~12-2R), diffuse-source geocoronal H[alpha] emission from Earth's 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 first light performance and H[alpha] observational results collected from observing nights across 2013 and 2014. Key Points FW-SHS instrument extends H alpha observations with high resolving power and long spectral baseline Field-widening prisms allow faint emission detection in compact instrumental design FW-SHS observations are consistent with WHAM observations and coincidentally obtained Fabry Perot observations