2003ApJ...592L.103E

An externally dispersed interferometer (EDI) is a series combination of a fixed delay interferometer and an external grating spectrograph. We describe how the EDI can boost the effective resolving power of an echelle or linear grating spectrograph by a factor of 2-3 or more over the spectrograph's full bandwidth. The interferometer produces spectral fringes over the entire spectrograph's bandwidth. The fringes heterodyne with spectral features to provide a low spatial frequency moiré pattern. The heterodyning is numerically reversed to recover highly detailed spectral information unattainable by the spectrograph alone. We demonstrate resolution boosting for stellar and solar measurements of two-dimensional echelle and linear grating spectra. An effective spectral resolution of ∼100,000 has been obtained from the ∼50,000 resolution Lick Observatory two-dimensional echelle spectrograph, and that of ∼50,000 from an ∼20,000 resolution linear grating spectrograph.